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MANAGEMENT OF ASPARAGUS ROTS

presented by

Lina Maria Rodriguez Salamanca

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MANAGEMENT OF ASPARAGUS ROTS
By

Lina Maria Rodriguez Salamanca

A THESIS

Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE

Plant Pathology

2010

ABSTRACT
MANAGEMENT OF ASPARAGUS ROTS
By

Lina Maria Rodriguez Salamanca

Asparagus rots, caused by F usarium oxysporum f. sp. asparagi and Phytophthora
asparagi, greatly impact Michigan asparagus production. Greenhouse and ﬁeld
experiments with asparagus were conducted to investigate the effect of selected
herbicides on (i) plant growth and (ii) F usarium crown and root rot incidence. In the
greenhouse, F usarium crown and root rot incidence was low, while reduction in crown
weight among plants grown in mesotrione-treated soil was observed. In the ﬁeld,
mesotrione caused phytotoxicity, herbicide effects on F usarium crown and root rot were
not tested. Current results suggest select herbicide applications can compromise fern
growth, which could inﬂuence yields in subsequent years. A series of growth chamber
studies using detached asparagus spears were conducted to (i) elucidate the inﬂuence of
temperature on spear infection by P. asparagi; (ii) investigate the susceptibility of three
regions of the spear to P. asparagi, (iii) evaluate susceptibility of asparagus to P.
cactorum, P. capsici, P. citricola, P. drechsleri, P. megasperma and P. nicotianae, (iv)
compare the susceptibility of various sized spears to P. capsici isolates. Phytophthora
nicotianae and P. capsici incubated at 25°C caused lesions comparable to those caused by
P. asparagi. Phytophthora capsici isolates caused larger lesions in small spears

compared to the larger ones.

ACKNOWLEDGMENTS

I would like to express special thanks to my advisor Dr. Mary Hausbeck for her
support, advice, encouragement, guidance and patience, whose faith in me has helped me
advance beyond my expectations. To my committee members, Dr. Mathieu Ngouajio
and Dr. Gene Saﬁr, who also provided me with invaluable advise, assistance and
encouragement.

To my dear friend, Lina Quesada, for believing in me. I also owe thanks to all the
members of the Hausbeck lab for their valuable help; especially Leah Granke, Jennifer
Foster, Brian Cortright, Blair Harlan and Bryan Webster. Thanks to Wei Wang for his
help, advise and discussions on all sorts of statistical topics.

To my parents Maria and Jorge, and my sisters Ilse and Liliana for their love and
support from home. To my dear husband Andrew, whose ability to listen makes the
difference in my life and kept me rational.

Last but not least, to God for keeping on track, Thank you.

iii

TABLE OF CONTENTS

LIST OF TABLES .............................................................................................................. v
LIST OF FIGURES ........................................................................................................... vi
LITERATURE REVIEW ................................................................................................... 1
Asparagus .................................................................................................................... 2
Asparagus diseases ...................................................................................................... 8
Fusarium crown and root rot ....................................................................................... 9
Phytophthora spear and root rot ................................................................................ 13
CHAPTER I ...................................................................................................................... 17
GREENHOUSE AND FIELD HERBICIDE EVALUATION ON ASPARAGUS
PLANTS ................................................................................................................... 17
Abstract ..................................................................................................................... 1 8
Introduction ............................................................................................................... 1 9
Materials and methods .............................................................................................. 20
Results ....................................................................................................................... 25
Discussion ................................................................................................................. 36
CHAPTER II ..................................................................................................................... 39

PHYTOPHTHORA ASPARAGI VIRULENCE IN DETACHED ASPARAGUS
SPEARS AND SUSCEPTIBILITY TO OTHER PHYTOPHTHORA SPECIES 39

Abstract ..................................................................................................................... 40
Introduction ............................................................................................................... 41
Materials and methods .............................................................................................. 43
Results ....................................................................................................................... 47
Discussion ................................................................................................................. 58
APPENDIX ....................................................................................................................... 63
Fungicide efﬁcacy on Phytophthora rot in asparagus seedlings in the greenhouse .......... 63
LITERATURE CITED ..................................................................................................... 67

iv

LIST OF TABLES -
Table 1. Differences between nursery and production asparagus ﬁelds ............................ 5
Table 2. Morphological characteristics of Phytophthora described infecting asparagus. 16

Table 3. Herbicide treatment rates applied to asparagus in greenhouse and ﬁeld
experiments. .............................................................................................................. 22

Table 4. Number of plants showing phytotoxicity in uninfested ﬁeld soil or soil infested
with F usarium oxysporum f. sp. asparagi following treatment with herbicides. ..... 26

Table 5. Effect of herbicide treatments on weeds counts (compared with the untreated
control) in asparagus ﬁeld, Oceana County 2009. .................................................... 33

Table 6. Effect of herbicide treatments on numbers of asparagus ferns and fern height at
60, 90 and 120 days after planting (DAP). ............................................................... 35

Table 7. Effect of fungicides on the area under the disease progress curve (AUDPC)
values for the disease incidence on asparagus seedlings caused by Phytophthora
asparagi. ................................................................................................................... 65

Table 8. Effect of fungicides on probability of disease on asparagus seedlings caused by
Phytophthora asparagi. ...................................................................................... L ..... 66

LIST OF FIGURES

Figure 1. Effect of soil treatment on asparagus fern length (tallest fern only) in
greenhouse experiments with asparagus plants grown in soil mixed with sterile
millet seed (solid bar) and in soil infested with F. oxysporum f. sp. asparagi (F 0A
white bar) across herbicide treatments. Bars with common letters are not
signiﬁcantly different, LSD P=0.05. ......................................................................... 27

Figure 2. Effect of soil treatment on asparagus fern dry weight in greenhouse
experiments with asparagus plants grown in soil mixed with sterile millet seed (solid
bar) and in soil infested with F. oxysporum f. sp. asparagi (F 0A white bar) across
herbicide treatments. Bars with common letters are not signiﬁcantly different, LSD
P=0.05. ...................................................................................................................... 28

Figure 3. A, Effect of soil treatment on crown dry weight in greenhouse experiments
with asparagus plants grown in soil mixed with sterile millet seed (solid bar) and in
soil infested with F. oxysporum f. sp. asparagi (F 0A white bar) across herbicide
treatments. B, Effect of soil treatment on crown dry weight in greenhouse
experiments with asparagus plants grown across soil treatments. Bars with common
letters are not signiﬁcantly different, LSD P=0.05. .................................................. 29

Figure 4. Effect of herbicide treatment on asparagus crown weight gain in greenhouse
experiments with asparagus plants grown across soil treatments. Bars with common
letters are not signiﬁcantly different, LSD P=0.05. .................................................. 30

Figure 5. A, Effect of soil treatment on asparagus total dry weight in greenhouse
experiments with asparagus plants grown in soil infested with F. oxysporum f. sp.
asparagi (solid bar) or in soil mixed with sterile millet seed (line bar) across
herbicide treatments. B, Effect of herbicide treatment on asparagus total dry weight
in greenhouse experiments with asparagus plants grown across soil treatments. Bars
with common letters are not signiﬁcantly different, LSD P=0.05. ........................... 31

Figure 6. Effect of herbicide treatment on asparagus spear counts 30 and 60 days after
planting (DAP) in the ﬁeld. Bars with common letters are not signiﬁcantly different,
LSD P=0.05. ............................................................................................................. 34

Figure 7. Mean lesion area on detached asparagus spears 5 days after inoculation with P.
asparagi isolates C013, SP3236 and SP319 on A, supermarket spears and B,
‘Millennium’ spears. Bars with common letters are not signiﬁcantly different, LSD
P=0.05. ...................................................................................................................... 48

vi

Figure 8. Effect of temperature on mean lesion area on detached asparagus spears 5 days
after inoculation with P. asparagi on A, supermarket spears, and B, ‘Millennium’
spears. Bars with common letters are not signiﬁcantly different, LSD P=0.05. ..... 49

Figure 9. Effect of spear region on mean lesion area on detached asparagus spears 5 days
after inoculation with P. asparagi on A, supermarket spears and B, ‘Millennium’
spears. Bars with common letters are not signiﬁcantly different, LSD P=0.05. ..... 50

Figure 10. Effect of temperature and spear regions on mean lesion area on detached
asparagus spears 5 days after inoculation with P. asparagi on A, supermarket spears

and B, ‘Millennium’ spears. Bars with common letters are not signiﬁcantly
different, LSD P=0.05. .............................................................................................. 51

Figure 11. A, Effect of Phytophthora spp. (P. asparagi SP319, P. nicotianae 13048, P.
capsici OP97, P. citricola 3200, P. drechsleri 4335, P. megasperma 3100 and P.
cactorum 4001) averaged across temperatures (15, 20 and 25°C) on mean lesion area
5 days after inoculation (0.07 was subtracted from the lesion average to account for
the effect of wounding). B, Effect of temperature averaged across Phytophthora
spp. on mean lesion area 5 days after inoculation. C, Phytophthora spp. and
temperatures interaction on mean lesion area 5 days after inoculation. ‘Jersey
Knight’ detached asparagus spears were used in this study. Bars with common
letters are not signiﬁcantly different, LSD P=0.05. .................................................. 53

Figure 12. A, Effects of P. asparagi (isolate SP319) P. capsici (isolates 1335], SF F3,
12889, SP98, OP97) averaged across temperatures (15, 20 and 25°C) on mean lesion
area 5 days after inoculation. B, Effect of temperature averaged across
Phytophthora spp. (P. caps‘ici and P. asparagi) on mean lesion area 5 days after
inoculation. C, Phytophthora spp. and temperatures interaction on mean lesion area
5 days after inoculation. All conducted on ‘Millennium’ detached asparagus spears.
Bars with common letters are not signiﬁcantly different, LSD P=0.05. .................. 55

Figure 13. A, Effects of P. asparagi (isolate SP319) and P. capsici (isolates 13351,
SFF3, 12889, SP98, OP97) averaged across temperatures (15, 20 and 25°C) on mean
lesion area 5 days after inoculation. B, Effect of temperature averaged across
Phytophthora spp. (P. capsici and P. asparagi) on mean lesion area 5 days after
inoculation. C, Phytophthora spp. and temperatures interaction on mean lesion area
5 days after inoculation conducted on ‘Millennium’ and ‘Jersey Knight’ detached

small asparagus spear. Bars with common letters are not signiﬁcantly different LSD
P=0.05. ...................................................................................................................... 56

Figure 14. A, Effect of P. asparagi C013 and P. capsici 13351 averaged across
temperatures (15, 20 and 25°C) on mean lesion area 5 days after inoculation on

vii

asparagus crowns (‘Tiessen’). B, Effect of temperature averaged across
Phytophthora spp. on mean lesion area 5 days after crowns inoculation. C,
Phytophthora spp. and temperatures interaction on mean lesion area 5 days after
crowns inoculation. Bars with common letters are not signiﬁcantly different, LSD
P=0.05. ...................................................................................................................... 57

viii

LITERATURE REVIEW

ASPARAGUS

Asparagus, described by Linnaeus in 1735, is a monocotyledonous genus in the
family Liliaceae, order Asparagales and contains 170 to 300 species (90). Asparagus
ofﬁcinalis L., or garden asparagus, is a perennial, dioecious crop widely cultivated for the
edible spears. Asparagus is considered native to Europe and Asia. In ancient Europe
asparagus was used as a diuretic, sedative and pain killer (18,32,46).

North America and Europe have historically been the largest asparagus producers.
Other production areas include South America, especially Peru (29,131) and Chile; Asia,
mainly Japan and China (81,117); and Australasia, with Australia and New Zealand
representing emerging markets (14). Michigan ranks third in United States asparagus
production behind Washington and California (6). In 2009, Michigan produced 12
million kg of asparagus valued at $16.5 million on 4,532 ha, accounting for 26% of the
total US. production. Harvesting, which is done by hand, begins in May for Michigan
and Washington and in February for California. Mechanical harvest has been proposed
and the economic advantage has been evaluated (89), but it has not been implemented by
asparagus growers in Michigan (30).

Biology and Physiology. The asparagus plant is composed of the crown and the
fern. The crown consists of three underground plant parts: rhizomes, adventitious roots
and storage roots. The rhizome begins as a cluster of buds with a growing tip, which
develop into new lateral buds producing a recurrent pattern of bud clustering. The
extensive network of ﬂeshy storage roots store water and nutrients to feed the buds,
which develop into spears. The root system, consisting of adventitious and storage roots,

can grow more than 1.5 m in length (99). In the crown, lateral roots are responsible for

absorbing water and nutrients; their numbers decrease yearly aﬁer crop establishment. As
storage roots grow, they create a dense network and cause the upward movement of the
crown in the following years (46).

The fern consists of a central stem with scale leaves from which lateral branches
arise. Lateral branches produce secondary branches with cladophylls. Cladophylls are
modiﬁed branches where photosynthesis takes place, resulting in enlarging of roots and
production of new bud clusters in the crown (46).

Stems arising from individual buds in the crown, if not harvested as spears,
develop into ferns reaching up to 2 m in height. In this stage, female asparagus plants
produce yellow or white ﬂowers, which develop into bright red berries with hard black
seeds. Wild asparagus plantings are mixtures of male and female plants (dioecious) (46).
Growth suppression and apical dominance signals differ between male and female plants;
male plants take less time to grow the next bud, have higher carbohydrate content and
less fern area. Male hybrids have greater yields, lower mortality rate, and a longer
production season than female plants. Also, male plants produce more spears, but female
plants produce larger spears (46). Breeders generate male hybrids for their multiple
advantages (69). Male hybrids such as ‘Jersey Giant’ and ‘Jersey Knight’ are popular
asparagus cultivars with increased vigor and yield potential. Currently, growers in
Michigan use ‘Millennium’ and ‘Jersey’ as their major asparagus varieties.

Cultural practices. Michigan’s harvesting season lasts from mid-April through
June (23,46), and the spears can be distributed for fresh or processing markets.
Processing asparagus spears for canning are harvested when they reach 12 cm in height,

whereas fresh market asparagus is picked when the spears are longer (approx. 20 cm) to

allow for trimming and uniformity (89,109). Spear freshness (turgidity), trimming,
straightness, lack of damage or decay symptoms, stalk diameter, and green color
percentage are important quality measures for fresh market asparagus (99).

The perennial nature of the crop makes it productive for 15 to 20 years under
optimal cultural practices and maintenance (46,109). Well-drained sandy or sandy loam
soils, free of perennial weeds and grasses, are needed to establish asparagus ﬁelds.
Acidic soils are not recommended to grow asparagus; the soil pH should range between
6.8 and 7.5, however, Michigan soils average a pH of 5.6 (82,109). Incorporation of
green manure crops or livestock manure before planting is beneﬁcial and increases
organic matter in the soil.

Asparagus ﬁelds can be direct-seeded(25,115), but most Michigan ﬁelds are
established by transplanting one-year-old crowns from seedling nurseries. Large crowns
are highly desired, since root density and activity after establishment will determine the
productivity and life span of the asparagus ﬁeld (83,109). Spacing between plants in the
ﬁeld depends on whether the grower is establishing a nursery or transplanting one-year- ‘
old crowns (Table 1). A nursery ﬁeld has a higher plant density than a production ﬁeld
(Table 1), because less space is required for crown expansion and development (115).

Seedling nurseries are established in mid May or when the soil is warm with temperatures

ranging from 15 to 27°C. After selecting the desired asparagus cultivar, seeds are sown

in a prepared soil bed (25). After one year in the ﬁeld, the crowns are dug in early spring
(March to April) and stored under cool conditions until planting in productions ﬁelds.
Asparagus plant development during the production season goes through the

following stages: bud break, spear growth, fern expansion, bud development, root

growth, fern senescence, and bud dormancy (46). Bud break and spear growth are

controlled by apical dominance and occur at 25°C (39,45). Spears are harvested at >20

cm in length, or subsequent spear growth will be delayed. The production of buds and
bud clusters depends on adequate fern expansion (46). The size of the plants depends on
their age, length of the growing season and any condition that can potentially affect the
performance of the crop in subsequent years (85). Spears, the edible part of the plant, are
the emerging stems. Inappropriate cultural practices and diseases can affect the longevity

of the crop, decreasing its productivity by 5 to 10 years (53,77).

Table 1. Differences between nursery and production asparagus fields.

 

 

Nursery Production
Row spacing 45 — 60 cm 1.2 — 1.5 m
In row spacing 8 — 10 cm 22 - 30 cm
Depth Seed: 2.5 — 4 cm Crown: 15 cm

 

Weed management. Weeds compete with crop plants for light, space and
nutrients, causing quality and yield reduction and crop losses (2,126). Weed
management is an integral part of agriculture; weeds can be managed based on weed life
cycles (e.g., annuals, biennials or perennials), production climatic conditions and the
portion of the crop plant that is harvested (e.g., the stem in asparagus) (84,123).
Herbicides have a signiﬁcant role in weed management in the production of vegetables,
omamentals, fruits, nuts, and other crops in US. and global agro ecosystems, having a
great impact on the economic value of the crops (26). Herbicide management is widely
used in asparagus production. Asparagus does not compete well with weeds during the

nursery stage, because the crop canopy is not dense enough, or during the harvest season,

when weeds can interfere with developing spears (123). In Michigan, losses in asparagus
in 1992 were 20% when weeds were managed with herbicides and hand weeding, and
70% when best management practices were used but no herbicides were applied (26).

In late spring, herbicides are commonly applied preemergence and incorporated
mechanically into the soil. During harvest, herbicides may be applied postemergence and
after the ﬁnal harvest (22). Effective herbicide usage in asparagus production eliminates
possible damage to the crown resulting from tillage to control weeds (70,135).
Herbicides are applied directly to soil in any combination of three crop stages: preplant,
preemergence or postemergence, but not during spear harvesting. Preplant herbicides can
be mechanically mixed into the soil, in contrast to the pre and postemergence herbicides
which are applied to the soil surface (34). Mechanically incorporated herbicides are
immediately effective without moisture, whereas some surface-applied herbicides must
be moved into the soil by water before they can become active. Herbicide half-lives
range from a few days to months from the application date, and some persist in the soil
for more than a year depending of the active ingredient (33,34).

Herbicides can cause weakening of the plant and increased vulnerability to
pathogens or saprobes. The effect of herbicides on plant disease can be direct or indirect
(1,4). Direct effects include stimulation or delay of pathogen growth, and increasing or
decreasing host susceptibility to the pathogen. Indirect effects can be related to soil
microﬂora activity, change in microclimate of the crop, and selection or elimination of
microorganisms (136). The increase in host susceptibility can be due to changes, such as
a weakening of structural defenses of the host, plant exudation stimulation, pathogen

growth augmentation, or inhibition of competing microﬂora. Changes in host reaction to

a pathogen is primarily due to herbicide-induced morphological and physiological
changes, such as reduction of wax formation on leaves, changes in carbohydrate,
nitrogen, or glucoside metabolism; or retardation or stimulation of plant growth (1,4).

Herbicide usage appears to have a positive effect in some pathosystems, as in
Phytophthora collar rot of various crops (1,4) where the disease is ameliorated. Several
well known cases show that herbicide usage can aggravate severity of diseases, as in
sudden death syndrome caused by F usarium solani f. sp. glycines (116), or in the root rot
and damping-off caused by Rhizoctonia solani Kuhn in soybean, sugar beet, and cotton
(75). From these cases, an herbicide-phytoalexin interaction has been identiﬁed; a
reduction of phytoalexin production is directly proportional to the concentration of the
herbicides applied in the Sclerotinia stem rot and soybean pathosystem (103).

Crop rotation and cover crops. Sustainable agricultural settings, especially in
vegetable crops, have been gaining importance in the last decade, mainly to lessen the
agrochemical effects on the environment, address public health concerns, and increase
interest in organic production (100). Cover crops, in contrast to traditional practices, are
an ecological alternative for weed management, causing weed seed decay, breaking
disease and pest cycles, and reducing pesticide usage (122). Cover crops can provide
greater yield stability of crops (124) with less fertilization, while improving soil
characteristics (104). In addition, cover crops could potentially reduce the reliance on

agrochemicals in disease management (112).

Perennial and herbicide resistant weeds present in the soil bank are favored and
their populations may increase in asparagus production, a monoculture that remains in

place for years. Thus, weed control is essential to achieve proﬁtability (138). Soil

improvement is difﬁcult, as tillage is not recommended for asparagus (70,135), and crop
rotation is not a possibility (8). However, cover crops represent an opportunity to
maintain productivity, soil health and weed control; it has been very useful in other crops
(104) as living or dying mulches in the ﬁeld (122). Currently, cover crops are
recommended in organic asparagus production (91) and could be introduced into
traditional asparagus cropping systems. Barley, used in Japan as living mulch (8),
suppressed weed emergence of lamb’s quarters (Chenopodium album L.). Extensive
research would be needed to assess the effect of cover crops on weeds common to

asparagus ﬁelds.

ASPARAGUS DISEASES

Diseases can be a limiting factor in asparagus anytime during production of this
perennial crop. Diseases can be present in newly-planted seedling ﬁelds and in old
asparagus ﬁelds, when production may be decreased due to a combination of pathogens
that can develop in the crop. Grogan and Kimble ﬁrst described asparagus decline
syndrome in 1959 as a “slow decline in the productivity of old asparagus plantings and
the inability to reestablish productive plantings” (74). A marked reduction in the size and
number of spears and death of the crown is characteristic of decline (5 3), making harvest
unproﬁtable, and resulting in premature abandonment of the asparagus ﬁeld (42). The
fungal components of asparagus decline syndrome include Puccinia asparagi DC. in
Lam. & DC., Stemphylium vesicarium (Wallr.) E. Simmons (telemorph: Pleospora
herbarum), Cercospora asparagi Sacc., and several F usarium spp., causing rust, purple
spot, C ercospora blight, and crown and root rot, respectively (53). Three viruses have

been associated with decline; asparagus virus I, asparagus virus 11, and tobacco streak

virus (56). Phytophthora spp. have also been reported as destructive pathogens
(60,73,118), but are not currently in the list of pathogens causing decline.

Due to the perennial nature of the crop and the important role of the crown and
roots in asparagus, pathogens able to infect these main organs compromise longevity and
productivity; thus, crown and root rots are management priorities (3 8). Fusau'ium crown
and root rot has been widely studied and characterized, but Phytophthora spear and root

rot has recently been identiﬁed as a threat in Michigan ﬁelds (118,119).

Fusarium crown and root rot

F usarium generalities. The genus F usarium Link include some of the most
common and important fungal pathogens, parasites and saprobes widely distributed in
soil and organic matter and associated with plants and animals (20). F usarium spp. are
primarily soilbome, but some are airborne (27,98). F usarium spp. are well known
necrotrophic, vascular wilt pathogens, causing dysfunction of the xylem (1).
Identiﬁcation of F usarium spp. is based on microscopic morphology of asexual
structures, and macroscopic colony characteristics. The genus F usarium produces
macroconidia in sporodochia and microconidia on primary conidiophores, as well as
chlamydospores and occasionally sclerotia (120). F alcate or fusiform macroconidia are
the most distinctive feature in genus identiﬁcation. Although other fungi may have
macroconidia with a similar shape, the ontogeny is different (120). Due to the plasticity
and instability of F usarium spp. in culture (105), identiﬁcation based on production of
secondary metabolites such as mycotoxins, and genetic sequences (such as elongation

factor, B tubulin) has been proposed and recently used (65,129).

Anamorph and teleomorph connections have been established for several
F usarium spp. The sexual reproduction, or teleomorphic stage of F usarium spp. are
perithecium-forming fungi in the genera Giberella and Nectria within the order
Hypocreales, class Sordariomycetes and phylum Ascomycota. Other related teleomorphs
such as Cosmospora, Calonectria, Hyphomyces and Bionectria have F usarium-like
anamorphs, but lack one or more of the microscopic features previously described (120).

F usarium species pathogenic to asparagus. F usarium can cause an array of
symptoms in asparagus that have yielded multiple disease names such as asparagus
dwarf, wilt, rot; seedling blight, foot rot, dead stem, and spear spot and rot, in addition to
the most common crown and root rot disease (48,51). Fusarium crown and root rot
symptoms are evident in seedlings, young plants and mature plants in established ﬁelds.
Seedling damping-off is common in nurseries. Chlorotic and stunted plants may be
present in ﬁelds that have been harvested for several years. Spears become shriveled and
stunted, which can be very similar to abiotic stresses such as winter injury, drought or
soil compaction (121). Fewer and smaller or damaged spears are produced as a
consequence of the infection and progression of the disease. When dormant infected
crowns grow fern in summer, the infection is noticeable as yellowing of the fern canopy
(51). Disease extends up from the base of stem, brown necrosis follows initial chlorosis,
and in advanced disease stages, stern and crown death become evident in the ﬁeld as
stand loss (48).

Symptoms are caused predominantly by F. oxysporum (Schlecht) f. sp. asparagi
(S. I. Cohen)(FoA) and F. proliferatum (Matsushima) Nirenb. (telemorph: Gibberella

fujikuroi (Sawada)) (51,52). The ﬁrst report of F usarium spp. infecting asparagus was

10

made in 1908 in Massachusetts by Stone (127). In 1941, Cohen and Heald described F.
oxysporum as the rot etiologic agent (35), followed by the addition of the term forma
specialis asparagi by Grogan and Kimble in 1959. F usarium oxysporum f. sp. asparagi
has a wide host range, opening the discussion of forma specialis term usage (51).

F usarium oxysporum f. sp. asparagi is seedbome, soilbome, and can be found in one-
year-old crown tissue, implying that crowns used to establish production ﬁelds can be a
source of inoculum (16). However, isolates can be pathogenic or nonpathogenic. For
example, only 15% of F usarium isolates from soil in Michigan ﬁelds were pathogenic on
asparagus (78).

Isolates of F. oxysporum f. sp. asparagi are classiﬁed in at least 6 different
vegetative compatibility groups (VCGs), and phylogenetic analysis has shown multiple
evolutionary origins (12). No association between pathogenicity and VCGs has been
found, at least in the forma specialis asparagi, which is composed of genetically diverse
populations (88). Some authors argue in favor of Fusarium crown and root rot as a
disease complex caused by F. oxysporum f. sp. asparagi, F. proliferatum and F. redolens
Wollenw in asparagus (13), but this concept is not widely accepted. Some other species
have been reported to cause a variety of symptoms on asparagus (41 ,52,68).

Among the other species, F. culmorum (W.G. Smith) Sacc. has been reported to
cause stem chlorosis, death of mature stems (51), and has contributed to crown and root
rot predisposition. F usarium redolens causes a postharvest spear spot mainly in Europe,
and is characterized by a tissue softening in storage (13). F usarium subglutinans

(Wollenw. & Reinking) Nelson Toussoun & Marasas and F. mom'liforme Sheld. have

11

been isolated from asparagus and showed pathogenicity as well (41,52), but are not major
asparagus pathogens.

Management. Effective management of Fusarium crown and root rot should
include a combination of cultural practices, adequate agrochemical programs, and
alternatives like biological control. Several asparagus varieties are vigorous and can
withstand adverse conditions and suppress crown and root rot (114,125). However, there
are no F usarium-resistant asparagus cultivars on the market, despite attempts to identify
resistance using somaclonal variation and variety screening (43).

Stress is a factor that can predispose asparagus plants to disease (106). Winter
injuries, drought, high weed pressure, and harvesting or overharvesting can increase
disease incidence (50,109,110). Soil with pH level <6.0 can enhance disease. With this
knowledge, it is critical to maintain the soil pH between 6.8 and 7.5 by application of
lime. Careful use of amendments such as nitrogen or sodium chloride (NaCl) may have a
positive effect on the crop (54). NaCl has been applied to decrease Fusarium crown and
root rot incidence in asparagus crops and increase yield (38,111). NaCl can have limited
success as a disease control strategy if the amount and periodicity is not regulated. The
mechanisms of F usarium suppression by NaCl are not known, but the plant produces
more feeder roots and the colonization of F. oxysporum and F. proliferatum is reduced.
It is possibly related to changes in the microbial soil composition (49).

Fungicides are an important part of disease management and are used at different
crop stages (110). F ungicide-treated seeds can be used to start nursery seedlings, one-
year-old crowns can be dipped in fungicide before planting, and untreated crowns can be

planted into fumigated soil or a combination of these practices used (15,79). Soil

12

fumigants include 1,3-dichloropropene/chloropicrin (Telone C35), metam sodium
(Sectagon 42, Vapam HL), or metam potassium (Sectagon-K54) (15,79).

Alternative strategies to reduce crown and root rot disease using biological
controls have been studied including Trichoderma (10,109,110), beneﬁcial bacteria
(133), mycorhizae (11) and nonpathogenic F. oxysporum isolates (109). Biological soil
disinfestations using Italian ryegrass has been shown to decrease the population diversity

and viability of F usarium spp. in abandoned asparagus ﬁelds (17).

Phytophthora spear and root rot

Phytophthora generalities. Among plant pathogenic oomycetes, Phytophthora
spp. are parasitic on diverse host plants, with broad or narrow host ranges (55). Diseases
caused by Phytophthora spp. produce rapid and destructive symptoms with important
socioeconomic impact (55). Morphological identiﬁcation of Phytophthora spp. is based
on antheridium location, sporangial size, length and breadth; sporangial caduceus nature,
presence of papillae in sporangia, chlamydospore presence and size, oospore size and
abundance, cardinal growing temperatures, hyphal swellings, and homo- or
heterothallism (55). At the DNA level, Phytophthora taxa are differentiated using
ribosomal DNA, internal transcribed spacer sequences (ITS), and B tubulin sequences to
support morphological classiﬁcation criteria (37).

Phytophthora species pathogenic to asparagus. Phytophthora causes spear and
root rot in asparagus. Flooded or overly wet soils are needed for Phytophthora zoospore
dispersal; therefore, the rot is favored by excessive rainfall and poor soil drainage
(60,118,119). Symptoms include distinctive water-soaked lesions on shoots and roots;

sometimes symptoms can be confused with herbicide damage (1 18,119), especially when

13

lesions elongate and turn brown, causing spears to shrivel and curve, resulting in
unmarketable spears (9,118). Early reports of Phytophthora rot were made in 1938 in
California (9). Phytophthora megasperma and some other Phytophthora spp. were
identiﬁed as the causal agents. Historically, ﬁve different species of Phytophthora have
been reported to cause disease in asparagus: P. megasperma Drechsler (60), P.
megasperma var. sojae Hildebrand (58), P. richardiae Buisman (55,60) , P. cryptogea
Pethybridge & Lafferty (55,58) and P. cactorum Lebert & Cohn (60) (Table 2).
Phytophthora megasperma taxa have been a subject of continuous discussion regarding
species delimitation and variety names. Due to morphological variability, P.
megasperma isolates that were divided according to host speciﬁcity are now considered
different species; P. megasperma var. sojae (118) is now renamed as P. sojae (36).

In Michigan, a homothallic Phytophthora sp. was reported in 2004 (119), when a
spear and root rot outbreak occurred due to the excessive precipitation and poor drainage
in asparagus ﬁelds during the harvesting season. This species was characterized based on
131 isolates with ovoid nonpapilate, noncaducous sporangia, amphigynous oospores, and
sensitivity to mefenoxam (100 ppm) and named P. asparagi (73,119).

Management. Strategies to manage Phytophthora in asparagus require
knowledge of the species associated with the crop, resistance to agricultural chemicals,
and cultural management. Correct irrigation is key to avoid plant stress, since ﬂooding of
the ﬁeld can be conducive for infection by Phytophthora spp., including P. asparagi
(59,73,119). Currently, few Michigan growers irrigate their asparagus spears.

Fungicide application is recommended and may occur before planting as crown

soaks prior to planting the crowns in ﬁelds. Soil fumigation is recommended only in

14

ﬁelds with high disease pressure, and the combination of crown soak and soil fumigation
is recommended in replanting ﬁelds (79). In the United Kindom, metalaxyl is considered
an acceptable Phytophthora spear rot management practice (73), but it could have
phytotoxic effects in high doses (>150 ppm) (57). Fungicides such as mefenoxam
(Ridomil Gold EC, Ultra Flourish), mono/dibasic sodium salts of phosphorous acid
(Phosphite), mono/dibasic sodium, potassium and ammonium phosphites (Phostrol or
Prophyt) are labeled to be used to control asparagus Phytophthora spear and root rot in
Michigan (15).

Phytophthora-resistant asparagus varieties have been developed using recurrent
selection in California (57), but their resistance has not been assessed in Michigan. Other
alternative control measures in the P. asparagi/asparagus pathosystem need further

research.

15

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CHAPTER I

GREENHOUSE AND FIELD HERBICIDE EVALUATION ON ASPARAGUS

PLANTS

Manuscript accepted in Acta Horticulturae

17

ABSTRACT

Pre and postemergence herbicides are used to control weeds in Michigan
asparagus nurseries and production ﬁelds. Greenhouse and ﬁeld experiments were
conducted to test the effect of 10 herbicides on (i) growth of asparagus plants and (ii)
susceptibility to crown and root rot caused by F usarium oxysporum f. sp. asparagi.
Crowns were planted in pots containing infested soil (F. oxysporum f. sp. asparagi) or
noninfested soil and sprayed individually with the selected herbicides and grown in the
greenhouse. Crown and fern health were evaluated three months after planting. Obvious
growth effects of the herbicide treatments on asparagus growth were not commonly
observed and incidence of crown and root rot was low. However, a reduction in crown
weight was observed among some plants grown in herbicide-treated soil. Another
experiment was conducted whereby crowns were planted in a commercial ﬁeld and
treated prior to emergence with one of the following herbicides: glyphosate, halosulfuron,
mesotrione, norﬂurazon, linuron, sulfentrazone, s-metolachlor, metribuzin, diuron, and
terbacil. Weed control, asparagus fern stand and height, and overall fem health were
assessed. In the ﬁeld, mesotrione had a negative effect on asparagus fern health, which
was also observed in the greenhouse. Current results suggest select herbicide

applications can compromise fern growth, which could inﬂuence yields.

18

INTRODUCTION

Herbicides play an important role in asparagus; maximizing crop production for a
given amount of land, and minimizing unwanted or harmful non-crop plants that
potentially can become established in asparagus ﬁelds and compete for space and
nutrients (76,84). Due to the perennial nature of the asparagus crop, tillage as a weed
control strategy has been reduced or eliminated, since crowns will be exposed to injury
and infection by F usarium spp., increasing Fusarium crown and root rot incidence (22).
However, absence of tillage promotes perpetuation of the weed bank in the soil when
annual and perennial weeds prevail (135), and as a result herbicide application (137)
and/or hand weeding are needed .

A considerable number of herbicides are available in the market; they differ in
toxicology, action spectrum, activity, crop safety and environmental effects (87). In the
United States and Canada a list of 27 herbicide groups (by active site of action), with an
average of four chemical families within the group, are available for weed control,
accounting for at least 200 active ingredients (97). In asparagus, 18 active ingredients are
recommended in Michigan for established ﬁelds, seven in seed beds for crown
production, and only ﬁve active ingredients can be used in newly planted asparagus
(137).

Herbicide modes of action target normal physiological processes in weeds, but the
same processes can be affected in crop plants. In fact, herbicides such as linuron, diuron,
norﬂurazon and metribuzin can be used to partially control volunteer asparagus while

controlling other weeds in the ﬁeld (22,23). Also, herbicides may have adverse effects

19

on crop health; ranging from phytotoxicity, harmful effects in plant stand, to inductive
stress causing predisposition to disease (4).

F usarium oxysporum f. sp. asparagi causing F usarium crown and root rot is a
concern in any developmental stage of the asparagus crop, contributing to asparagus
decline worldwide (51). The characteristic symptoms of the disease such us destruction
of feeder roots, fern yellowing and senescence, and crown rot and death, are evidence of
the damage cause by this soil inhabitant (53). Management of Fusarium crown and root
rot relies on a combination of strategies, such as crown fumigation, planting in ﬁelds with
no history of decline and adequate cultural practices (15,53). Currently, the effects of
herbicides on asparagus plants and their interaction with Fusarium crown and root rot are
unknown. The purpose of this study was to determine the effect of herbicides on
asparagus plant stands and on Fusarium crown and root rot incidence in one-year-old

asparagus crowns.

MATERIALS AND METHODS

Greenhouse herbicide studies. One-year-old, untreated ‘Millenium’ asparagus crowns
from a nonfumigated commercial nursery (Dillinghams Farms in Oceana County, MI)
were rinsed of debris and visually screened to ensure absence of disease. Crowns were
weighed (between 25 to 45 g) and stored in individual plastic bags overnight. Sandy
loam soil was steam-pasteurized 18 h for two consecutive days to decrease microbial load
that could interfere with the following soil infestation process.

Inoculum was prepared using a pathogenic F. oxysporum f. sp. asparagi isolate
F 0A 50 from the culture collection at M. K. Hausbeck’s laboratory at Michigan State

University (MSU). The isolate was recovered originally from a Michigan asparagus ﬁeld

20

by W. Elmer (109). Milk jugs containing 1 lb of millet seed and 150 ml of water were
autoclaved for 1 hour on two consecutively days. A millet seed sterility test per container
was conducted on potato dextrose agar media (PDA). Eight 0.7-mm plugs of fungal
mycelium from ﬁve-day-old cultures of F. oxysporum f. sp. asparagi (F 0A) were used to

inoculate containers with 1 lb of sterile millet, and allowed to grow for two weeks in

laboratory environmental conditions at 21 : 20C under ﬂuorescent lighting, and shaken

occasionally to avoid clumping. Fungal growth was assessed visually and using

microscopy. F 0A -infested millet (400 g) and 40 liter of soil (10 g/liter) were mixed with

steamed sandy loam soil in a cement mixer (109,133), yielding 4 x 104 colony forming

units (cfu) per gram of soil (pooled average for both experiments). Control soil consisted
of sterile millet seed mixed with the soil in the same proportion as the infested one.

Of 220 pots, 1 10 were ﬁlled with a mixture of 10 g infected millet seed per liter of
sandy loam soil. The remaining 110 pots were ﬁlled with a mixture of sterile millet seed
and sandy loam soil, as a negative control. Two-gallon pots (Hummert International,
Earth City, M0) were ﬁlled to 1/4 with the soil and millet mixture (F 0A infested or
noninfested), then the crowns were transferred to the pot, and pots were ﬁlled to the top
with the respective soil mixture.

Ten herbicides and two soil treatments were tested in a complete randomized
design (CRD), and the trial was conducted twice. Twenty plants per herbicide treatment
and 10 plants per soil treatment were used. Soil herbicide application treatments (Table
3) were conducted one week after the crowns were transplanted to the pots. Herbicide
application was preemergence of weeds and spears, and the rate used followed the MSU

extension recommendation and manufacturer instructions. Herbicide rates were chosen

21

based on a hypothetical high weed pressure in the ﬁeld when a grower would use the
herbicides at higher recommended rates (Table 3). Treatments were applied in the spray
chamber of the pesticide application laboratory at MSU, for each herbicide treatment,
starting with the control soil pots and followed by the F 0A infested ones. The nozzle was
rinsed three times prior to a new treatment being applied. The nozzle was 33 cm from the
soil surface, the nozzle (8001 E) roll at 1 mile per hour, using a 25 psi (172/5KPa)
pressure at the sprayer head, simulating 20 gallons per acre (GPA) (187 liter/ha),
dispensing 0.077 gallons per minute (0.29 liter/min) from the nozzle.

Table 3. Herbicide treatment rates applied to asparagus in greenhouse and ﬁeld
experiments.

 

 

Greenhouse Field
Treatment Herbicide
No. active ingredient (AI) AI 1‘8 113.1 AI kg 113-1

1 Linuron 1.121 1.682
2 Norﬂurazon 4.484 1 .121
3 s-metolachlor 2.130 1.491
4 Sulfentrazone 0.420 0.280
5 Halosulfuron 0.005 0.067
6 Glyphosate 4.484 3.363
7 Diuron 0.897 1.121
8 Mertibuzin 1.121 0.740
9 Flumioxazin 0.215
10 Mesotrione 0.270 0.213
1 1 Terbacil 0.280
12 Mixturez 1.682

 

 

z Mixture contains sulfentrazone 0.348 kg ha], metribuzin 0.561 kg ha], s-metolachlor
1.682 kg ha", glyphosate 3.363 kg ha".

22

Irrigation was carefully controlled in the greenhouse; after herbicide application
the pots were watered to fulﬁll the requirements of water-dependent herbicides, but
avoiding herbicide leaching. A week after herbicide application, pots were watered as

needed every three days. In order to allow complete fern expansion, fertilizer was

applied 60 days after planting (DAP), with NH4NO3 (42-0-0) and KCl (0-0-62) at rates

of 0.07 and 0.04 lb/ (31.7 and 18.1 g) per plant, respectively.

Herbicide injury was monitored and recorded, as the ﬁrst shoots appeared and
throughout the duration of the trial. Disease symptom appearance and development in
stems were monitored, as well as phytotoxicity or abnormal growth. Numbers of stems
and fern length were recorded three times. Plant stand counts (number of stems per plant
and total fern length) were recorded during both trials. A destructive measurement was
conducted at the end of the trial for variables such as crown fresh weight, percentage of
crown weight gain (subtracting ﬁnal fresh weight from the crown initial fresh weight),
presence of crown and root disease symptoms (reddening), fern dry weight, crown fresh
and dry weight, and total plant dry weight. Disease was assessed before obtaining the dry
weight variables, and consisted of the percentage of roots exhibiting lesions or
discoloration (l=0-10%, 2=11-20%; 3=21-30%, 4:31-40 %, 5=>40%). The reisolation
of F usarium for 5% of plants was conducted to conﬁrm F 0A infection (10,133).

Field herbicide studies. One-year—old ‘Millennium’ crowns were planted in
sandy loam soil on a commercial asparagus farm in Oceana County, MI previously
planted to cucurbits. Fertilizer, insecticides, and fungicides were applied according to
commercial practices. The ﬁeld was fumigated in fall with sodium

methyldithiocarbamate (Sectagon 42, Tessenderlo Kerley, Inc Phoenix AZ) at 40 gal/acre

23

(378 liters/ha) and planted in the spring with ‘Millennium’ asparagus crowns grown in a
fumigated nursery. Eleven herbicide treatments and an untreated control (Table 3) were
arranged in a completely randomized block design with four replications. Each treatment
plot was 1 row wide (152 cm) and 6 m long, with crowns spaced 18 cm apart. Eleven

herbicide treatments (Table 3) were applied according to the rate commonly used by

growers in Michigan, prior to emergence, with a C02 backpack sprayer and a 3-nozzle

boom equipped with 50-mesh screens and 8003 XR nozzles (Teejet technologies
Wheaton, IL) spaced 48.3 cm apart, calibrated to deliver 50 GPA (407 L/ha). The
numbers of healthy bleached ferns or ferns with epinasty were counted 45 DAP. The
efﬁcacy of the herbicides for control of grass and broadleaf weeds were evaluated 25 and
45 DAP by counting the number of each kind of weeds: grasses or narrowleaf that were
presented together and; broadleaf (i.e. pigweed, lambsquarters, eastern black nightshade)
in plots and compared with the control plots an expressed as the percentage. Phytotoxic
effects on the fern were evaluated 30 DAP using a 1 to 5 rating scale (1 = healthy, 2 =
minor chlorosis, 3 = moderate chlorosis, 4 = major chlorosis, 5 = fern death). The
numbers of healthy ferns were recorded and fern height was measured 60, 90 and 120
DAP.

Statistical analysis. Descriptive statistics were performed for seven continuous
variables and four categorical variables. Normal distribution and equality of variances
were checked, and if not fulﬁlled, appropriate transformation or grouping was conducted
when needed. When normal distribution and equal variance assumption were ﬁilﬁlled;
analysis of variance (ANOVA) was conducted using PROC MIXED and PROC

GLIMMIX procedure (SAS institute Inc., Cary, NC), treatment means were compared

24

using Fisher’s protected least signiﬁcant difference (LSD) and were considered

signiﬁcant using a=0.05.

RESULTS
Greenhouse herbicide studies. After soil pasteurization, assessment of the

microbial community was conducted using dilution plating, resulting in high numbers of

miscellaneous bacteria and fungi (2 x 104 cfu/g soil). Prevalent organisms were tested in

vitro to determine whether they inhibit F oxysporum f. sp. asparagi (F 0A ) growth on

PDA, with no apparent in vitro inhibition. The infested soil had 3 x 104 and 5 x 104 FoA

cfu per gram of soil for the ﬁrst and second trial respectively.

During both trials fem-yellowing incidence was low among herbicide treatments.
F usarium crown and root rot disease incidence in crowns and roots was low; 78% of the
crowns showed minor or no reddening symptoms (disease scale rating=l), and only 4%
showed symptoms rating between 3 and 4 (from 20 to 40% lesion and discoloration
coverage) when the crowns were grown in F 0A infested soil. From crowns planted in
control soil, 17.9% of the crowns rated as 2 and 3, and 82% of the crowns showed 510%
lesion coverage. Five crowns were dead (no spear emergence).

Phytophthora asparagi symptoms were observed when the crowns were rated for
Fusarium crown and root rot. The lesions were brown and water soaked but the
incidence was low. For both soil types, 68% of crowns showed 510% lesion coverage
for Phytophthora rot symptoms, 27% of the crowns showed from 20 to 30% lesion
coverage, while only 5% showed from 30 to 40% crown lesion coverage. Disease

severity for both asparagus rots were tested using Chi square or PROC GLIMMIX, as a

25

result no signiﬁcant differences were found for herbicide or soil factors, or for their
interaction.

Phytotoxicity was documented as abnormal growth (Table 4), but only 13% of the
total plants showed distorted growth, stunting or a combination of the two. Damage was
observed in the ﬁrst emerging spear/fem but the following ferns did not show damage. In
pots sprayed with sulfentrazone, 20% of the plants showed phytotoxicity, independent of
the presence of the pathogen (infested and noninfested soil). Plants growing in sterile
millet (20%) and growing in F 0A infested soil (15%) showed phytotoxicity in the
metolachlor treatment.

Table 4. Number of plants showing phytotoxicity in uninfested ﬁeld soil or soil infested
with F usarium oxysporum f. sp. asparagi following treatment with herbicides.

 

Soil treatment

 

 

 

Herbicide treatment Sterile millet F 0A infested soil Total
Linuron 3 (20)Z 4 (20) 7 (40)
Norﬂurazon 3 (20) 3 (20) 6 (40)
s-Metolachlor 4 (20) 3 (20) 7 (40)
Sulfentrazone 4 (20) 4 (20) 8 (40)
Halosulfuron 2 (20) 0 (20) 2 (40)
Glyphosate 2 (20) 4 (20) 6 (40)
Diuron 3 (20) 2 (20) 5 (40)
Metribuzin l (20) 2 (20) 3 (40)
Flumioxazin 2 (20) 4 (20) 6 (40)
Mesotrione 3 (20) 0 (20) 3 (40)
Control 2 (20) 2 (20) 4 (40)
Total 29 (220) 28 (220) 57 (440)

 

ZNumber in parenthesis indicates total number of plants.

26

From seven variables (presence of crown and root disease symptoms, tallest fern,
fern dry weight, percentage of crown weight gain, crown dry weight, and total plant dry
weight), only tallest fern, fern dry weight, crown dry weight, and total plant dry weight
showed signiﬁcant differences within soil treatments, and three (crown weight gain and
crown dry weight, and total plant dry weight) showed signiﬁcant differences among
herbicide treatments (P<0.05). None of the variables showed signiﬁcant interaction
between soil and herbicide treatments.

When taking into account only the tallest fern of every crown (plant), asparagus
ferns growing in soil infested with FoA were signiﬁcantly smaller (P=0.02) than ferns

growing in the control soil (Figure 1).

 

160 I
1..- 1 -

 

120—
100;

Highest fern (cm)

o3888

 

 

 

 

 

 

1
Control FoA
Soil treatment

Figure 1. Effect of soil treatment on asparagus fern length (tallest fern only) in
greenhouse experiments with asparagus plants grown in soil mixed with sterile millet
seed (solid bar) and in soil infested with F. oxysporum f. sp. asparagi (FoA white bar)
across herbicide treatments. Bars with common letters are not signiﬁcantly different,
LSD P=0.05.

27

Fern, crown and total dry weight showed signiﬁcant differences between soil
treatments; asparagus plants grown in soil infested with F 0A had a higher average weight

compared to the plants growing in soil mixed with sterile millet (Figures 2, 3A and 5A).

 

 

l
J
a

Fern dry weight (g)

 

 

 

 

 

 

0 1
Control FoA

Soil treatment
Figure 2. Effect of soil treatment on asparagus fern dry weight in greenhouse
experiments with asparagus plants grown in soil mixed with sterile millet seed (solid bar)
and in soil infested with F. oxysporum f. sp. asparagi (FoA white bar) across herbicide
treatments. Bars with common letters are not signiﬁcantly different, LSD P=0.05.
The effect of herbicide was signiﬁcant for three variables: crown weight gain, crown dry
weight, and total dry weight. When making comparisons among herbicides across soils,
crowns growing in pots treated with mesotrione showed the smallest weight gain. Plants
growing in pots sprayed with diuron, linuron, glyphosate and ﬂumioxazin were
signiﬁcantly different form the ones in mesotrione but no with the control plants.
Norﬂurazon, s-metolachlor, sulfentrazone, halosulfuron and metribuzin showed

homogeneous averages not signiﬁcantly different form mesotrione or the control (Figure

4).

28

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Asparagus plants growing in pots sprayed with mesotrione and sulfentrazone
showed the lowest crown dry weight average and were signiﬁcantly different from the
control (Figure 33), whereas crown dry weight averages for plants sprayed with
glyphosate, diuron, s-metolachlor, metribuzin, linuron, norflurazon, halosulfuron and
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sulfentrazone treatments.

 

Crown weight gain (9)

 

 

Herbicide treatment

Figure 4. Effect of herbicide treatment on asparagus crown weight gain in greenhouse
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letters are not signiﬁcantly different, LSD P=0.05.

Results for asparagus plant total dry weight (Figure 5) were similar to crown dry
weight (Figure 3). Plants growing in pots sprayed with mesotrione showed signiﬁcantly

smaller total dry weight than the control (Figure 5B).

30

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31

Field herbicide studies. Herbicide control efﬁcacy was evaluated for grasses and
three main broadleaf weeds: Chenopodium album L. (lambsquarters), Amaranthus
retroﬂexus L. (pigweed) and Solanum ptycanthum Dunn. (eastern black nightshade).
Many of the herbicides tested showed effective weed control (280%) 25 DAP. Grass
control was signiﬁcantly different (P<0.0001) among herbicide treatments (Table 5), with
glyphosate showing the highest percentage of weed control (95.7%).

Table 5. Effect of herbicide treatments on weeds counts (compared with the untreated
control) in asparagus ﬁeld, Oceana County 2009.

 

Weed control efficacy (%)Z

 

 

 

Broadleaf weeds y
Herbicide Eastern black
Treatment Grass weeds x Pigweede Lambsquartersv nightshade u
Linuron 51 .3 det 83 .8 abc 89-4 “38 100-0 “55
Norﬂurazon 43 .8 de 95.0 ab 100.0 100.0
s-Metolachlor 51.3 de 57.5 cd 100.0 100.0
Sulfentrazone 15 .0 ef 100.0 a 95.3 100.0
Halosulfuron 6.3 ef 100 a 100.0 86.2
Glyphosate 95 .7 a 38.8 (1 100.0 95.8
Diuron 53.8 cd 85.0 abc 82.5 100.0
Mertibuzin 87.5 b 67.5 bcd 100.0 94.2
Mesotrione 3 1 .3 def 97.5 ab 94.2 100.0
Terbacil 71.3 abc 45.0 d 90.9 90.9
Mixture 99.0 abc 96.3 ab 100.0 92.1

 

2 Percentage based on number of weeds at the control plot

y Data collected 45 DAP. x Data collected 25 DAP

WAmaranthus retroﬂexus. v Chenopodium album. u Solanum plycanthum
tColumns with common letters are not signiﬁcantly different, LSD P=0.05.
5 not signiﬁcant (P>0.05)

32

Phytotoxicity was observed as chlorosis in the asparagus spears with some degree
of epinasty and curving. Mesotrione showed the highest rate of phytotoxicity with an
average of 4.5, and signiﬁcantly differed from the remaining herbicide treatments
(P<0.0001). The remaining herbicide treatments did not show signiﬁcant phytotoxic
effects with averages ranging from 1 to 1.75. Stand counts signiﬁcantly differed among
treatments when comparing the number of healthy spears to spears with phytotoxicity
(curving and bleaching). Only 4.8% of the spears in plots sprayed with mesotrione
exhibited bleaching while 10% of spears in plots sprayed with glyphosate showed
curving as previously described (3).

The percentage of change was estimated by comparing the initial numbers of
spears at 30 DAP to the number of spears and new fern development at 60 DAP.
Although not signiﬁcantly different from the untreated, plots treated with mesotrione and
halosulfuron showed fewer new spears and young fern growth. Terbacil, glyphosate and
the herbicide mixture had more spears per plot compared to the control (Figure 6).

Additional stand counts and fern height measurements were taken at 60, 90 and
120 DAP to determine negative herbicide residual effects and weed competition that limit
asparagus plant expansion. Herbicide treatments showed signiﬁcant differences among
asparagus plant heights (P<0.0001). Linuron and diuron consistently had taller plants
than the control at 60 and 120 DAP, while plots sprayed with terbacil had the highest fern
number for all DAP measurements (Table 6). The smallest fern height averages were
obtained from plots sprayed with mesotrione and sulfentrazone (Table 6). At 60 DAP,
fern heights on plots sprayed with mesotrione and the herbicide mixture were comparable

to the untreated control. However, the herbicide mixture had a signiﬁcantly greater

33

number of ferns than the control and mesotrione (Table 6). At 90 and 120 DAP,
mesotrione-treated plots produced average fern heights that were signiﬁcantly less than

the untreated control and all other treatments, with the exception of sulfentrazone.

“I. Change in spear stand counts

 

Herbicide treatment

Figure 6. Effect of herbicide treatment on asparagus spear counts 30 and 60 days after
planting (DAP) in the ﬁeld. Bars with common letters are not signiﬁcantly different, LSD
P=0.05.

The number of ferns at 60, 90 and 120 DAP in plots sprayed with sulfentrazone
were not signiﬁcantly different from the control or the plots sprayed with mesotrione.
Nonetheless, plots treated with sulfentrazone showed the smallest fern counts and heights
of all the herbicide treatments at 60 and 90 DAP. At 120 DAP, plots sprayed with
sulfentrazone showed fern heights that were similar to mesotrione; both were

signiﬁcantly smaller than the control ferns (Table 6).

34

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DISCUSSION

Asparagus production relies on herbicide usage for weed management (137).
However, herbicide selection poses challenges in terms of selectivity to decrease the
potential adverse effects over the crop health. The effects of herbicides on Fusarium
crown and root rot in asparagus were inconclusive in the greenhouse experiments due to
low disease incidence. Low disease incidence could be attributed to the presence of (i)
innocuous crown inhabitants and/or (ii) microbial community activity in the
rhizosphere—both of which may compete with F 0A establishment (134). It is also
possible that the environment did not favor disease development. Even though herbicides
have been shown to have different effects on soil microbial community composition
and/or activity (4,95), we did not include these interactions in our original objectives.

Phytotoxicity was low but observed among the herbicide treatments and in F 0A-
infested and noninfested soil, signiﬁcant difference among herbicides treatments or
herbicide-soil interaction was not observed. The majority of the herbicide tested had
some plants showing mild phytotoxic effects in the greenhouse. However abnormalities
were observed in the ﬁrst emerging spears only. Subsequent spears and ferns were
normal, suggesting a contact rather than residual effect.

Plants sprayed with mesotrione showed the smallest crown weight gain in both
soils (FoA-infested and noninfested) compared with the control, but crowns were smaller
in noninfested soil. This pattern was observed also for crown, fern and total dry weight,
suggesting mesotrione can have a detrimental effect on asparagus crown health.

Sulfentrazone showed the second smallest crown and total dry weight averages

after mesotrione. Despite the warnings on ﬂumioxazin and s-metolachlor as injurious to

36

asparagus, neither of them caused signiﬁcant phytotoxicity or decrease in plant growth
when applied on the higher recommended rates (137) in the greenhouse experiments.
Glyphosate has been reported as causing spear deformation (3), but it did not show any
phytotoxicity in these experiments.

The greenhouse experiment addressed application of individual herbicide active
ingredients at the higher recommended rate (137), whereas in the ﬁeld individual and a
mixture of herbicides (an additional treatment) were evaluated (Table 3) using rates half
the maximum recommended rate (137). In the ﬁeld experiment, the herbicide mixture
covers a broad spectrum of weeds grasses and broadleaf weeds, which is a common
grower practice. Herbicide treatments were effective in controlling S. ptycanthum and C.
album, and no signiﬁcant differences were observed. Glyphosate, terbacil, and s-
metolachlor, were the least effective in controlling A. retroﬂexus (Table 5). Ineffective
grass control (Table 5) and, more importantly, phytotoxicity were observed in the plots
sprayed with mesotrione, which could explain the signiﬁcantly lower fern heights
observed later in the growing season.

When herbicide phytotoxicity in the greenhouse and the ﬁeld was observed, only
the ﬁrst-emerging spears were initially affected, but over time the secondary ferns and
spears appeared normal. In the ﬁeld, extreme phytotoxic symptoms were observed in
plots sprayed with mesotrione. Crop injury has also been reported on potato, carrot,
broccoli, cucumber, and onion plots treated with mesotrione (24,113).

The application of a single herbicide appeared to be less effective in controlling
weeds than the herbicide mixture used in this study. Despite minor growth abnormalities

witnessed with the lone sulfentrazone greenhouse treatment, no noticeable phytotoxicity

37

was observed in the ﬁeld. Its lack of control against grasses may have contributed to the
smaller number of spears and reduced fern height. Our data indicate that a mixture of
products provides effective weed control, higher fern numbers and greater fern height
than any of the individual herbicide tested.

During asparagus plant development, the ferns expand and store carbohydrates in
the crown for the following season’s growth (46). Consequently, crowns increase in size
and weight. Crown fresh weight gain and crown dry weight represent the degree of
expansion and growth. Enlargement of the crown is highly desirable since it will result in
more buds, increased carbohydrate storage, and fern biomass production. Any condition
that limits fern growth or crown expansion may impact plant performance in the
subsequent growing seasons (46,53,121).

Asparagus growers must take into consideration a broad spectrum of weed control
(grasses and broadleaf), but also avoid using herbicides that can cause detrimental effects
on asparagus plants. Care should be taken when using herbicides such as mesotrione,

since our experiments showed a detrimental effect on asparagus plant health.

38

CHAPTER 11
PHYTOPHTHORA ASPARA GI VIRULENCE IN DETACHED ASPARAGUS

SPEARS AND SUSCEPTIBILITY TO OTHER PH Y T OPH THORA SPECIES

39

ABSTRACT

Phytophthora spear and crown rot, caused by P. asparagi, was recently identiﬁed
in Michigan as a major limiting disease of asparagus. Although different species of
Phytophthora have been reported in asparagus production areas worldwide, only P.
asparagi has been found infecting asparagus in Michigan. Growth chamber studies were
conducted to (i) elucidate the inﬂuence of temperature on spear infection by P. asparagi;
(ii) investigate the susceptibility of three regions of the spear to P. asparagi, (iii) evaluate
susceptibility of asparagus to P. cactorum, P. capsici, P. citricola, P. drechsleri, P.
megasperma and P. nicotianae, (iv) compare the susceptibility of various sized spears to
P. capsici isolates, and (v) test P. asparagi virulence and P. capsici pathogenicity in

asparagus crowns. When detached spears were wounded and inoculated at 2, 9 or 16 cm

from the asparagus tip and incubated at 20°C, similar-sized lesions developed at all

inoculated regions of supermarket spears. When ‘Millennium’ spears were inoculated,
lesions at the spear base were larger than the other inoculated regions. Phytophthora

nicotianae and P. capsici incubated at 250C caused lesions comparable to those caused
by P. asparagi. The pathogenicity among P. capsici isolates was investigated in larger

spears (>O.8 cm in diameter) and small spears (50.8 cm in diameter). Small spears

developed larger lesions compared to larger spears.

40

INTRODUCTION

Michigan ranks third in US. asparagus production, after California and
Washington. In 2009, asparagus producing counties in Michigan planted 4,532 ha,
producing 12 million kg of asparagus spears valued at $16.5 millions (6). Diseases can
be a limiting factor in asparagus at any point during production of this perennial crop.
Historically, the most important soilborne disease affecting asparagus has been F usarium
crown, root and stem rot. The causal agents F. oxysporum f. sp. asparagi and F.
proliferatum reside in the soil, crop debris, or may be introduced on asparagus crowns
used to establish production ﬁelds (48,51). When infection by F. oxysporum f. sp.
asparagi and F. proliferatum occurs, disease symptoms include fern yellowing and
crown death (51) .

Phytophthora is a major genus of plant pathogens, consisting of at least 60 species
(55). Phytophthora spp. can infect a broad range of hosts including asparagus, and ﬁve
species have been reported to infect this perennial crop (7,58,119,132). Phytophthora
was not a concern in Michigan asparagus ﬁelds until 2004, when Saude et. a1. (2005)
reported P. asparagi infecting spears and roots during the harvest season. Disease
symptoms on spears included brown, water-soaked lesions at the base, shriveling, and
twisting (119). On the crown, water-soaked lesions and shriveling of the storage roots
predominates (119). Symptoms are most common following excessive precipitation and
typically occur in areas of the ﬁeld with poor drainage (119).

In addition to P. asparagi, other Phytophthora spp. in Michigan may pose a threat
to asparagus production. Phytophthora megasperma Dreshler infects a broad range of

hosts and various plant parts (55). Phytophthora megasperma taxa. are a broad group that

41

had been divided based on morphological variability and complexity (55,62).
Phytophthora megasperma var. sojae, P. megasperma var. medicaginis and P.
megasperma var. trifoli were previously considered to belong to P. megasperma taxa but
are now considered separate species: P. sojae Kaufman & Gerderman, P. medicaginis
Hansen & Maxwell and P. trifoli Hansen & Maxwell, respectively (55). In the late 805,
P. megasperma and P. sojae (formerly P. megasperma var. sojae) were reported infecting
asparagus in New Zealand (19,55,58,60), and California (9,55,58,60). In 2003, P.
megasperma Drechsler was reported on asparagus in Canada (132). In California, P.
sojae Pethybridge & Lafferty predominated among asparagus ﬁelds and occasionally P.
cryptogea Pethybridge & Lafferty was isolated from asparagus spears with mild disease
symptoms (60). Phytophthora nicotianae Galindo & Holt infects roots, stems, trunks,
leaves, and fruits of a wide host range including 255 genera in 90 families (55). In 2008,
Aragon-Caballero described a heterothallic Phytophthora sp. (Mating Type -MT: A2)
inciting asparagus root rot in Peru (7) that was identiﬁed as P. nicotianae based on
morphological and molecular characteristics.

Management of diseases caused by Phytophthora spp. includes effective
fungicides application, appropriate crop rotation, and a variety of cultural practices (i.e.
raised beds, plastic mulch and drip irrigation) (80). The fungicide metalaxyl provided
disease control and improved asparagus yields in California (58). Control of
Phytophthora spp. using chemical control is hampered by the presence of fungicide
resistance in pathogen populations (28,55,107,130). Phytophthora asparagi isolates form
Michigan were sensitive to mefenoxan (119). The efﬁcacy of crop rotation as a disease

management strategy is limited by the broad host range of some Phytophthora spp.

42

(55,61,93). The ability of P. asparagi to infect crops commonly growing in asparagus
production areas was investigated by Saude et. a1. (2008). Phytophthora asparagi caused
lesions on cucurbit fruit and was reisolated from the roots of asymptomatic red clover,
alfalfa, and soybean plants (119). Studies to evaluate the susceptibility of asparagus to
Phytophthora spp. will help determine if this perennial crop could be used in rotational
scheme to plant in soils where other crops have failed or were abandoned due to a history
of Phytophthora infestation (i.e. P. capsici Leonian) (80,108).

The objectives of this study were to (i) elucidate the inﬂuence of temperature on
spear infection by P. asparagi; (ii) investigate the susceptibility of regions of the spear to
P. asparagi, (iii) evaluate susceptibility of asparagus to P. cactorum, P. capsici, P.
citricola, P. drechsleri, P. megasperma and P. nicotianae, (iv) compare the susceptibility
of various sized spears to P. capsici isolates, and (v) test P. asparagi virulence and P.
capsici pathogenicity in asparagus crowns.

MATERIALS AND METHODS

Phytophthora spp. selection and culture. Isolates of P. cactorum, P. capsici, P.
citricola, P. drechsleri, P. megasperma and P. nicotianae were obtained from the
Phytophthora spp. culture collection maintained in M. K. Hausbeck’s laboratory at
Michigan State University. Isolates were transferred from long-term stock cultures onto

AR-V8 (100 ppm of ampicillin and 30 ppm of rifampicin amended unclariﬁed. V8 juice

agar) (72) and maintained at room temperature (21i20C) under continuous ﬂuorescent

lighting. Agar plugs (4-mm in diameter) from actively growing colonies were used to

inoculate spears.

43

Phytophthora asparagi isolates C013, SP319 and SP3236 were recovered from
asparagus crown (C013) or spear (SP319 and SP3236) tissue from northwest Michigan in
2005 (119) and determined to be sensitive to mefenoxan. Other Phytophthora spp. were
included: P. nicotianae (isolate 13048) from snapdragon, P. cactorum (isolate 4001) from
ginseng, P. drechsleri (isolate 4355) from poinsettia, P. megasperma (isolate 3100) from
an unknown host, P. citricola (isolate 3200) from an unknown host and P. capsici (isolate
OP97) from pickling cucumber. To compare P. capsici isolates for virulence in
asparagus, a variety of isolates in terms of mating type (A1 or A2) and sensitivity to the
fungicide mefenoxam (S: sensitive, or I: insensitive) were included as follows: P. capsici
OP97 (A1 S) from pickling cucumber, SP98 (A2 S) from pumpkin, 12889 (A1 I) from
pepper, SF F3 (A2 I) from pickling cucumber and 13351 from eggplant (A2 S).

Spear inoculation and incubation. Commercial grade spears (>0.8 cm in
diameter) were visually screened for disease and mechanical damage, selected and
surface disinfested with 5% sodium hypochlorite for 5 seconds, rinsed three times in
distilled water for 5 seconds and air-dried at room temperature. After drying, spears were
trimmed to 18 cm, and surface wounded with a ﬂame-sterilized needle prior to
inoculation (119). A 0.4 cm mycelial plug was placed over the wound and secured with
paraﬁlm. Humid chambers consisted of rectangular polystyrene containers (23x10x32
cm, Potomac display, Hampstead, MD) ﬁlled with lliter of tap water. A WatchDog
(Spectrum Technologies, Inc., Plainﬁeld, IL) was placed inside the humid chamber to
record temperature and relative humidity during the incubation time. The spears were
placed on a clear acrylic platform (0.8 cm thick, 26x21 cm x H=2.5 cm) inside the humid

chambers and incubated in growth chambers (Conviron: model CMP3244, Pembina, ND)

44

with a 16-hour photoperiod for 5 days at 15, 20 or 25°C. After incubation, the length and

width of each lesion was measured and presence of mycelia noted. The lesion area was

calculated based on the ellipse area (113* r1 *r2, where r1 was length/2 and r2 was width/2).

Approximately 10% of the spears where sampled to re-isolate the pathogen from the
spear tissue.

Susceptibility of spear regions to P. asparagi. A ﬂame-sterilized needle was
used to wound each spear at 2, 9, and 16 cm from the apical end (also referred to as tip,
middle and base spear regions, respectively). All wounds were covered with a mycelial
plug (as described above) of P. asparagi isolates C013, SP319 or SP3236. Uninfested
AR-V8 media plugs were used as a negative control. Five spears per isolate were used.
Spears were placed in a humid chamber and incubated in a growth chamber.
Experiments were replicated six times; four times using supermarket spears and twice
with ‘Millennium’ spears.

Susceptibility of asparagus to Phytophthora spp. The pathogenicity of six
Phytophthora spp.: P. capsici, P. cactorum, P. citricola, P. drechsleri, P. megasperma
and P. nicotianae were compared to P. asparagi isolate (SP319). Uninfested AR-V8
media plugs were used as a negative control. Six spears were inoculated per isolate.

Spear inoculation and incubation were performed as described above. Incubation

temperatures of 15, 20 and 25°C were used. Experiments were replicated three times

using ‘Jersey Knight’ spears. Jersey Knight’ spears were inoculated at 9 cm (middle)
from the tip because bacterial spear tip rot was common on supermarket spears regardless

of incubation temperature.

45

Susceptibility of various-sized asparagus spears to P. capsici isolates. Five
isolates of P. capsici (13351, SFF3, 12889, SP98, OP97) were evaluated in two
experiments and compared to P. asparagi isolate SP319 and a negative control using
uninfested AR-V8 media plugs. The ﬁrst experiment used spear grades that were 0.8 to
1.3 cm in diameter and was conducted twice with ‘Millennium’ spears using the middle
inoculation point. Five spears were used per isolate.

The second experiment used smaller asparagus spears (<0.8 cm in diameter) that
were not of a marketable grade. Small spears were trimmed at 14 cm from the apical
end, and inoculated in the middle (7 cm from the tip). The experiment was conducted
four times using ‘Millennium’ spears and twice with ‘Jersey Knight’ spears; there were

two replicate spears inoculated for each P. capsici isolate. Incubation temperatures of 15,
20 and 25°C were used for the two experiments conducted using P. capsici.
Crown inoculation experiments. One-year-old ‘Tiessen’ dormant crowns

obtained from a commercial nursery (Malburg Farm in Oceana County, MI), were

washed and visually screened for disease, mechanical damage and size homogeneity, and

stored in a cold room (4°C) until they were used. Crown roots were measured and roots
20.3 cm in width and 214 cm in length were selected. Phytophthora asparagi C013 and
P. capsici 13351 were used to inoculate the crowns. Crowns were wounded with a

ﬂame-sterilized needle and 0.2-cm mycelial plugs were attached with paraﬁlm to the

roots. Inoculated and non-inoculated crowns were placed in the humid chambers and

incubated in a growth chamber at 15, 20 and 25°C as described above for the spears.

Uninfested AR-V8 agar plugs were used as a negative control. Crowns in humid

chamber were incubated for ﬁve days in darkness (Diurnal growth chamber 3740,

46

Therrno Scientiﬁc: formerly F orrna Scientiﬁc, Waltham, MA). These experiments were
conducted four times and six crowns per isolate were included.

Statistical analysis. A split-split plot design with three ﬁxed factors was used as
follows: experimental replicate as the blocking factor, temperature as the whole-plot
factor within each block (trial), and isolate as the sub-plot factor within each temperature.
For the experiments investigating the susceptibility of spear regions to P. asparagi, an
additional factor was included: the sub-sub-plot factor spear regions within each isolate.
The PROC MIXED and PROC GLIMMIX were used as implemented in SAS statistical
analysis software (SAS Institute Inc., Cary, NC). Data were tested for equal variances
and normal distribution. A square root transformation was conducted to fulﬁll normal
distribution assumptions when necessary. ANOVA was evaluated using type 3 effects
output (P<0.05). Signiﬁcant differences were determined using Fisher’s protected least
signiﬁcant difference (LSD) for investigated factor (i.e spear regions, isolates and
temperatures) and factor interaction for all the experiments. Differences were considered
signiﬁcant with 0t=0.05.

RESULTS
Susceptibility of spear regions to P. asparagi. Infection and lesion development

occurred when spears were inoculated with P. asparagi and incubated at 15, 20 and

250C. The three P. asparagi isolates caused lesions that were similar in appearance.
Dark brown water-soaked lesions and spear shriveling were characteristic. When
supermarket spears were inoculated, there were no signiﬁcant differences in lesion size

among P. asparagi isolates (Figure 7A). Isolate SP319 caused signiﬁcantly smaller

lesions (P=0.03) on ‘Millennium’ asparagus spears (Figure 7B) compared to isolates

47

SP3236 and C013. Neither sporulation nor mycelia were observed within the lesions.

All P. asparagi isolates were successfully reisolated from the lesions.

 

    
  
 
 
   

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Phytophthora asparagi isolate
Figure 7. Mean lesion area on detached asparagus spears 5 days after inoculation with P.
asparagi isolates C013, SP3236 and SP319 on A, supermarket spears and B,

‘Millennium’ spears. Bars with common letters are not signiﬁcantly different, LSD
P=0.05.

Lesion area caused by P. asparagi differed signiﬁcantly among incubation
temperatures. At 20°C, P. asparagi isolates caused the largest lesions in both
‘Millennium’ and supermarket spears (Figure 8A and B). When supermarket asparagus
spears were used, the smallest lesions occurred at 25°C (Figure 8A). When pooling
means by spear region inoculation on supermarket spears, there were no signiﬁcant
differences in lesion size (P=0.701) (Figure 9A). However, lesions caused by P.
asparagi in the spear tip when incubated at 15 and 25°C were signiﬁcantly different from
lesions at the middle and base of the spear at the same temperatures. Similarly, lesions

caused by the pathogen at the tip when incubated at 15°C were signiﬁcantly larger than

48

those developed at the tip incubated at 25°C (Figure 10B). Lesions on ‘Millennium’
spears were similar at 15 and 25°C but signiﬁcantly smaller than those at 20°C when

lesions were pooled across inoculation region and across isolates (Figure 8B).

 

 

 

 

     

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Temperatures (°C)
Figure 8. Effect of temperature on mean lesion area on detached asparagus spears 5 days
after inoculation with P. asparagi on A, supermarket spears, and B, ‘Millennium’ spears.
Bars with common letters are not signiﬁcantly different, LSD P=0.05.
Signiﬁcant differences among spear regions were found when the experiments
were conducted using ‘Millennium’ spears (P<0.001, Figure 9B); lesion means were
larger compared with those observed in supermarket spears.

A signiﬁcant interaction between spear regions and temperature was observed,

although interaction patterns differed between experiments using supermarket or

‘Millennium’ spears (Figure 10A and B). In general, lesions on spears incubated at 20°C

were larger than for other temperatures tested, regardless of the spear region inoculated.

49

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51

In addition, lesions at the base of the spear were commonly larger than those at
the middle; lesions at the tip of the spear were the smallest (Figure 108). At all
temperatures tested, lesions at the base of the spear were larger than at the tip or middle
of the spear.

Susceptibility of asparagus to Phytophthora spp. Spear lesions caused by P.
asparagi were larger than those caused by all other Phytophthora spp., when means were

pooled among temperatures tested (Figure 11A). Lesions caused by P. nicotianae and

P. capsici were larger (0.56 and 0.37 cm2 respectively) than those caused by P. cactorum,
P. citricola, P. drechsleri, and P. megasperma. Phytophthora asparagi was recovered
from spear tissue readily (92%), while P. nicotianae and P. capsici were isolated less
frequently (22% and 11%, respectively). Phytophthora cactorum, P. citricola, P.

drechsleri, and P. megasperma were not successfully recovered from the spear tissue.

When average lesion sizes were pooled among Phytophthora spp. lesions were

signiﬁcantly larger (P<0. 0001) when spears were incubated at 250C compared to 200C

and 15°C (Figure 1 1B). The smallest lesions developed when the incubation temperature
was 15°C (Figure 118).
Average lesion size caused by P. asparagi 319 at 250C was not signiﬁcantly

different from any of the other Phytophthora spp.-temperature combinations, except for

P. capsici OP97 and P. nicotianae 13048. Lesions caused by P. nicotianae at 20 and

250C, and by P. capsici at 25°C were not signiﬁcantly different from lesions caused by P.

asparagi at 15 and 200C (Figure 11C)

52

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Susceptibility of various sized spear asparagus to P. capsici. When larger
‘Millennium’ asparagus spears were inoculated with P. capsici, lesions were signiﬁcantly
smaller compared to lesions resulting from inoculation with P. asparagi (P=0.0001,

Figure 12A) regardless of the incubation temperature (Figure 12C). Lesion size by
temperature showed the same pattern (i.e. lesions were favored at 200C) observed in
previous P. asparagi experiments (Figure IZB). Reisolation of P. capsici from asparagus
tissue was achieved for isolate 13351 (25%) and less frequently for SFF3 (5%) when

spears were incubated at 250C. Recovery was not possible at 15 or 20°C, for isolates
13351 and SFF3. Reisolation from the spear tissue was not successful for P. capsici
isolates OP97, SP98 and 12889.

P. asparagi caused lesions on small spears, that were comparable in size to

lesions formed on larger spears. In small spears, virulence varied among P. capsici

isolates (Figure 13A). When incubated at 250C, P. capsici 13351 caused lesions similar

in size to those caused by P. asparagi at all temperatures. Similarly P. capsici SF F 3

caused lesions similar in size to those caused by P. asparagi at 15 and 250C (Figure

13C).

Crown experiments. Phytophthora asparagi caused restricted light brown
water-soaked lesions on the roots of crowns. Phytophthora capsici caused lesions that
were barely discernible, without characteristic color, although the inner tissue had turned

reddish brown. Lesions caused by P. asparagi were signiﬁcantly bigger than those

caused by P. capsici 13351 (Figure 14A).

54

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57

There were no signiﬁcant differences among temperatures (Figure 14B) or in the
interaction between temperature and Phytophthora spp. (Figure 14C). However, P.

capsici and P. asparagi showed a common pattern where the larger lesions occurred at

20°C and the smallest lesions were observed at 15°C (Figure 14B). Reisolation from the

crown tissue was not successful for P. capsici and low (<5%) for P. asparagi.
DISCUSSION

When asparagus spear were inoculated with P. asparagi. P. nicotianae, and P.
capsici, lesions developed and the pathogens were recovered from the symptomatic
tissue. Lesions were necrotic and water-soaked in appearance in agreement with
previous descriptions of P. asparagi (119) and P. nicotianae (7) symptoms in asparagus.
Conversely, no mycelia were observed within the lesions or in adjacent tissue as
commonly reported for P. capsici (66). Phytophthora asparagi was more virulent on
asparagus spears than the other Phytophthora spp. tested in our experiments. The lesions
that formed on spears inoculated with P. citricola, P. drechsleri, P. megasperma, and P.
cactorum were signiﬁcantly larger than the lesions on control spears. However, since
none of these species could be recovered from the spears, the lesions may be due to a
wounding response or perhaps these Phytophthora spp. are only weakly pathogenic to
asparagus spear. Phytophthora megasperma, P. sojae, P. cryptogea, P. cactorum, P.
richardiae, P. nicotianae and P. asparagi have been previously reported as pathogens to
asparagus either in the ﬁeld or post-harvest (55,59-61). The results of this study agree
with previous reports of P. asparagi (118,119) and P. nicotianae (7) as pathogens of
asparagus. The isolates of P. cactorum and P. megasperma used in this study did not

cause disease despite previous reports of pathogenicity (5 8). Only a single isolate of each

58

species was used in our studies; further experiments with additional isolates of P.
cactorum and P. megasperma may be necessary.

Lesions were largest on spears inoculated with P. asparagi and incubated at 15 or

20°C and on spears inoculated with P. nicotianae and incubated at 25°C. Lesions were
also observed on spears inoculated with P. nicotianae and incubated at 20°C and on

spears inoculated with P. capsici and incubated at 25°C. Phytophthora spp. growth on
culture media varies among species. P. cactorum and P. megasperma have similar
minimum, optimum, and maximum temperatures (2°C, 25°C, and 31°C, respectively).
Although while P. nicotianae and P. capsici have optimum growth temperatures from 27-
32°C and can grow in media up to 35°C, these temperatures can vary depending on the

isolates (101). Since larger lesions caused by P. nicotianae and P. capsici occurred at the

higher temperatures used in our study (20°C and 25°C), it would be interesting to
determine the infective capability of these pathogens at higher temperatures (above
25°C).

In Michigan, air temperatures the harvest season would be expected to range
between 13 to 27°C (http://c1imate.geo.msu.edu/index.html). Lesions caused by P.
asparagi in our experiments were favored at 20°C but also occurred at 15 and 25°C,
which is not surprising given that the minimum, optimum, and maximum temperatures
for growth of P. asparagi are 10, 25, and <30°C, respectively (119). Asparagus spear
emergence occurs when soil temperatures range from 12.7 to 17.7°C one day before

emergence. According to our results, P. asparagi can grow and infect spears in the same

59

range of temperatures required for spear emergence. It is possible that in the ﬁeld, P.
asparagi infects emerging spears only under a narrow range of environmental conditions
but additional studies are needed to investigate this further.

The largest mean lesion size was observed when the base of ‘Millennium’ spears

was inoculated with P. asparagi and incubated at 20°C. The base of the spear has higher

ﬁber and sugar content, and lower protein and metabolic activity (i.e. respiration rate)
(3 9,86,96) compared with the middle and tip regions. These characteristics of the spear
base could be more conducive to P. asparagi disease compared to the middle or tip of the
spear. However, to the best of our knowledge, no studies have been published exploring
the effect of sugar, ﬁber, and protein content and metabolic activity on Phytophthora
infection. Larger lesions were observed on ‘Millennium’ spears, suggesting they were
more susceptible to Phytophthora asparagi than the supermarket or ‘Jersey Knight”
spears. A lack of freshness or differences in cultivar may have inﬂuenced susceptibility
of supermarket spears. Structural changes within the spear occur as soon as 1 day aﬁer
harvest (31,96). Supermarket spears originated from California, Mexico and Peru. The
main cultivars grown in these areas differ from those grown in Michigan (5,102,115,128).
In California production areas, the main varieties planted are ‘UC157’, ‘Grande, Apolo’,
‘Brock imperial’, ‘Ida Lea’, and ‘Atlas’ ‘Mary Washington’, ‘Palmeto’, ‘Argentenil’,
‘UC157’ and ‘UC 72’ are grown in Peru and Mexico among others. Whereas in
Michigan growers favor ‘Jersey’, ‘Millennium’ and ‘Tiessen’.

Phytophthora capsici is widespread in Michigan ﬁelds used for production of
susceptible vegetables such as cucurbit and solanaceous crops (55,63,80). Due to the

importance and prevalence P. capsici in Michigan studies were conducted, to determine

6O

whether asparagus is susceptible to this pathogen. In larger ‘Millennium’ asparagus
spears of commercial grade, P. capsici isolates did not cause signiﬁcant infection and
lesions were not comparable in size with those caused by P. asparagi. Homogeneity of
lesion size was observed among P. capsici isolates infecting larger spears. Conversely,
when small spears that were not of commercial grade were inoculated with P. capsici,

virulence was variable among the isolates. Small spears inoculated with P. capsici
isolates from eggplant (13351) and pickling cumber (SFF3) and incubated at 250C

developed lesions comparable in size to those caused by P. asparagi regardless of
temperature. Crown inoculation needs to be reﬁned, since the conditions used in our
experiments were not conducive for P. asparagi infection and characteristics lesion
formation observed in naturally infected crowns from ﬁeld nurseries (119).

Based on our studies, we do not consider P. capsici a signiﬁcant threat to

“Millennium’ asparagus spears. However, during warm harvest seasons (approximately

250C) infection of small spears and perhaps asparagus seedlings by P. capsici could

occur. Field studies are required to establish whether P. capsici can infect asparagus
under natural ﬁeld conditions and the pathosystem needs to be studied further to
determine the impact on crop rotation strategies. Over a dozen of different asparagus
varieties are grown in the US (47,128). Future research could compare P. asparagi. P.
nicotianae and P. capsici virulence on a broad range of asparagus cultivars using more
and diverse isolates, since cultivar resistance is a preferred strategy to manage
Phytophthora spear and root rot in asparagus ﬁelds.

Phytophthora spp. have been found in rivers, ponds, ditches and irrigation

systems (67,92), and are dynamic pathogens capable of infecting a broad range of hosts

61

(55,61). In soil, Phytophthora spp. may be present as mycelia (55) or oospores
(21,44,64) that can persist in ﬁelds for many years serving as primary inocula and
limiting grower’s ability to plant susceptible crops (40). The inbreeding in homothallic
species such as P. asparagi, limits genetic variability (71). In species such P. nicotianae
and P. capsici (heterothallic) sexual reproduction is a source of genetic variation (94),
which gives these pathogens an increased probability of gaining traits such as increased
virulence and/or pathogenicity on additional hosts. Further studies could investigate
whether these three Phytophthora spp. are present in Michigan asparagus ﬁelds and

determine the risk of disease

62

APPENDIX

FUNGICIDE EFFICACY ON PHYTOPHTHORA ROT IN ASPARAGUS
SEEDLINGS IN THE GREENHOUSE

63

ASPARAGUS (Asparagus oﬂicinalis) ‘Millenium’ M. Hausbeck, B. Harlan, and

Phytophthora spear and root rot; L.M. Rodriguez-Salamanca
Phytophthora asparagi Michigan State University
Department of Plant Pathology

East Lansing, MI 48824-1311
Evaluation of fungicides to control Phytophthora spear and root rot on asparagus
seedlings, 2009.
This study was conducted in the greenhouse using Phytophthora asparagi

inoculum, prepared by growing the pathogen in ﬂasks containing sterile millet for 3

weeks. Inoculum. was mixed with soilless media (8 oz/ft3) and distributed into 2 x 3 cell

trays, where untreated asparagus ‘Millenium’ seeds were planted on 10 Aug. Treatments
were replicated six times in randomized complete design. Fungicides were applied as a
drench, using drench bottles, starting 10 Aug and ending on 24 Sep. The numbers of
emerged seedlings and diseased seedlings were counted and a disease severity rating was
taken (1 to 5; 1=no disease, 2=slight seedling curving, 3=moderate curving/water-
soaking, 4= extensive water-soaking, =seedling death) were recorded on 25 and 27 Aug,
and 1, 3, 8, 10, 15, 17 and 24 Sep, and used to calculate the area under the disease
progress curve (AUDPC).

Disease severity for the untreated control was 73.69, with 26 infected seedlings
out of the 39 germinated. Based on the ANOVA, treatments had a signiﬁcant effect on
AUDPC, and AUDPC differed among treatments with the untreated control. All
treatments decrease disease severity compare with the untreated control. In ascending
order, Revus, Acrobat, Gavel, Aliette, and Ranman were especially effective and had the
lower AUDPC values. Although fungicide treatments reduced seedling infection by P.

asparagi, different numbers of infected seedlings were observed among fungicides.

64

Kocide and Curzate had the highest probability of infection with the disease ratings
ranking among 2 or 3, while Revus and Acrobat had the smallest probability of infection
in 31 days.

Table 7. Effect of fungicides on the area under the disease progress curve (AUDPC)

values for the disease incidence on asparagus seedlings caused by Phytophthora
asparagi.

 

Severity AUDPCZ

 

Treatment and rate/50 gal

Mean

std erroxy

 

Untreated ..................... 73 '69 9'62
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Revus sc 0.5 pt ............. 29-77 a 1-03
Previcur Flex SC 1.2 pt. 43'“ ab 4-87
Manzate DF 3 lb ............ 38‘85 ab 2'68
Tanos DF 0.5 lb ............ 40'08 ab 3-87
Ranman sc 0.17 pt .......... 32°46 a 1-81
Bravo Weather Stik SC 2 pt “'19 ab 5-57
Gavel DF 2 1b ............... 31““ a 2-64
Aliette WG 5 lb ............. 31-46 a 1.15
Ridomil Gold EC 1 pt...... 42°58 ab 3-72
Kocide 2000 DP 2 lb ....... 4931 b 8-50
Acrobat WP 0.4 lb .......... 30'62 a 0-56

49.19 b 920

Curzate DF 0.31 lb .........

 

ZAUDPC values for P. asparagi disease incidence on asparagus seedlings. Calculated
using nine dates of disease severity ratings. AUDPC minimum=30, maximum=150.

y Treatments have unequal variances (shown in standard error)
xColumns with common letters are not signiﬁcantly different, LSD P=0.05.

65

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66

LITERATURE CITED

67

10.

LITERATURE CITED

Agrios, G. N. 2005. Plant Pathology. Fifth ed. Elsevier Academic Press, Boston.

Aldrich, R. J ., and Kremer, R. J. 1997. Principles in Weed Management. Iowa
State University Press, Ames.

Alister, C., and Kogan, M. 2004. Effect of glyphosate applied over emerged
asparagus spears. Crop Protection 23:169-172.

Altman, J ., and Campbell, C. L. 1977. Effect of herbicides on plant diseases.
Annual Review of Phytopathology 15:361-385.

Anonimo. 2009. Esparrago ﬁcha tecnica. Ministerio de agricultura del Peru No.
4.

Anonymous. 2010. Vegetables 2009 summary January 2010. USDA National
Agricultural Statistic Service. Vg 1-2 (10).

Aragon-Caballero, L. M., Hurtado-Gonzales, O. P., Flores-Torres, J. G., Apaza-
Tapia, W., and Lamour, K. H. 2008. First report of Phytophthora nicotianae
causing asparagus spear and root rot in Peru. Plant Disease 92:982.

Araki, H., and Tamura, H. 2008. Weed control and ﬁeld management with

barley living mulch in asparagus production. Acta Horticulturae (ISHS) 776:51-
54.

Ark, P. A., and Barret, J. T. 1938. Phytophthora rot of asparagus in Califomia.
Phytopathology 28:754-756.

Arriola, L., Hausbeck, M. K., Rogers, J., and Saﬁr, G. R. 2000. The effect of
T richoderma harzianum and arbuscular mycorrhizae on F usarium root rot in

asparagus. HortTechnology 10:141-144.

68

11.

12.

13.

14.

15.

l6.

17.

18.

19.

20.

Arriola, L. L. 1997. Arbuscular mycorrhizal fungi and Trichoderma harzianum
in relation to border cell production and F usarium root rot of asparagus. MS.
Thesis. Michigan State University, East Lansing.

Baayen, R., O'Donnell, K., Bonants, P., Cigelnik, E., Kroon, L., Roebroeck, E.,
and Waalwijk, C. 2000. Gene genealogies and AFLP analyses in the F usarium
oxysporum complex identify monophyletic and nonmonophyletic formae
speciales causing wilt and rot disease. Phytopathology 90:891-900.

Baayen, R. P., van den Boogert, P. H. J. F ., Bonants, P. J. M., Pol], J. T. K., Blok,
W. J ., and Waalwijk, C. 2000. F usarium redolens f.sp. asparagi, causal agent of

asparagus root rot, crown rot and spear rot. European Journal of Plant Pathology
1062907-912.

Benson, B. L. 1999. World asparagus production areas and periods of
production. Acta Horticulturae (ISHS) 479:43-50.

Bird, G., Bishop, B., Hausbeck, M. K., Jess, L. J ., Kirk, W., Pett, W., and Warner,
F. 2009. Insect, disease and nematode control for commercial vegetables. in:
Michigan State University Extension Bulletin 312.

Blok, W. J ., and Bollen, G. J. 1996. Inoculum sources of F usarium oxysporum f.
sp. asparagi in asparagus production. Annals of Applied Biology 128:219-231.

Blok, W. J ., Coenen, T. C. M., Termorshuizen, A. J., and Lamers, J. G. 2008.
The potential of biological soil disinfestation to manage F usarium foot and root
rot in asparagus. Acta Horticulturae (ISHS) 776:135-144.

Blumenthal, M. 2000. Herbal Medicine: Expanded Commission E Monographs.
Integrative Medicine Communications, Newton, MA.

Boesewinkel, H. J. 1974. Phytophthora on asparagus in New Zealand. Plant
Disease Reporter 58:525-529.

Booth, C. 1971. The genus F usarium. Commonwealth Agricultural Bureaux for
the Commonwealth Mycological Institute, Farnham Royal, UK.

69

21.

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

Bowers, J. H., Papavizas, G. C., and Johnston, S. A. 1990. Effect of soil
temperature and soil-water matric potential on the survival of Phytophthora
capsici in natural soil. Plant Disease 74:771-777.

Boydston, R. A. 1995. Effect of tillage level and herbicides on weed control and

yield of asparagus (Asparagus oﬂicinalis) in the Paciﬁc Northwest. Weed
Technology 9:768-772.

Boydston, R. A. 1988. Seedling volunteer asparagus, Asparagus ofﬁcinalis,
control with herbicides. Weed Technology 2:294-298.

Boydston, R. A., and Al-Khatib, K. 2008. Exudation of mesotrione from potato
roots injures neighboring plants. Weed Science 56:852-855.

Brastsch, A. 2009. Specialty crop proﬁle: Asparagus. in: Virginia cooperative
extension bulletin 43 8-102.

Bridges, D. C., ed. 1992. Crop Losses Due to Weeds in the United States. Weed
Science Society of America, Champaign, IL.

Burgess, L. W. 1981. General ecology of the F usaria. Pages 357-402 in:
F usarium: Diseases, Biology, and Taxonomy, P. E. Nelson, T. A. Toussoun and
R. J. Cook, eds. Pennsylvania State University Press, University Park, PA.

Cafe-Filho, A. C., and Ristaino, J. B. 2008. Fitness of isolates of Phytophthora
capsici resistant to mefenoxam from squash and pepper ﬁelds in North Carolina.
Plant Disease 92:1439-1443.

Casas, A., and Sanchez, J. 2008. Developments in asparagus cultivation under
desert conditions in Peru. Acta Horticulturae (ISHS) 776:29-32.

Cembali, T., Folwell , R. J ., Huffaker, R. G., McCluskey, J. J ., and
Wandschneider, P. R. 2008. Economic evaluation of selective mechanical
harvesting for asparagus. Acta Horticulturae (ISHS) 776133-44.

Chang, D. C. N. 1983. Fine structural change of asparagus spear during storage.
Acta Horticulturae (ISHS) 138:305-312.

70

32.
33.
34.
35.

36.

37.

38.
39.
40.

41.

42.

Chin, C. K., Garrison, S. A., Ho, C. T., Shao, Y., Wang, M., Simon, J., and
Huang, M. T. 2002. Functional elements from asparagus for human health. Acta
Horticulturae (ISHS) 589:233-241.

Cobb, A. 1992. Herbicides and Plant Physiology. Chapman and Hall, London.

Cobb, A., and Kirkwood, R. C. 2000. Herbicides and their Mechanisms of
Action. Shefﬁeld Academic Press, CRC Press, Boca Raton, FL.

Cohen, S. I., and Heald, F. D. 1941. A wilt and root rot of asparagus caused by
Fusarium oxysporum (Schlecht). Plant Disease Reporter 25:503-509.

Cooke, D. E. L., Drenth, A., Duncan, J. M., Wagels, G., and Brasier, C. M. 2000.
A molecular phylogeny of Phytophthora and related oomycetes. Fungal Genetics
and Biology 30:17-32.

Cooke, E. L., and Duncan, J. M. 1997. Phylogenetic analysis of Phytophthora
species based on the ITSl and ITS2 sequences of ribosomal DNA. Mycological
Research 101:667-677.

Counts, J. W. 2006. Strategies for managing Fusarium crown and root rot on
asparagus. MS. Thesis. Michigan State University, East Lansing.

Culpepper, C. W., and Moon, H. H. 1939. Changes in the composition and rate
of growth along the developing stem of asparagus. Plant Physiology 14:677-698.

Curl, E. A. 1963. Control of plant diseases by crop rotation. The Botanical
Review 29:413-479.

Damicone, J. P., and Manning, W. J. 1985. Frequency and pathogenicity of
F usarium spp. isolated from ﬁrst year asparagus grown from transplants. Plant
Disease 69:413-416.

Damicone, J. P., Vineis, P. D., and Manning, W. J. 1988. Cross-pathogenicity of
F usarium moniliforme isolates from corn and asparagus. Plant Disease 72:774-
777.

71

53.

54.

55.

56.

57.

58.

59.

60.

61.

62.

63.

Elmer, W. H., Johnson, D. A., and Mink, G. I. 1996. Epidemiology and
management of the diseases causal to asparagus decline. Plant Disease 80:117-
126.

Elmer, W. H., and La Mondia, J. A. 1999. Studies on suppression of Fusarium
crown and root rot of asparagus with NaCl. Acta Horticulturae (ISHS) 479: 21 1-
218.

Erwin, D. C., and Ribeiro, O. K. 1996. Phytophthora Diseases Worldwide.
American Phytopatological Society Press, St Paul, MN.

Evans, T. A. 1985. Asparagus viruses and their contributions to Michigan
asparagus decline. Ph.D Thesis. Michigan State University, East Lansing.

Falloon, P. G., F alloon, L. M., and Andersen, A. M. 2002. Breeding asparagus
varieties resistant to Phytophthora. Acta Horticulturae (ISHS) 589: 1 85-191.

Falloon, P. G., Falloon, L. M., Benson, B. L., and Grogan, R. G. 1986. Effect of
Phytophthora megasperma var. sojae on yield of Asparagus oﬂicinalis. Plant
Disease 70:15-19.

F alloon, P. G., F alloon, L. M., Mullen, R. J., Benson, B. L., and Grogan, R. G.
1983. Effect of Phytophthora spear rot on asparagus yield. Calif. Agric. 37:16-
17.

Falloon, P. G., and Fraser, H. A. 1988. Isolation, distribution, pathogenicity and
identiﬁcation of Phytophthora spp. on asparagus in California. Plant Disease
72:495-497.

Farr, D. F., and Rossman, A. Y. 2009. Fungal Databases, Systematic Mycology
and Microbiology Laboratory. USDA, ARS. Retrieved February 20, 2009. From
http://nt.ars-grin.gov/fungaldatabases/.

Forster, H., Kinscherf, T. G., Leong, S. A., and Maxwell, D. P. 1988. Estimation
of relatedness between Phytophthora species by analysis of mitochondrial DNA.
Mycologia 80:466-478.

Foster, J. M., and Hausbeck, M. K. 2010. Resistance of pepper to Phytophthora
crown, root, and fruit rot is affected by isolate virulence. Plant Disease 94:24-30.

73

64.

65.

66.

67.

68.

69.

70.

71.

72.

73.

French-Monar, R. D., Jones, J. B., Ozores-Hampton, M., and Roberts, P. D.
2007. Survival of inoculum of Phytophthora capsici in soil through time under
different soil treatments. Plant Disease 91 :593-598.

Geiser, D., del Mar Jime’nez-Gasco, M., Kang, S., Makalowska, I.,
Veeraraghavan, N., Ward, T., Zhang, N., Kuldau, G., and O'Donnell, K. 2004.
FUSARIUM-ID v. 1.0: A DNA sequence database for identifying F usarium.
European Journal of Plant Pathology 110:473-479.

Gevens, A. J ., Ando, K., Lamour, K. H., Grumet, R., and Hausbeck, M. K. 2006.
A detached cucumber fruit method to screen for resistance to Phytophthora

capsici and effect of fruit age on susceptibility to infection. Plant Disease
90:1276-1282.

Gevens, A. J ., Donahoo, R. S., Lamour, K. H., and Hausbeck, M. K. 2007.
Characterization of Phytophthora capsici from Michigan surface irrigation water.
Phytopathology 97:421-428.

Gilbertson, R. L. 1983. Contamination of asparagus ﬂowers and fruit by airborne
spores of F usarium moniliforme. Plant Disease 67:1003-1004.

Gonzalez Castaﬁon, M. L. 1990. Evaluation of male and female asparagus
plants. Interest in obtaining male or dioecious hybrids. Acta Horticulturae (ISHS)
271 :83-90.

Gonzalez, M. 1., France, A., Del Pozo, A., Pedreros, A., and Kramm, V. 1999.
Winter tillage systems and their effect on asparagus yield and weed population.
Acta Horticulturae (ISHS) 479:453-462.

Goodwin, S. B. 1997. The population genetics of Phytophthora. Phytopathology
87:462-473.

Granke, L. L., and Hausbeck, M. K. 2010. Effects of temperature, concentration,

age, and algaecides on Phytophthora capsici zoospore infectivity. Plant Disease
94:54-60.

Green, K. R., Dyer, W., Falloon, P. G., Cooke, D. E. L., and Chimento, A. 2008.
Management of Phytophthora rot on UK asparagus crops. Acta Horticulturae
(ISHS) 776:175-182.

74

74.

75.

76.

77.

78.

79.

80.

81.

82.

83.

84.

Grogan, R. G., and Kimble, K. A. 1959. The association of F usarium wilt with
the asparagus decline and replant problem in California. Phytopathology 49: 122-
125.

Harikrishnan, R., and Yang, X. B. 2001. Inﬂuence of herbicides on grth and
sclerotia production in Rhizoctonia solani. Weed Science 49:241-247.

Harminder, P. S., Daizy, R. B., and Ravinder, K. K., eds. 2006. Handbook of
Sustainable Weed Management. Food Products Press, New York.

Hartmann, H. D. 1996. Economic problems of declining asparagus ﬁelds. Acta
Horticulturae (ISHS) 415:377-382.

Hartung, A. C., Stephens, C. T., and Elmer, W. H. 1990. Survey of F usarium
populations in Michigan's asparagus ﬁelds. Acta Horticulturae (ISHS) 271:395-
401.

Hausbeck, M. K., and Cortright, B. 2008. New management techniques for
F usarium and Phytophthora control in asparagus production. Pages 6-8 in:

Asparagus Session Summaries. Proceedings of the Great Lakes Fruit, Vegetable
and Farm Market EXPO.

Hausbeck, M. K., and Lamour, K. H. 2004. Phytophthora capsici on vegetable

crops: research progress and management challenges. Plant Disease 88:1292-
1303.

Helin, X., Mingsheng, P., and Xiaotang, F. 1996. Asparagus production in
China. Acta Horticulturae (ISHS) 415:41-44.

Hodupp, R. M. 1983. Investigation of factors which contribute to asparagus
(Asparagus ofﬁcinalis L.) decline in Michigan. MS. Thesis. Michigan State
University, East Lansing.

Huffman, L. 1982. Asparagus production guidelines. Pages 153-157 in:
Ministry of Agriculture and Food, Ont. Hortic. Conf, Ontario.

Inderjit, 8., ed. 2004. Weed Biology and Management. Kluwer Academic
Publishers, Boston.

75

85.

86.

87.

88.

89.

90.

91.

92.

93.

94.

95.

Kidner, A. W. 1959. Asparagus. Faber and Faber, London.

King, G. A., Woollard, D. C., Donald, E. I., and Borst, W. M. 1990.
Physiological changes in asparagus spear tips after harvest. Physiologia
Plantarum 80:393-400.

Kishore, G. M., Padgette, S. R., and F raley, R. T. 1992. History of herbicide-
tolerant crops, methods of development and current state of the art: emphasis on
glyphosate tolerance. Weed Technology 6:626-634.

Kistler, H. C. 1997. Genetic diversity in the plant-pathogenic fungus F usarium
oxysporum. Phytopathology 87:474-479.

Knicely, D. R. 1962. Harvesting asparagus mechanically; economic aspects and
physical properties. M.S. Thesis. Michigan State University, East Lansing.

Kubitzki, K. 1990. The Families and Genera of Vascular Plants. Springer-
Verlag, Berlin.

Kuepper, G., and Thomas, R. 2001. Organic Asparagus Production. in: NCAT
Agriculture Specialists, Publication #CT100 ATTRA.

Lamour, K. H., Daughtrey, M. L., Benson, D. M., Hwang, J ., and Hausbeck, M.
K. 2003. Etiology of Phytophthora drechsleri and P. nicotianae (=P. parasitica)
diseases affecting ﬂoriculture crops. Plant Disease 87:854-858.

Lamour, K. H., and Hausbeck, M. K. 2003. Effect of crop rotation on the
survival of Phytophthora capsici in Michigan. Plant Disease 87:841-845.

Lamour, K. H., and Hausbeck, M. K. 2000. Mefenoxam insensitivity and the

sexual stage of Phytophthora capsici in Michigan cucurbit ﬁelds. Phytopathology
90:396-400.

Levesque, C. A., and Rahe, J. E. 1992. Herbicide interactions with fungal root
pathogens, with special reference to glyphosate. Annual Review of
Phytopathology 30:579-602.

76

96.

97.

98.

99.

100.

101.

102.

103.

104.

105.

Lil], R. E., King, G. A., and O'Donoghue. 1990. Physiological changes in
asparagus immediately after harvest. Scientia Horticulturae 44: 191-199.

Mallory-Smith, C. A., and Retzinger, E. J ., Jr. 2003. Revised classiﬁcation of
herbicides by site of action for weed resistance management strategies. Weed
Technology 17:605-619.

Matos, A. P., Sanches, N. F., and Costa , J. L. 1997. Patterns in diurnal and
seasonal airborne spore concentrations of F usarium subglutinans in a pineapple
orchard in Brazil. Acta Horticulturae 425:515-522.

Maynard, D. N., and Hochmuth, G. J. 1997. Knott's Handbook for Vegetable
Growers. John Wiley and Sons. Inc, New York.

McGiffen M.E. Jr., Ehlers, J. D., and Aguiar, J. L. 2000. Introduction to organic
horticulture colloquium. HortTechnology (10):661—662.

Mchau, G. R. A., and Coffey, M. D. 1995. Evidence for the existence of two
distinct subpopulations in Phytophthora capsici and a redescription of the species.
Mycological Research 99:89-102.

Mullen, R., Mayberry, K., and Laemmlen, F. 1996. Aparagus production in
California. in: University of California division of agriculture and natural
resources, publication 7234.

Nelson, K. A., Renner, K. A., and Hammerschmidt, R. 2002. Cultivar and
herbicide selection affects soybean development and the incidence of Sclerotinia
stem rot. Agronomy Journal 94:1270-1281.

Ngouajio, M., McGiffen, M. E., and Hutchinson, C. M. 2003. Effect of cover
crop and management system on weed populations in lettuce. Crop Protection
22:57-64.

Nicholson, P. 2001. Molecular assays as aids in the detection, diagnosis and
quantiﬁcation of F usarium species in plants. Pages 176- 192 in: F usarium: Paul
E. Nelson Memorial Symposium, B. A. Summerell, J. F. Leslie, D. Backhouse,
W. L. Bryden and L. W. Burgess, eds. American Phytopathological Society Press,
St. Paul, MN.

77

106.

107.

108.

109.

110.

111.

112.

113.

114.

115.

Nigh, E. L. 1990. Stress factors inﬂuencing F usarium infection in asparagus.
Acta Horticulturae (ISHS) 271:315-322.

Parra, G., and Ristaino, J. B. 2001. Resistance to mefenoxam and metalaxyl
among ﬁeld isolates of Phytophthora capsici causing Phytophthora blight of bell
pepper. Plant Disease 85:1069-1075.

Quesada-Ocampo, L. M., Fulbright, D. W., and Hausbeck, M. K. 2009.
Susceptibility of Fraser ﬁr to Phytophthora capsici. Plant Disease 93:135-141.

Reid, T. C. 2000. Evaluation of strategies for the control of F usarium crown and
root rot of asparagus. M.S. Thesis. Michigan State University, East Lansing.

Reid, T. C., Hausbeck, M. K., and Kizilkaya, K. 2002. Use of fungicides and
biological controls in the suppression of F usarium crown and root rot of

asparagus under greenhouse and growth chamber conditions. Plant Disease
86:493-498.

Reid, T. C., Hausbeck, M. K., and Kizilkaya, K. 2001. Effects of sodium
chloride on commercial asparagus and of alternative forms of chloride salt on
F usarium crown and root rot. Plant Disease 85:1271-1275.

Ristaino, J. B., Parra, G., and Campbell, C. L. 1997. Suppression of
Phytophthora blight in bell pepper by a no-till wheat cover crop. Phytopathology
87:242-249.

Robinson, D. E. 2008. Atrazine accentuates carryover injury from mesotrione in
vegetable crops. Weed Technology 22:641-645.

Sadowski, C., and Knaﬂewski, M. 1990. Susceptibility of selected asparagus

cultivars to F usarium spp. under ﬁeld conditions. Acta Horticulturae (ISHS)
271:343-352.

Sandsted, R. F., Wilcox, D. A., Zitter, T. A., and Muk, A. A. 2009. Vegetable
Crops: Asparagus Information Bulletin. in: Cornell University cooperative
extension bulletin 202.

78

116.

117.

118.

119.

120.

121.

122.

123.

124.

125.

Sanogo, S., Yang, X. B., and Scherm, H. 2000. Effects of herbicides on
F usarium solam' f. sp. glycines and development of sudden death syndrome in
glyphosate-tolerant soybean. Phytopathology 90:57-66.

Sato, T., and Motoki, S. 2002. Past and present Japanese asparagus production
and marketing. Acta Horticulturae (ISHS) 589:41-47.

Saude, C., Hausbeck, M. K., Hurtado-Gonzales, O., and Lamour, K. H. 2005.
Detection of a Phytophthora sp. causing asparagus spear and root rot in Michigan.
Plant Disease 89:1011.

Saude, C., Hurtado-Gonzales, O., Lamour, K. H., and Hausbeck, M. K. 2008.
Ocurrence and characterization of a Phytophthora sp. pathogenic to asparagus
(Asparagus ofﬁcinalis) in Michigan. Phytopathology 98 1075-1083.

Seifert, K. A. 2001. F usarium and anamorph generic concepts. Pages 15-28 in:
F usarium: Paul E. Nelson Memorial Symposium, B. A. Summerell, J. F. Leslie,
D. Backhouse, W. L. Bryden and L. W. Burgess, eds. American
Phytopathological Society Press, St. Paul, MN.

Shelton, D. R. 1978. Effect of stresses on growth and yield of asparagus
(Asparagus oﬂicinalis L.). M.S. Thesis. Michigan State University, East
Lansing.

Singh, H. P., Batish, D., and Kohli, R. K. 2006. Handbook of Sustainable Weed
Management. Food Products Press, New York.

Smith, A. E., ed. 1995. Handbook of Weed Management Systems. M. Dekker,
New York.

Snapp, S. S., and Borden, H. 2005. Enhanced nitrogen mineralization in mowed
or glyphosate treated cover crops compared to direct incorporation. Plant and
Soil 270:101-112.

Sonoda, T., Tairako, K. T., and Uragarni, A. 2002. Comparative evaluation of
resistance of Asparagus oﬂcinalis L cultivars and breeding lines to F usarium stem
and crown rot. Acta Horticulturae (ISHS) 589:387—390.

79

126.

127.

128.

129.

130.

131.

132.

133.

134.

135.

136.

Souza, I. F., and Wagner, L. 2004. Weed management under no-tillage systems
in tropical regions. Pages 253-270 in: Weed Biology and Management, S.
Inderjit, ed. Kluwer Academic Publishers, Boston.

Stone, G. E., and Chapman, G. H. 1908. Report of the Botanist. Pages 127-128.
Massachusetts Agr. Exp. Stat.

Stone, N. K., and Roose, M. L. 1999. Field evaluation of new asparagus varieties
at the university of California, riverside. Acta Horticulturae (ISHS) 479:185-188.

Thrane, U. 2001. Developments in the taxonomy of F usarium species based on
secondary metabolites. Pages 450-475 in: F usarium: Paul E. Nelson Memorial
Symposium, B. A. Summerell, J. F. Leslie, D. Backhouse, W. L. Bryden and L.
W. Burgess, eds. American Phytopathological Society Press, St. Paul, MN.

Timmer, L. W., Graham, J. H., and Zitko, S. E. 1998. Metalaxyl-resistant
isolates of Phytophthora nicotianae: occurrence, sensitivity, and competitive
parasitic ability on citrus. Plant Disease 82:254-261.

Toledo, J. 1990. Asparagus production in Peru. Acta Horticulturae (ISHS)
271:203-210.

Vujanovic, V., Hamel, C., Jabaji-Hare, S., and St.Arnaud, M. 2003. First report
of root rot on asparagus caused by Phytophthora megasperma in Canada. Plant
Disease 87:447.

Wacker, T. L. 1988. Role of vesicular-arbuscular mycorrhizal fungi in the
asparagus (Asparagus oﬂz‘cinalis L.) agroecosystem. M.S. Thesis. Michigan
State University, East Lansing.

Wardle, D., and Parkinson, D. 1990. Inﬂuence of the herbicide glyphosate on
soil microbial community structure. Plant and Soil 122:29-3 7.

Wilcox-Lee, D., and Drost, D. T. 1991. Tillage reduces yield and crown, fern,
and bud growth in a mature asparagus planting. Journal of the American Society
for Horticultural Science 1 16:93 7-941.

Wisler, G. C., and Norris, R. F. 2005. Interactions between weeds and cultivated
plants as related to management of plant pathogens. Weed Science 53:914-917.

80

137. Zandstra, B. H. 2009. Weed Control Guide for Vegetable Crops. in: Michigan
State University Extension Bulletin 433.

138. Zimdahl, R. L. 2004. Weed-Crop Competition: aReview. Blackwell Publisher
Professional, Ames, IA.

81