DAMPING-OFF OF SPINACH AND BEET
SEEDLINGS IN NATURALLY AND

I
I THE EFFECTS OF SEED TREATMENTS ON
I
' ARTIFICIALLY INFESTED MUCK SOILS

Thesis for the Degree OI M. S.
MICHIGAN STATE UNIVERSITY

Robert A. Davis
1960

 

 

 

 

filLSES

 

 
   
 

LIBRARY

I Michigan State
University

  

ABSTRACT

THE EFFECTS OF SEED TREATMEQTS ON DAMPINC-OFF
OF SPINACH AND BEET SEEDLINGS IN NATURALLY
AND ARTIFICIALLY INFESTED MUCK SOILS

by Robert A. Davis

Nine seed treatment chemicals, p-dimethyl amino
benzene diazo sulfonate (Dexon), l-benzoyl-l-Q-p-nitroso
phenyl hydrazine (Chemagro B-lSOSO), copper 2-pyridinethione
l—oxide (Omadine-copper), captan (Captan 75), methylmercury
dicyandiamide (Panogen 15), manganous dithiocarbamate
(Tennam 10), yellow cuprous oxide, a chlorinated heterocyclic
sulfur compound (Diamond Alkali 6N49), and trans 1,2, bis
n-propyl sulfonyl ethylene (Chemagro B-lBAB), from commer-
cial and experimental stocks were evaluated for control of
damping-off of spinach and beet seedlings. The degree of
specificity of the chemicals toward the pathogenic fungi,
the extent of chemical control of disease in various soil
infestations, and the interaction between soil fungi, seed
treatments and the host plants were determined in a series
of greenhouse experiments. Seeds were planted in pots or
flats of naturally infested muck soil and in soil artificially
infested with Rhizoctonia solani, Pythium irregulare,
Fusarium sp., and the various combinations of these fungi.

Evaluation of seed treatment chemicals was based on the

Robert A. Davis

final seedling stand and the amount of post-emergence
damping-off.

The most severe pre- and post-emergence damping-
off occurred in soils artificially infested with Pythium,
Rhizoctonia and their various combinations. The Fusarium
isolate used was only mildly pathogenic and appeared to
have reduced severity of damping-off by Rhizoctonia in one
experiment.

Nearly all seed treatments significantly increased
stands of spinach and beets in pathogen-infested soils.
Those which gave most consistent overall protection for
spinach and beets, considering all soil infestations as a
whole, were Dexon, Chemagro B-15080, Chemagro B-1843,
Captan 75, and Tennam 10. None of the seed treatments
protected spinach or beet seedlings effectively in soil
infested with Rhizoctonia alone. Pythium-specific materials

were most effective in these trials.

THE EFFECTS OF SEED TREATMENTS ON DAMPING-OFF
OF SPINACH AND BEET SEEDLINGS IN NATURALLY
AND ARTIFICIALLY INFESTED MUCK SOILS

by Robert A. Davis

A THESIS

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

MASTER OF SCIENCE
Department of Botany and Plant Pathology

1960

Approved AQMU}% 2424

V U

ACKNOWLEDGEMENTS

The author is grateful to Dr. Donald J. deZeeuw
for the advice and suggestions given in the course of this
study; for the use of equipment and materials, and for assist-
ance and criticism in the preparation of the manuscript.

Acknowledgement is also made to the following
companies who have sponsored an Assistantship for seed and
soil treatment research, employing the author. The funds,
materials, and technical information supplied by these

companies have been valuable aids in this research.

American Cyanamid Company

California Spray-Chemical Corporation

Chemagro Corporation

Chipman Chemical Company, Inc.

Corona Chemical Div., Pittsburg Plate Glass Company
Diamond Alkali Company

E.I. duPont de Nemours & Company, Inc.

Eli Lilly Company

Ferry-Morse Seed Company

Gallowhur Chemical Corporation

Gerber Products Company

Haviland Chemical Company

Hercules Powder Company

Monsanto Chemical Company

Naugatuck Chemical Company

Niagara Chemical Div., Food Machinery & Chemical Corp.
Nitrogen Div., Allied Chemical and Dye Corporation
Norwich Pharmacal Company

Olin-Mathieson Chemical Corporation

Panogen, Inc.

Shell DeveIOpment Company

Tennessee Corporation

Union Carbide Chemicals Company

Upjohn Company

Velsicol Chemical Corporation.

ii

TABLE OF CONTENTS

ACKNOWLEDGEMENTS .
LIST OF TABLES . . . .
LIST OF ILLUSTRATIONS. . . . . . . . . .
INTRODUCTION . . . . . . . . . . . . . .
REVIEW OF LITERATURE . . . . . . . . . .
MATERIALS AND METHODS
EXPERIMENTAL RESULTS . . . . . . . .
Preliminary Experiments . .
Spinach Seed Treatment
Experiment 9 . . .
Experiment 10 . . . . . . .
Experiment 11
Beet Seed Treatment
Experiment 12 . . . . . . .
Experiment 13 . . . . .

Experiment 14 . . . . . . .

DISCUSSION . . . . . . . . . . . . . . .
LITERATURE CITED . . . . . . . . . .

iii

Page

ii
iv

18
22
22

28
32
38

46

51
55

69

Table
1.

3--5. A Duncan Multiple Range comparison of percent
stands of Giant Thick-Leaved Nobel spinach
produced by treated seed in variously infested

4A.

5.
5A.

6--8. A Duncan Multiple Range comparison of stands of
Detroit Dark Red beets produced by treated seed
in variously infested soils.

6.
6A.
7.
8.
8A.

LIST OF TABLES

Seed treatment chemicals applied to Giant
Thick-leaved Nobel spinach or Detroit Dark

Red beet seeds. .

Percent stand of Giant Thick-leaved Nobel
spinach seeds treated with various seed
protectants and planted in various soil
infestations (Preliminary Experiments).

muck soils.

Experiment 9.

Experiment 10.
Experiment l0.
Experiment 11.
Experiment 11.

Experiment 12.
Experiment 12.
Experiment 13.
Experiment 14.

Experiment 14.

iv

Page

19

51
56

57

AS

u8
A9
52
57

Figure

1--4.

LIST OF ILLUSTRATIONS

Percent stand and total emergence of Giant
Thick-leaved Nobel spinach seed treated
with various seed protectants and planted
in variously infested muck soils.
Preliminary Experiments. . . . . . .
Experiment 9. . . . .
Experiment 10. . . . . . . . . . . . .
Experiment 11. . . . . . . . . . . .
Experiment 11. . . . . . . . . . . .
Stand and total emergence of Detroit Dark
Red beets treated with various seed protect-
ants and planted in variously infested muck
soils. _

Experiment 13. . . . . . . . . . .

Experiment 14. . . . . . . . . . . . .

Page

30
EA
140

SA
60

INTRODUCTION

Damping-off is a severe disease of field and
vegetable crops under conditions which favor its develop-
ment. The disease is caused by invasion of the seedling
by one or several pathogenic fungi which disorganize,
weaken, or rot the tissues. Damping-off may be either
pre-emergence or post-emergence depending on the stage
of seedling development at which the plant succumbs to
fungal invasion. Pre-emergence damping-off includes seed
rotting or killing of the young seedling by fungi before
it emerges from the soil.

The deve10pment of damping-off is influenced by
various interactions of the environment on both host and
pathogen. Generally the conditions most favorable for the
pathogen that are at the same time unfavorable for the
host will lead to.maximum disease develOpment. Delayed
growth of the soft seedling tissue, for example, lengthens
the susceptible period through which the seedling passes
before its tissues become lignified or "hardened-off"
sufficiently to resist invasion. At the same time the
fungus may be able to grow vigorously and the probability
of infection is increased.

Damping-off occurs in the field as well as in
the greenhouse and affects both large and small-scale
growers. Greenhouse operators have problems with damping-

off in flats, pots, coldframes, and seedbeds. In spite of

expensive soil steaming processes, contamination of
greenhouse flats and pots may occur as a consequence of
careless handling or improper procedures (51).

Chemical seed treatment offers a simple and
moderately effective solution to damping-off problems,
either as a supplementary treatment or as the sole treatment
where the damping-off complex is not severe. Seed treatment
offers two types of protection for the growing seedling A)
protection from invasion by fungi which are borne externally
on the seed and B) at least partial protection of the
emerging seedling while it is in it's most vulnerable
state (58).

The studies reported here are concerned with the
damping-off of Spinach and beet crops in the greenhouse.

The effectiveness of some promising chemical seed protect-
ants was investigated particularly with regard to disease
control and to the specificity of the chemicals. An
equally important objective has been that of studying the
characteristics and interactions of fungal soil microflora
in naturally and artificially infested muck soil by
observation of the behavior of selected seed treatments

in those soils. Attempts were made to approximate a
natural pathogenic field soil by artificially infesting
steamed muck with controlled mixtures of soil fungi
(Rhizoctonia, Pythium, and Fusarium) in order that an

analysis of the damping-off phenomena could be made.

[\1

REVIEW OF LITERATURE

Damping-off of Vegetable Crops

 

Damping-off diseases are particularly severe in
vegetable, conifer, and ornamental plants. The disease
or group of diseases is a potential threat in most crop
growing areas and few plant Species are resistant when
environmental conditions and stage of deve10pment of the
host plant favor attack by damping-off fungi (9, 50).

One of the earliest observations on damping£off or root
rot was made by De Candolle in 1815 who demonstrated the
relation of Rhizoctonia to root rot (39). In 1874 Hesse,
end others in Germany, described Pythium debaryanum as a
plant parasite and described its effect on plants.

Apparently the damping-off phenomenon was well
known in this country prior to 1891, but it was considered
to be caused by excessive dampness in the soil (31, 34).
In 1891, Humphrey (34) reported the occurrence of damping-
off of cucumbers in Massachusetts and described the
appearance of mycelium in the rotted tissues. He identified
the mycelium as that of Pythium debaryanum and concluded
that this was the same disease described by Hesse in
Germany. The first detailed accounts of this fungus-disease
relationship and that of the "sterile fungus” Rhizoctonia
were given by Atkinson (2, 3). The parasitic nature of
Rhizoctonia and its relationship to plant diseases was
subsequently reviewed by Duggar and Stewart (21) and by

\N

Peltier (50) in Experiment Station bulletins emphasizing

the seriousness of root diseases caused by this fungus on

a wide variety of crops. More recent reviews of damping-

off and its control with particular regard to vegetable

crops has been given by Alexander (1), Kadow and Anderson (39)
and Ellis (23).

Host Range

Rhizoctonia, Pythium, and Fusarium, the most
common damping-off fungi, are widely distributed and have
an extensive host range, as evidenced by reports of
damping-off disease in the literature (9, 39). Peltier (50)
listed the distribution and host range of Rhizoctonia on
various crops in the United States, Canada, South America,
the West Indies, Europe, India and Australia. Plants
belonging to the families Amaranthaceae, Caryophyllaceae,
Cruciferae, Leguminosae, Solanaceae and Compositae were

especially susceptible to Rhizoctonia species. Some

 

strains of Rhizoctonia have a very restricted host range

while others are less specialized (56).

Economic Importance

The cost of vegetable production is increased
considerably by the damping-off hazard. The grower must
pay for preventive measures such as soil steaming, chemical
soil treatment, fumigation, seed treatment, and special

cultural practices or he must be prepared to absorb cost

of reseeding if disease becomes severe (10, 13, 33, 39).
Damping-off is often responsible for as much as 90% kill
of seedlings and in especially susceptible varieties,
seedling losses of 25--75 percent occur yearly (39).
Secondary losses in yield or quality may occur as a
result of mild infection of seedlings after they have
begun to mature. Although such plants may survive, the
injury to the meristematic or conductive tissue causes
poor growth and yield.

Damping-off in seedling flats is important
because it represents loss of labor and valuable seed as
well as waste of greenhouse space and disrupted planting
schedules. Healthy-appearing plants weakened by disease
may succumb to the shock of transplanting. As an example
of the seriousness of this disease, one large producer of
tomato seedlings in New York discarded nearly a half
million plants grown in 500 seedling flats as a result of
damping-off (31). Cook (14) estimated that 20--3O percent
less spinach seed was required in field seedings when the
seed was treated for protection against damping-off.
According to Natti (49) spinach is subject to a further
loss because of damping-off disease. If seed is sown at
the normal rate and large gaps result from damping-off
disease, the remaining spinach plants grow too large and
coarse for a quality product. If spinach is sown at a
heavier rate to compensate for seedling disease loss and

disease does not become severe, the plants must be thinned

or the lamina of the leaves will be decreased considerably
in area without a corresponding decrease in the size of the
midribs. Not only is this type an undesirable product but
the crowded plants deve10p stem rot more readily.

It has also been pointed out that aged seed or
seed of low vitality is benefited especially by seed
treatment. The protection afforded by seed treatment

enables the weaker seedlings to survive (58, 60, 61, 62).

Causal Organisms

According to Kadow and Anderson (39) most
workers agree that Rhizoctonia,.§ythium, Fusarium, Botrytis
and Phytophthora are the most important fungi involved in
damping-off of vegetable crops. The species most commonly
involved are Pythium ultimum, Pythium debaryanum, Rhizoctonia
solani (l, 5, 32) and Fusarium oxysporum (5). Other fungi,
capable of causing damping-off under more restricted
conditions are Phgm§.b§£g§ (l6) and certain species of
Sclerotinia, Sclerotium, Glomerella and Thielavia (39).

Damping-off may also be caused by fungi which are
more specific in their host range. This type is represented
by Aphanomyces laevis, and Aphanomyces cochliodes on beet
(7, 24) and Ascochyta pinoidella and Mycosphaerellg|pinodes,

root parasites of peas (38).

Symptoms

The most conspicuous symptom of damping-off is
that of the toppling of the seedling after emergence from
the soil. Post-emergence damping-off occurs as a result
of fungal invasion of the hypocotyl at or just below the
ground line. The tissues become rotted and soft at that
point and the seedling collapses. The post-emergence
phase of damping-off by Pythium is characterized generally
by a water soaked and discolored appearance of the
hypocotyl, particularly below the soil line. Plants
which do not tOpple but have diseased roots or hypocotyl
are stunted, abnormally dark green, and the cotyledon
leaves roll downward (l). Invasion of the hypocotyl by
gh;zoctonia produces a dry, shrivelled lesion instead of
the water soaked one caused by Pythium (l). Tissues are
frequently browned and sunken and roots may be covered
with hyphae (50). Rhizoctonia may cause a soft rot which
progresses rapidly without any browning or lesion formation,
or invasion may cause the formation of reddish brown lesions
which gradually deepen until they reach the vascular
tissue. If the lesion is confined to the superficial
tissues, the plant may recover but penetration to the
vascular tissues, especially when the lesion girdles the
stem, usually results in the death of the plant (3).

Fusarium causes a different type of seedling

disease than Rhizoctonia or Pythium. Instead of attacking

the hypocotyl at the soil line, Fusarium penetrates the
plant through the root (27), and often invades the plant
systemically producing severe wilt symptoms and often
death (35). The early stages of infection of spinach
are recognized by the pale color of the leaves and the
tendency of the leaf margins to roll inward. Leaf
symptoms become progressively more severe and permanent
wilting and death follow within three or four weeks.
The roots of a diseased plant appear blackened and the
vascular tissue is often discolored (15, 35). Older
infected plants may survive until maturity or may die at
any intermediate period. Infected plants may or may not
be stunted, but the leaves yellow and wilt starting with
the older outer leaves and Spreading progressively to the
younger ones (15). Although Fusarium is considered to be
primarily a vascular pathogen, a strain of Fusarium
oxysporum, causing a seedling blight of asparagus, was
found to act primarily in the cortical region of the
root (26). Penetration was through the root tip or
stomata on the hypocotyl and the fungus grew cellularly
and intercellularly through the cortex. In contrast to
vascular strains, symptoms were associated with collapse
of sections of the primary root and the roots of older
seedlings had reddish-brown elliptical lesions.

The effects of pre-emergence damping-off can
be observed in pots, seedling flats, cold frames or in

the field where gaps in the rows show that seedlings have

not emerged. Infestation may radiate from the initial
infection point outward in all directions, killing
seedlings as it progresses (39).

Closely related diseases known as ”wire stem",
"stem rot" or "bottom rot" result from late Seedling
stage infection by the damping-off fungi. These seed-
lings, though they may not tOpple over, are slow in
development and generally are stunted and of little

commercial value (39).
Environment

Severity of damping-off, particularly of the
pre-emergence type, is determined by several factors, among
which soil temperature, moisture, and pH are usually the
most important.

Temperature-- There is evidence that pre-emergence
damping-off may be correlated with the effect of temperature
on the growth of the host (4, 20, 37) as indicated by
temperature studies with wheat and corn. Studies by
Leach (45) have shown that the effect of temperature on
the growth rate of both the host and the pathogen bears
a definite relationship to disease severity. Using spinach,
sugar beets, watermelon and peas in combination with
Rhizoctonia, Pythium, and Phgm§_he found little correlation'
between temperature effect on the severity of infection
and the growth rate of either the host or the pathogen.

However, by determining the coefficient of velocity of

1O

emergence of the host plant by the method of Kotowski (40)
and the rate of growth of tne organism in culture at
various temperatures, Leach predicted the range of disease
severity for a particular combination of host and pathogen.
The percentage of seedlings emerging from infested soil at
different temperatures agreed closely with the ratio
between the coefficient of velocity of emergence and the
growth rate of the organism at the same temperatures (42, 45).
Spinach, which germinated equally well between 4 and 25° C
became most severely diseased in Pythium-infested soil
between 12 and 20° C. In Rh;zoctonia-infested soil
pre-emergence damping-off was least at 12° C or below,
moderate at 16° C and severe at 20° C or above. Sugar
beets suffered most severe pre-emergence damping—off in
Pythium-infested soil between 12 and 20° C and in
Rhizoctonia-infested soil between 16 and 30° C. In all
combinations of host and pathogen pre-emergence infection
was most severe at temperatures that were relatively less
favorable to the host than to the pathogen as measured by
the ratio of their growth rates (45).

Experiments with damping-off of Ladino clover
and Lespedeza caused by Rhizoctonia solani, Pythium
debaryanum and Fusarium roseum indicated that pre-
emergence damping-off was greatest at temperatures which
were relatively unfavorable to the host and that post-
emergence damping-off with the exception of that caused
by Fusarium, was greatest at temperatures favoring the

growth of the host (27).

11

Studies on the influence of temperature and
other factors on the damping-off of Red pine have shown
that although Red pine germinated well between 18 and 33° C ,
about half of the seedlings were killed in Pythium-infested
soil at the higher temperature and 90 percent were killed
at temperatures near 12° C. At these low temperatures
Rhggoctonia caused only a small loss, but damage increased
to a maximum of about 58 percent at 24--30° C and then
declined at 33° c (53).

Kadow and Anderson (39) in summarizing the results
of various workers listed Pythium as being destructive
over a wide range of temperatures, but usually most
serious between 24 and 30° C (75—-85° F). Rhizoctonia
was listed as most destructive at temperatures between
16 and 25° c (6l--77°F). In field and greenhouse
experiments with many kinds of vegetables, thium was
found to be the cause of damping-off at temperatures as
low as 7° C (45° F) and as high as 33° C (900 F) and in
serious form between 13 and 30° c (55--85° F).

Soil Moisture-- Beach (4) pointed out that
damping-off can be severe when the soil holds just enough
moisture for good plant growth, or about 50 percent water-
holding capacity. Increasing soil moisture above this
value leads to progressively poorer stands since this
condition is less favorable to the host and more favor—

able to certain fungi.

12

Pythium irregulare caused damping-off at a soil
moisture of 20 percent and the percentage of disease
showed a continuous increase with increase in soil
moisture up to saturation (53). Rhizoctonia damping-off
gradually increased from 47 percent at 13 percent soil
moisture to a maximum (65 percent) at 68 percent soil
moisture and then decreased to a minimum at saturation.

Pythium is sensitive to drying especially at
high temperatures but Rhizoctonia is able to survive in
dry soil (4, 52). In controlled greenhouse experiments,
growth of Rhizoctonia through the soil was greatest at

30 percent soil moisture and least at 80 percent (6).

The Interrelationship of Temperature and Moisture

In experiments with tomato seedlings under controlled

 

moisture and temperature conditions, it was demonstrated
that Rhizoctonia and Pythium have a wide range of
parasitism. Disease development was retarded by high
soil temperature and low soil moisture. Pythium injury
increased as soil temperature was lowered to 18° C
even though soil moisture was maintained at 35 percent.
As soil moisture was increased at the low temperatures,
damping-off became more severe. Rhizoctonia solani was
most severe around 24° C at all soil moisture values
tested (1).

Roth and Riker (53, 54) found that temperature

was more important in determining severity of total

13

damping-off of Red Pine while soil moisture determined
which fungus would predominate. Except for early pre-
emergence and some post-emergence damage caused by
Pythium at low temperatures, warm weather favored total
damping-off irrespective of the fungus acting. When
temperature was low, post-emergence damping-off was at
a minimum.

Soil Acidity-- The fungi most concerned in
damping-off are adapted to a pH range wider than that of
most cultivated plants, or from pH 4 to pH 9. If the
pH of the soil is Optimum for a particular crop, it is
better able to resist or escape attack, probably because
the seeds germinate faster and more uniformly. In
experiments with spinach, beets and tomatoes, damping-off
tended to be two to three times greater below pH 6.5 than
throughout the range above this level (4).

Variations in soil acidity between pH 5.5 and 7.0
had little influence on total damping-off of Red Pine.

A pH of 5.5--6.0 was favorable to both Rhizoctonia and
Pythium. The more acid soils favored Rhizoctonia while
Pythium damping-off occurred in soil more nearly neutral.
Increase in damping-off by both fungi at levels above pH 7.0

appeared to be associated with decline in host deve10pment (54).

Soil Solute Concentration-- An excess of solutes
in the soil, caused by overfertilization may be a direct

cause of physiogenic damping-off or in less severe form

14

may simply delay germination and prediSpose the seedling
to fungal attack. It has been shown that common damping-
off fungi grow well in concentrations of soil solutes
which seriously inhibit growth of seed plants. As

solute concentration increases, the growth rates of both
fungus and host plant decrease, but the host plant is
more severely affected and disease incidence becomes

greater (5).
Control

Seed treatment for seed and soil borne disease
control has been reviewed by a number of investigators
(l, 8, 23). Leukel (47) surveyed the use of various
organic and inorganic fungicides for seed treatment, and
the materials and methods for seed treatment of cereals,
forage crops, cotton, sugar beets and vegetables. Reviews
with particular emphasis on vegetable crops have been
written by Taylor and Rupert (57) and by Walker (59).

Prior to 1937 most of the chemicals used for
treatment of spinach seed were inorganic metal salts such
as cOpper sulfate, red and yellow oxides of cOpper, and
zinc oxide (11, 12, l3, 14, 39, 51). Later the deve10p-
ment of the organic fungicides led to the recommendation
of thiram, dichlone and the organic mercuries along with
the cOpper and zinc oxides for spinach seed treatment (25).
Dichlone was reported to be less effective than the other

materials for treatment of beet and Spinach seeds (57).

15

In New Zealand, 40 chemicals, including copper
compounds, quinones, organic mercury compounds, dithio-
carbamates and other organic materials, were compared as
spinach seed protectants. Yellow cuprous oxide, dichlone,
organic mercuries, thiram” ferbam, copper-8-quinolinolate,
nitrosopyrazole and captan were found to be most effective (36).
Dichlone was more effective than chloranil as a quinone
seed treatment and mercury combined with methoxy ethyl,
ethyl phosphate, and dinaphthyl methanedisulphonate was
more effective than other formulations. Of the dithio-
carbamates, thiram in concentrations of not less than
50 percent was effective but cupram, ziram, and zineb
were not effective for protecting spinach seeds.

Tests in the United States have shown that
yellow cuprous oxide, Arasan, Phygon, Orthocide 75,

Panogen (18, 48, 49), zinc 2,4,5 trichlorophenate and
Vancide 51 (48) were effective as spinach seed treatments.
It was noted that treatment with Panogen (1 percent by
weight of seed) caused some seed injury (49).

The early recommendations for treatment of beet
seed were cuprous oxide, copper sulfate seed soak, and
hydroxymercurichlorOphenol (Semesan) (39). Red oxide
of c0pper was found to be a satisfactory seed treatment
for spinach and sugar beets where damping-off was caused
by Pythium ultimum. In the case of accompanying Rhizoctonia
and Phgmg infestation however, seed treatment with

organic mercury compounds was more effective (41).

16

Field tests in 1943 indicated the usefulness of
several inorganic and organic fungicides as vegetable
seed protectants (25). Those which were effective as
beet seed treatments were Arasan, Ceresan, Semesan and
2,4,5 trichlorophenol. Cooperative tests in 1944, in both
greenhouse and field, indicated that Arasan, Ceresan and
yellow cuprous oxide gave beneficial results in 60 percent
of the areas in which tests were conducted (43, 44). In
flat tests all three compounds were equally effective
against Pythium but yellow cuprous oxide was less effect-
ive than the others in controlling Rhizoctonia. It was
concluded from these tests that Detroit Dark Red beets
are less susceptible to Pythium attack than other strains
of garden or sugar beets (43).

In order to eliminate some of the objectionable
features of dust treatments, a number of soluble or
wettable treatments have been investigated (46). With
beet seed, a .15 percent solution of ethyl mercury
phosphate applied at 4 percent of seed weight was as
effective against Pythium damping-off as Ceresan M or
Phygon. The use of this material as a seed dip also
controlled seed-borne Phgm§.§gtge.

Dichlone and thiram were highly suitable as beet
seed treatments and both were superior to yellow cuprous
oxide or chloranil, while captan, Vancide 51, and

Panogen were moderately effective treatments in Michigan (18).

17

The effectiveness of captan and Vancide 51 was confirmed
in other studies (48, 49). Arasan, captan, dichlone,
chloranil, Semesan, Vancide 51 and zinc 2,4,5 trichloro-
phenate proved to be highly effective as beet seed treat-
ments in Louisiana. Chloranil and thiram were somewhat
less effective than the other materials (48). Dichlone,
captan, and Vancide 51 were recommended as the best
materials for beet seed treatment in New York (49).
Dichlone consistently appeared best and thiram was less
effective than the above materials.

Greenhouse experiments with various seed protect-
ants on beets have shown that Dexon (p-dimethyl amino
benzene diazo sodium sulfonate), captan, and Tennam
(manganous dithiocarbamate) gave good overall protection

in naturally and artificially infested muck soils (17).

18

MATERIALS AND METHODS

Ruby King pepper, Black Beauty eggplant, Giant
Thick-leaved Nobel spinach and Detroit Dark-Red beets
were selected for greenhouse experimental work [3 .
Seed treatment chemicals were obtained from companies
participating in the support of a graduate assistantship,
employing the author, for seed and soil treatment research

at Michigan State University.
§gg§_2reatment

Seed treatments were applied as slurries or
liquid treatments (Table 1). The seeds were tumbled in
an Erlenmeyer flask to insure uniform distribution of the
chemical over the seeds. Extra chemical (10% by weight)
was added to approximately compensate for loss of material
on the walls of the flasks. After drying, the seeds were

stored in the laboratory for subsequent plantings.
Soil Infestation

Inoculum for infesting soil was grown on petri
plates of Potato Dextrose agar (Fusarium sp. and
Rhizoctonia solani Kflhn), Nutrient Dextrose agar
(Rhizoctonia solani Kfihn), and Corn Meal agar (Pythium
irregulare Buisman) until the mycelium covered the plate.
The cultures were then chOpped separately in a small-cup
Waring Blendor with a small amount of distilled water for

[3 Seeds were furnished by Ferry—Morse Seed Co.
Detroit, Michigan

Table l.

19

Seed-treatment chemicals applied to Giant Thick-

leaved Nobel spinach or Detroit Dark Red beet seeds.

 

Material & Mfr.

Dexon
(Chemagro)

B-lSOBO
(Chemagro)

Omadine-Copper
(Olin-Mathieson)

Captan 75
(Stauffer)

Panogen l5 (liq.)
(Panogen) [i

Tennam 10
(Tennessee Corp.)

Cuprous oxide
(Rohm & Haas)

DAC 6N49
(Diamond Alkali)

B-1843
(Chemagro)

AC-l4307
(American Cyan.)

TEA-l
(Tennessee Corp.)

Actidione M
(Upjohn Co.)

Arasan 75
(duPont Co.)

Omadine-Zn—disulfide

(Olin-Mathieson)

B-856
(Chemagro)

20%
20%
50%

75%

Active Ingredient

p-dimethyl amino benzene diazo
sulfonate.

l-benzoyl-l—2 p-nitrosophenyl
hydrazine.

copper 2-pyridinethione l-oxide.

captan.

2.2% methylmercury dicyandiamide.

90%
100%
50%
20%
50%
2%
1%
75%
50%

50%

manganous dithiocarbamate.
yellow cuprous oxide.
a chlorinated heterocyclic sulfur

compound.

trans 1,2 bis (n-prOpyl sulfonyl
ethylene).

trichloro methyl chlorobenzene
thiosulfonate.

phytoactin-antibiotic.
cycloheximide.

thiram.

Zn-disulfide 2-pyridinethione

l-oxide.

1,3-dichloro-5,5 diphenyl
hydantoin.

 

Ag Panogen 15 applied to
All others

of seed.

seeds at the rate of 4 oz./100 lb.
at 8 oz./100 lb.

20

30--60 seconds at slow speed. The resulting fragments were
about 1 mm in diameter. Screened muck soil pastuerized in
flats was infested by distributing inoculum (1 plate
suspended in 200 m1 of water for each flat) in trenches
made by a 10 row marker. The soil was allowed to stand for
3 to 5 days for colonization. The colonized soils were
combined variously and mixed uniformly in a clean poly-
ethylene-lined mixing bin. The various mixtures were
placed in either steamed pots or flats and were planted

immediately.

Planting

Seeds were planted in 4-replicate 25-seed units
either in 4 inch pots or in 14 inch rows in flats (10 rows
per flat). An effort was made to provide the same amount
of soil in each planting unit and to plant the seeds at a
uniform depth and spacing. Watering was done carefully to

avoid splashing and cross contamination between flats or pots.

Egyg

After emergence, post-emergence damping-off was
recorded daily or at 2-day intervals until the seedlings
reached a resistant stage of maturity; generally within
14 days. Surviving seedlings were also recorded at this
time. Pre-emergence data is graphically shown by difference
between total emergence and germination of treated seeds in

steamed soil. Analysis of variance was carried out on both

5:1

total emergence and survivor data. Wherever multiple-unit
experiments were conducted, using both seed and soil
treatment variables, a split-plot analysis was applied on
the survivor or survivor and total emergence data and a
Duncan Multiple Range (22) comparison was carried out

wherever appropriate.

22

EXPERIMENTAL RESULTS
Selection of Experimental Materials

Preliminary experiments with treated eggplant and
pepper seeds in flats of unsteamed mineral soil aided in the
selection of the 15 materials listed in Table 1. Nineteen
materials were tested in separate 4-replicate experiments
using these crOps. Both experiments were repeated and the
data was analyzed statistically. Eight of the effective
materials were selected for further use. The remaining
seven materials were selected because of their known Specific
activity on certain soil fungi.

Although pepper and eggplant were satisfactory
hosts for damping-off studies, a period of 12 to 16 days
was required for emergence when they were grown at temperatures
near 60° F. For this reason, spinach and beet were selected
as test plants in subsequent experiments. Both germinate
readily in 3 to 4 days at fairly low temperatures and are
very susceptible to damping-off in infested soil if the seeds

are unprotected.
Seed Treatment Effects in Artificially Infested Soils

Preliminary_§xperiments

Since seed treatment chemicals differed in
effectiveness at certain stages of seedling development
in unsteamed soil, a series of experiments was set up to

determine the behavior of each seed treatment in a given

23

type of artificially infested muck soil. Soils were
artificially infested with Rhizoctonia solani Kflhn,
Pythium irregulare Buisman, Fusarium sp. or combinations
of these fungi. Spinach seeds treated with each of 15
chemicals were planted in the variously infested soils at
intervals over a seven month period. Seeds from the same
treated lots were used in each experiment of the series.
Stand averages of the various seed treatments from each of

the experiments appear in Table 2 and Fig. 1.

Rhizoctonia Soil (Expt. 1) -- In Rhizoctonia-infested muck
soil, Chemagro B-1843 was the only seed treatment significant-
ly better (5% level) than the untreated control. Cuprous
oxide was significantly poorer at the same level of
significance. Post-emergence damping-off was nearly the

same in all treatments (ranging from 11.0--20.0%) including
the control (Fig. l).

Pythium Soil (Expt. 2) -- In Pythium-infested soil, 10
seed treatments produced stands significantly (1% level)
higher than those of untreated seed. Both pre-emergence
(2.0--l4.0%) and post-emergence (3.8--6.8%) damping-off
losses were small for Chemagro Dexon, Chemagro B-15080 and
Chemagro B-1843. For the other seven effective materials,
the average pre- and post-emergence damping-off was 15.2%
and 34.5% respectively. Pre-emergence damping-off was very
high (56.0--100.0%) for American Cyanamid 14307, Tennessee
TEA-l, Diamond Alkali 6N49, Actidione M and the untreated

control.

Table 2.

Percent stand of Giant Thick-leaved Nobel Spinach

seed treated with various seed protectants and planted
in various soil infestations.

 

Experiment #

 

1/1 2 3 4 5 6 7 8 9
Seed Treatment R -' P F RF PP RP _RPF U 8 Ave.
1. Cholagro Dexon 43.2 79.2 74.0 56.0 48.0 31.2 23.2 81.2 76.8 57.0
2. Chemagro B-15080 46.0 72.0 63.2 65.2 52.0 22.0 22.0 74.0 72.0 54.3
3. Omadine-copper 51.2 22.0 69.2 68.0 39.2 12.0 25.2 54.0 78.0 46.6
4. Captan 75 59.2 54.0 74.0 70.0 24.0 22.0 19.2 67.2 86.0 52.9
5. Panogen 15 58.0 31.2 72.0 71.2 27.2 26.0 34.0 64.0 82.0 51.8
6. Tennam 10 53.2 46.0 68.0 82.0 21.2 30.0 24.0 64.0 68.0 50.7
7. Amer.Cyan.14307 42.0 0.0 64.0 67.2 1.2 1.2 17.2 63.2 75.2 36.8
8. Tenn.Corp. TBA-1 46.0 0.0 63.2 54.0 0.0 1.2 12 6.0 64.0 27.4
9. Arasan 75 51.2 43.2'75.2 73.2 18.0 37.2 33.2 62.0 75.2 52.1
10. Cuprous oxide 28.0 27.0 73.2 72.0 15.2 14.0 27.2 65.2 74.0 44.0
11. Chemagro B-1843 68.0 76.0 79.2 72.0 32.0 31.2 28.0 64.0 76.0 58.5
12. Diamond Alk.6N49 44.0 4.0 74.0 73.2 7.2 3.2 23.2 53.2 74.0 39.6
13. Actidione'M, 45.2 0.0 75.2 63.2 0.0 3.2 13.2 9 2 75.2 31.6
15. Onad.Zn-disu1f. 47.2 32.0 64.0 60.0 17.2 19.2 23.2 53.2 78.0 43.8
16. Chemagro B-856 34.0 11.2 75.2 59.2 17.2 3.2 27.2 49.2 77.2 39.2
0. Control 48.0 1.2 79.2 70.0 0.0 3.2 9.2 5 2 72.0 32.0

Awe. 47.7 31.2 70.3 67.2 20.0 16.3 22.6 52.2 75.4
L.S.D. 5% 17.5 15.3 -- 13.8 20.5 14.1 -- 9.8 --
1% 23.2 20.3 -- -- 27.4 18.8 -- 13.1 --
[3_ Soil Infestations
R - Rhizoctonia P - Pythium F - Fusarium

 

U - unsteamed.

S I steamed.

25

 

 

 

 

 

 

 

 

mocvoma

 

 

 

 

 

 

mama-"7mm "TmUI-FMIUI RHIZOCTONIA- FUSARIUI

 

 

 

 

 

 

 

 

 

 

 

 

RHIZWTWIA- PYTHIUI- PM”. muss

[:J as man. snuo POST-EMEkefllct saunas-o"

pigure 1. Percent stand and total emergence of Giant Thick-
leaved Nobel Spinach seed treated with various
seed protectants and planted in variously infested
muck soils. See Table 2 for individual treatments

U.

26

Fusarium and Rhizoctonia-Fusarium Soils (Expts. 3 and 4) --

Seed treatments produced no significant increase in stands
over those of untreated seed. Fusarium pre-and post-emergence
damping-off ranged from l.0--5.8% and 3.0--22.0% respectively.
In RF 8011, stands were generally high (54.0--75.0%) and
post-emergence damping-off was negligible. Some pre-emergence

damping-off (3.0--21.2%) was evident in this soil.

Pythium-Fusarium Soil (Expt. 5) -- In contrast to Experiments
3 and 4, the stands from treated seeds in PF infested soil
were low (0--51.8%) and both pre- and post-emergence damping-
off were high. Five seed treatments gave significant
increases in stands over those of untreated seed. Post-
emergence damping-off was low (5.3% and 0% respectively) for
Chemagro Dexon and Chemagro B-15080, moderate (12.8 and 15.0%)
for Omadine-cOpper and Panogen 15, and higher (31.2%) for
Chemagro B-l843 as compared to 27.0--40.0% for Captan 75,
Tennam 10, Arasan 75, Cuprous oxide, Omadine-Zn-disulfide

and Chemagro B-856, all of which were not effective seed
treatments in this experiment. Pre-emergence damping-off
caused losses of 22.8--44.0% for the effective treatments as
compared to 55.0--80.0% for the poorer treatments (American
Cyanamid 14307, Tennessee TPA-l, Diamond Alkali 6N49,
Actidione M) and the untreated control. In the latter

group, the combined losses of pre- and post-emergence
dampingfoff reduced stands to zero. The results of this

experiment were similar to those for Pythium-infested soil.

27

Rhizoctonia-Pythium Soil (Expt. 6) -- Stand averages ranged
from 1.2--37.0% in soil infested with RP in combination.

Six of the seed treatments produced stands significantly
greater than those from untreated seeds. For the effective
materials, pre- and post-emergence damping-off averaged

21.6 and 34.8% respectively. Pre-emergence damping-off

was high (ave. 75.2%) for American Cyanamid 14307, Tennessee
TPA-l, Diamond Alkali 6N49, Actidione M and the control.

The additional post-emergence loss (ave. 8.0%) practically

eliminated stands for these treatments.

figgzoctonianythium-Fusarigm_§2;l,(Expt. 7) -- There were

no significant differences between seed treatments in RPF
infested soil. Stands were generally low for all treatments,
ranging from 34.1% for the best treatment to 9.4% for the
untreated control. Differences between treatments were
slight and pre- and post-emergence damping-off averaged
53.2% and 11.0%. Either pre-emergence damping-off or a

loss in viability caused a general stand reduction for all
treatments. The latter is suspected, since this experiment

was conducted much later than the others in the series.

Unsteamed Soil (Expt. 8) -- Soil for this experiment was
unsteamed field muck. Untreated seed produced the lowest
stand and 13 treatments gave stands significantly greater
than the untreated control. Both pre- and post-emergence
damping-off losses were small for Dexon, Chemagro B-15080,
Panogen 15, Cuprous oxide, and Chemagro B-1843. Pre-emergence
losses were high (69.0--80.0%) for Tennessee TPA-l,

Actidione M and the control.

25

Steamed Soil (Expt. 8a)-- Although the differences between
seed treatments in steamed soil were not statistically
significant, stands from the treated seeds were uniform
and somewhat better than those of untreated seeds. The
control stand average was 72.0% and 12 of the 15 seed

treatments had stands averaging from 74.0 to 86.0%.

Spgpach Seed Treatment

Analysis of the preceding experiments indicated
the desirability of comparing the various soil treatments
at one time in flats or pots in order to minimize some
variability caused by environment. Both spinach and beets
were used in this way in subsequent trials. Nine of the
more effective and distinctive seed treatments were selected
for these experiments (Table 3). Seed treatments were
replicated in each type of inoculum with steamed and

unsteamed soil as controls for the soil treatments.

Experiment 2 -- Flats were infested as previously
described and planted immediately after mixing the inoculum
components. Average total emergence, final stand and post—
emergence damping-off are shown graphically in Fig. 2.
Pre-emergence damping-off values may be approximated by
extending the bars to 72.0 (the percent germination in
steamed soil). Ere-emergence damping-off was relatively
high and post-emergence damping-off was low in this

experiment. Analysis revealed no significant interaction

Figure 2.

 

 

Percent stands and total emergence of Giant Thick-
leaved Nobel spinach seed treated with various
seed protectants and planted in variously infested
muck soils (Experiment 9).

Seed Treatments Soil Infestations

Dexon. R—- Rhizoctonia solani.

Chemagro B-15080. P-- Pythium irregulare.

Omadine-COpper. F-- Epggpgpp_sp.

Captan 75. RF- Combination of above.

Panogen 15. PF- "

Tennam 10. RP- ”

Cuprous oxide. RPF- “

Diamond Alkali 6N49. U-- Unsteamed.

Chemagro B-1843. S-- Steamed.

Control.

 

 

 

 

 

 

 

 

 

WOCTONIA

 

FUWIUfl

PYTHIUH

 

 

 

 

 

 

 

 

 

 

 

 

 

UNSTEAMED STEAHED

R-P-F

POST- ENERGENCE DAHPIM- OFF

[:3 as mm. snub

Figure

Soil Infestation

Table 3

51

. A Duncan Multiple Range comparison of stand differences due
to soil infestation and seed treatment of Giant Thick-leaved
Nobel spinach.

 

Seed Treatment

 

3 9 4 7 2 l 5 6 8

S 66.0 63.2 59.2 72.0 60.0 62.0 64.0 52.0 55.
U 62.0 58.0 57.2 52.0 63.2 68.0 63.2 56.0 57.
PF 44.0 50.0 45.2 36.0 48.0 42.0 46.0 35.2 34.
F 48.0 39.2 34.0 35.2 34.0 25.2 36.0 40.0 35.
P 41.2 34.0 44.0 32.0 36.0 42.0 23.2 26.0 19.
RP 29.2 26.0 33.2 44.0 26.0 21.2 25.2 26.0 22.
RPF 23.2 36.0 32.0 27.2 27.2 27.2 26.0 30.0 23.
RF 21.2 25.2 23.2 25.2 21.2 21.2 20.0 23.2 23.
R 25.2 25.2 17.2 20.0 15.2 16.0 16.0 19.2 19.
ygppp 40.0 39.6 38.4 38.0 36.8 36.0 35.2 34.0 32.

Means bracketed by the same line

from each other.

OOQVO\U'L‘UNH

I"

Seed Treatments

Dexon.

Chemagro B-15080.

Omadine-copper.

Captan 75.
Panogen 15.
Tennam 10.

Cuprous oxide.

Diamond Alkali 6N49.

Chemagro B-1843.

Control.

R--
p--
F--
RF-

Soil Infestations

PF-
pp-

RPF-

u--
5--

10
63.
58.
50.
39.
34.
26.
36.
25.
25.

25.

male
60.4
56.0
42.0
36.0
31.2

27.6

 

27.6

 

21.6

 

18.8

are not significantly different

fl
1'

n"

Unsteamed.
Steamed.

Rhizoctonia solani.
Pythium irregglare.
Fusarium sp.
Combination of above.

differences between seed and soil treatments or between

seed treatments with all inoculum types taken as a whole.

All seed treatments, except Diamond Alkali 6N49, significant-
ly increased germination. Germination was also significantly
affected by the various soil treatments (Table 3). In this
experiment, stands of treated seed in unsteamed soil were

not Significantly different from those in steamed soil.

Stand averages in Pythium, Fusarium and PF soils were
essentially the same and stand reduction was greatest in

soils containing Rhizoctonia (R, RF, RP, and RPF).

Experiment 10 —- Seeds treated with the nine
fungicides were planted in pots of freshly infested soil.
The inoculum was adjusted to give the same initial concentrat-
ion for each component whether used in combination or alone.
In previous trials, the initial concentration of each
component was one-half or one-third that of the component
when it was used alone. There was a definite increase in
post-emergence damping-off in RP and RPF soils (Fig. 3).

A Duncan multiple Range analysis of stand averages, shows
three significantly different groups (Table 4). The first
group (stand ave. 51.2-{78.Q%) is composed for the most
part of seed treatments which were effective primarily
against Pythium. The second group (22.2jf51.2%)was
represented largely by seed treatments of intermediate
effectiveness in P and PF soils. The last group (stand ave.

O--21%)' encompassed nearly all of the seed treatments

Figure 3.

Percent stand and total emergence of Giant Thick-
Leaved Nobel spinach seed treated with various
seed protectants and planted in variously infested

muck soils (Experiment 10).

Seed Treatment

Dexon.

Chemagro B-l5080.
Omadine-copper.
Captan 75.

Panogen 15.

Tennam 10.

Cuprous oxide.
Diamond Alkali 6N49.
Chemagro B-1843.

Control.

W
R-- Rhizoctonia solani.
P-- Pythium irregulare.
F-- Fusarium Sp.

RF- Combination of above.
PF- "

PtP" H

U-- Unsteamed.

S—- Steamed.

 

 

 

 

 

 

 

 

 

 

 

 

 

RHIZOCTONIA PYTHIUM FUSARIW

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   

7
s s s c
2
uusrsmso STEAMED
[:1 as rum. snuo 9031- awesome: saunas-on

Figure 5.

Table 4.

KOCDNmUT-PUJIUH

H
O

A Duncan Multiple Range comparison of percent stands
of Giant Thick-leaved Nobel spinach produced by
treated seed in variously infested muck soils.

Seed Treatments
Dexon.

Chemagro B-l5080.
Omadine-cOpper.
Captan 75.

Panogen 15.

Tennam 10.

Cuprous oxide.
Diamond Alkali 6N49.
Chemagro B-1843.

Control.

Soil Infestations
Rr- Rhizoctonia solani.
P-- Pythium irregulare.
F-- Fusarium sp.
RF- Combination of above.
PF- ”
RP- .

U-- Unsteamed.

 

- rib—#9 T—

Table 4. Experiment 10.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Treatment Means
57 78.0 _
S4-86 76.0
88 75.2
Sl-F3 74.0
83-85 72.0
S9-F7 68.0
U4-U6-F2-P1-F6 66.0
R6-F8-810 65.2
R8-U9 64.0
82-R9 63.2
Uz-RS-PZ-Flo 62.0
F4 61.2
R7-R10 60.0
P1 59.2
P9-F5-F9 58.0
U1-U7 57.2
R2 56.0
R4-U5 55.2
R1 53.2
PFS 51.2
P6 49.2
R3-PF4 47.2
PF2-PF7 46.0
PPl-U3 45.2
PF6 43.2
PF3 42.0
PF9 40.0
P5 35.2
P4 32.0
RPFS 25.2
RP6-PF8-PF10 24.0
P7 23.2
RPS-P3-RP3 21.2
RP9 20.0
RPF6-RP10 15.2
RPP9-US 14.0
RPS-RPP2-UIO 13.2
RF6 12.0
RPFl-RF4 11.2
RF3 10.0
RP7-RPl-RP4 9.2
RP2-RP9 8.0
RPF3 7.2
RPS 6.0
RF7 5.2
RPF4 4.0
RPl-RPZ-RFS 3.2
RPF7-RF10 2.0
PlO-RPPlO-RPFS-PS 0.0

Means bracketed by the same line are not significantly different
from each other.

 

Table 4A. A Duncan‘Multiple Range comparison of stand differences due
to soil infestation and seed treatment-of Giant Thick-leaved
Nobel gpinpch. '
Seed.Treatment
6 9 5 2 1 4 7 3 8 10 ‘Means
S 76.0 68.0 72.0 63.2 74.0 76.0 78.0 72.0 75.2 65.2 71.6
F 66.0 58.0 58.0 66.0 59.2 61.2 68.0 74.0 6522 62.0 63.0 I
g 'R 63.2 63.2 62.0 56.0 53.2 55.2 60.0 47.2 64.0 60.0 58.4 |
E U 66.0 64.0 55.2 624.0 57.2 66.0 57.2 45.2 14.0 13.2 49.6 I
#3 pr 43.: 40.0 51.2 46.0 45.2 47.2 46.0 40.0 24.0 24.0 40.8 I
'3 P 49.2 58.0 35.2 62.0 66.0 32.0 23.2 21.2 0.0 0.0 34.4
3 RP 24.0 20.0 21.2 8.0 9.2 9.2 9.2 21.2 13.2 15.2 14.8
RPF 15.2 14.0 25.2 13.2 11.2 4.0 2.0 7.2 0.0 0.0 9.2
RP 12.0 8.0 3.2 3.2 3.2 11.2 5.2 10.2 6.0 2.0 6.4
Means 46.0 43.6.42‘.4 42.

H

<3~o<n~u<msm.>iatoru

0 41.6 40.0 38.8 37.6 29.2 26.8

Means bracketed by the same line are not significantly different
from each other.

Seed Treatments

_Soil Infestations

 

 

 

Dexon. R-- Rhizoctonia solani.
Chemagro B—15080. P-- Pythium irgggnlare.
Omadine-copper. F-- Fusarium sp.

Captan 75. RP- Combination of above.
Panogen 15. PF- "

Tennam 10. RP- "

Cuprous oxide. RPF- "

Diamond Alkali 6N49. U-- Unsteamed.

Chemagro B-1843.

Control.

S-- Steamed.

58
in RF, RP, and RPF soils. Rhizoctonia was apparently less
virulent in this experiment than in previous ones. The
cause for this was not specifically determined. Compared
to the previous experiment, stands in PF soil remained
about the same. Post-emergence damping-off was increased
considerably in RP and RPF soils and both pre- and post-
emergence damping-off were higher in RF infested soils (Fig. 3).
Stand differences due to seed treatment alone remained
unchanged but differences due to soil treatment were more

pronounced (Table 4A).

Experiment 11 -- Seed treated with the same
materials was again planted in freshly infested muck soil
in flats. The inoculum was adjusted as described above.
After planting the flats were placed on shaded platforms
outside the greenhouse. Pre-emergence damping-off was very
low in this experiment and post-emergence damping-off was
higher than in previous experiments (Fig. 4 and 4A). The
distribution of stand averages for the seed and soil treat-
ment combinations is given in Tables 5 and 5A. In this
experiment, Fusarium-infested soil was non-virulent and
allowed for stands comparable to steamed soil. Two seed
treatments, Dexon and Chemagro B-15080, in U, P, and PF
soils gave stands comparable to those in steamed soil.
Other materials, especially B-1843, which are known to be
effective against Pythium constitute most of the second

significance group (stand ave. 55.2--65.2%).

Figure 4.

Percent stands and total emergence of Giant Thick-
Leaved Nobel spinach seed treated with various seed
protectants and planted in variously infested muck
soils (Experiment 11).

 

 

 

 

Seed Treatments SoilZInfestations
Dexon. R-- Rhizoctonia solani.
Chemagro B-15080. P-- Pythium lgregulare.
Omadine—copper. F-- Fusarium sp.

Captan 75. R.- Combination of above.
Panogen 15. PF- "

Tennam 10. RP- ”

Cuprous oxide. RPF- "

Diamond Alkali 6N49. U-- Unsteamed.

Chemagro B-1943. S-- Steamed.

Control.

no

 

 

 

 

 

 

 

Euuuuuuunuunmmwu 9

 

 

 

0 cos... sees. s 0.000000

O... ‘

s 0.0.000 000 .00

 

 

.0

w «

PYTHIUI FUSARIUU

RHIZOCTONIA

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

o
o o s so...
assassssassssssnsos

so. 3

 

 

 

 

 

   

 

 

 

 

 

 

«

O
z

STEAMED

UNSTEAMED

F

R-P-

E % FINAL STAND

Pos'r-sussesucs DAMPING-OFF

SHEER

Figure A.

Figure 4A.

Percent stand and total emergence of Giant Thick-
Leaved Nobel spinach seed treated with various
seed protectants and planted in variously infested
muck soils (Experiment 11).
Soil Infestations

R-- Rhizoctonia solani.

P-- Pythium irregulare.

F—- Fusarium sp.

RF- Combination of above.

PF“ '9

RP- ll

RPF" II

U-- Unsteamed.

S-- Steamed.

 

8
.11: .
a

 

‘3 a s s s o s's's
‘ ‘ a .0 :.:.:.. 0:0. 0:0:o.s

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DEXON MOMS-COPPER CAPTAN 75

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

04c- ems anemone s-Iass UNTREATED cannon.
E 7. man. snuo POST-EMERGENCE DAMPING-OFF

Figure AA.

Table 5.

\OCD'QONU'I-h-UJMH

H
O

A Duncan Multiple Range comparison of percent stands
of Giant Thick-Leaved Nobel spinach produced by
treated seed in variously infested muck soils.

Sged Treatments
Dexon.

Chemagro B-15080.
Omadine—copper.
Captan 75.

Panogen 15.

Tennam 10.

Cuprous oxide.
Diamond Alkali 6N49.
Chemagro E-1843.

Control.

Soil Infestations
R-- Rhizoctonia solani.
P-- Pythium lgregnlare.
F-- Fusarium sp.
RF- Combination of above.
PF _ u
PP- "
RPF- "
U-- Unsteamed.

S-- Steamed.

Table 5. Experiment 11

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Treatment Means

33 86.2

22 83.2

24 82.0

25 81.2

$9 80.0

s4-21-27 78.0

$5 77.2

PF2-F3-SZ-S6-88 76.0

F10-F6-S7 75.2

01 74.0 i

F8~F9 72.0 '

221-02-310-21-22 71.2 I

81 65.2

229 64.0

U4 52.0

U9 48.0

29 43.2

05 40.0

U7 39.2

229 38.0

225 37.2

RPFl-RG-RPFZ 35.2

RP2-RP6 34.0

mm9 312

224-229 32.0

06 31.2

29-222 30.0

224-25-221 29.2

22-24-210 27.2 .
RF6-RF10 26.0 g . 1
223-225 25.2 : ; 3 _ 1 3
R3 24.0 I Q ' I 1 ; i
RPF6-P7-RF5-R8-RP7 23.2 I 1
223-224-227-227 >22.0 1
24 21.2 1
2225 20. 0

P6-R7 19.2

2224-21-2227 18.0

RPS 16.0

PF6 15.2

03 13.2

221 12.0 1
2223 10.0 I
RP8 9.2

08 7.2

23-25 6.0

RPF8 5.2

2210-010-223 3.2

210-22210 2.0

28-228-2210 1.2

Means bracketed by the same line are not significantly different
from each other.

 

 

 

Soil Infestation

115

Table 5A. A Duncan.Mn1tip1e Range comparison of stand differences due
to soil infestation and seed treatment of Giant Thick-leaved
' Nobel spinach.

 

222‘

Means

H

OomwasmbuNo-l

76.0
83.2
71.2
76.0
71.2
34.0
27.2
30.0
35.2

56.0

Means bracketed by the

65.2
78.0
74.0
71.2
71.2
29.2
18.0
12.0
35.2

48.4

80.
72.
48.
24.
43.
38.
30.
32.
33.

48.

78.0
82.0
52.0
29.2
21.2
32.0
27.2
22.0
18.0

40.0

Seed Treatment

5

6

7

3 8

77.2 76.0 75.2 85.2 76.0

81.2
40.0
25.2

6.0
37.2

29.

N

23.2
20.0

37.2

75.2
31.2
15.2
19.2
34.0
35.2
26.0
23.2

37.2

78.0
39.2
22.0
23.2
23.2
19.2
22.0
18.0

35.6

 

from each other.

Seed Treatments

Dexon.
Chemagro B-15080.
Omadine-copper.
Captan 75.
Panogen 15.
Tennam 10.
Cuprous oxide.
Diamond Alkali 6N49.
Chemagro B-1843.
Control.

76.0 72.0
13.2 7.2
3.2 1.2
6.0 1.2
25.2 9.2
24.0 23.2
22.0 20.0
10.0 5.2

29.2 23.2

10
71.2
75.2

3.2

1.2

2.0

3.2
27.2

26.0

23.2

Means

76.0
77.2
38.0
30.4
26.4
26.4
26.0
23.2

20.0

 

 

same line are not significantly different

Soil Infestations

 

 

 

R-- Rhizoctonia solani.
P-- Pgthium irrggnlare.
F-- Fusarium sp.

RF- Combination of above.
PF“ n

RP- "

RPF- "

Uu- Unsteamed.

S-- Steamed.

hé

The third group (stand ave.£18--35.2%) is the largest and
is represented principally by treatments #2, 4, 5, 6, and

7 (B-lSOBO, Captan 75, Panogen 15, Tennam lO and CuO) in

R, RP, RF and RPF soils. Tennam lO, CuO, and Captan 75
appeared most frequently in this group. Untreated controls
in U, P, PF, RP, and RPF soils had stands ranging from 1.2
to 3.2% while in R and RF soils the stands were 27.2% and
26.0% respectively. Rhizoctonia was less pathogenic than
Pythium, in general, and none of the treatments gave obvious
control.‘ In general, pre-emergence damping—off in the flat
experiment was not as severe as in either the uniform inoc—
ulum concentration or adjusted inoculum concentration pot
experiments, but the post-emergence damping-off was

greater (Fig. 4). Differentiation between seed treatments
was greater than in the pot experiments, but differences

due to soil treatment were not as distinct (Table 5A).

Beet Seed Treatment

Experiment 12 -- Nine seed treatments of beets
were compared in variously infested soils at the same time,
using the standard amounts of inocula (l plate/flat for
single infestation, 1/2 plate of each fungus per flat for
double infestation, and 1/3 plate of each fungus per flat
for triple infestation). There was a broad distribution
of stand averages ranging from l.O--48.0 seedlings per 25
seedballs for the various combination interactions (Table 6

and 6A).

Table 6. A Duncan Multiple Range comparison of stands of
Detroit Dark Red beets produced by treated seed
in variously infested muck soils (Experiment 12).

\OCD'flmU'l-L‘UJIUH

l-’
O

Seed-Treatmemts
Dexon.

Chemagro B-lSOBO.
Omadine-copper.
Captan 75.
Panogen 15.
Tennam lO.

Cuprous oxide.

Diamond Alkali 6N49.

Chemagro B-1843.

Control.

Soil Infestations
R-- Rhizoctoniasolani
P-- Pythium irregulare.
F-- Fusarium sp.
RF- Combination of above.
PF- "
RP- u
RPF- "
U-- Unsteamed.

S-— Steamed.

 

118

    

Table 6. Experiment 12.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
   
   

 

 

 

 

 

 

 

 

 

Treatment Means
S6 48.0
39 46.5
S3 46.0
31 45.7
F5 45.2
RPF8 44.5
F7 44.2
34-57 44.0
52 43.5
ss 43. 2 in:
RPP4 42.2 . .1
F6-RF4 42.0 ‘
P3-F9-PF2 41.5 I
'RPF9 41.2 '
RP10~PP8-ss-310 41.0
F1~RPP6 40.7
PP4 40.2
F8~RF6 40.0
P4~RP3~Ul-U9 39.2
PF9 39.0
RP1 38.7
RP2 38.5
RP9 38.2
P10 38.0
P4 37.7
P9-U8 37.5
RPFl 37.2
RPFZ-PFS 37.0
RP4 36.7
RP8~F2-PP1 36.5
U4 36.2
P1 36.0 1
RFS-PF6 35.5
RPFS-RP6 35.2
RPF7 35.0
RF7 34.7
P2 33.2
P6 32.7
RPl 31.7
RPS 31.5
PF7 30.7
U6 29.7
RP9 29.0
U2-RP2 28.5
RP8 26.7
RPF3 26.0
P8 23.2
P5 20.7
R1 18.2
R3 18.0
R5 17.5
Q R6~R8 16.7
‘ RP7 16.5
R4 16.0
U7 15.5
R7 15.2
P7 13.5
R9 12.2
PF3 11.0
US 10.7
R2-R10 9.7
RPFlO 9.0
U3-RP3 5.0
RP10 4.2
PP10 3.0
U10 2.2
P3 - 2.0
P10 1.0

 

Means bracketed by the same line are not significantly different
from each other.

Soil Infestation

49

Table 6A. A Duncan Multiple Range comparison of stand differences due
to soil infestation and seed treatment of Detroit Dark Red

 

 

Beets.
Seed Treatment
4 9 1 6 8 2 5 7 3 10 Means

S 44.0 46.5 45.7 48.0 43.2 43.5 41.0 44. 46.0 41.0 44.3

F 39.2 41.5 40.7 42.0 40.0 36.5 45.2 44. 41.5 38.0 40.9

RF 42.0 38.2 38.7 40.0 36.5 38.5 35.5 34. 39.2 41.0 38.5 4 I

RP! 42.2 41.2 37.2 40.7 44.5 37.0 35.2 35. 26.0 9.0 34.8 |
. PF 40.2 39.0 36.5 35.5 41.0 41.5 37.0 30. 11.0 3.0 31.6 I

RP 36.7 29.0 31.7 35.2 26.7 28.5 31.5 16. 5.0 4.2 24.5
4 U 36.2 39.2 39.2 29.7 37.5 28.5 10.7 15. 5.0 2.2 24.4

P 37.7 37.5 36.0 32.7 23.2 32.2 20.7 13. 2.0 1.0 23.7

R 16.0 12.2 18.2 16.7 16.7 9.7 17.5 15. 18.0 9.7 15.0
Means 37.2 36.1 36.0 35.6 34.4 33.0 30.5 27. 21.5 16.6

p.-

 

 

Means bracketed by the same
from each other.

OOQNO‘U‘kUNt-i

Seed Treatments

Dexon.

Captan 7S.
Panogen 15.
Tennam 10.

. Control.

Chemagro B-15080.
Omadine-copper.

Cuprous oxide.
Diamond Alkali 6N49
Chemagro B-1843

line are not significantly different

Soil Infestations

3--
p--
F--
RF-
pp-
RP-

RPF-

n--
3--

Rhizoctonia solani.
Pythium irregulare.

 

Fusarium sp.

Combination of above.

H
H
H

Unsteamed.

Steamed.

50
Non-treated seed averaged between 1.0 and 9.7 surviving
seedlings per 25 seedballs in R, P, PF, RP, RPF and U soils
and 38.0 or more in steamed soil and soil infested with F
or RF. A large group of seed treatment-soil treatment
interactions fell in the 37.0--48.0 range of survivors and
did not differ significantly from each other. Most of
these good stands are represented by the less virulent soil
infestations and by the effective seed treatments used in
the virulent soils (P, PF, RPF and Unsteamed). Chemagro
Dexon, Captan 75, Diamond Alkali 6N49 and Chemagro B-1843,
all of which are known to be effective against Pythium,
provided good disease control. The combination of
Rhizoctonia and Fusarium was less pathogenic to beets in
this trial than was Rhizoctonia alone. Stands were nearly
the same, regardless of seed treatment, as in the mildly
pathogenic Fusarium soil.

The next significance range (26.7-~37.0) is
composed largely of inoculum types in which Pythium control
by seed treatment was decisive in determining the stand.
The soil treatments represented in this group are P, PF,
RP, RPF and Unsteamed soil. From the relatively high stand
averages of the Pythium-effective materials in unsteamed
muck, it seems reasonable to assume that Pythium is a
virulent component in this soil. The Fusarium inoculum
used in this experiment appeared to be relatively none
virulent and the seed treatments in Rhizoctonia—infested

soil allowed a stand average significantly below most stand:

51
in the P, PF, RP, RPF, U group. The evidence, therefore,
suggests that Pythium control was the factor determining
stands in this group. The third group, ranging in stand
from 9.0--26.0 is represented mainly by seed treatments in
Rhizoctonia-infested soil and those treatments which were

less effective in Pythium-infested soil.

Experiment 12 -- Because of the interesting
"protective" effect of the Rhizoctonia-Fusarium combination
observed in the beet experiment above, it was decided to
replant in the same soil for confirmation. Parallel results
were obtained even though there were no statistically
significant differences due to the interaction of seed
treatment and soil infestation. There were significant
differences between soil treatment averages (Table 7).

8, F, and RF infested soils were again represented in the
higher stand averages. Although Rhizoctonia soil was
significantly different from other types, it produced less
severe damping-off and more nearly resembled the RF soil
than at the time of the first planting (Fig. 5). Soils
infested at least in part with Pythium (RP, PF, P, RPF, U)
were most severe and were nearly alike in respect to stand
averages. As in the previous experiment, the seed treat-
ments with best overall effectiveness were those which were
effective against Pythium. Differences due to seed treat-
ment, soil treatment, and their interactions were obscured

by replanting in the same infested soil (Table 6A and 7).

Soil Infestation

Table 7. Surviving seedlings of Detroit Dark Red Beets in variously
infested muck soils after treatment with seed protectants.

 

S 43.0 37.
F 38.5 39.

RF 39.0 38.

RP 37.5 37.
PP 36.2 32.
U 28.5 32.
RPF 32.5 24.

7 P 40.0 33.

Means 36.4 34.

40.
41.
37.
20.
30.
35.
26.
31.
39.

33.

45.0
40.7
39.2
28.2
30.7
27.5
24.0
25.7
19.0

31.2

6

42

41.
43.
30.
18.
27.
23.
26.
13.

29.

Seed Treatment

8

.0 42.5

2 27.0
2 30.2
2 26.7
2 24.5

2 16.5

5

37.
40.
38.
37.
18.
15.
19.

12.

24.

7

7

42.
40.
35.
28.
12.
18.
19.
12.

7.

24.

5 40.7 38.

7 24.2 22.

N
N
1‘9
H

0 19.0 16.

 

Means bracketed by
from each other.

Seed Treatments

oomuomswnw

H

Dexon.
Chemagro B-15080.
Omadine-copper.
Captan 75.
Panogen 15.
Tennam 10.
Cuprous oxide.
Diamond Alkali 6N49.
Chemagro B-l843.
Control.

 

the same line are

Means.

41.0
40.1
38.6
29.1
22.7
22.3
21.2
18.6

17.4

 

not significantly different

Soil Infestations

R--
p--
F--
RF-
PF-
RP-
RPF
0--
5--

Rhizoctonig solani.
Pythium irregulare.

Fusarium sp.
Combination of above.

0'
N
H

Unsteamed.
Steamed.

 

Figure 5.

\OCDNOU'l-L‘UJMH

H
0

Stand and total emergence of Detroit Dark Red beets
treated with various seed protectants and planted
in variously infested muck soils (Experiment 13).

Seed Treatments
Dexon.

Chemagro B—l5080.
Omadine-copper.
Captan 75.

Panogen 15.

Tennam lO.

Cuprous oxide.
Diamond Alkali 6N49.
Chemagro B—1843.

Control.

Soil Infestations
R-- Rhizoctonia solani.
P-- Pythium irregulare.
F-- Fusarium sp.
RF- Combination of above.
PF- "
RP- u

U-- Unsteamed.

S-- Steamed.

54

 

 

 

 

 

 

 

 

 

 

 

 

50

20

IO

FUSARIUM

PYTHIUM

RHIZOCTONIA

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

50

20

IO

20

IO

UNSTEAMED STEAMED

R-P-F

ST-EMERGENCE DAMPING -0FF

PC

FINAL STAND

[:3

Figure 5.

55

Experiment 14 -- The beet experiment was repeated
in freshly infested muck soil. Inoculum was adjusted, as
in the spinach experiments, to provide the same concentrat—
ion of each component in all flats. The highest average
stands were obtained in steamed soil and Fusarhnn~infested
soil (Table 8 and 8A). Certain Pythium-effective treatments
produced stands in unsteamed soil comparable to those in
steamed soil. The Fusarium proved to be more virulent in
this experiment than before and significant differences in
stand averages between seed treatments and between Fusarium-
infested and steamed soil were obtained.

The first range of significance (40.8--48.8)
included most of the seed treatments used in steamed soil.
The second range (32.0--39.0) represents the seed treatments
in Fusarium-infested soil. Chemagro B-15080, Diamond
Alkali 6N49, and Panogen 15, which were moderately effective
in Pythium-infested soils, allowed good stands in the range
22.0--29.8. The next significance group (l2.0--18.5) was
represented by Dexon, Tennam 10, and Chemagro B-1843 in
PF soil and CuO in unsteamed soil. The significance group
(1.75--9.75) included most of the seed treatments used in
R or P soils and treatments # 2, 3, 4, 5, 7, and 8 (Chemagro
B-15080, Omadine-copper, Captan 75, Panogen 15, CuO, and
Diamond Alkali 6N49) in PF soil.

The lowest range (O--l.75) was represented mostly
by the remaining seed treatments in R and P soils as well

as nearly all materials used in RF, RP, and RPF soils.

Table 8.

A Duncan Multiple Range comparison of stands of
Detroit Dark Red beets produced by treated seed
in variously infested muck soils (Experiment 14).

Seed Treatments

Dexon.

Chemagro B-15080.
Omadine-copper.
Captan 75.
Panogen 15.
Tennam lO.

Cuprous oxide.

Diamond Alkali 6N49.

Chemagro B-1843.

Control.

8011 Infestations
R-- Rpgzoctonia solani.
P-- Pythium irregulare.
F-- Fusarium sp.

RF- Combination of above.
PF- n
RP- "
RPF- "
U-- Unsteamed.

S-- Steamed.

 

 

 

 

 

 

 

 

 

 

 

 

57

 

Table 8. Experiment 14.

Treatment Means
85 48.8
86-89 43.5
82 42.2
31 42.0'
83 41.0
88-04 40.8
810 39.0
S4-F4 38.8
87 38.0
F9 37.5
09 36.5
F3 36.0
F7 35.5
01 34.8
F2 33.8
F5-F6 32.2
06 32.0
F8 30.3
U2 29.8
F10 27.5
Fl 27.3
05-08 22.0
PFl 18.5 | I
PF6 15.5
07-PF9 12.0
PPS 9.75
PF4 9.25
PF2 8.75
PF7 8.50
PF8 6.25
R5-RF5-P1-P2 6.00
P6 . 4.75
03-RPF5 4.50
R3 3.00
RPS 2.75
R6-P9 2.50
RF6-R4-R7 2.25
P4-R10 2.00
PF3-RPF6 1.75
R8-R9 1.50
RF4-RPF9-Rl-P5-P7 1.25
P3-RF9-RF10-R2-RP2-010 1.00
RP7-PF10-RF2-RPF2-RPF4-P10 .75
RFl-RFB-RP3-RP4-P8-RPF7-RP9 .50
RF7-RP1-RP8-RPF1-RPF3-RPF10 .25
RP6-RP10-RPF8-RF8 .00

Means bracketed by the same line are not significantly different
from each other.

 

 

 

Soil Infestation

Table 8A. Surviving seedlings of Detroit Dark Red Beets in variously
' infested muck soils after treatment wdth seed protectants.

 

F 37.5 38.8 32.

0 36.5 40.8 32.

PF 12.0 9.3 15.5

RF 1.0 1.3
RPF 1.3 .8

RP .5 .5

Means 15.2 14.9 14.9 14.8 14.

0.0

42.
27.
34.

18.

2

8

Seed Treatment

0 42.2 40.8 38.0 41

3 33.

8 29.

 

Means bracketed by the
from each other.

Seed Treatments

Dexon.

Panogen

OOCDNO‘UI9WNH
as a case...

pa

Control.

15.

Tennam 10.
Cuprous oxide.
Diamond Alkali 6N49.
Chemagro B-1843.

Chemagro B-15080.
Omadine-copper.
Captan 75.

8 ame

.8 6.

.8 11.

line

8 30.

8 22.

3 35.5 36.

3 11.0 9.

10

.0 39.0

0 27.5

Means

41.
33.

23.

are not significantly different

Soil Infestations

Rhizoctonia solani.

 

Pythium irregulare.

Fusarium sp.
Combination of above.

H
H

H

Unsteamed.
Steamed.

Figure 6.

(gamma-um};

 

 

 

 

Stands and total emergence of Detroit Dark Red beets
treated with various seed protectants and planted in
variously infested muck soils (‘xperiment l4).

Seed Treatments Soil Infestations

Dexon. R-- Rhizoctonia solani.

Chemagro B-15080. P-- Pythium irregulare.

Omadine-COpper. F-- Fusarium sp.

Captan 75. RF- Combination of above.

Panogen 15. PF- "

Tennam 10. RP- "

Cuprous oxide. RPF- "

Diamond Alkali 6N49. U-- Unsteamed.

Chemagro B-1843. S-- Steamed.

Control.

60

 

 

 

 

 

    

  

 

 

  
 

   

 

 

c ”on-"susasousus

9 sasassssssuonssasusossoossoassassnu
8 "33.3..
7w....mm....m“..n..mn

 

 

 

 

 

a... so u a assess-0”

’.. ."5"

 

 

 

50

40

20

w 0

FUSARIUM

PYTHIUM

RHIZOCTONIA

 

 

 

 

 

 

 

 

50

40

3O

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

50

4O

30

STEAMED

UNSTEAMED

POST- EMERGENCE DAMPING-OFF

FINAL STAND

F1Sure 6.

61

Stand averages in the artificially infested soils were very
low due to the severe pre- and post-emergence damping-off
(Fig. 6). In this trial there was no apparent antagonism
between Rhizoctonia and Fusarium. The stands in the RF
soils were in the lowest range, in contrast to previous
experience.

In genera1,both pre- and post-emergence damping-
off was more severe than in the uniform inoculum concentrat-
ion experiment. However, since the pre- and post-emergence
damping-off losses were also high for Rhizoctonia and
Pythium alone, it is difficult to attribute the increased
losses in the combination infestations to increased inoculum
concentration (Fig. 6). Seed treatment, soil treatment and
interaction differences were more distinct than those of

the previous beet experiments (Table 8A).

DISCUSSION

All of the seed treatments, except Diamond
Alkali 6N49, significantly increased stands of spinach in
the pathogen-infested soils. In two of the experiments,
none of the seed treatments differed significantly from
each other with the exception of Diamond Alkali 6N49 which
was not effective. In the third experiment of the series,
three seed treatment groups were apparent and differed
significantly from each other: Dexon, Chemagro B-l5080,
and B-1843 were in the most effective group; Captan 75,
Panogen 15, Tennam 10, and Cuprous oxide were intermediate;
and Omadine-COpper was least effective.

Except for one experiment where damping-off was
less severe, all beet seed treatments gave a definite
increase in stands. Dexon, Chemagro B-15080 and B-1843,
Captan 75, and Tennam 10 provided best overall protection
in all soil infestations. Panogen 15, Diamond Alkali 6N49
and Cuprous oxide were also effective seed protectants in
some of the infested soils.

None of the seed treatments protected spinach or
beet seed effectively in Rhizoctonia-infested soil. There
were no interaction differences in Fusarium-infested soil,
except in Experiment 14 where Captan 75, Chemagro B-1843
and Omadine-cOpper provided protection against damping-off
of beets. There were also no significant differences due

to the interaction of seed and soil treatments in

65
Rhizoctonia-Fusarium infested soil. Dexon, Chemagro B-l5080
and B-1843, Captan 75, Panogen l5 and Cuprous oxide
significantly increased stands of both spinach and beets
in P, PF, RP, RPF and Unsteamed soils, all of which
contained pathogenic 21thium. Tennam 10 provided protect-
ion for beets but not for Spinach in PF infested soil.
Diamond Alkali 6N49 also increased beet stands significantly
in one experiment with RP and RPF soils. Omadine-cOp-er was
only moderately effective as a spinach and beet seed treat—
ment in these soils.

Comparison of spinach stands (average of all treat-
ments in a given soil infestation) showed that RF, RP, and
RPF soils were not significantly different from each other
(Tables 3, 4A, and 5A). The P and PF soils were also
essentially alike in all three experiments. Overall stand
averages (average of all seed treatments) in fihpgoctonia-
infested soil were comparable to those in P, RP, RF, and
RPF soils in two of the experiments but the stand average
was distinctly different from that group in Experiment 10.
Damping-off by Rhizoctonia in the latter experiment was
much less severe and stands were comparable to those in
Fusarium-infested soil.

No consistent relationships between the various
soil infestations could be determined in the case of beet
seed treatments, except for Rhizoctonia which was consist-
ently different from other infestation types. In two of

the three beet experiments, P, RP and U soils had essentially

64
the same stand averages for all treatments. Stands in F
soil were similar to steamed soil as in the spinach
experiments, and F was comparable to RF-infested soil.
This latter is in contrast to spinach where no protective
effect of Fusarium against Rpgzoctonia infestation was seen.

Stand averages in unsteamed soil were comparable
to those in P, RP, PF, and RPF with treated beets and to
R, PF, P, and RP with treated spinach seeds. Although
difficult to demonstrate conclusively from this type of
comparison, it appears that Pythium was the most pathogenic
component among the damping-off organisms in the unsteamed
muck soil used in these trials.

Increasing the inoculum concentration, as in
several of the combination infestation experiments, increased
the amount of pre- and post-emergence damping-off to some
extent. The principle result of this increase, however,
was the sharpening of differences due to soil treatment,
seed treatment or their interactions. Soil treatment
differences were more pronounced (Table hA)-in the spinach
pot experiment; seed treatment differences were more
distinct in the spinach flat experiment; and differences
due to seed and soil treatment interactions were significant
in both experiments as compared to the standard inoculum
concentration experiment (Expt. 9) where no significant
interaction differences occurred. Replanting of treated
beet seed in artificially infested soils (standard inoculum

concentration) which had been used for a previous test

65
tended to obscure differences due to soil treatment, seed
treatment, and their interactions.

The sharpest distinctions between seed treatment,
soil treatment, and seed and soil treatment interactions
were obtained with beets as test plants in soil in which
the inoculum concentration of each pathogen was 1 plate per
flat, whether used alone or in combination with other
organisms. Under these conditions beets were apparently
more satisfactory than spinach as test plants.

An interesting observation was made in the prelim-
inary experiments with treated spinach seed and in subsequent
experiments with treated beet seed in Fusarium and
Rhizoctonia-Fusarium infested soils. Stand averages in
the F and RF soils were essentially the same and were
similar to those in steamed soil. The absence of signif-
icant differences between seed treatments in Fusarium-
infested soil was probably due to the low virulence of the
Fusarium species used in these experiments. This species,
which was isolated from a damped-off Michelite bean seedling,
appeared to be quite virulent in laboratory and greenhouse
tests with spinach in mineral soil. In the experiments
with muck soil, this Fusarium species failed to show a high
level of virulence. Sanford (55) has shown that Rhizoctonia
was less virulent in steamed soil than in naturally infested
soil. This was thought to be the result of conditions which
favored marked vegetative growth of the pathogen and thus

had a tendency to depress its virulence. .Perhaps this

66

phenomenon may also occur with Fusarium species since
they are generally regarded as vigorous saprophytes.
It is not known, why the stand averages in the
RF infested soil were so high. Since Rhizoctonia was
highly virulent, one might expect stand averages in
RF soil to be intermediate between R and F or nearer to
R alone, if a simple physical competition for Space were
reSponsible. A possible explanation may lie in the initial
inoculum concentration of each of the components in the
combination infested soil. Where the "protective" effect
was observed only 1/2 or 1/3 as much of each component was
seeded into the steamed muck soil for combination infestations
as in later trials when an attempt was made to achieve more
uniformity. This view is supported by the increased
damping-off in the combination infested flats when the
inoculum concentration was increased, and by the absence of
the "protective" effect with both spinach and beets.
Another possibility is that there may have been
some antagonistic or competitive reaction between R and F
which reduced the virulence of Rhizoctonia. However, no
antagonism was apparent when the cultures were grown
together in vitro. The situation encountered here may be
similar to that described by He (30) in which two pathogens,
Pythium debaryanum and Gibberella saubenetti, in artificially
infested soil exhibited an additive effect on disease

severity with corn while a combination of a pathogen and

67
a non-pathogenic fungus, Gibberella saubenettl and
Aspergillus pigpp (or Penicillium oxalicum) resulted in
an inhibitive effect and the disease was less severe than
with the pathogen alone.

In retrospect, the study of the interactions
between soil fungi in various combinations would have been
more meaningful had a more virulent strain of Fusarium
been used. Any further study should involve the use of a
pathogenic Fusarium and perhaps other pathogenic or sapro—
phytic fungi (Verticilllpp, Ppppg, Botrytis, Trichoderma,
Penicillium or others). Evidence indicates that not only
the fungus microflora but the actinomycete and bacterial
populations in the soil have a definite influence on the
pathogenicity or survival of organisms in the soil (28, 29, 63).

The use of other materials with known specific
activity such as PCNB (pentachloronitrobenzene), would
have aided in evaluation of interactions between soil fungi.
By manipulating environmental conditions and using Specific
seed treatments, it might be possible to correlate stands
or rate of damping-off with a particular fungus pathogen
or complex. For example, in this study a comparison of
stands and damping-off in unsteamed muck soil and soils
containing Pythium seemed to indicate that Pythium caused
the most damage in unsteamed soil and that damping-off was

most effectively controlled by chemicals which were highly

68

effective against Pythium. A rapid evaluation by this
process would afford a basis for selecting fungicides or
other measures that might be effective for disease control.
The ideal goal, of course, would be to have some basis

for selecting specific fungicides which would be effective
in controlling a pathogen without radically disturbing the

microfloral balance and soil fertility.

10.

ll.

12.

13.

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