The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
Gulf Coast Research
and Education Center
5007 60th St. E., Bradenton, Florida 34203-9324
SInstitute of Food and Agricultural Sciences
University of Florida
GULF COAST RESEARCH AND EDUCATION CENTER
IFAS/UNIVERSITY OF FLORIDA
5007 60TH STREET EAST
BRADENTON, FL 34203
Bradenton GCREC Research Report BRA1991-14 August
Effects of Bravo 720 on Watermelon Fruit
D. N. Maynard and J. P. Jones1
Applications of the Bravo 720 formulation of chlorothalonil (ISK Biotech
Corporation, Mentor, OH 44061-8000) have been reported to cause injury, similar
to sunburn, on the surface of watermelon fruit. When the injury occurred, it was
usually associated with applications of the fungicide to watermelon crops nearing
maturity with sparse vine cover during periods of intense sunlight and high
Based on information available prior to the 1991 watermelon season, ISK Biotech
issued an information bulletin (1) to growers which provided the following
guidelines for Bravo 720 use on watermelons: (a) do not tank mix with any other
product, (b) do not apply within 21 days of first harvest if periods of intense
sunlight and high temperatures are expected, and (c) do not apply within 21 days
of first harvest when vines do not provide shading of fruits, or if vines are
stressed due to drought.
The objective of this experiment was to determine the effects of weekly
applications of Bravo 720, with applications omitted at designated periods before
anticipated first harvest date, on four watermelon varieties that varied in rind
color and pattern.
MATERIALS AND METHODS
Soil in the experimental area was sampled before fertilization and analyzed by
the IFAS Extension Soil Testing Laboratory (2): pH = 6.9 and Mehlich I
extractable P = 25, K = 14, Mg = 104, Ca = 767, Zn = 2.4, Cu = 0.9, and Mn = 0.9
The EauGallie fine sand was prepared in late February 1991 by incorporation of
0-2.1-0 lb N-P205-K2O per 100 linear bed feet (lbf). Beds were formed and
fumigated with methylbromide:chloropicrin (67:33) at 2.3 lb/100 lbf. Banded
fertilizer was applied in shallow grooves on the bed shoulders at 2.5-0-3.5 lb
N-P20O-K20/100 lbf after the beds were pressed and before the black polyethylene
mulch was applied. The total fertilizer applied was equivalent to 120-100-167
lb N-P, 0-K 0/A. The final beds were 32 in. wide and 8 in. high, and were spaced
on 9 ft centers with four beds between seepage irrigation/drainage ditches which
were on 41 ft centers.
iProfessors of Vegetable Crops and Plant Pathology, respectively.
'Crimson Sweet', 'Royal Jubilee', 'Sangria', and 'Southern Belle' watermelons
were direct-seeded on 11 March in holes punched in the polyethylene at 3 ft in-
row spacing. The 30 ft long plots had 10 plants and were replicated four times
in a randomized, complete block design. Weed control in row middles was by
cultivation and applications of paraquat.
Bravo 720 treatments were applied weekly at 3 pt/100 gal/A according to the
Time of Last Application
Treatment Number of Days Before (-) or
Number Applications After (+) First Harvest
1 10 + 4
2 8 9
3 7 -16
4 6 -23
5 5 -30
Additional pesticides were applied as needed on separate days for control of
sweetpotato whitefly endosulfann and esfenvalerate), aphids endosulfann),
rindworm (Bacillus thuringiensis), and downy mildew (metalaxyl).
The plots were evaluated for foliar disease, primarily gummy stem blight, on 30
May using the Horsfall-Barratt procedure (3) and converted to percentages.
Surface temperatures of five fruit of each variety in full sun or shaded by the
watermelon vines and leaves were obtained with a Fisher Scientific digital
thermometer equipped with a skin temperature probe on 29 May.
The watermelons were harvested on 30 May and 7 June. Marketable melons (U.S. No.
1 or better), according to U.S. Standards for Grades (5), were separated from
culls and counted and weighed individually. Soluble solids determinations were
made with a hand-held refractometer on 13 to 16 fruit of each variety in each
treatment over two harvests, and the incidence of hollowheart was recorded for
these fruits. Where possible, the resulting data were subjected to analysis of
variance and mean separation was by Duncan's multiple range test.
RESULTS AND DISCUSSION
Temperature and rainfall during the experimental period from 11 March to 7 June
deviated from the 35-year averages (4) at the Gulf Coast Research & Education
Center. March, April, and May temperatures were above normal and rainfall in
April and May were considerably above normal (Table 1). Because of the frequent
showers during the last two weeks in May, light intensity was not as high as
No detectable injury on watermelon fruit was observed that could be associated
with Bravo 720 applications. The injury had been associated previously with high
light intensity and temperatures in the period immediately proceeding harvest.
These conditions did not occur in this trial because of overcast skies and
frequent showers during the last two weeks of May and in early June. Sparse vine
cover, also associated with Bravo 720 injury, did not occur in this trial except
in plots that had not received Bravo 720 applications for 23 and 30 days before
Since no significant interactions were found between variety and number of Bravo
720 applications, the data are presented separately.
Early and total yields, average fruit weight, and soluble solids varied among the
four varieties included in this trial (Table 2). This was to be expected since
they were representative of different watermelon types. The incidence of
hollowheart, however, did not vary among varieties. 'Southern Belle' was more
susceptible to gummy stem blight than the other three varieties.
The number of Bravo 720 applications did not affect early and total yield,
average fruit weight, soluble solids concentration, and incidence of hollowheart
(Table 3). On the other hand, the incidence of gummy stem blight was
significantly greater in those plots that received five or six Bravo 720
applications compared to those that received seven, eight, or ten Bravo 720
The distribution of watermelon fruit weight varied among varieties as would be
expected because they were representative of different types (Table 4). However,
the number of Bravo 720 applications did not affect the distribution of fruit
into various weight classes (Table 5).
The surface temperature of watermelon fruit greatly exceeded air temperature
regardless of whether the fruit was in the shade or sun, and temperature of fruit
in the sun exceeded that of shaded melons (Table 6). Temperature of shaded fruit
was similar regardless of variety, whereas considerable difference in temperature
among varieties was recorded for fruit in the sun. Temperature had no apparent
relationship to rind color or pattern. The rind temperatures from darkest to
lightest rinds were 'Southern Belle', 103.8; 'Sangria', 108.4; 'Crimson Sweet',
110.3; and 'Royal Jubilee', 104.70F. Therefore, the lowest rind temperature
occurred in the darkest and lightest varieties.
A relationship between frequency of Bravo 720 applications and the occurrence of
fruit injury was not established in this experiment. If previous observations
relating the injury to high light intensity and high temperature are correct, the
results might be explained by the high frequency of overcast skies during the two
week period before harvest. Another possibility is that the observed fruit
injury was related to some factor other than application of Bravo 720.
The information contained in this report is a summary of experimental results and
should not be used as recommendations for crop production. Where trade names are
used, no discrimination is intended and no endorsement is implied.
1991. Bravo 720 Information Bulletin. ISK Biotech,
2. Hanlon, E. A. and J. M. DeVore. 1989. IFAS Extension Soil Testing
Laboratory Chemical Procedures and Training Manual. Fla. Coop. Ext.
3. Horsfall, J. C. and R. W. Barratt. 1945. An Improved Grading
System for Measuring Plant Disease. Phytopathology 35:566 (Abstr.).
4. Stanley, C. D. 1990. Temperature and Rainfall Report for 1989.
GCREC Res. Rept. BRA1990-5.
5. U.S. Standards for Grades of Watermelon.
Table 1. Mean temperature and rainfall at the Gulf Coast Research &
Education Center from 11 March to 7 June 1991 and 35-year
Average daily temperature (OF)
1991 35-year average Rainfall (in.)
Month (date)' Max. Min. Max. Min. 1991 35-year average
March (11-31) 80 58 77 55 2.47 3.43
April 85 63 82 60 5.31 1.56
May 89 70 87 64 9.34 3.10
June (1-7) 89 71 91 70 0.31 7.65
'1991 data are for the dates shown; 35-year averages are for the entire
Table 2. Yield, average fruit weight, soluble solids, incidence of hollowheart and incidence of gummy stem blight on four watermelon varieties. Gulf Coast
Research & Education Center. Spring 1991.
Early Harvest' Total Harvest Gummy
Weight Avg. fruit Hollowheart Weight Avg. fruit Soluble Hollowheart stem
Variety No./A2 (cwt/A) wt (ib) (%) No./A' (cwt/A) wt (lb) solids (%) (%) blight(%)
Royal Jubilee 1178 c3 261 c 22.0 a 5.0 a 2630 b 548 a 20.9 a 10.1 b 4.8 a 7.5 b
Crimson Sweet 2065 b 363 a 17.8 b 1.3 a 2678 b 450 b 16.8 b 10.7 a 2.1 a 9.5 b
Sangria 2017 b 343 ab 17.1 b 5.0 a 2573 b 427 b 16.6 b 10.4 ab 2.5 a 13.5 b
Southern Belle 2508 a 280 bc 11.1 c 2.5 a 3299 a 354 c 10.6 c 10.0 b 1.0 a 37.0 a
'First of two harvests.
'Acre = 4840 Ibf.
'Mean separation in columns by Duncan's multiple range test, 5% level.
Table 3. Yield, average fruit weight, soluble solids, incidence of hollowheart, and incidence of gummy stem blight as influenced by number of Bravo 720
applications. Gulf Coast Research & Education Center. Spring 1991.
Early Harvest' Total Harvest Gummy
Bravo 720 Weight Avg. fruit Hollowheart Weight Avg. fruit Soluble Hollowheart stem
applications (No.) No./A2 (cwt/A) wt (1b) (%) No./A' (cwt/A) wt (Ib) solids (%) (%) blight(%)
5 1785 286 16.5 0 2460 386 15.7 10.2 0 60.5
6 1845 309 18.0 3.1 2743 459 17.1 10.5 2.8 40.5
7 2138 345 17.6 0 2995 483 16.7 10.2 3.1 4.1
8 1704 272 16.5 9.4 2773 436 15.8 10.3 4.4 6.8
10 2238 344 16.5 4.7 3005 448 15.8 10.2 2.6 5.9
Significance NS' NS NS NS NS NS NS NS NS **
'First of two harvests.
'Acre = 4840 Ibf.
'NS = Not significant, ** = significant at the 1% level of probability.
Table 4. Fruit weight distribution of four watermelon varieties.
Gulf Coast Research & Education Center. Spring 1991.
Fruit weight (Ib)
< 15 15.1 20 20.1 25 >25
Variety Percentage of Fruit
Crimson Sweet 43 bi 33 a 19 b 5 b
Royal Jubilee 15 c 33 a 30 a 23 a
Sangria 41 b 38 a 18 b 3 c
Southern Belle 89 a 11 b 0 c 0 c
'Mean separation in columns by Duncan's multiple range test, 5% level.
Table 5. Fruit weight distribution as affected by number of Bravo 720
applications. Gulf Coast Research & Education Center.
Bravo 720 Fruit weight (1b)
Applications < 15 15.1 20 20.1 25 >25
(No.) Percentage of Fruit
10 49 26 17 9
8 49 30 16 6
7 44 29 16 11
6 42 28 21 10
5 50 31 15 3
Significance NS' NS NS NS
'NS = Not significant.
Table 6. Surface temperatures of watermelon fruit. Air temperature .
was 89.40F. Gulf Coast Research & Education Center. Spring
Variety' Sun Shade
Crimson Sweet 110.3 a2 96.9 a
Royal Jubilee 104.7 c 96.7 a
Sangria 108.4 b 97.6 a
Southern Belle 103.8 c 96.7 a
Average 106.8 a3 97.0 b
'Means of five observations in sun or shade of each variety.
Mean separation in columns by Duncan's multiple range test, 5% level.
Mean separation of averages by Duncan's multiple range test, 5% level.
The Gulf Coast Research and Education Center
The Gulf Coast Research and Education Center is
a unit of the Institute of Food and Agricultural Sci-
ences, University of Florida. The Research Center
originated in the fall of 1925 as the Tomato
Disease Laboratory with the primary objective of
developing control procedures for an epidemic out-
break of nailhead spot of tomato. Research was ex-
panded in subsequent years to include study of sev-
eral other tomato diseases.
In 1937, new research facilities were established
in the town of Manatee, and the Center scope was
enlarged to include horticultural, entomological, and
soil science studies of several vegetable crops. The
ornamental program was a natural addition to the
Center's responsibilities because of the emerging in-
dustry in the area in the early 1940's.
The Center's current location was established in
1965 where a comprehensive research and extension
program on vegetable crops and ornamental plants is
conducted. Three state extension specialists posi-
tions, 16 state research scientists, and two grant
supported scientists from various disciplines of
training participate in all phases of vegetable and
ornamental horticultural programs. This interdisci-
plinary team approach, combining several research
disciplines and a wide range of industry and faculty
contacts, often is more productive than could be ac-
complished with limited investments in independent
The Center's primary mission is to develop new
and expand existing knowledge and technology, and
to disseminate new scientific knowledge in Florida, so
that agriculture remains efficient and economically
The secondary mission of the Center is to assist
the Cooperative Extension Service, IFAS campus
departments, in which Center faculty hold appropri-
ate liaison appointments, and other research centers
in extension, educational training, and cooperative
research programs for the benefit of Florida's pro-
ducers, students, and citizens.
Program areas of emphasis include: (1) genetics,
breeding, and variety development and evaluation;
(2) biological, chemical, and mechanical pest manage-
ment in entomology, plant pathology, nematology,
bacteriology, virology, and weed science; (3) produc-
tion efficiency, culture, management, and counteract-
ing environmental stress; (4) water management and
natural resource protection; (5) post-harvest physiol-
ogy, harvesting, handling and food quality of horti-
cultural crops; (6) technical support and assistance to
the Florida Cooperative Extension Service; and (7)
advancement offundamental knowledge ofdisciplines
represented by faculty and (8) directing graduate
student training and teaching special undergraduate
0 The Institute of Food and Agricultural Sciences,
University of Florida.
Q A statewide organization dedicated to teaching,
research and extension.
L Faculty located in Gainesville and at 13 research
and education centers, 67 county extension
offices and four demonstration units throughout
D A partnership in food and agriculture, and natural
and renewable resource research and education,
funded by state, federal and local government,
and by gifts and grants from individuals, founda-
tions, government and industry.
O An organization whose mission is:
Educating students in the food, agricultural,
and related sciences and natural resources.
Strengthening Florida's diverse food and
agricultural industry and its environment
Enhancing for all Floridians, the application
of research and knowledge to improve the
quality of life statewide through IFAS exten-