.
v
v
v -
...- .u .v . .. v.
F an?» “23.9”...n9 . $.19 Li»;
[I

 

[lily
|I|II
L

 

 

QH517207

"IMICHIGAN STATE UNIVERSITY‘LIBRARIES L

MWWWWWL

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

l
LIBRARY 3 1293 00620 3347

Michigan State
University

 

 

 

This is to certify that the

thesis entitled

Flood Subirrigation Systems for
Greenhouse Production and the
Potential for Disease Spread

presented by

Renee Kay George

has been accepted towards fulfillment
of the requirements for

M.S. degree in Horticulture

. .
Major professor

 

 

Date November 8, 1989

0.7539 MS U is an Affirmative Action/Equal Opportunity Institution

 

PLACE IN RETURN BOX to remove this checkout from your record.
TO AVOID FINES return on or before dete due.

——_—;——-—-——T——fi
DATE DUE DATE DUE DATE DUE
' i

'l f.‘ fltd’ihgl

1‘ 1‘. i
DEE: 0 9 i994.
W5»

 

 

 

 

 

 

 

 

 

 

 

 

m 011999

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

JL :1

 

 

MSU Is An Affirmative Action/Equal Opportunity lnditution

 

FLOOD SUBIRRIGATION SYSTEMS FOR GREENHOUSE PRODUCTION
AND THE POTENTIAL FOR DISEASE SPREAD

By

Renee Kay George

A THESIS

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

MASTER OF SCIENCE

Department of Horticulture

1989

ABSTRACT

FLOOD SUBIRRIGATION SYSTEMS FOR GREENHOUSE PRODUCTION
AND THE POTENTIAL FOR DISEASE SPREAD

By

Renee Kay George

Therer was no significant difference between plant height, dry
weight, flower number or postharvest quality of poinsettias ‘Gutbier V-
14 Glory’ (Euphorbia pulcherrima) or Easter Lily ‘Nellie White’ (Lilium
Iongiflorum) when grown using topwatering or flood subirrigation.

Geraniums (Pelargom'um X hortorum L.H. Bailey ‘Ringo Scarlet’) were
grown in trays which contained 3 non-inoculated plants and one plant
inoculated with Pythfum ultimum which were topwatered or subirrigated with
recycled solution. Spread of P. ultimum occurred into water and into
plants.

Geraniums inoculated with P. aphanidermatum were grown in trays
which contained non-inoculated geraniums in either Baccto, Baccto
drenched with metalaxyl or Naturally Suppressive Ball Growing Mix 2. There
was no significant difference in spread of P. aphanidermatum between
plants grown with either irrigation system or between plants grown in

either media.

To my brother, Ronny, who through his mental retardation
has taught me more about life than all of my formal education.

ACKNOWLEDGEMENTS

Special thanks to the members of my guidance committee, Drs. John
A. Biernbaum, Royal D. Heins, and Chris T. Stephens for their support,
encouragement and technical assistance. I am grateful to the
undergraduate students who assisted with my research, Jim Adams and John
Kusnier, as well as the students and staff of Dr. Stephens lab.

I wish to also thank the Michigan Agriculture Experiment Station and

the American Floral Endowment for their financial support.

iv

Guidance Committee:

The paper format was adopted for this thesis in accordance with
departmental and university regulations. Sections I and II are to be
submitted to Hortscience and Section III is to be submitted to Elan;

Disease.

TABLE OF CONTENTS

Page
LIST OF TABLES ......................... vii
LITERATURE REVIEW ......................... 1
History of flood subirrigation ......... 1
Advantages of flood subirrigation ........ 3
Disadvantages of flood subirrigation ...... 4
Diseases .................... 6
Pythium .................... 9
Disease assessment and management ........ 10
Research objectives and goals .......... 12
Literature Cited ................ 13

Section I Comparison of growth and water use of poinsettia and
Easter lily with topwatering and flood subirrigation . 17

Abstract .................... 18
Literature Cited ................ 26
Section II Growth of Easter lily when irrigated with a bromine
biocide in recycled subirrigation water ........ 30
Literature Cited ................ 31

Section III Spread of Pythium ultimum and P. aphanidermatum in
production of seedling geraniums with subirrigation

versus topwatering with recycled solutions ...... 38

Abstract .................... 39

vi

LIST OF TABLES

SECTION I Page
Poinsettia and Easter lily. Nutrient content of subirrigated
and topwatered root media as measured by saturated paste
extract ............................ 27
Poinsettia. Distribution of soluble salts in subirrigated
root media as measured by saturated paste extract ....... 28
Poinsettia and Easter lily. Leaf tissue analysis of plants
grown with topwatering or subirrigation ............ 29
SECTION III
Spread of Pythium aphanidermatum from an inoculated plant
to non-inoculated plants with topwatering or subirrigation
in Expt. 2 ........................... 53
Comparison of spread of Pythium aphanidermatum from an
inoculated plant to non-inoculated plants in different root
media in Expt. 2 ........................ 54

vii

Literature Review
Flood Subirrigation Systems for Greenhouse Production
and the Potential for Disease Spread
Subirrigation of plants with recirculated irrigation water and
fertilizer solution is an important consideration as the greenhouse
industry works to limit water and fertilizer runoff. While some cultural
factors in the greenhouse have changed, the basic concepts of flood
subirrigation have been around for many years. Flood subirrigation is
becoming more popular as flood subirrigation systems become more
economical and are recognized for their environmental benefits. One of
the key issues deterring more growers from using flood subirrigation with
recirculated solutions. is the potential for' pathogen dispersal with

recirculated irrigation water.

History and types of subirrigation

E. C. Green and v. S. Turner used subirrigation almost a century
ago for lettuce production in beds as an attempt to prevent lettuce rot
(Green and Green, 1895). To test the theory that reducing the amount of
water on the foliage would reduce rot, a few lettuce plants were placed
in a box containing an irrigation tile. The plants were disease free so
they enlarged the experiment to include other vegetable plants. After
five years of research they concluded that subirrigation was superior to
ordinary methods of irrigation for both bed and bench production.

Subirrigation is not mentioned again until 1940 when Post described
a flood subirrigation method of container grown plants. Potted plants were

placed on a watertight bench covered with gravel. Water was injected into

2
the gravel until the bottom one third to one half of the pot was
submerged. When moisture was observed at the surface of the pot, the
water was drained either into a tank for recycling or to a sewer.

Two types of constant water level irrigation were used by Seeley
(1948) for a variety of crops. In one method the pots were plunged into
a layer of sand, in the other method the plants were set on top of a layer
of sand. For the constant water level subirrigation with the plants
plunged in sand, pots of plants were submerged in a sand medium up to one
inch below the top of the pot. This sand layer was in contact with a
gravel bed saturated with water. Water moved from the gravel into the
sand and into the pot by capillary action. Post and Seeley (1947) used
the constant water level method to successfully grow roses.

In the other method the plants were placed on top of an inch of sand
on top of the saturated gravel. All plants were surface watered to
establish capillarity before placement on the constant water level
benches. Both methods produced satisfactory results for poinsettias,
geraniums, cineraria, begonia, and kalanchoe, except for those plants in
which water touched the bottom of the pot (Seeley, 1948). These methods
were not adapted in greenhouses presumably because of the difficulty in
maintaining watertight benches and obtaining and moving the sand and
gravel.

Another method of watering container plants from the bottom is the
capillary mat. Originally plants were placed on a thin (2.5-4 cm) layer
of sand which was irrigated with drip tubes. This method was replaced by
synthetic mats in the early 1970’s. (Hammer and Langhans, 1972). The

capillary mat has been reported to produce quality plants including

3

Chrysanthemum (Rosenbaum et al., 1979; Hammer and Langhans, 1972) and
poinsettia (Freeman, 1974; Wilfret and Harbaugh, 1977). Some
investigators report advanced plant growth, (Freeman, 1974) and earlier
maturation, (Hammer and Langhans, 1972) while others report that
poinsettias grown on capillary mats grew taller and remained vegetative
longer (Wilfret and Harbaugh, 1977) than those poinsettias which were
hand-watered. Subirrigation by capillary matting was widely used in
Europe, where most flowering container plants are grown in three, four or
five inch pots because it was more practical to use capillary mats than
drip tubes with smaller pots (Kiplinger et al., 1975).

The first ebb and flow flood subirrigation benches were built in
Denmark in 1976 (Hamrick, 1986). In ebb and flow flood subirrigation, a
molded plastic tray on top of a bench frame is flooded with water. The
water is left on the tray for a period of time so the plants can take up
water by capillary action. The trays are then drained, usually into a
holding tank, from'which the solution may be recirculated. The difference
between constant water level subirrigation or capillary mat irrigation and
ebb and flow flood subirrigation is that in ebb and flow flood
subirrigation the water is in direct contact with the pot.

Advantages of flood subirrigation

Ebb and flow flood subirrigation is an easy, economical way of
irrigating container root media in a unifOrnImanneru Conventional surface
watering of plants is more time consuming and has a higher labor cost than
flood subirrigation. Flood subirrigation provides more even watering than
conventional drip tube watering, where blocked tubes are often a problem

(Firth, 1986). Also with flood subirrigation there is less labor involved

4

in shipping and handling of the crop compared to drip tubes, because there
are no drip tubes to remove or install (Ball, 1987). The humidity of the
greenhouse is kept lower because plant leaves, walks and aisles do not
get wet, as in conventional surface watering methods (Hamrick, 1986).

The interest in ebb and flow flood subirrigation has also increased
due to an increase in awareness of groundwater contamination issues in the
United States. The Environmental Protection Agency has made groundwater
its number one priority (Hamrick, 1987). One way to reduce the amount of
possible ground water contaminants released from a greenhouse is to reduce
the gross amount of water used to produce the crop. In systems where the
water is recirculated, water savings of up to 39% have been reported (Koch
and Holcomb, 1983). In systems with constant liquid fertilizer, recycling
leachate would also reduce the gross amount of nutrients applied and would
reduce the potential for groundwater contamination. Many European
growers using flood subirrigation recirculate their irrigation water
(Ball, 1985).
Disadvantages of flood subirrigation

While flood subirrigation has many advantages, growers have also
expressed concern over potential problems with flood subirrigation. Many
of the concerns that growers have about flood subirrigation are the same
as those raised with the first use of subirrigation in the 1890’s, again
during the 1940’s and in the 1970’s with the capillary mat. These
concerns include the potential for salt accumulation in the upper layers
of the pot, especially on a long term crop, due to the capillary movement
of the water in the pot (Kiplinger et al., 1975; Koch and Holcomb, 1983)

Many growers assume that to avoid this layer of soluble salts in the top

5

of the container they must leach with clear water at regular intervals
which is time consuming and thus costly. Flood subirrigation may not be
as flexible as growers would like, because the best quality is achieved
when each bench is used for the same size pot, same crop and same media
(Ball, 1987). It is difficult to have proper moisture for two different
size pots on the same bench because the media will increase in dryness
with an increase in the distance from the water to the top of the media
(Seeley, 1948). Therefore the upper surface of a 15 cm pot will tend to
be drier than the surface of a 10 cm pot on the same bench.

For proper drainage benches must be kept level. Solid plastic trays
may also inhibit air movement around the plants, although there are trays
with raised holes to provide air circulation even during flooding (Firth,
1986). The cost of flood subirrigation benches ranges from $3.75 - $4.00
per square foot for the flood benches and trays. The longevity of the
plastic trays is questionable (Ball, 1987). With flood subirrigation
trays there is concern about algae growth, as some investigators have
reported this to be a problem with capillary mats, (Tayama, 1986) while
others have reported no algae problems on mats in continuous use for over
12 months (Hannings, et al., 1974).

It is also necessary in a recirculating solution system to monitor
and adjust the solution to insure the proper pH and soluble salts level
(Firth, 1986). Another concern growers have is the potential for disease
spread through recirculating the irrigation water (Aimone, 1984, Ball,
1985, Ball, 1987, Firth, 1986, Hamrick, 1986, Hamrick, 1987, Kiplinger et
al., 1975, Koch and Holcomb, 1983).

Diseases

Koch and Holcomb (1983) witnessed no disease development in a
subirrigation capillary mat system where the nutrient solution was not
recirculated despite the wetness of the root medium nor in a system using
capillary mats with recirculated water for the production of marigolds.
In Europe, research has shown that re-using solutions that have passed the
root zone, as in re-using water that has leached from a top watered plant,
without disinfecting, resulted in a rapid spread of pathogens, compared
to a low risk with flood subirrigation and aeroponics or NET (Molitor,
1990). A limited number of growers in the United States have reported no
problems with soil-borne disease in their flood subirrigation systems
(Aimone, 1984; Ball, 1985; Firth, 1986; Hamrick, 1986) as long as good
sanitation is practiced, such as cleaning and disinfecting benches between
crops.

The vigor of the pathogen and its ability to cause disease is
influenced by the availability of nutrients necessary for the stimulation
of germination of the pathogen and its subsequent infection, colonization
of and sporulation in plant tissue. The quantity of inoculum present is
determined by the type of dormant structure the pathogen forms, and the
ability of the inoculum to survive temperature and moisture extremes.
Some spores of Pythium, for example have been found to survive for 12
years. The age of the inoculum can also influence its ability to infect
plants (Hoppe, 1966).

The environment in which the host and pathogen grow can greatly
influence infection by favoring either the host or the pathogen (Joiner,

ed. 1981). Any environmental condition which stresses the host can

7

increase its susceptibility' to disease. 'This includes stress from
excessive levels of soluble salts from over-fertilization and stress from
over- or under- watering, or under-fertilization. Different pathogens can
also be favored at different moisture levels or temperatures. 0n
soybeans, Pythium aphanidermatum was more virulent at 24 - 36°C while P.
debaryanum and P. ultimum were more virulent at 15 - 20°C (Thomson et al.,
1971). Susceptibility to pathogens can vary between cultivars. Hausbeck
et al. (1988) showed that geranium cultivars varied in their
susceptibility to Pythium ultimum. Individual isolates of each organism
can also vary in virulence ( McCarter and Littrell, 1970).

When considering the pathogen host interaction, it is important to
realize that different pathogens penetrate plants in different ways. All
plant pathogenic viruses and many bacteria enter plants through wounds;
bacteria and certain fungi enter through natural plant openings; and many
fungi are able to penetrate the intact surfaces of plants (Roberts and
Boothroyd, 1984).

While there is no evidence of disease spread through a recirculating
solution where an organic substrate is used to support the plant, there
are many reports of disease spread through hydroponic systems (Bates and
Stanghellini, 1982; Evans, 1979; Gold and Stanghellini, 1985; Jenkins and
Averre, 1983; Molitor, 1990; Stanghellini and Russell, 1973; Stanghellini
et al., 1984; Stanghellini et al.,1988) which, like flood subirrigation,
include the recirculation of nutrient solution.

The growing of plants without soil or other organic media, commonly
referred to as hydroponic culture, has been used in commercial production

at least since the mid-1930’s (Ellis and Swaney, 1938). Disease spread

8

through a system with the plants supported by an inert inorganic medium
may be more likely to occur because organic growing media contain natural
predators to many soil - borne fungi. These natural predators play an
important role in the suppression of fungal development (Lawson and
Dienelt, 1988). Disease development may be further suppressed in plants
grown in an organic medium because they often have a higher oxygen level
near the root zone than those grown hydroponically (Kiplinger, 1975;
Lawson and Dienelt, 1988).

Pathogens known to attack hydroponically grown plants include
species of the fungi Pythium, Phytophthora, Fusarium, Colletotrichum, and
Pyrenochaeta and the bacteria Erwinia and Corynebacterium (Lawson and
Dienelt, 1988). It is possible for bacteria such as Xanthomonas sp.,
Erwinia sp. and Pseudomonas sp. to be moved with water in any type of
watering system. It is also possible for them to enter natural openings
or wounds in the roots (Roberts and Boothroyd, 1984) There have, however,
been no reports of serious bacterial disease in hydroponics due to their
relative inability to infect roots when present in solution (Stanghellini,
personal communication).

Some species of Pythium and Phytophthora have the greatest potential
for disease spread in recirculated water because some of their spores are
motile in water (Plaats-Niterink, 1981). Pythium can become a severe
problem in mature plants grown in hydroponic systems if the fungus gets
into the nutrient solution. Once one plant is infected and releases
zoospores into the solution circulated to other plants, severe losses may

occur (Rowe, 1986).

Pythiu-

Pythium spp. are widely distributed throughout the world. (Hendrix
and Campbell, 1973). The most common long term survival structure of the
fungus is the oospore, a thick walled spore that can survive a long time
even under adverse conditions. These spores are easily distributed with
soil particles moved by wind, machinery, or water (Stephens et al.,
1983). These oospores can germinate to form mycelia which can infect
plants. Depending on the species, the oospores may also form sporangia
that give rise to many small, swimming zoospores, each of which may cause
a separate infection (Hendrix and Campbell, 1973). These zoospores can
move about in the water film surrounding soil particles (Rowe, 1986).

Once a plant is infected with Pythium the fungus will quickly
colonize the tissues, causing a rapid breakdown of roots and succulent
stems (Roberts and Boothroyd, 1984). Research in North Carolina (Rowe,
1986) showed that a transplant infected with Pythium can spread to other
plants within a hydroponic system in less than one week. Disease losses
may be quite severe, up to 100% loss in hydroponically produced tomatoes
infected with Pythium (Lawson and Dienelt, 1988). The general disease
of root rot is widely attributed to Pythium spp. One species of Pythium
known to incite root rot in poinsettia and Easter lilies (Lilium
longiflorum) and stem rot in geranium (Pelargonium hortorum), is Pythium
ultimum (Scheffer and Haney, 1940, Miller and Sauve, 1979). Different
species of'Pythium have varying environmental conditions which favor their
growth and ability to infect plants. Temperatures between 10 - 20 °C are
most favorable for oospore production in Pythium ultimum. Oospores are

dormant at first but over time become increasingly germinable.

10

Germination can exceed 90% after contact with soil extract for three
weeks (Ayers and Lumsden, 1975). P. ultimum was more virulent in
infecting soybean seedlings at 15 - 20 °C or after preconditioning at 4,
8, or 12°C for more than four days than at 22.5-369C (Thompson et al.,
1971). Both plant age and mycelia age can affect the virulence of'Pythium
ultimum. Nearly 100% of soybean seedlings 8 - 10 days old were killed
with 4 to 8 day old mycelium. The percentage killed decreased as the
mycelium age and/or the plant age increased (Laviolette and Athow, 1971).
Snapdragon (Antirrhinum majus) seedlings less than 15 days old were killed
within 6 days when infected by Pythium ultimum . However, plants 25 days
old or older tolerated the infection and completed their life cycle, with
a decreased tolerance for heat stress as the only visible symptom (Mellano
et al., 1970). Soil amendments can also influence germination of Pythium
ultimum sporangia, with soils amended with sodium nitrate, sodium nitrite,
ammonium nitrate and urea inhibiting germination (Agnihotri and Vaartaja,
1967). Sporangia germination in Pythium ultimum increases with increasing
soil moisture and is highest in soil temperatures between 15 and 25%:
(Agnihotri and Vaartaja, 1967).
Disease assessment and management

There are many cultural practices which can greatly reduce the risk
of disease problems with recirculated water systems. The same sanitation
practices which apply to topwatering apply to hydroponics and flood
subirrigation. Growers could use pathogen free stock, and disinfest
benches, pots and greenhouse floors. The pH and soluble salts content of
the media should be carefully monitored to be sure they are in the range

most favorable for plant growth. Media that is well aerated could be used

11
and irrigations could be scheduled based on plant water usage to avoid
extremes in soil moisture. Growers should know the pathogens which may
cause disease on their crop, and the type of environment which favors them
(Rowe, 1988).

An important concern with recirculated water is that there are
currently no fungicides labelled for use in recirculated irrigation
systems. The effect of low doses of fungicide within the flood
subirrigation system is not known. The efficacy of an initial fungicide
drench at planting may be prolonged due to the absence of leaching, but
has not been demonstrated.

There are now commercially available Pythium suppressive media,
(Ball Growing Mix 2, Ball Seed Co., West Chicago, IL), which contain
composted hardwood bark which has been shown to have fungicidal properties
(Daft et al., 1979, Hoitink, 1980, Stephens et al., 1981, Chen et
al.,1987, Chen et al., 1988). Other forms of biocontrol include
incorporation of competitive organisms such as StreptomyceS' sp. or
Trichoderma sp., which have produced varying amounts of control (Gregory
et al., 1952, Bolton, 1978). With flood subirrigation, biocontrol may be
more effective as the absence of Teaching may provide a more favorable
environment for the establishment of organisms antagonistic to plant
pathogens.

Another problem of disease management in any of these irrigation
systems is identifying the presence of pathogens in the water. Gill
(1970) sampled irrigation ponds using susceptible plants floating in
styrofoam boards to trap Pythium. Lemons (Klotz et al., 1959), lemon

leaves and Millipore filters (Thomson and Allen, 1974) have been used to

12
trap Phytophthora. There are companies which are currently formulating
quick antibody immunoassay kits for early detection of specific plant
diseases (Agri-Diagnostics, Cinnaminson, NJ).

Methods for treating water before recirculating include treating
with ozone, chlorine or bromine (Hamrick, 1987). In hydroponic systems,
ultraviolet irradiation of the recirculating solution has been used to
control root rot of spinach caused by Pythium. Because iron is destroyed
by ultraviolet irradiation, it must be added to the system following each
irradiation (Stanghellini et al.,1984). The addition of a surfactant
(Agral) was effective in reducing the number of zoospores produced by
Olpidium radicale, the fungal vector of lettuce big vein disease
(Tomlinson and Thomas, 1986). Methods that work well in hydroponics may
not work as well nor be economical in systems which use organic media.
Some growers currently using flood subirrigation with recirculated
nutrients have had success in chlorinating their irrigation water or
treating it with bromine (Agribrom, Great Lakes Chemical Co., West
Lafayette, IN).

Research objectives and goals

The overall objectives of this research were to investigate the
potential for salt accumulation and the potential for disease spread in
flood subirrigated pot plants. Experiments were done with poinsettias
and Easter lilies to compare water use and plant growth with subirrigation
and topwatering. Geraniums were grown to investigate the disease spread
in topwatering where the leachate is recirculated and in flood
subirrigation with recirculated solutions as a model system for Pythium

infection of geraniums had been established (Hausbeck et al., 1988).

13
ite ture ite

Agnihotri, V. P. and O. Vaartaja. 1967. Effects of amendments, soil
moisture contents, and temperatures of the germination of pythium
sporangia under the influence of soil mycostasis. Phytopathology
57:1116-11120.

Aimone, Teresa. Nov. 1984. Watering by flooding. Grower Talks.

Ayers, W. A. and R. D. Lumsden. 1975. Factors affecting production and
germination of three Pythium species. Phytopathology 65:1094-1100.

Ball, Vic. Dec. 1985. Ebb and flow irrigation. Grower Talks.
Ball. Vic. Mar. 1987. I like ebb and flow. Grower Talks.

Bates, M. L. and M. E. Stanghellini. 1984. Root rot of hydroponically
grown spinach caused by Pythium aphanidermatum and Pythium
dissotocum. Phytopathology 72:996.

Bolton, A. T. 1978. Effects of amending soilless growing mixtures with
soil containing antagonistic organisms on root rot and blackleg of
geranium (Pelargonium hortorum) caused by Pythium splendens. Can.
J. Plant Sci. 58:379-383.

Daft, G. C., H. A. Poole and H. A. J. Hoitink. 1979. Composted hardwood
bark: a substitute for steam sterilization and fungicide drenches
for control of poinsettia crown and root rot. HortSci. 14:185-187.

Ellis, C. and M. W. Swaney. 1938. Soilless growth of plants. Reinhold
Publishing Corp. New York. 155 pp.

Evans, S. G. 1979. Susceptibility of plants to fungal pathogens when grown
by the nutrient-film technique (nft). Plant Path. 28:45-48.

Firth, Kristin M. Aug. 1986. Growers go with the flow. Greenhouse
Grower.

Freeman, Ralph N. Dec. 1974. Poinsettias and capillary watering. Florists’
Rev. pp 27-29.

Gill, D. L. 1970. Pathogenic Pythium from irrigation ponds. Plant Dis.
Rep. 54:1077-1079.

Gladstone, L. and G. Moorman. 1987. Geranium mortality due to Pythium root
rot associated with high levels of nutrient salts. Phytopathology
77:986.

Gold, S. E. and M. E. Stanghellini. 1985. Effects of temperature on
Pythium root rot of spinach grown under hydroponic conditions.
Phytopathology 75:333-337.

14

Green, W. J. and E. C. Green. 1895. Sub-irrigation in the greenhouse. Ohio
Agr. Expt. Sta. 61:57-76.

Gregory, K. F., O. M. Allen, A. J. Riker and W. H. Peterson. 1952.
Antibiotics and antagonistic microorganisms as control agents of
damping-off of alfalfa. Phytopathology 42:613-622.

Hammer, P. Allen and R. W. Langhans. Aug. 1972. Something new for
capillary watering. Florists’ Rev. pp 15,54.

Hamrick, Debbie. Jan. 1986. A danish grower on ebb and flow. Grower
Talks.

Hamrick, Debbie. Mar. 1987. Recirculated water - flow of the future?
Grower Talks.

Hannings, D. W., P. A. Hammer, J. Kumpf and R.W. Langhans. Mar. 1974.
Further studies with the capillary mat. Florists’ Rev. pp 17,55.

Hausbeck, M. K., C. T. Stephens and R. D. Heins. 1988. Control of disease
caused by Pythium ultimum in seed-propagated geraniums sprayed or
not sprayed with silver thiosulfate. Plant Dis. 72:764-768.

Hendrix, F. F. Jr. and W. A. Campbell. 1973. Pythiums as plant pathogens.
Ann. Rev. of Phytopathology 11:77-98

Hoitink, Harry A. J. 1980. Composted bark, a lightweight growth medium
with fungicidal properties. Plant Dis. 64:142-147.

Hoppe, P. E. 1966. Pythium species still viable after 12 years in air-
dried muck soil. Phytopathology 56:1411.

Jenkins, S. F. Jr. and C. W. Averre. 1983. Root diseases of vegetables in
hydroponic culture systems in North Carolina greenhouses. Plant Dis.
67:968-970.

Joiner, Jasper N. Ed. 1981. Foliage plant production. Prentice-Hall, Inc.
Englewood Cliffs, N. J. 614 pp.

Kiplinger, D. C., Harry Tayama and Hugh Poole. Sept. 1975. Pointers on
subirrigation of potted plants. Ohio Florist Assn. Bull. No. 551.

Klotz, L. J., Po-Ping Wong and T. A. DeWolfe. 1959. Survey of irrigation
water for the presence of Phytophthora spp. pathogenic to citrus.
Plant Dis. Rep. 43:830-832.

Koch, Gary M. and E. J. Holcomb. 1983. Utilization of recycled irrigation
water on marigolds fertilized with osmocote and constant liquid
fertilizer. J. Amer. Soc. Hort. Sci. 108:815-819.

15

Laviolette, F. A. and K. L. Athow. 1971. Relationship between age of
soybean seedlings and inoculum to infection by Pythium ultimum.
Phytopathology 61:439-440.

Lawson, Roger H. and M. M. Dienelt. May 1988. A hazard of hydroponics.
Greenhouse Manager. pp125-128.

McCarter, S. M. and R. H. Littrell. 1967. Influence of temperature on the
liberation, mobility, and germination of zoospores of Pythium
aphanidermatum and Pythium myriotylum. Phytopathology 57:821.

Mellano, H. M., D. E. Munnecke and R. M. Endo. 1970. Relationship of
seedling age to development of Pythium ultimum on roots of
Antirrhinum majus. Phytopathology 60:935-942.

Miller, H. N. and R. J. Sauve. 1975. Etiology and control of Pythium stem
rot of geranium. Plant Dis. Rep. 69:122-126.

Molitor, Heinz Dieter. 1990. The European perspective with emphasis on
subirrigation and recirculation of water and nutrients. Acta Hortic.
(In press).

Plaats-Niterink, A. J. Van Der. 1981. Monograph of the genus Pythium.
Centraalbureau voor Schimmelcultures. 242 pp.

Post, Kenneth. 1940. A comparison of methods of watering greenhouse
plants and the distribution of water through the soil. Proc. Amer.
Soc. Hort. Sci. 37:1044-1050.

Rasmussen, S. L. and M. E. Stanghellini. 1988. The effect of salinity
stress on the development of Pythium blight of Agrostis palustris.
APS Abstracts.

Roberts, Daniel A. and Carl W. Boothroyd. 1984. Fundamentals of plant
pathology. Second edition. W. H. Freeman and Co. New York. 432 pp.

Rosenbaum, S. E., B. K. Harbaugh, T. A. Nell and G. J. . 1979. Growth
responses of potted Chrysanthemum to controlled-release

fertilizers with two irrigation systems. Proc. Fla. State Hort.
Soc. 92:360-363.

Rowe, Randall C. Dec. 1986. Control of Pythium on greenhouse vegetables.
American Vegetable Grower. pp 52-56.

Scheffer, R. P. and W. J. Haney. 1940. Causes and control of root rot in
Michigan greenhouses. Plant Dis. Rep. 40:570-579.

Seeley, John G. 1948. Automatic watering of potted plants. Proc. Amer.
Soc. Hort. Sci. 51:596-604.

l6

Stanghellini, M. E. and J. D. Russell. 1973. Germination in vitro of
Pythium aphanidermatum oospores and sporangia. Phytopathology
63:133-137.

Stanghellini, M. E., L. J. Stowell and M. L. Bates. 1984. Control of root
rot of spinach caused by Pythium aphanidermatum in a recirculating
hydroponic system by ultraviolet irradiation. Plant Dis. 68:1075-
1076.

Stanghellini, M. E., J. G. White, J. A. Tomlinson and C. Clay. 1988. Root
rot of hydroponically grown cucumbers caused by zoospore producing
isolates of Pythium intermedium. Plant Dis. 72:358-359.

Stephens, C. T., L. J. Herr, A. F. Schmitthenner and C. C. Powell. 1983.
Sources of Rhizoctonia and Pythium spp. in a bedding plant
greenhouse. Plant Dis. 67:272-275.

Tayama, Harry K., Roger E. Smith and Virginia Zrebiec. 1986. A New
biocide/disinfectant for the floriculture industry. Ohio Florists’
Assn. Bull. 685:1-4.

Thompson, T. B., K. L. Athow and F. A. Laviolette. 1971. The effect of
temperature on the pathogenicity of Pythium aphanidermatum, P.
debaryanum and P. ultimum on soybean. Phytopathology. 61:933-935.

Thomson, S. V. and R. M. Allen. 1974. Occurrence of phytophthora species
and other potential plant pathogens in recycled irrigation water.
Plant Dis. Rep. 58:945-949.

Tomlinson, J. A. and B. J. Thomas. 1986. Studies on melon necrotic spot
virus disease of cucumber and on the control of the fungus vector
(Olipidium radicale). Ann. Appl. Biol. 108:71-80.

Wilfret, Gary J. and Brent K. Harbaugh. 1977. Evaluation of poinsettia
cultivars grown on two irrigation systems. Proc. Fla. State Hort.
Soc. 90:309-311.

Section 1 HortScience Subject Category: Production and Culture
Comparison of growth and water use of poinsettia and Easter lily with

topwatering and flood subirrigation.

Renee K. George, John A. Biernbaum, Royal Heins, and Christine Stephens*

Qaaartment of Horticulture. Michigan State University, East Lansing, MI
48824

 

*Deaartment of Botany:and Plant Pathology, Michigan StateiUnivarsity. East
_ansing. MI 48824

Additional Indeszords: Euphorbia pulcherrima, Lilium‘lonqiflorum, soluble

salts, fertilizer.

Acknowledgement is made to the Michigan Agricultural Experiment Station
and the American Floral Endowment for their support of this research.

Plant tissue analysis was provided by the W. R. Grace Company.

17

18
Abstract. Poinsettia ‘Gutbier V-14 Glory' (Egahorbia gglcherrima) and
Easter Lily‘ ‘Nellie» White' (Lilium longiflorum) were grown using
traditional topwatering methods (hose or drip emitters) or subirrigation
by flooding with recirculated solutions. Subirrigation of poinsettias
with the same nutrient solution recommended for constant liquid fertilizer
levels for topwatering resulted in an accumulation of soluble salts to 4.0
ms (saturated media extract) in the root zone. The fertilizer rate for
the subirrigated poinsettias was reduced from 350 mg liter" to 250 mg
liter" on 1 Nov. Poinsettia plant height, dry weight, bract size and
number, and post harvest keeping quality'were not influenced by irrigation
method. There was no significant difference in the results of biweekly
root media analysis for the poinsettias but there were small but
statistically’ significant differences in the poinsettia leaf ‘tissue
analysis for P, Ca, and Mo. Approximately 40% of the water applied was
not utilized by the crop with topwatering. There was no significant
difference in plant height, fresh weight, dry weight, days to flower,
number of flower buds, root quality, and postharvest keeping quality
between Easter lilies subirrigated with 100 mg liter" constant liquid
fertilizer and those topwatered with 200 mg liter" constant liquid
fertilizer. In the Easter lily root media the EC, N, K and Mg were
significantly higher in the drip emitter treatment, but there was no

significant difference in the results of the leaf tissue analysis.

19

Limiting water and fertilizer use and the nitrate effluent from
greenhouses is important to prevent surface water and groundwater
contamination. In many commercial greenhouses water and fertilizer are
applied to excess, with the drainage water percolating into the greenhouse
floor or moving away from the greenhouse in drainage tiles.

Flood subirrigation with recirculated nutrient solutions is widely
used in greenhouses in Denmark and the Netherlands for a variety of
flowering container plants including kalanchoe, roses and begonias. Flood
subirrigation is beginning to be used in the United States. The amount
of water and fertilizer used is minimized and can be closely monitored.
Flood subirrigation has advantages other than preventing runoff and saving
water and fertilizer. With subirrigation water is more evenly distributed,
large numbers of small pots can be watered easily, and less labor is
required for watering and handling plants. The use of subirrigation can
lower the humidity of the greenhouse because plant leaves, walks and
aisles do not get wet (Green and Green, 1895; Post, 1940; Seeley, 1948;
Colacello, 1949; Bunt, 1988).

Our objectives were to quantify the water and fertilizer use with
topwatering and subirrigation with poinsettias and Easter lilies and to
investigate fertilization and irrigation practices with subirrigation by
flooding with recirculated nutrient solutions.

Poinsettia (Euphorbia oulcherrima ‘Gutbier V-14 Glory’) cuttings
were potted in 15 cm azalea (1250 cm3) pots on 21 August, 1987.
Treatments were initiated on 2 October, 1987 and the experiment was
terminated 18 December, 1987. Three irrigation treatments consisted of

subirrigation, hand watering with a hose and breaker and drip emitters

20

(Chapin Watermatics, Watertown, NY). Each treatment consisted of one
bench with forty five plants per bench. All three benches were in a glass
greenhouse. All treatments initially received 350 mg liter'1 of N (87.5%
NO3-N) and K from KNOS, Ca(NO3)2, and NH4NO3 at each irrigation. The
electrical conductivity (EC) of the irrigation water without any added
fertilizer was 0.65 to 0.70 mS. The EC of the initial nutrient solution
was 2.70 mS. Root media samples were analyzed by the MSU Soil Testing
Laboratory (East Lansing, MI) every two weeks. Four weeks after the
treatments began, which coincided with the beginning of bract color
development, the EC level in the root media of the subirrigated plants
reached 4.0 mS measured by saturated media extract (SME) root media
analysis. At this time all plants were leached with 600 ml of S.T.E.M.,
(soluble trace element fertilizer, 60 mg liter", Peters, Fogelsburg, PA)
and MgSO, (60 mg liter") solution. The subirrigation tank was diluted
with water by 45% of its volume changing the EC from 2.87 mS to 1.77 mS.
The stock solution for all treatments was changed to 250 mg liter'1 N by
the deletion of the NH‘N03. Phosphoric acid (85%, 0.40 ml liter") was
added to lower the nutrient solution pH. The new fertilizer solution for
the drip emitters and hand watering had an EC of 1.7 mS and a pH of 5.5.
Fertilization was discontinued on 27 November.

At the termination of the experiment, root media was partitioned
into three sections, approximately 3 cm in depth, and analyzed by the MSU
Soil Testing Laboratory with the SME method. Plant height, bract number
and bract width were recorded at this time. The most recently expanded
green leaves were collected for tissue analysis and the remaining plant

material was oven dried for dry weights (60°C for 48 hours).

21

Easter Lily (Lilium lonqiflorum ‘Nellie White’) bulbs were potted
on 12 October, 1987 in 15 cm (1500 cm3) standard pots. Pots were held in
a greenhouse at 22°C for two weeks, then in a cooler at 5°C for six weeks.
Plants were drenched with 10 mg liter"1 "mtalaxyl (Subdue, Ciba Geigy,
Greensboro, NC) and 60 mg liter" benomyl (Benlate, DuPont, Wilmington DE)
on 17 October, 18 December and 15 January. A wetting agent was applied
to all plants 1500 mg liter'1 (Aqua-Gro, Aquatrols Corporation of America,
Pennsauken, NJ) on 3 Mar 1988.

Pots were moved to the greenhouse on 17 December. Irrigation
treatments were initiated 2 January, 1988 and the experiment was
terminated 31 March, 1988. There were two irrigation treatments,
subirrigation with recirculated fertilizer solution and drip emitters.
There were two replicates of each treatment with 50 plants per replicate.
The subirrigation treatments were fertilized with 100 mg liter" N (87.5%
rug-N) and K, and the topwatering treatments with 200 mg liter" N and K
from KNO3, Ca(N03)2,and NH4N03. The EC of the nutrient solution was 1.4 mS
for the subirrigation treatments and 1.7 ms for the topwatering
treatments. Root media samples were analyzed by the MSU Soil Testing
Laboratory every two weeks with SME. Leaf tissue samples were taken every
two weeks beginning 4 February. A 5 g fresh weight sample of the most
recently fully expanded leaves of randomly selected plants constituted a
sample.

A commercially available peat based soilless mix was used for both
experiments. (Baccto Professional Growers Mix, Michigan Peat, Houston,
TX). All plants were grown on subirrigation benches 1.8 m wide by 3 m long

(Campbell'O’Brien Ltd, Georgetown, Ontario). Each subirrigation treatment

22

had an independent 200 liter reservoir. At each irrigation submersible
pumps (Little Giant Model NK-l) within each reservoir ran for 10 minutes,
filling the bench to an approximate depth of 2 cm, using 150 liters of
solution. It took approximately 30 minutes for the nutrient solution to
drain back into the reservoir. The fertilizer solution retained by the
pots was measured and replaced after each irrigation. The amount of water
held by the pots was estimated by subtracting the amount of water left on
the bench with no pots present from the amount replaced. Five plants per
replicate were weighed before and after irrigation. The difference of
these weights was also used as an estimate of water use.

Topwatering treatments were grown on the same benches to facilitate
the collection of leachate. 'Total water applied was estimated by
measuring the length of time of application and the flow rate of the
fertilizer solution as it was applied by either drip emitters or hose and
breaker. Percent waste was calculated by dividing amount collected as
leachate by the total applied. These estimates would vary based on amount
of Teaching fraction allowed. The amount of leaching was comparable to
observed grower practices, with a leaching fraction of 30% for the
poinsettias and 45% for the Easter lilies. The drip emitters ran for 5-
,8 minutes at 55 ml pot"min"1 for the poinsettias and 4-6 minutes at 140
ml pot"1 min'1 for the Easter lilies.

Plants from both experiments were placed in a simulated post
harvest environment at 22°C with 0.7 umols m'2 s'1 from cool white
fluorescent lights for 24 hours per day. All plants were topwatered.

Analysis of variance was performed by BMDP 2V PC software. When the

F test was significant means were separated by LSD.

23

Poinsettias. There was no significant difference in plant height,
bract number, bract width, nor in bract, stem and leaf dry weight between
irrigation methods. There was no significant difference in the results
of biweekly root media analysis averaged over the experiment (Table 1).
The EC and the nutrient content was significantly different in the
partitioned root media (Table 2). In the upper layer of media the EC and
all elements tested, except P, were 2-3 times higher than the reported
optimum (Warncke and Krauskopf, 1983). The macro nutrients analyzed
accounted for 58% of the total estimated soluble salts (EC x 700). There
were small but statistically significant differences in the leaf tissue
content of P, Ca and Mo (Table 3). The leaf tissue content of Ca was lower
in the subirrigated treatment while the leaf tissue content of Mo was
higher in the subirrigated plants. The leaf tissue content of P for the
subirrigated plants was higher than the leaf tissue P content of plants
irrigated with drip emitters but lower than the leaf tissue content of
those plants irrigated by hand.

The water waste for the hand watering with hose and breaker was 43%
over 10 irrigations. The waste water in this treatment consisted of
leachate and fertilizer solution lost between pots. The average EC of the
hand watering leachate was 3.3 m5 when the fertilizer concentration was
350 mg liter" and 2.3 mS when the fertilizer concentration was 250 mg
liter". With drip emitters the water waste was 29.3% over 7 irrigations.
This was only leachate and the EC 3.2 mS when the fertilizer concentration
was 350 mg liter" and 1.9 mS when the fertilizer concentration was 250 mg

1

liter'. For the poinsettias the estimated daily water use was similar for

all treatments and averaged 75 ml per pot per day and ranged from 33 ml

24
to 171 ml per pot per day over the course of the experiment.

There was no significant difference in cyathia retention and foliage
quality between plants grown with different irrigation methods after 35
days in a simulated post harvest environment.

Easter Lily. There was no significant difference in plant height,
number of flower buds, root quality nor in shoot fresh weight, and shoot
dry weight between plants grown with different irrigation methods. The
EC, and the N, K and Mg content of the biweekly root media samples
averaged over the course of the experiment was significantly higher in the
topwatering treatments (Table 1). There was not, however, any significant
difference in the leaf tissue content (Table 3).

There was an average fertilizer solution waste of 42% for the drip
emitters, calculated over 13 irrigations. The average EC of the drip tube
leachate was 1.8 ms. The estimated daily water use for the Easter lilies
was 60 ml per pot per day for the subirrigated treatments and 72 ml per
pot per day for the drip emitters. Daily water use ranged from 35 to 101
ml per pot per day.

There was no significant difference in flower keeping quality
between treatments after 19 days in a simulated post harvest environment.
While the subirrigated poinsettias and Easter lilies (data not shown) had
a higher level of soluble salts and nutrients in the upper third of root
media, topwatering of these plants in a simulated post harvest environment
did not reduce the keeping quality of the plants as compared to plants
grown with topwatering methods.

Though there was no significant difference in the root media

analysis for the poinsettias, there was a significant, though small,

25

difference in the leaf tissue content of P, Mo and Ca. All values were
in a range suitable for plant growth, and did not have a significant
effect on plant growth or quality. While there were significant
differences in the root media analysis for the Easter lilies, there was
no significant difference in leaf tissue nutrient content. Thus while the
root media content was lower, none of the essential plant nutrients were
limiting in plants subirrigated with half the fertilizer rate used for the
topwatered plants.

While water use will vary with location, crop and weather, it is
important to estimate the amount of water needed to grow a crop.
Estimates of water use are useful in scheduling irrigations based on plant
demand rather than time elapsed. Observations of grower leaching
practices indicate areas of waste which are major contributions to runoff.
Limiting leaching should be a major priority for the greenhouse industry.
With subirrigation systems and recirculated nutrient solutions there is
no runoff. Some changes in cultural practices, such as using lower
fertilizer concentrations due to the absence of leaching, will be required
with these systems. Subirrigated plants were comparable to topwatered
plants in growth and development, with application of a lower

concentration of nutrients and no production of effluent.

26
Literature Cited

Bunt, A. C. 1988. Media and mixes for container grown plants. Uwin
Hyman Ltd. pp 229-234.

Colacello, F. J. 1949. Comparison of Water Utilization and labor
involved in the several methods of watering. Roses, Inc.Bull.
138:5.

Green, W. J., and E. C. Green. 1895. Subirrigation in the greenhouse.
Ohio Ag. Expt. Sta. Bull. 61:57-76.

Post, Kenneth. 1940. A comparison of methods of watering greenhouse
plants and the distribution of water through the soil. Proc.
Amer. Soc. Hort. Sci. 37:1044-1050.

Seeley, John G. 1948. Automatic watering of potted plants. Proc. Amer.
Soc. Hort. Sci. 51:596-604.

Warncke, Darryl D., and Dean M. Krauskopf. 1983. Greenhouse growth
media: testing and nutrition guidelines. MSU Ext. Bull. E-1736.

27
Table 1. Poinsettia and Easter lily. Nutrient content of subirrigated

and topwatered root media as measured by saturated paste extract.

 

(mg liter")

 

 

Irrigation EC N P K Ca Mg
Method (mS) PH
Poinsettia"
Topwateredx 1.9 6.3 380 7 208 256 87
Subirrigated 2.4 6.3 516 8 247 349 107
NSy NS NS NS NS NS NS

Easter lily

Drip emitters 1.4 6.0 138 27 112 108 73
Subirrigated 1.0 6.1 83 11 79 91 56
* NS ** NS *9: NS *

 

"Average of six samples taken at two week intervals analyzed with time
treated as a random effect in the analysis of variance.

xTopwatered is a combined sample from hand watering and drip emitters.
YAverage of seven samples taken at two week intervals analyzed with time
treated as a random effect in the analysis of variance. NS, *, **:
Analysis of variance F test not significant, significant at P=0.05,

significant at P=0.01, respectively.

28

Table 2. Poinsettia. Distribution of soluble salts in subirrigated root
media as measured by saturated paste extract.

 

(mg liter")

 

Sample EC N P K Ca Mg
Position (mS) pH

 

Hand Watered

Topx 2.57y 6.3 282 37 261 300 125
Middle 1.64 6.9 213 20 261 225 90
Bottom 1.64 6.8 208 18 239 210 81
Drip Emitters
Top 3.88’ 6.2 558 19 322 495 203
Middle 1.39 6.8 124 10 141 135 62
Bottom 0.85 7.3 89 12 122 100 42
Subirrigated
Top 6.532 6.3 878 22 480 780 475
Middle 1.34 6.7 147 46 183 120 62
Bottom 0.70 6.5 69 6O 98 67 24
LSD (.05) 0.38 0.2 129 8 56 72 14

 

xRoot media was partitioned into three equal sections approximately three
cm tall.

Y Value of a non-replicated single analysis of a sample which was a
composite from three plants taken on 18 Dec.

2Mean of three samples taken on 18 Dec. Each sample was a composite from
three plants.

Table 3.

subirrigation.

Poinsettia and Easter lily.

29

Leaf tissue analysis of plants grown with topwatering or

 

Irrigation Method
Hand
Drip tubes
Subirrigation
Statisticsy

LSD .05

.01

Drip tubes
Subirrigation

Statistics

1 Dry Weight

 

4.1

3.9

4.0

NS

NS

3.0

3.1

NS

0.42
0.37

0.39

0.02

0.03

0.21

0.37

NS

2.89
3.00

2.77

NS

NS

4.26
4.63

NS

Ca

1.21
1.19

1.06

0.07

NS

0.79
1.22

NS

-1

 

ug 9 Dry Weight
Mg Fe Mn Zn Cu 8 Mo
Poinsettiax
0.71 85 58 40 2 51 1.2
0.67 88 50 44 3 48 1.4
0.64 74 50 49 2 50 1.4
NS NS NS NS NS NS 0.06
NS NS NS NS NS NS 0.09
Easter lilyz
0.59 44 9 18 2 20 0.9
0.60 51 15 26 3 27 0.9
NS NS NS NS NS NS NS

 

xAverage of three samples taken 18 December. A sample was five 9 fresh weight of newest green leaves.

YNS, Analysis of variance F test not significant.

P=.01.

LSD calculated at level of significance, P=.05 or

2Average of two samples taken 31 March. A sample was five 9 fresh weight of newest green leaves.

Section 11 Subject Category: HortScience Notes
Growth of Easter lily when irrigated with a bromine biocide in recycled

subirrigation water.

Renee K. George, John A. Biernbaum, Royal 0. Heins and Christine T.

Stephens*

Department of Horticulture, Michigan State University, East Lansing, MI
48824

*Department of Botany and Plant Pathology. Michigan Stata University, East
Lansing. MI 48824

 

Acknowledgement is made to the Michigan Agricultural Experiment Station,
Great Lakes Chemical Corporation, and Dosatron, Inc. for their support of
this research. Leaf tissue analysis was provided by the W. R. Grace

Company.

30

31

Continued growth in the use of irrigation systems with recirculated
solutions for greenhouse container production is inevitable. The
elimination of waste water containing fertilizer seems critical to the
future of the greenhouse industry. Flood subirrigation with recycled
solutions is an efficient method for irrigation, which has low labor
requirements and no production of waste water. One of the major problems
with recirculating solution production has been control of plant
pathogenic organisms and algae (Tayama et al., 1986; Jenkins and Averre,
1983). A halogenated bromine compound (1-bromo-3-chloro-5, 5-dimethyl-
2, 4-Imidazolidenedione, Agribromm, Great Lakes Chemical Company, West
Lafayette, IN) has been shown to control algae on subirrigation mats
(Tayama et al., 1986) and is labelled for use as a biocide in greenhouse
irrigation systems. The objectives of this research were to study the use
of Agribrom'" for treatment of recirculated water with a flood
subirrigation system and possible phytotoxicity on the growth of Easter
lilies.

The Easter lilies used for the experiment were ’Nellie White’, case
cooled bulbs, 20.3-22.9 cm in circumference. Bulbs were potted in 15 cm
standard (1500 cm3 volume) on 17 Dec. 1987 in a soilless media (Baccto,
Michigan Peat, Houston Texas) composed of peat, perlite and vermiculite
with a starting pH of 5.6 and EC of 1.0 (Saturated Media Extract).
Initially there were 90 plants per subirrigation bench at a spacing of 25
plants meter".

The average date of shoot emergence was 1 Jan. 1988 and 80-90% of the
shoots emerged in a 4 to 5 day period. Bulbs were topwatered after

potting and drenched with 10 mg liter" a.i. metal axyl (Subdue, Ciba Geigy,

32

Greensboro, NC) and 60 mg liter"'a”i. benomyl (Benlate, DuPont, Wilmington
DE) on 15 Jan. 1988. A wetting agent, 1500 mg liter"' (Aqua-Gro,
Aquatrols Corporation of America, Pennsauken, NJ) was applied on 18 Feb.
1988. Six subirrigation benches 1.2 meters wide and 3 meters long (Rough
Brothers, Cincinnati, OH) each with an independent 200 liter reservoir
were flooded at each irrigation with approximately 150 liters of nutrient
solution for 15 to 20 minutes. The solutions were then drained back into
the original reservoir and the reservoir was refilled to its original
volume with fresh nutrient solution. The nutrient solution contained 100
mg liter"1 N and K and 40 mg liter" Ca from KN03, NH4NO3 and Ca(NO3)2.
Phosphoric acid was also added to the nutrient solution as needed to
maintain the pH of the solution in the range of 6.0-6.2.

There were three irrigation treatments consisting of 20-25 mg
liter" free bromine (high rate), 5-6 mg liter" free bromine (label rate)
and no AgribromTM (control). Irrigation treatments were initiated on 22
Jan. 1988 and terminated on 31 March 1988 for a total of 69 days. The
experimental design was a randomized complete block with three treatments
and two replicates. The nutrient solutions were pumped onto the bench
with a submersible pump (Little Giant Model NK-l). The Agribromm was
injected through a Model 7gpm Dosatron (Dosatron International, Inc.,
Clearwater, FL) at a 1:100 dilution.

AgribromT" stock solutions were prepared fresh at each irrigation.
A near saturated solution was prepared from AgribromT" granules, by
heating to 40-50°C on a heated stir plate. This solution was then diluted
to a concentration that would yield 20-25 mg liter'1 free bromine (high
rate) after 1:100 dilution. A portion of this stock was then diluted 1:3

33
with water to yield a stock providing 5-6 mg liter" free bromine (label
rate) after 1:100 dilution. The label recommendation is 5-10 mg liter‘
1. Stock solutions were prepared in the laboratory and carried to the
greenhouse in 2 liter containers. An average of 1.6 liters of stock
solution was used for each irrigation.

Root media samples were taken biweekly. One set of samples was
analyzed by the MSU Soil Testing Lab using the SME procedure and a
second set was checked with a 1 part media and 2 parts water analysis.
Plant tissue samples were collected biweekly. Plant height, number of
flower buds, root evaluation and days to flower were recorded on 31 March
1988 for 72 plants from each replicate for a total of 144 values per
treatment. Root evaluation was made on a visual rating scale of one to
five. A rating of 1 was given to a healthy root system, 2 to a yellow
root system with 25% of the roots necrotic, 3 to a root system with 50%
of the roots necrotic, 3 to a root system with 75% of the roots necrotic
and 5 to a root system with more than 75% of the roots necrotic. Free
bromine was measured using a titration kit (DPD test kit, Great Lakes
Chemical Corporation, West Lafayette, IN).

There was no significant effect of Agribromn'treatment on the pH and
EC of the nutrient solution nor on final plant height, number of flower
buds, days to flower and dry weight of plant samples taken at two week
intervals during the crop. Root system evaluations were significantly
better, 2.5 versus 2.9 (1 best and 5 worst), with the highest AgribromTM
treatment. There was no significant difference between the root systems
of the control and the label rate plants. With the high Agribrom rate a

significant amount of leaf tip burn developed at the time of flowering.

34

At the termination of the experiment, twelve of the plants from each
treatment were placed in a simulated postharvest environment at 22°C with
0.7 micro mols nfz from cool white fluorescent lights for 24 hours per
day. All plants were topwatered. Plants were evaluated after 19 days in
this environment. There were no treatment effects on flower development
in this environment. The further development of leaf tip burn on plants
from the high treatment in the postharvest environment was significant and
resulted in a poorer rating for these plants ( 2.75 for high vs. 1.83 for
control, scale l=best, 5=worst). After 19 days in the post harvest
environment all of the plants from the high bromine treatment displayed
leaf tip burn.

There were no differences in the results of root media analysis done
at two week intervals. There was no significant difference in foliar
nutrient levels, which is consistent with research conducted on
Chrysanthemum (Tayama and Carver, 1989). However, the level of Na in the
plant tissue was significantly higher in the Agribrom"‘treatments for the
last two weeks of the experiment. Tissue and media levels of bromine and
chlorine were not determined.

The average actual tested free bromine concentration over the course
of the experiment as the nutrient solution entered the benches was 7 and
20 mg liter" bromine for the two treatments. A sample of the nutrient
solution and Agribrom” mixture was also drawn from the far end of the
bench after the bench was full. The average concentration of free bromine
over the course of the experiment on the bench was 3 mg liter" bromine

for the low treatment and 5 mg liter" bromine for the high treatment.

35

The final concentration of the label and high treatments was very
similar considering the initial concentrations were almost 3 fold
different. The concentration on the bench was influenced by the ambient
level of sunlight and whether the sample was taken from the edge or the
interior of the bench. Samples in full sunlight (approximately 600 umols
nfz s") had lower levels of free bromine. To test the effect of light on
bromine level, we flooded the benches after dark for one irrigation. The
bromine levels on the bench was 24 mg liter" for the high rate when
irrigated in the dark, compared to 7 mg liter" when irrigated in the
daylight.

The residual free bromine level in the reservoir one hour after
irrigation averaged 3 mg liter" bromine for the high treatment and 2 mg
liter" bromine for the low treatment. The residual activity in the
barrels after 24 hours was less than one mg liter-l for the label rate,
and 1-2 mg liter" for the high rate. Since the presence of organic matter
on a bench will significantly reduce the oxidizing activity of the
Agribrom“ treated nutrient solution, and the residual activity 0d the
bromine, it is important to note that there was little or no root media
or other organic media on the bench surface during this test.

It was not possible to draw conclusions about the beneficial effects
of Agribrom” on limiting fungi, bacteria and algae in the nutrient
solution in this study because there were no major algae or pathogen
problems in the control plants. The beneficial effects of'Agribromn‘could
best be evaluated in a system where the fungal pathogen or the algae is
artificially introduced. With regard to subirrigation systems, an

important variable is the minimization of root media on the benches.

36
Another concern that could be addressed in totally closed subirrigation
systems is whether Agribrom“ needs to be injected at every flooding or
at some regular interval.

This study has provided some basic knowledge about the use of
Agribrom""h1 recirculated nutrient solution systems for the production
of greenhouse container plants in a peat based media. The primary
conclusions were that there were no phytotoxic effects on Easter lilies
when Agribrom“ was injected at the label rate (5 to 6 mg liter" free
bromine) at each irrigation during almost the entire production period.
However there was no significant difference between the root evaluation
results between the control plants and those grown with the label rate of
Agribrom"K The root evaluation results from those plants grown with the
high (20-25 mg liter") of Agribrom” were significantly better than the
controls, but approximately 10 to 15% of the plants from the high
Agribrom treatments were not marketable at the end of the experiment.
Twelve plants grown in production with the high rate of Agribrom” were
grown for 19 days in a post harvest environment. All 12 were not
marketable at the end of the post harvest treatment because of tip burn.
Higher leaf tissues of Na could have been associated with or contributed
to the leaf tip burn. The leaf tip burn may have also been associated
with chlorine or bromine in the tissue or media, as lilies are sensitive

to fluoride (Marousky and Woltz, 1977).

37
Literature Cited

Jenkins Jr., S. F. and C. W. Averre. 1983. Root diseases of vegetables in
hydroponic culture systems in North Carolina greenhouses. Plant
Dis. 67:968-970.

Marousky, F. J., and 5.5. Woltz. 1977. Influence of lime, nitrogen, and
phosphorus sources on the availability and relationship of soil
fluoride to leaf scorch in Lilium longiflorum Thunb. J. Amer. Soc.
Hort. Sci. 88:799-804.

Tayama, Harry K., and Steven A. Carver. 1989. Agribrom biocide - an
update. Ohio Florists’ Assn. Bull. No. 713:4—5.

Tayama, Harry K., Roger E. Smith, and Virginia Zrebiec. A new
biocide/disinfectant for the floriculture industry. Ohio Florists’
Assn. Bull. No. 685:1-4.

Section 111

Spread of Pythiun ultieua and P. aphanidemtue in production of seedling

geraniums with subirrigation versus topwatering with recycled solutions.

Renee K. George, John A. Biernbaum, Christine T. Stephens*, Royal 0. Heins

Dapartment gf Horticulture, Michigan State University,I East Lansingaghl
48824

 

 

 

De artment of Botan and nt Patholo Michi an te Universit East

Lansing. MI 48824

Acknowledgement is made to the Michigan Agricultural Experiment Station,
and the American Floral Endowment for their support of this research.

Cultures were provided by Dr. A. F. Schmitthenner, Columbus, Ohio.

38

39

Abstract. Geranium (Pelargoniunx hortorun L.H. Bailey ‘Ringo Scarlet’)
seedlings were grown with subirrigation (sub) or topwatering (top) with
recycled solutions. Irrigation trays contained 3 non-inoculated plants
and either a control plant or a plant inoculated with Pythium ultieue.
Pythium ultimum was detected in recycled water in 3 of 4 topwatered and
2 of 4 subirrigated trays. Plants became diseased in 1 of 4 topwatered
and 1 of 4 subirrigated trays.

In a separate experiment with Pythium aphanidermatum, topwatered or
subirrigated trays contained non-inoculated geraniums in either Baccto
Professional Growers Mix, Baccto drenched with metalaxyl or Naturally
Suppressive Ball Growing Mix 2 and either a control plant or an inoculated
plant. Pythium aphanideneatwe was detected in recycled water in 4 of6
topwatered and 3 of 6 subirrigated trays. Plants became diseased in 3
of 6 topwatered and 3 of 6 subirrigated trays. Spread of Pythium
aphanidennatua occurred into plants in all three media. Similar results
were observed in a repeat of this experiment.

The awareness of groundwater contamination issues and the need for
more labor efficient methods of watering greenhouse crops have created
interest in flood subirrigation in recent years. Systems which
recirculate waste water containing fertilizer are critical to the future
of the greenhouse industry. While there has been research in disease
spread through the recirculating solution of hydroponics, no research to
date has been published in the United States on plant to plant disease
spread in a container production system with recirculated nutrient
solutions.

There have been reports of Pythium sp. spreading through the

40

recirculated solutions of hydroponic and nutrient film technique (NFT)
systems (Bates and Stanghellini, 1984, Daughtery and Schippers, 1980,
Evans, 1979, Jenkins and Averre, 1983, Stanghellini and Russell, 1971,
Stanghellini et al., 1984). Plant losses as high as 100% from Pythium
aphanidermatum Edson (Fitzp.) were shown on hydroponically grown spinach
(Stanghellini et al., 1984) and tomato seedlings (Stanghellini and
Russell, 1971) under research conditions. Pythium ultimum caused 100%
disease in hydroponically grown cucumbers and tomatoes 22 days after
introduction of the inoculum into the system (Jenkins and Averre, 1983).
P. ultimum also caused 100 %1 death in cucumbers 10 weeks after
inoculation of the water in an NFT system (Evans, 1979). In contrast,
little spread of pathogens in NFT culture has been found by other
researchers (Staunton and Cormican, 1978 and 1980).

It is not clear what effect the organic peat based media used in
container plant production has on the spread of pathogens in a
recirculated solution. Hockenhull and Funk-Jensen (1983) suggested that
pathogen spread would be less in a hydroponic system with exposed roots
than in container culture with organic media because the constant flow of
the nutrient solution would sweep root exudates and zoospores away from
the root zone. Alternately it has been hypothesized that pathogen spread
would be less when plants are protected by pots and peat medium (Staunton
and Cormican, 1978). Kiplinger et al. (1975) suggested that diseases were
not a problem with subirrigation because water can only move up in the
capillary pores, which leaves sufficient oxygen in the non-capillary pores
to discourage disease development.

To determine the degree of pathogen spread in a flood subirrigation

41
system with recirculated nutrient solutions, geranium plants growing in
media inoculated with either Pythium ultimum or Pythium aphanidermatum
were grown with disease free plants. Pathogen spread and the impact of
the pathogen on plant growth were evaluated.

As an additional bio-indicator, geraniums were sprayed with silver
thiosulfate (STS). STS application to seed-propagated geraniums infected
with even a low level of Pythium can result in premature plant death
caused by lower stem blight (Hausbeck, et al. 1988). Application of STS
to Pelargonium X hortorum L.H. Bailey ‘Ringo Scarlet’ plants increased the
percent of plant death to 62 to 100% compared to 0 to 38% without STS.

Experiment 1. Twenty day old geranium seedlings were transplanted
into round plastic pots 9 cm in diameter and 8.5 cm tall with four one cm
holes on the bottom of the pot. Each pot contained 250 cm3 of either
Pythium ultimum inoculated media (I) or non-inoculated media (NI). A
commercially available peat based medium (Baccto Professional Growers Mix,
Michigan Peat, Houston, TX) composed of peat, perlite, and vermiculite
with a starting pH of and 5.6 and EC of 1.0 mS (Saturated Media Extract)
was used for all treatments. A pathogenic isolate of Pythium ultimum
Trow, known to cause root rot, lower stem rot, plant stunting and delay
in flowering in geranium (Hausbeck, et al.,1988) was used to produce the
inoculum using the potato medium procedure developed by K0 and Hora
(1971). Fifty grams of finely chopped potato was added to 500 ml of the
peat based medium and autoclaved twice, for one hour, 24 hours apart.
Cultures of P. ultimum were maintained on 20 ml of water agar (Difco
Laboratories, Detroit, MI) and grown in 10 cm plates for two days at 21°C.

Two mycelial disks 12 mm in diameter were selected from the edge of the

42
culture and used to inoculate 500 ml of the sterilized potato medium. The
inoculum was grown in 1.0 liter closed flasks for two weeks and shaken
daily. The inoculum was air dried for two days and sieved through a 3 mm
screen. The rate of inoculum used was 3.0 g of inoculated media liter"
of fresh media.

Plants were grown in a 20°C greenhouse for ten days before treatments
began. All plants received 200 mg liter-1 N and K from Ca(NO3)2.and KNO3
four days after transplant. One foliar application of 750 mg liter-l
chlormequat (Cycocel, American Cyanamid, Wayne, NJ) was made 15 days after
transplant. Three N1 and one I plant were placed in each of eight trays,
22 cm in diameter, 6 cm high. Eight trays with four NI plants in each
served as controls. Half the trays were subirrigated and half were
topwatered. For the subirrigated treatments the trays were each connected
by tubing to a four liter opaque reservoir containing fertilizer solution.
Plants were irrigated as needed by filling the tray with approximately 400
ml of solution (2 cm deep). The solution was in the trays for a total of
seven minutes, including the time to fill and drain. For the topwatering
treatments the trays were not connected to the reservoirs and were watered
from the top. A 1 cm tall waffled riser was placed in the topwatered
trays to allow the leachate to drain away from the plants into a
container. A small funnel, one per tray, was used to direct water into
the pot. Plants were irrigated to a 20% leaching fraction and the
leachate was returned to the reservoiru Approximately 100 ml were applied
per plant, approximately 75 ml total leachate was recycled at each
irrigation. All plants in all treatments were kept from contacting each

other by transparent plastic sheets between plants.

43

Treatments were initiated on 15 July, 1989 with an initial fertilizer
concentration of 50 mg liter" N and K from Ca(NO_,')2 and KNO3 EC of 1.05
mS). The fertilizer used to replenish the reservoirs as needed was
increased to 75 mg liter" N and K from Ca(NO3)2 and KNO3 (EC of 1.18) on
11 Aug 1989. All plants received a subirrigated application of 630 mg
liter" S.T.E.M. (Soluble Trace Element Mix, Peters, Fogelsville, PA) and
0.32 ml liter" 85% M.,,PO4 on 5 Sept. 1989. This solution had a pH of 4.5
and an EC of 0.87. During the course of the experiment the NI plants had
a pH in the range of 6.3 - 7.3 and an EC between 0.28 and 0.86 m5 (2
water:1 media). The treatment arrangement was a randomized complete
block.with four treatments and four replicates per treatment. Plants were
grown in a 20°C glass greenhouse with a shade curtain. Supplemental
lighting from high pressure sodium lights providing a PPF of 130 umols m'
2 s'1 for 18 hours per day were used from 2 Aug. 1989 to 4 Sept. 1989.
This lighting arrangement was implemented to help maintain day
temperatures i2°C in the greenhouse.

A 0.25mM application of STS (Heins et al.,1984) was applied on 6 Sept.
Eight weeks after the initiation of irrigation treatments pathogen
presence was determined and plant growth was evaluated by measuring plant
dry weight. Roots were washed in running tap water to remove the potting
medium. Root sections, residue filtered from the solution reservoirs, and
media samples were plated on antibiotic selective agar, (10 mg Pimaricin,
200 mg Ampicillin, 50 mg PCNB, 10 mg Rifampcin and 17 9 corn meal agar per
liter, 20 ml per 10 cm Petri dish). For each plant, two root sections 3
cm long were washed for 10 minutes in running tap water. Approximately

0.4 g of root medium taken from the perimeter of the root ball 2 cm from

44
the bottom of the pot was used as a sample. Water residue, 0.1 ml per
plate, was filtered from the reservoirs with a #325 mesh screen which was
surface sterilized with a 0.5% sodium hypochlorite solution and rinsed
with sterile distilled water between each use. Plates were incubated at
15°C.

Root medium and stem tissue from the NI plants in I trays and residue
filtered from the solution reservoirs were further tested for P. ultimum
with an ELISA kit (Agri-Diagnostics, Cinnamonson,NJ). A sample consisted
of 0.4 g of fresh stem tissue, or 0.4 g of medium, (sample taken as
described for plating). All of the residue obtained from the water
constituted a sample.

Experiment 2. Twenty eight day old geranium seedlings were
transplanted into round standard pots 9 cm in diameter containing Baccto
media (NI), Baccto media drenched with 100 ml of 10 mg liter" a.i.
metalaxyl (NIM) or into Naturally Suppressive Ball Growing Mix 2 (Ball
Seed, West Chicago, IL) (N15) and were grown for ten days before
treatments began as in Expt 1.

Twelve plants in Baccto media were inoculated with Pythium
aphanidermatum Edson (Fitzp.). To prepare inoculum pure cultures of
Pythium aphanidermatum #246, known to be pathogenic on geranium, (A.F.
Schmitthenner, personal communication), were grown on 20 ml of V-8 agar
in 10 cm Petri plates for four days at 26°C. After four days, plates were
cut into 25 pieces and were added to one liter of sterile tap water. One
plate was used per liter. The water was kept in a flask wrapped in foil
at 26°C for 24 hours, to allow zoospore development. The agar'was filtered

from the water with sterile cheesecloth after 24 hours. Each plant to be

45
inoculated (I) was placed in a tray and watered with 140 ml of the water
containing zoospores. Approximately 25 ml of the water leached into the
trays. Plants in the trays were incubated at 269C for 24 hours before
being moved to the greenhouse. Twelve plants planted in Baccto media
which were watered with sterile tap water in the same manner served as
controls, (C).

Three non-inoculated plants in selected media and one inoculated plant
or one healthy plant were placed in each irrigation tray. One half of
the trays were subirrigated and one half were topwatered as in Expt. 1.

Treatments were initiated on 21 July, 1989 with the same fertilization
treatment as in Expt. 1. The NI plants had a pH in the range of 6.3 - 7.5
and an EC between 0.34 and 1.08 mS (2 water:l media) during the course
of the experiment. There were twelve treatments and two replicates per
treatment. Plants were grown in a greenhouse under ambient light with a
shade curtain pulled when PPFD exceeded 1000 umol m'2 s". The day
temperature set point was 27°C and the night temperature set point was
24°C. Temperatures were maintained i 2°C. A 0.25mM STS application was
applied on 30 Aug. and again on 8 Sept. 1989. Plant growth was evaluated
and pathogen presence determined after eight weeks with the same procedure
as Expt. 1 except plates were incubated at 26°C.

Experiment 3. Experimental set up and execution was the same as Expt.
2 except 21 day old geranium seedlings were used. Thermostatically
controlled electrical resistance heating mats were placed beneath the
reservoirs to maintain the temperature of the fertilizer solution at 270C.
Irrigation treatments were initiated on 13 August with an initial

fertilizer concentration of 75 mg liter" N and K from Ca(NO3)2 and KNO3

46

(EC of 1.18). The fertilizer used to replenish the reservoirs was
increased to 100 mg liter" N and K from Ca(N03)2 and KNO3 and 0.26 ml
liter" 85% H3PO4 (EC of 1.26). During the course of the experiment the NI
plants had a pH in the range of 6.2 - 7.1 and an EC between 0.15 and 1.19
mS (2 water:1 media). A 0.25mM STS application was applied on 8 Sept.
and 16 Sept., 1989. Plant growth was evaluated and pathogen presence
determined seven weeks after treatments began with the same procedure used
in Expt. 2.

A randomized complete block treatment arrangement was used for Expt.
2,3, and 4. Root media analysis was done at the termination of all
experiments at the~ MSU Soil Testing Laboratory (East Lansing, MI).
Analysis of variance was performed on all data with BMDP 2V PC software.

Experiment 1. P. ultimum was isolated from the roots of one
symptomless control plant at harvest. P. ultimum was isolated from all
inoculated plants and media on selective agar. Four of the eight
inoculated plants died and severe stunting occurred in the remaining four
within two weeks after irrigation treatments began. After spraying with
STS, one of the four stunted inoculated plants developed stem rot.

P. ultimum was isolated from N1 plants in trays containing an
inoculated plant in two of the topwatered (2 of 3 plants, 1 of 3 plants)
and one of the subirrigated treatments (3 of 3 plants), indicating plant
to plant spread via the water. P. ultimum was isolated from the recycled
water but disease did not occur in healthy plants in two of the topwatered
and one of the subirrigated treatments.

The average dry weight of the subirrigated NI plants which were in

trays with inoculated plants was significantly lower than the average dry

47
weight of the topwatered NI plants which were in trays with inoculated
plants and significantly lower than the NI plants in the topwatered
control trays.

Experiment 2. No P. aphanidermatum was isolated from trays containing
only healthy plants. P. aphanidermatum was isolated from all inoculated
plants and root media on selective agar. Plant mortality in seven of the
twelve inoculated plants and stunting in the remaining five within two
weeks after irrigation treatments began. One inoculated plant developed
stem rot four weeks after treatments began and three of the remaining four
developed stem rot after spraying with STS.

There was no significant difference in dry weight between plants grown
in the different media or between subirrigated and topwatered plants.
There was a significant difference in the average dry weight of the non-
inoculated plants in trays which contained an inoculated plant and the
non-inoculated plants in trays which contained only healthy plants, 3.98
g per plant and 5.91 g per plant respectively. This difference was due
to disease spread in the trays which contained an inoculated plant.
Pathogen isolation data from the non-inoculated plants is shown in Tables
1 and 2. Pythium aphanidermatum was detected in recycled water in 1
topwatered tray and plants became diseased in 3 of 6 topwatered and 3
of 6 subirrigated trays. Spread occurred into plants in all three media.

Experiment 3. P. aphanidermatum was isolated from all inoculated
plants and root media on selective agar. Mortality occurred in six of the
twelve inoculated plants and stunting in the remaining six within two
weeks after irrigation treatments were initiated. Five of the six stunted

inoculated plants developed stem rot after being sprayed with STS.

48
Pythium aphanidermatum was detected in recycled water in 3 topwatered
trays and in one subirrigated tray. Plants became diseased in 2 of 6
topwatered and 4 of 6 subirrigated trays. Spread of P. aphanidermatum
occurred in two trays which contained non-inoculated plants potted in
Baccto, one tray with non-inoculated plants potted in Baccto drenched with
metalaxyl and in three trays with non-inoculated plants potted in Ball 2.

Media nutrient levels were not significantly different in the different
treatments for any of the experiments (Data not shown).

There are many factors which can influence the degree of spread of
organisms in subirrigation systems when the water is recirculated or in
hydroponic systems. It has been suggested that the variability of results
found by different researchers in NFT and hydroponic studies have been due
to different inoculum or inoculation techniques (Staunton and Cormican,
1980), variation in the temperature of the nutrient solution (Bates and
Stanghellini, 1984), different initial populations of fungal flora in the
systems (Price, 1980), and the absence of predisposing factors, such as
water stress (Daughtrey and Schippers, 1980).

Salinity and fertility levels can also influence disease incidence.
Rasmussen and Stanghellini (1988) found an increase in disease incidence
of cottony blight caused by Pythium aphanidermatum of creeping bentgrass
as salinity was increased. Gladstone and Moorman (1987) reported an
increase in mortality of seedling geraniums from root rot caused by
Pythium ultimum as levels of nitrogen and phosphorus fertilization were
increased.

The plants in Expt. 1 were grown at a temperature which favored the

49

pathogenicity of Pythium ultimum (Alexander, et al., 1932). The optimum
temperature for infection by Pythium aphanidermatum is 35-40°C (Plaats-
Niterink, A. J. Van Der, 1981). Plants in Expts. 2 and 3 were grown at 25
- 30°C which is the optimum temperature for the zoospores production in
Pythium aphanidermatum and is a temperature more suitable for geranium
growth (Carlson and Hilliard, 1986). Less infection occurred from water
reservoirs containing zoospores in Expt. 3 than in Expt. 2 possibly due
to lower daily temperatures in Expt. 3. Plants in Expts. 1 and 2 had
symptoms of nutritional stress, which may have contributed to higher
levels of infection. All but one of the infected plants in Expt. 2 had
visible stem rot at harvest, whereas over half of those plants in Expt.
3 which were infected did not have visible symptoms.

An interaction between STS application and the expression of stem rot,
as was previously reported for Pythium ultimum (Hausbeck et al., 1988)
also occurred with Pythium aphanidermatum, with 5 of 6 stunted inoculated
plants developing stem rot after STS application in Expt. 3. 'De BJSA
was as effective as plating in detecting P. aphanidermatum in infested
media. However, the ELISA was not as effective as plating in detecting
P. ultimum in infested media presumably due to the poorer distribution of
P. ultimum propagules in the soil. The ELISA was less effective than
plating for isolation from water. Use of plating or the ELISA on fruit
or leaves used to trap the organism may be more effective (Klotz, et al.,
1959; Thomsom and Allen, 1974).

In Experiments 2 and 3 there was no difference in the amount of disease
spread between the topwatered and subirrigated treatments combined over

media nor between the media types combined over irrigation type based on

50
a normal binomial distribution. Neither the naturally suppressive Ball
2 media nor a single drench of metalaxyl protected plants from P.

aphanidermatum for eight weeks.

51

Literature Cited

Alexander, L.J., Young, H.C., and Kiger, C.M., 1932. Causes and control
of damping off of tomato seedlings. Phytopathology 22:3 (Abs.)

Bates, M.L., and Stanghellini, M.E., 1984. Root rot of hydroponically
grown spinach caused by Pythium aphanidermatum and P. dissotocum.
Plant Dis. 68:989-991.

Carlson, W. H. and Janette Hilliard. 1986. Producing seed geraniums for
profit. MSU Ext. Bull. E-1996.

Daughtrey, Margery L., and Schippers, P.A., 1980. Root death and
associated problems. Acta Hortic. 98:283-291.

Evans, S.G., 1979. Susceptibility of plants to fungal pathogens when
grown by the nutrient-film technique (NFT). Pl. Path. 28:45-48.

Hausbeck, M.K., Stephens, C.T., and Heins, R.D., 1988. Control of disease
caused by Pythium ultimum in seed-propagated geraniums sprayed or
not sprayed with silver thiosulfate. Plant Dis. 72:764-768.

Heins, R. D., H. N. Fonda and A. Cameron. 1984. Mixing and storage of
silver thiosulfate. BPI News 15:1-2.

Hockenhull, J., and Funck—Jensen, D., 1983. Is damping-off, caused by
Pythium, less of a problem in hydroponics than in traditional
growing systems? Acta Hortic. 133:137-145.

Jenkins, Jr., S. F., and Averre, C.W., 1983. Root diseases of vegetables
in hydroponic culture systems in North Carolina greenhouses. Plant
Dis. 67:968-970.

Kiplinger, D.C., Tayama, Harry, and Poole, Hugh, 1975. Pointers on
subirrigation of potted plants. Ohio Flor. Assn. Bull. No. 551,p.5.

Klotz, L. J., Po-Ping Wong and T. A. DeWolfe. 1959. Survey of irrigation
water for the presence of Phytophthora spp. pathogenic to citrus.
Plant Dis. Rep. 43:830-832.

K0, Wen-Hsiung, and Hora, F.K., 1971. A selective medium for the
quantitative determination of Rhizoctonia solani in soil. Phytopath.
61:707-710

Price, 0., 1980. Fungal flora of tomato roots in nutrient film culture.
Acta Hortic. 98:269-275.

Stanghellini, M.E., and Russell,J.D., 1971. Damping-off of tomato
seedlings in commercial hydroponic culture. Prog. Agric. Ariz.
23:15-16.

52

Stanghellini, M. E., Stowell, L. J., and Bates, M.L., 1984. Control of
root rot of spinach caused by Pythium aphanidermatum in a
recirculating hydroponic system by ultraviolet irradiation. Plant
Dis. 68:1075-1076.

Staunton, W. P., and Cormican, T.P., 1978. The behaviour of tomato
pathogens in a hydroponic system. Acta Hortic. 82:133-135.

Staunton, W. P., and Cormican, T.P., 1980. The effects of pathogens and
fungicides on tomatoes in a hydroponic system. Acta Hortic. 98:293-
297.

Thomson, S. V. and R. M. Allen. 1974. Occurrence of phytophthora species
and other potential plant pathogens in recycled irrigation water.
Plant Dis. Rep. 58:945-949.

 

53
Table 1. Spread of Pythium aphanidermatum from an inoculated plant to

non-inoculated plants with topwatering or subirrigation in Expt. 2.

 

Topwatered Subirrigated

 

Trays with plant to

water spreadxy 4 3

Trays with plant to
plant spreadxy 3 3

 

* Number of trays added over 3 media types. Total number of trays per
irrigation method was six.

Y Not significantly different based on a normal binomial distribution.

 

54
Table 2. Comparison of spread of' Pythium aphanidermatum from an
inoculated plant to non-inoculated plants in different root media in Expt.

2.

 

 

Baccto Baccto Ball 2
w/Metalaxyl Suppressive
Trays with plant to
water spreadxy 4 l 2
Trays with plant to
plant spreadxy 3 1 2

 

"Number of trays added over two irrigation methods. Total number of trays
per media type was 4.

Y Not significantly different based on a normal binomial distribution.

 

MICHIGAN STATE UNIV. LIBRARIES
||lll1111111111111111111111“ 1111111111
31293006203347