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Copyright 2005, Board of Trustees, University
Ft. Pierce ARC Research Report RL-1975-1
CONTROL OF DAMP-OFF IN TOMATOES PLANTED 9-LGIX METHOD
IN PREVIOUSLY CROPPED SI
R. M. SonodaV/ L1 ARY
Abstract 22 916
Damp-off of field-seeded tomatoes incited b -f &rmanidermatum
P. myriotylum and Rhizoctonia solani was controlit, ;ri icides
into plug-mix. Superior treatments in soils artificially in
P. aphanidermatum and R. solani were the combinations: Benlate 50W + Terrazole 35W,
Benlate 50W + Dexon 35W and Terrachlor 75W + Dexon 35W. In naturally infested
soil superior treatments were: Truban 30W, Dexon 35W, Truban 30W + Benlate 50W
and Tersan SP 65W + Dexon 35W.
Loss of seedlings to damp-off in plug-mix (2) planted tomatoes occurs frequent-
ly when wet weather follows planting in non-fumigated soils. The most frequently
isolated pathogens from diseased tomato seedlings in previously cropped soil at the
Agricultural Research Center, Fort Pierce (ARC-FP) in order of occurrence were
Pythium aphanidermatum (Eds.) Fitz., P. myriotylum Drechs. and Rhizoctonia solani
Kuhn. Two Pythium spp., P. myriotylun and P. arrhenomanes Drechs. were the only
pathogens found on seedlings planted by the plug-mix method on virgin soil (3).
Fungicidal control of P. myriotylum and P. arrhenomanes has been reported (4).
Safe levels of fungicides with activity against either P. aphanidermatum or
R. solani or both were determined in greenhouse tests (Sonoda, unpublished data).
The efficacy of fungicides in controlling seedling diseases in soils artificially
infested with either P. aphanidermatum or R. solani was determined in greenhouse
tests (Sonoda, unpublished data). The following tests were conducted to determine
the efficacy of several fungicides and fungicide combinations in controlling the
Pythium-Rhizoctonia seedling disease complex in plug-mix planted tomatoes.
Materials and Methods
Fungicides used in the following tests were: Benlate 50W, benomyll), (Methyl-
1-(butylcarbamoyl)-2-benzimidazolecarbamate); Tersan SP 65W or Demosan 65W,
(chloroneb), (l,4-dichloro-2,5-dimethoxybenzene); Dexon 35W (p-(Dimethylamino)-
benzenediazo sodium sulfonate); Difolatan 4 Flow (cis-N-((l,l,2,2-tetrachloroethyl)
thio)4-cyclohexene-l,2-dicarboximide); Orthocide 50W (captan)(N-((Trichloromethyl)
thio)4-cyclohexene-l,2-dicarboximide); Terrazole 35W or Truban 30W (ethazole)
I/ The results presented in this paper are only for information and do not
constitute or imply recommendation of any fungicide for use in plug-mix.
The mention of any trade name or proprietary product does not imply approval
of its use nor of its use to the exclusion of other products that may be
2/ Associate Plant Pathologist, University of Florida, Institute of Food and
Agricultural Sciences, Agricultural Research Center, Fort Pierce 33450.
(5-ethoxy-3-trichloromethyl-l,2,4 thiadiazole); and Terrachlor 75W (PCNB) (Penta-
chloronitrobenzene). Aqueous suspensions of the fungicides were 1i&e and the sus-
pensions added to a commercially prepared planting mix (Jiffy Mix Plus, a 1:1 mix
of shredded sphagnum peat moss and horticultural vermiculite plus 7-40-6 Magamp (2)).
Test 1: Two isolates each of P. aphanidermatum and R. solani were obtained
from diseased tomato seedlings at the ARC-FP. The fungi were grown on twice-
autoclaved Panicum fasciculatum seeds at room temperature for two weeks. Virgin
Oldsmar fine sand top-soil was obtained from an uncropped area at the ARC-FP.
The soil was air-dried and passed through a two mm mesh screen. An equivalent of
1000 Ib per acre dolomitic limestone and 600 lb per acre of a 4-16-4 analysis
fertilizer was added to the soil. The soil was infested with inoculum by in-
corporating five infested P. fasciculatum seeds of each of the four fungus iso-
lates in each 100 gm of air-dried soil. Three hundred gm of infested soil was
then placed in each nine-oz capacity styrofoam cup.
The small end of a #7 rubber stopper was used to make a hole in the soil in
each styrofoam cup. One tablespoon of the planting mix containing fungicide was
placed in the hole and ten fungicide-free Walter tomato seeds were placed on top
of the mix. Then another tablespoon of the same planting mix was placed over the
seed and the mix tamped down with the large end of the #7 rubber stopper. There
were four cups for each of the 18 treatments (Table 1). The cups were taken to
the field and buried upright leaving about 3/4 of an inch of the cup exposed.
The plot area was irrigated each day, for 19 days following planting, with about
one acre-inch of water, using a Model #30 Rain Bird sprinkler head.
Numbers of emergep plants and of damped-off plants were determined daily.
On the 19th day of th- experimentt E 0'.lings were removed and a rating was made
on severity of root and lower stem lesions. The rating system used was 1= no
disease to 5= plant dead. A disease severity index (DSI) was calculated by
determining the mean severity rating for each replicate of a treatment then cal-
culating a mean for the four replicates. The emergence rate was determined by
summing the products of the number of plants emerging each day times the days
after planting and dividing the sum by the total number of plants emerged. A
rating of qualitative appearance was made immediately before the plants were
harvested. The healthy plants of the untreated control served as standards.
The rating system used was 1= excellent growth, no difference in appearance
from healthy control to 4= very poor growth. Analysis of variance was run on
Test 2: Twenty-four grams of fungicide-free Walter tomato seed were mixed
with 6000 gm of Jiffy Mix Plus in a portable cement mixer. The mix was divided
into thirteen lots of 450 gm each and the fungicides listed on Table 2 added as
aqueous suspensions. The mixtures were deposited with a hand operated applica-
tor (2) at a rate of a quarter cup of loose mix per hill in a field at the ARC-
FP. There were five rows with one replicate of each treatment per row. There
were eight adjacent hills per replicate. The number of plants emerged six days
after planting was counted. The number of damped-off plants was recorded daily
from five days after planting to 12 days after planting. The number of missing
hills was counted 12 days after planting. Analysis of variance was run on all
Test 1: Significantly better control of the P. aphanidermatum and R. solani
seedling disease complex was obtained with nine of the 17 treatments when compared
to untreated planting mix (Table 1). Of the nine treatments, the Benlate 50W +
Terrazole 35 W, Benlate 50W + Dexon 35W, and Terrachlor 75W + Dexon 35W combination
appeared to be superior on the basis of disease control, emergence rate of seedlings
and appearance of seedlings. None of the single compounds, including Orthocide 50W
captain) currently being used in plug-mix by many growers, gave significantly
better control than untreated planting mix.
Test 2: Either or both P. .phanidermatVm and P. myriotylum w~re '.sc.ated
from each of 25 diseased seedlings obtained from untreated planting mix r.'.d plated
out on water agar. Three of the diseased seedlings also yielded R. colan!i in
addition to the Pythiums.
The better treatments in this test (Table 2) in terms of disease control and
emergence percent were Truban 30W, Dexon 35W, Truban 30W + Benlate 50W, Tersan SP
65W + Dexon 35W and Benlate 50W + Dexon 35W. The other combinations, although
controlling disease, slowed down the rate of seedling emergence and reduced total
emergence. Terrachlor 75W (PCNB) by itself significantly increased disease inci-
Excellent control of the Pythium-Rhizoctonia seedling disease complex in
previously cropped soil was obtained with the incorporation of fungicides into
"Plug-Mix". Although Truban 30W or Dexon 35W, compounds effective against Pythiums,
were effective in controlling the disease in the field in Test 2, combinations
should be used to preclude the possibility of losses to R. solani which did not
appear to be a significant factor in Test 2.
Significant increase of losses to Pythium sp. has been reported with the use
of PCNB (1). Previous work with PCNB in plug-mix incorporation tests support this
finding (Sonoda, unpublished data).
Significant reduction of yield as compared to control by Orthocide 50W but not
by Truban 30W or Dexon 35W was obtained in a yield trial at the ARC-FP (Sonoda,
unpublished data). Additional tests need to be conducted to determine the effect
of the various combinations of fungicides on yield, fruit size and fruit quality.
1. Gibson, I. A. A. 1961. An anomalous effect of pentachloronitrobenzene
on the incidence of damping-off caused by a Pythium sp. Phytopathology
2. Hayslip, N. C. 1974. A "Plug-Mix" seeding method for field planting tomatoes
and other small-seeded crops. Ft. Pierce ARC Research Rept. RL-1974-3.
3. Sonoda, R. M. 1973. Occurrence of a Pythium disease in virgin sandy soils
of south Florida associated with a new method of field seeding tomatoes.
Plant Disease Reporter 57:260-261.
4. Sonoda, R. M. 1973. Development and control of a seedling disease of tomato
in virgin sandy soils of south Florida. Ft. Pierce ARC Research Rept.
RL-1973-2. 3 pP.
Table 1. Effect of fungicides and fungicide combinations added to "Plug-Mix"
on severity of tomato seedling disease, rate of seedling emergence,
and appearance of seedlings in soil artificially infested with
Pythium aphanidermatum and Rhizoctonia solani.
Fungicides/I Kg severe y Emergeg~e Appearap9e
dry weight Jiffy Mix Plujl/ index2/ rate/ rating-/
Benlate 50W 0.3g + Terrazole 35W 2.2g 1.50 a8/ 6.0 bo/ 1.0 a5/
Benlate 50W 0.3g + Dexon 35W 1.7g 1.52 a 5.7 ab 1.2 ab
Demosan 65W 0.4g + Terrazole 35W 2.2g 1.70 ab 8.1 g 3.0 cde
Demosan 65w 0.4g + Dexon 35W 1.7g 1.95 ab 6.8 ef 2.2,,abcde
Terrachlor 75W 0.2g + Dexon 35W 1.7g 2.32 abc 5.8 ab 1,2 ab
Demosan 65W 0.4g + Difolatan 4F 0.6mls 2.58 abcd 7.2 f 3.2 de
Demosan 65W 0.4g + Orthocide 50W 2.5g 3.05 abcde 8.2 g 3.2 de
Benlate 50W 0.3g + Demosan 65W 0.4g 3.10 bcde 6.6 cdef 2.0 abcd
Benlate 50W 0.3g + Difolatan 4F 0.6 mis 3.12 bcde 6.0 be 2.0 abcd
Difolatan 4F 0.6mls 3.20 bcdef 6.0 be 2.5 bcde
Terrazole 35W 2.2g 3.28 bcdef 6.2 bcde 1.8 abc
Demosan 65W 0.4g 3.62 cdef 7.1 f 2.3 abcde
Orthocide 50W 2.5g 4.08 def 6.1 bcd 2.0 abce
Benlate 50W 0.3g + Orthocide 50W 2.5g 4.10 def 6.2 bcde 2.5 bcde
Terrachlor 75W 0.2g + Orthocide 50W 2.5g 4.25 ef 6.4 bcdef 3.0 cde
Benlate 50W 0.3g 4.52 ef 5.2 a 1.0 a
Terrachlor 75W 0.2g + Difolatan 4F 0.6ml 4.75 f 6.8 def 3.5 e
Control untreated planting mix 4.75 f 5.1 a 1.0 a
1/ Four styrofoam cups per treatment; each seeded with ten Walter tomato seeds and
placed in a randomized complete block design under sprinkler irrigation in the
2/ Disease Severity Index = mean of the mean disease severity readings made for
each replicate of a treatment. 1= no disease to 5= plant dead.
3/ Emergence Rate= Sum of (number of plants emerging per day x days after planting)
Total number of plants emerged
Larger number indicates slower emergence.
4/ Appearance rating = qualitative reading of appearance of seedlings,
1 = no difference from control to 4 = very poor growth.
5/ All means in a column having a common letter are not different at the 5%
level of significance by Duncan's multiple range test.
Table 2. Effect of fungicides and fungicide combinations added to "Plug-Mix"
on severity of tomato seedling damp-off and on seedling emergence.
dry weight Jiffy Mix Plusal /
Truban 30W 2.2g
Truban 30W 2.2g + Tersan SP 65w 0.3g
Truban 30W 2.2g + Terrachlor 75W 0.2g
Tersan SP 65w 0.3g + Dexon 35W 0.6g
Truban 30W 2.2g + Benlate 50W 0.6g
Dexon 35W 0.6g + Terrachlor 75W 0.3g
Dexon 35W 0.6g + Benlate 50W 0.6g
Dexon 35W 0.6g
Orthocide 50W 2.5g
Tersan SP 65W 0.3g
Benlate 50W 0.6g
Terrachlor 75W 0.3g
1/ Five replications of each treatment in
a randomized block design.
2/ Number of damped-off plants recorded from five days
after planting to 12 days
3/ Number of hills without plants 12 days after seeding.
4/ Number of plants emerged per eight hill replicate six days after planting.
5/ Means in a column having a common letter are not different from each other
at the 5% level of significance by Duncan's multiple range test.
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