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Copyright 2005, Board of Trustees, University
/ Fort Pierce ARC Research Report RL-1977-2 March 1977
EFFECT OF BENOMYL DRENCHES ON FUSARIUM CROWN
ROT OF TOMATOES
R. M. SonodaI/
The Fusarium oxysporum inciting Fusarium crown rot of tomatoes was slightly
more sensitive to benomyl and thiophanate methyl in vitro than Fusarium oxysporum f.
sp. lycopersici race 1 or race 2. Benomyl was applied as a drench at different time
intervals to Floradel tomatoes in a commercial field near Jupiter, Florida. The
most effective treatment reduced incidence of Fusarium crown rot about 50%. The
lowest incidence of Fusarium crown rot occurred when benomyl treatments were first
applied at the time of planting. The field test was destroyed by a freeze. No data
was obtained on the effect of the benomyl drenches on yield.
Fusarium crown rot of tomatoes incited by a Fusarium oxysporum different from
F. oxysporum f. sp. lycopersici race 1 (F. o. 1. race 1) or race 2 (F. o. 1. race 2)
caused heavy losses in fruit yield on a farm near Jupiter, Florida in the winter of
1974-75 (1). Losses to the disease occurred in the Juptter, North Palm Beach,
Lake Worth and Delray Beach, Florida areas on farms operated by the same commercial
firm in the winter of 1975-1976.
The tomatoes on these farms were grown on plastic mulch covered beds fumigated
with 67% methyl bromide-33% chloropicrin (about 285 Ib/treated acre). This treat-
ment has been ineffective in controlling Fusarium crown rot. A field test in the
winter of 1975-76, indicated that different rates of 33% methyl bromide-67% chloro-
picrin were only as effective as the standard 67% bromide-337. chloropicrin treat-
ment (2). Preplant incorporation of 30 Ib active ingredient/acre sodium azide was
less effective than the standard methyl bromide-chloropicrin treatment (2).
Preliminary tests in 1975-1976 showed that drenching with benomyl reduced the
incidence of plant death due to Fusarium crown rot (Sonoda, unpublished data).
The research reported below was undertaken to determine the effectiveness of
benomyl used as a drench in the control of Fusarium crown rot.
L/ Associate Plant Pathologist, University of Florida, Institute of Food and
Agricultural Sciences, Agricultural Research Center, Fort Pierce.
JUNW 2 1977
Materials and Methods
Two isolates of the pathogen (QW-1 and QW-4) inciting nFuartim crown rot were
obtained from plants exhibiting symptoms of the disease. One isolate each of
F. o. 1. race 1 (626-1) and F. o. 1. race 2 (548-10-4) was obtained from J. P. Jones,
University of Florida, AREC, Bradenton. The fungi were grown on acidified Difco
potato dextrose agar until used.
The effect of benomyl and thiophanate methyl on the fusaria was determined by
incorporating aqueous suspensions of Fungo 50 (thiophanate methyl) and Benlate 50W
benomyll) in Difco potato dextrose agar to make suspensions of 3.2, 6.4, 12.8 and
25.6 ppm active ingredient. Four mm disks of agar containing the F. oxysporum were
transferred to four plates of each concentration of fungicide. The plates were
incubated on a laboratory bench (24-28 C) under Westinghouse Agro-lite bulbs. Dia-
metrical growth was measured 8 days after transfer.
A 360 X 150 ft area on a commercial farm near Jupiter was selected for the
field test. Plants of the tomato variety Floradel were transplanted into 2.5 in.
dia. holes 1 ft. apart in polyethylene mulch covered beds on October 19, 1976. The
plants were hand-drenched with 1000 ppm suspensions of benomyl at different time
intervals. One hundred ml of a 1000 ppm suspension were drenched per hill at the
time of planting on hills scheduled to receive drenches at that time. Seventy mls
of suspension were applied to hills scheduled to receive drenches 2 or more weeks
after planting. There were five replications in randomized complete block design
per treatment (Table 2). Each replicate consisted of 3 rows each containing 30
plants. Drenches were applied at designated intervals from October 19, 1976 until
January 17, 1977. Severe cold weather on January 18-20 killed the top growth of
the plants and drenching was terminated.
Thirty plants from each replicate of a treatment (the middle row) were lifted
from February 15 through February 22 and rated for disease severity. The lower 6"
of the stem and the upper 6" of the tap root were split open for examination. The
rating system used was: 1 (healthy root and stem), 2 (no necrosis visible on
cursory examination of stem and root surface, but internal lesions present), 3 -
(slight necrosis of root or stem surface with moderate internal necrosis)and 4 -
(severe necrosis of root and stem surface of internal tissue).
All data were subjected to analysis of variance. Percentages were transformed
to arc sine before analysis of variance. Means were separated by Duncan's multiple
Results and Discussion
Benomyl was more effective in vitro than thiophanate methyl (Table 1) at the
same concentration in reducing diametrical growth of the tomato fusaria. The crown
rot, E. oxysporum (QW-1 and QW-2) were slightly more sensitive to both benomyl and
thiophanate methyl than were F. o. 1. race 1 and F. o. 1. race 2. (Table 1).
Treatment 8 (Table 2) was originally scheduled to receive weekly treatments.
After applying benomyl at the time of planting and one week later, plants in treat-
ment 8 were smaller than in treatments receiving no benomyl or benomyl biweekly,
thus treatment 8 was changed to receive drenches of benomyl biweekly.
When drenching was terminated orrty two-plntsaad been-kil4led by Fusarium
crown rot (the result of quick wilt syndrome (1)). The two dead plants were in a
treatment receiving its first drench on the fifth week after transplanting. At the
time disease severity ratings were made, plants were making a regrowth from lower
stem areas undamaged by cold weather.
The disease was not distributed evenly between replicates as there was a sig-
nificant difference in disease incidence between replicates of a treatment. The
data in Table 2 indicate that plots drenched at the time of planting had the lowest
incidence of Fusarium crown rot.
Further work is necessary to determine if the reduction of incidence of the
disease conferred by benomyl drenches will be enough t- reduce losses in yield.
The disease incidence on nontreated plants, about 37., wras relatively low compared
to disease incidences observed in earlier years, when G00% of the plants in some
fields were affected. Whether benomyl drenches would be effective when disease
pressure is higher will have to be investigated.
Further work is needed to determine if other methods of applying benomyl, such
as a preplant root dip, or continuous watering of seedlings with benomyl before
transplanting to the field is more effective.
Drenching with a tractor-drawn water wagon can be easily done in the fir9t 2-3
weeks after planting but once stakes are placed in the field for training tomatoes,
use of the water wagon becomes nearly impossible. After about 4 weeks, hand-drench-
ing becomes difficult as plant growth begins to cover the holes at the base of the
plant. If benomyl shows promise as a post-plant soil application another system
of drenching will have to be developed.
1. Sonoda, R. M. 1976. The occurrence of a Fusarium root rot of tomatoes in
south Florida. Plant Disease Reporter 60:271-274.
2. Sonoda, R. M. and R. T. McMillan, Jr. 1976. Comparison of several wide
spectrum biocides in the field of Fusarium crown rot of tomato.
Ft. Pierce ARC Research Report RL-1976-1. 3 pp.
Table 1. Diametrical growth of Fusarium isolates after 8 days at
24-28 C on Difco potato dextrose agar containing benomyl
or thiophanate methyl
f. sp. lycopersici
race 1 (626-1)
F. oxysporum f. sp.
lycopersici race 2
0 7.2 a 7.2 a
1.6 6.4 b 7.2 a
3.2 0.9 c 6.9 a
6.4 0 d 6.2 ab
12.8 0 d 4.7 b
0 6.2 a 6.2 a
1.6 6.5 a 6.0 a
3.2 3.2 b 6.0 a
6.4 0 c 6.0 a
12.8 0 c 5.7 a
1/ Mean diameters in each column for each Fusarium isolate followed
by the same letter are not significantly different at the 5%
level (Duncan's new multiple range test).
Table 2. Incidence and severity of Fusarium crown rot on Floradel
tomatoes treated with benomyl aq a drench in a commercial
planting near Jupiter, Floridal!
Treatment Time of treatment % plants Disease
no. (week) affected severity index-/
1 none3z 37.7 ab/ 1.62 abc4/
2 none-' 36.7 ab 1.79 ab
3 nqe-6 35.7 abc 1.57 abcd
4 0L- 11.0 e 1.15 e
5 0,2 20.6 abcde 1.37 cde
6 0,2,4 15.6 cde 1.28 cde
7 0,2,4,6,8,10,12 16.8 bcde 1.32 cde
8 0,1,2,4,6,8,10,12 12.5 de 1.24 de
9 0,4,8,12 27.6 abcde 1.54 abed
10 1,3,5,7,9,11,13 22.9 abcde 1.35 cde
11 3,5,7,9,11,13 26.2 abcde 1.45 bcde
12 5,7,9,11,13 31.3 abcd 1.55 abed
13 9,11,13 27.5 abcde 1.43 bcde
14 11,13 41.2 a 1.83 a
15 13 22.5 abcde 1.47 abcde
1/ Plants transplanted on Oct. 19, 1976. Top growth of plants killed
by a freeze on Jan. 18-20, 1977. Symptoms rated on Feb. 15-22, 1977.
2/ Disease severity index for 30 plants in center row of each three-row,
90 plant plot, except treatment number 3. Rating system: healthy
to 4=severe necrosis of root and stem surface and of internal tissue.
3/ Untreated because of freeze.
4/ Means in the same column followed by the same letter are not different
at the 5% level of significance (Duncan's new multiple range test).
5/ Center row of three-row control plot.
6/ East row of three-row control plot.
7/ 0 drenched on day of planting.