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
UNIVERSITY OF FLORIDA
3 1262 05304 1728
WATERMELON/CANTALOUPE FIELD DAY
Wednesday, June 6, 1990
1:30 5:00 pm
Terry Courneya, Lake county Extension Director Moderator
Charles Conover, Center Director, Leesburg
James Crall, Plant Pathologist, Leesburg (pp. 1-3)
Jubilee II and near future projected releases
Breeding for mosaic virus, gummy stem blight, and Race 2 Fusarium wilt
Gary Elmstrom, Horticulturist, Leesburg (pp. 4-21)
Cucurbit variety evaluation
Seedless watermelon breeding/evaluation/production
Don Hopkins, Plant Pathologist, Leesburg (pp. 22-26)
Biological control of Fusarium wilt
Cantaloupe fungicide test
Watermelon fungicide test
Fungicides for watermelon disease control
Bacterial fruit blotch of watermelon
Susan Webb, Entomologist, Leesburg (pp. 27-29)
Stylet oil to reduce spread of watermelon mosaic virus
Dennis Gray, Developmental Biologist, Leesburg (p. 30)
Accelerated development of seedless varieties
Development of virus resistant seedless watermelon
TOUT of trial plots. Faculty will be stationed at location near
their research plots. Instruction for visiting plots will be provided
following the individual talks.
Refreshments (Courtesy of FOREMOST FERILIZER COMPANY)
J. M. Crall, Plant Pathologist
A newly-released cultivar, Jubilee II, is being grown commercially in Florida
this season for the first time, and will be available to growers in other states for
the 1990-91 season. Plant Variety Protection (PVP) certification has been requested
and Asgrow Seed Company is the sole licensee for production and sale of seed of this
Jubilee II is a Jubilee-type cultivar with resistance to races 0 and 1 of the
Fusarium wilt organism and resistance to anthracnose (race 1). It is superior to
Jubilee, also, in most plant and fruit characters. Reports on its performance in
this season's Florida grower plantings indicate enthusiastic endorsement by growers
of Jubilee II.
In 1986 three cultivars, Charlee, Minilee, and Mickylee, were released from this
Center's watermelon breeding program. Charlee, with PVP certification, is licensed
solely to the Petoseed Company, while Minilee and Mickylee, also with PVP
certification, is licensed to both Petoseed and Pennington Seed Company (Hollar).
Seed of all three cultivars are available from other seed companies.
Charlee is a Charleston Gray-type cultivar with resistance to anthracnose
(race 1) and resistance to both races 0 and 1 of the Fusarium wilt organism. It
produces good yields of high quality fruits similar in size, shape, and weight to
those of Charleston Gray. Reports from growers indicate satisfactory performance in
commercial plantings, but the extent of its use commercially is not known.
Minilee and Mickylee are icebox-type cultivars with excellent fruit quality and
resistance to anthracnose (race 1) and Fusarium wilt (races 0 and 1). These two
icebox cultivars have been produced in Central America for the past 5 winter seasons
and have been on domestic markets in increasing volume during that time. Both
Central American and domestic growers have reported increasing export shipments to
Canada, Europe, and Japan. The USDA, through its Orlando Research Station, has
conducted storage and shipping trials, including shipments to Europe, since 1987.
They regard Minilee and Mickylee as the most promising icebox cultivars for
watermelon shipments to export markets, especially to Europe. (See article by
Dr. Larry Risse in our 1988 Field Day Research Report)
Mickylee is perhaps the variety most utilized as a pollinator in seedless
watermelon production fields.
As a result largely of the release of Minilee and Mickylee, and particularly
because of their excellent fruit qualities and the uniqueness of their fruits with
regard to size, flesh and rind characteristics, keeping qualities and other
characteristics, there has been a significant buildup of interest by both growers
and consumers in small-fruited watermelons. We view these happenings as favorable
towards reversing the decline in per capital consumption of watermelon (over 30%)
that has occurred in the United States over the past 20 years.
A second line from our Charleston Gray backcrossing program, S84GS(N), also
known as our SW4 line and tentatively named Graylee, has been approved for release
by the IFAS Cultivar Release Technical Advisory Committee. A release circular
manuscript is being prepared for submission to the Cultivar Release Committee for
their consideration. It is resistant to both anthracnose (race 1) and Fusarium wilt
(races 0 and 1). It produces good yields of high quality, shipping-type fruits that
are somewhat larger than those of Charlee. Fruit size approaches that of Jubilee.
It has performed well for several years in the SCWT Replicated Trial. In 1987 it
was second highest in marketable yield and had the second highest overall rating
score of 11 entries in the test.
There are a number of other lines that are further in the future with regard to
eventual release as cultivars. With the increasing interest in icebox sizes, we
have several other lines grouped as Small-seeded Dixielee lines (SSDL) that are in
the replicated field test stage. SSDL and 86C8-5 performed well in Dr. Don
Maynard's test in 1989 and they, as well as S89J39-1 and F89C10-6, look promising in
this season's trials. Even further in the future but also at the field test stage
are lines from the Crimson Sweet backcrossing program and some other large round
stripe lines (LRS) that have shown promise and are in the replicated trials for the
first time this season (S89K26-2 and F89A25-1).
In addition to the Jubilee II release and later projected releases (Graylee and
other lines in replicated tests), we have a number of lines in earlier stages of the
breeding program. Perhaps most important, in view of the threat to the watermelon
and cucurbit industries from mosaic virus diseases, are lines from the Nigerian line
"Egun" being selected for resistance to WMV (WMV2). These lines are in the F3 to F6
generations after 2 to 4 back crosses to some of our better advanced selections. We
have 2 lines (F89A1-6 and F89CW3-4) in replicated trial this year for the first
Second in importance to breeding for resistance to mosaic (WMV) is our program
for resistance to gummy stem blight (GSB). GSB lines are mostly in the F5
generation after 6 crosses with selected advanced lines to progenies developed from
PI 189225. Studies on resistance to the race 2 Fusarium wilt organism are in the
early stages, but have significance because of the known occurrence of this race in
Europe, Asia, Florida and other states in this country and its likely occurrence
throughout the world.
Limited work is being done in our program on tetraploid and triploid lines and
on dwarf lines with dwarfing genes from the Kentucky watermelon program. The dwarf
(short-internode) lines are in early stages of evaluation, but have interesting
long-range potential. Initiated this year are studies on small-seeded accessions of
watermelon. Two lines ("tomato seed" and PI 271771) have exceptionally small seeds
that could lead to improved fruit quality in progenies developed from them.
FIELD PLOT LOCATIONS OF REPLICATED TRIALS AND SPECIFICALLY NAMED
CULTIVARS AND BREEDING LINES
1. Replicated Trial of advanced Jubilee and Charleston Gray types plus two Crimson
Sweet/LRS lines and two WMV-Resistant Lines: Ranges A, B, C, D
see also Elmstrom's Fertilizer Trial, ranges UVWX
Crimson Sweet/LRS lines:
A7, 8; C7, 8
WMV Resistant lines:
F89A1-6: C9, 10
F89CW3-4: Bll, 12; C17, 18
2. Replicated Icebox Trial: Ranges E, F
Mickylee: F19, 20; El,
SSDL: E7, 8; E19, 20
86C8-5: F5,6; E15, 16
S89J39-1: F1,2; F17, 18
F89C10-6: F3, 4
3. Replicated Combining Trial: Ranges G, H
Main plots: Calhoun Gray crosses,
Small Round Gray crosses,
two Crimson Sweet crosses
Minilee, Mickylee, SSDL
4. Breeding plots: Ranges I, J, K
Gummy Stem Blight Resistance: 11-12
Crimson Sweet/LRS lines: I25-40; J1-8
Dwarf lines: J9-14
Race 2 Wilt Resistance: (not PI 296341-related)
Race 2 Wilt Resistance: (PI 296341) J35-40
Mosaic Resistance: KI-40
S89I3-1: K2, K16
S89131-5: K6, K20
G. W. Elmstrom, Horticulturist
(Location of field plots are noted on the map, Page 9.)
CUCURBIT VARIETY EVALUATION
The following reports, which summarize the cucurbit variety evaluation work at CFREC
Leesburg, are currently available:
A. Cucurbit Variety Evaluation, 1988. Leesburg CFREC Research Report (LBG 88-7).
B. Cucurbit Variety Evaluation, 1989. Leesburg CFREC Research Report (LBG 89-4).
C. Cantaloupe Variety Evaluation, 1980-1989. Leesburg CFREC Research Report
D. Watermelon Variety Evaluation, 1980-1989. Leesburg CFREC Research Report
E. Winter Squash Variety Evaluation, 1980-1989. Leesburg CFREC Research Report
F. Pickling Cucumber Variety Evaluation, 1980-1989. Leesburg CFREC Research Report
G. Fresh Market Cucumber Variety Evaluation, 1980-1989. Leesburg CFREC Research
Report (LBG 90-6).
H. Green Summer Squash (Zucchini) Variety Evaluation, 1980-1989. Leesburg CFREC
Research Report (LBG 90-7).
I. Yellow Summer Squash Variety Evaluation, 1980-1989. Leesburg CFREC Research
Report (LBG 90-8).
Watermelon Variety Trials (See Pages 10 to 12)
Icebox Watermelon Variety Trial (See Pages 13 and 14) a
Cantaloupe (Muskmelon) Variety Trials (See Pages 15 to 20)
SEEDLESS (TRIPLOID) WATERMELON BREEDING/EVALUATION/PRODUCTION
Since flowers on triploid watermelon plants lack sufficient pollen to induce
fruit set and fruit enlargement, seeded watermelon varieties are interplanted with
triploids to serve as pollenizers. An adequate bee population is necessary to
ensure that the transfer of pollen occurs. There has been some debate as to which
varieties are best suited as pollenizers.
In 1989, I obtained the best early yield when Mickylee and Sugar Baby served as
pollenizers. However, total yield from triploid plants was nearly equal regardless
of pollenizer variety. Other pollenizer varieties included Jubilee II, Royal
Jubilee, and Prince Charles.
TRIPLOID POLLENIZER TRIAL
MEAN YIELDS (LBS/ACRE)
Treatments and plot diagrams
on Page 21.
for the 1990 triploid pollination trial are presented
WATERMELON FERTILIZER TRIAL
The 1989 trial was initiated to determine the affect of preharvest fertilizer
application on yield, fruit size, quality, and hollow heart occurrence in Royal
Jubilee (seeded) and Jack of Hearts (seedless) watermelons. All plots received the
same fertilizer in the bedding operation -- 800 lb/A of a 6-8-8 plus 100 lb/A of a
15-0-14 at emergence. At layby and preharvest (2 weeks prior to the 1st harvest)
nitrate of soda-potash, 15-0-14, was applied in a 3 x 4 factorial experiment. Rates
at layby were 500, 750, and 1000 lb/A and preharvest rates were 0, 200, 400, and 800
lb/A. Differences among the treatments were few as shown on the next page.
,%;<"/ '/ ''
. . . .. .
. . . . . . I . .
. . . . . 1 . .
JACK OF HEARTS
Yield (cwt/A) Soluble
Total Early Solids
839 az 258 a 10.9 a
917 a 269 a 10.6 a
876 a 308 a 10.9 a
850 a 246 a 10.6 a
Layby Yield (cwt/A) Soluble lb/ Hollow
lb/acre Total Early Solids fruit Hearty
500 836 a 262 a 10.8 a 14.8 ab 1.4 a
750 973 a 302 a 10.8 a 15.7 a 1.3 a
1000 802 a 248 a 10.7 a 14.1 b 1.1 a
ZMean separation by Duncan's Multiple Range Test, 5% level.
YRated from 0, no hollow heart; to 5, severe hollow heart.
Layby Yield (cwt/A) Soluble lb/
lb/acre Total Early Solids fruity
500 1171 az 611 a 10.8 a 23.9 ab
750 1042 a 479 a 10.7 a 23.7 a
1000 1122 a 587 a 10.8 a 25.4 b
ZMean separation by Duncan's Multiple Range Test, 5% level.
YRated from 0, no hollow heart; to 5, severe hollow heart.
In 1990, I am repeating a 4 x 3 factorial experiment conducted in 1988.
0, 100, 200, & 400 lb/A 15-0-14 at emergence
0, 200, & 400 lb/A 15-0-14 preharvest
A seeded variety (Jubilee II) and a seedless variety (Queen of Hearts) were direct
seeded March 6, 1990. Plots were harvested for the first time on Monday, June 4.
Insects are required for pollination of cucurbits. Honeybees are the most
commonly used insect. Without sufficient transfer of pollen by honeybees, fruit set
does not occur or off-shaped fruit result. Bee attractants have been used in the
past, with varying degrees of success, to increase bee activity. In preliminary
studies in 1989, Bee Scente was applied to watermelons at CFREC Leesburg and in most
cases increased bee activity was evident in treated areas.
Cooperative studies were conducted in 1990 with Dr. Don Maynard, Gulf Coast
Research & Education Center, Bradenton. In many cases increased bee activity was
noted. In the Bradenton area, early, uniform fruit set occurred in treated areas.
In the Leesburg area, increased yield in two of three treated fields was noted.
Complete results from the 1990 trial are not available at the present time.
Purpose. To evaluate the combining ability of some varieties and breeding lines
and to develop parental lines with genetic properties suitable for Fl hybrid seed
Procedure. Almost without exception, the highest quality muskmelon fruits in
Florida are produced by hybrid varieties. However there is a reluctance on the part
of growers to plant hybrid seed since the cost is 10 to 15 times greater than that
of open-pollinated varieties. The high price of seed is the result of the need for
hand emasculation and hand pollination to produce hybrid seed. At present, I am
attempting to incorporate various characters into parental lines which would make
them more suitable for parental lines and reduce the cost of hybrid seed. A new
male-sterile gene was released to seed companies in 1983 by the CFREC Leesburg.
Studies are continuing on the usefulness of either the monoecious or gynoecious
flowering habit for production of hybrid muskmelon seed.
Gynoecious. The goal is to incorporate the gynoecious flowering habit into an
inbred line adapted to Florida. WI 998 is essentially a 100% gynoecious line in
Florida and is being utilized in this program. Backcrosses are being made to
western type melons.
Monoecious. As above, the goal is to incorporate the monoecious flowering habit
into inbred lines. Because of the number of genes which modify fruit shape, it has
been difficult to develop round monoecious lines. Selection of only round fruit is
extremely important. Backcrosses are being made to western types.
Male Sterile. The current emphasis in on the incorporation of Fusarium wilt
resistance and non-sutured melon types into my male sterile lines.
Zucchini Yellow Mosaic Virus. I am attempting to incorporate the ZYMV
resistance/tolerance from PI 371795 and PI 414723 into my male-sterile breeding
lines and also into non-sutured types.
Powdery Mildew. Resistance to powdery mildew has been transferred from
Cucurbita martinezii to C. pepo. After several seasons of backcrossing and
selection, an inbred PM-resistant zucchini type will be released to 1990. PM-
resistant, inbred yellow summer CN and SN types with and without the precocious gene
will be also released in 1990.
Zucchini Yellow Mosaic Virus. Attempts to transfer ZYMV resistance from C.
ecuadorensis to C. pepo are continuing. Sterility factors and lack of male blossoms
on F1 plants are causing problems in completing this transfer. Crosses with a ZYMV-
resistant C. moschata from Nigeria were made in fall 1987. These are being selfed
in spring 1990 for field evaluation this fall.
To Farm Buildings 4>
SEEDED WATERMELON VARIETY TRIAL 1990
Crisby (Nun 1839)
SCWT 301 (NV 4309)
Nun 1645 (Samos)
SCWT 278 (Jubilee
II) Leesburg CFREC
Abbott & Cobb
Abbott & Cobb
SEEDLESS WATERMELON VARIETY TRIAL 1990
Jack of Hearts
King of Hearts
No. 157 (SWM 8702)
No. 158 (SWM 8802)
Queen of Hearts
ASM 8900 F
ASM 8907 C
FL P1 x Minilee
FL P17 x P16
Watermelon Variety Trial Spring 1990
)n (7 L ) oQ oM 0, o 00- N M T in
SCE 0, 0 00 0 01 0 01 i 0I 1 C0
MY~ (0 ?T 1, 7O 0)ML 1 0 OOIC 0 T000N 3M
( q -O
B ~ ~ N C\j
'0: O If 0 ^ C rr m m r ^ r O ar 01 O 0, 0,
U)U) ~ ()f) ) U) j ) 0) U)2~2 00 2~2
LO CJ (n Lo 0 0) 0 LO ^ % ^ 0)
'T Lc) M OD C^ ^ C^j M^ 0 0 0) 1"^0 0) 00- C\ 0 'T N 00? N ?
q I I N N N)N~ O@0 NeC~
1 2 3 4 5 6 7 8 9 1011 1213141516171819202122232425262728293031323334353637383940
CIE cc CIE EC 0, 0 cl[ 0, 1 T- 0 01 CL 0 0 0 0 0 0 3: (J) o
LO 0 r,- CO 0 0) 0 N cq 'T M L n
C\I 'T O (D "t N C 0 0) 1 1 1 1 N C\ N C\J
c O CL Ir CIL I I r 01hih
3: U) U) : co U) 3: w w w U) U) U) : U) w 3: U ) : U) ( V)U) : U) 0
1 34 67 9101 2 3 4 5 6 7 8 9 0222232425267--8290 1 2 3 4 5 63 3 34
ICEBOX WATERMELON VARIETY TRIAL 1990
N 1-9 1-101-11 1-6 1-2 1-10 1-3 1-4 1-1 1-7 1-10
M 1-5 1-6 1-7 1-8 1-5 1-1 1-11 1-6 1-9 1-2 1-8
L 1-1 1-2 1-3 1-4 1-7 1-9 1-4 1-8 1-3 1-5 1-11
26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
ORANGE FLESH CANTALOUPE VARIETY TRIAL 1990
SME 8101 (Exp. 62)
Orange Flesh Cantaloupe Variety Trial Spring 1990
<01 0o b0 v- N C* to 0 N. Go m7 0or~ O
: ir fl: f: (r a: (E (E P: n/ : Q: IrC ir M LL / '& l C A
IL L 1 LUU ILI LLL LL L LL L .. LL LL W W LL E U. LL LLL LL
II III I I II 0ooooooo/ o o00 00000o o
LJ ~ V 10 1 2
IL0 0IL 0000/ IL"-
O ecr c 0 N/ ..
=I l- IL i l .
U. LLU. U. LL L LL L L =
oo0o0o0o 0,, 0
S0 c co Nc :c P
a~a ~a aa~a~ a
II 1 1 1 rI l I llII iI IN IIIC
000000000O000L I L 0L LLL
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1/0000000 / 0 0 0 0
16 17 18 19 20 21 2223 24 2526 27 28 29 30 31 32 33 34 35 36
1 2 3 4 5 6 7 8 9 1011 12 131415
SOUTHERN COOPERATIVE MUSKMELON VARIETY TRIAL 1990
Southern Cooperative Muskmelon
Variety Trial Spring 1990
I\/ iI I I i 0 I I I
CO ac 0
L0 0 1
AU ( u = o u0 Uo
0U 0 0
I I I
Tr r Crr
I OI I t_
(D( ) (J )U o J t CO (DU )
n- o o
35 36 37
40 41 42 43 44 45 46
GREEN-FLESHED MUSKMELON (NETTED & SMOOTH) VARIETY TRIAL 1990
Hyb. 89 (SME 8501)
Passport (HSR 444)
FL (SC43-2)2 open
FL (SC39-4)2 orange
FL (SC44-4) orange
FL (SC45-2)2 orange
Variety Trial -
O / N o- LO
// T- T- IT I /
I I I I 5 I I I I I
ScG /E oTo o 0 c/
oLL L LL L LL
H 11OOOOOC 0 1 1
H LOooooo I -
LL LL LL LL LL LL 0
o 0 o3 0 3 0,.
47484 M0 5N 4 55 5O 57 c5859 0 61 6 2 63 46
I dI I I I I I I I II I I I
47 48 49 50 51152 53 54 55 56
57 5859 60
61 62 63 64 65 66
Triploid Pollination Trial Spring 1990
9 1011 12 16 1617 18
1 = Mickylee
21 222*24 2728 29 0 $3 4 56 8940 41 42 45464748 51 525354 57 5859 80 6364 6566
Pollenizer outer two rows
Middle two rows are Queen of Hearts
( = Jubilee II
2 = Mickylee all fruit removed
3 = Sugar Baby
5 = Royal Jubilee
fl Bl ff ~iV
ffl 11 n M W f
ffl ffl Wn \S&
CUCURBIT DISEASE CONTROL
D. L. Hopkins, Plant Pathologist
BIOLOGICAL CONTROL OF FUSARIUM WILT OF WATERMELON
Fusarium wilt is the major, limiting production problem in watermelon in
Florida. Watermelon cultivars are described as resistant or susceptible to Fusarium
wilt, but they actually form a continuum from susceptible to highly resistant (See
table). Resistant cultivars and a long rotation are the only controls used by most
growers. It is becoming increasingly difficult to find pastureland that has not
been planted with watermelons for 6-8 years. Therefore, we have been conducting
studies to develop the methods to shorten the interval of crop rotation.
Ten watermelon cultivars with a gradation of wilt resistance were compared in a
cultivar monoculture for the development of Fusarium wilt and for the buildup of the
wilt fungus in the soil. After 3-4 years, all of the cultivars except Crimson Sweet
wilted severely regardless of previously described resistance levels. Only the
resistance of Crimson Sweet was stable in the monoculture.
Resistance 2-year monoculture 11-year monoculture
Cultivar ranking1 % wilt Yield(T/acre) % wilt Yield(T/acre)
Calhoun Gray HR 12 a 9.8 a 45 0.3
Smokylee HR 12 a 9.5 a 23 2.5
Crimson Sweet MR 19 ab 10.7 a 8 12.6
Charleston Gray MR 41 b 5.0 b 74 0.7
Florida Giant S 82 c 0.0 c 75 0.0
1HR = highly resistant, MR = moderately resistant, S = susceptible.
At this time, we do not recommend growing Crimson Sweet in a monoculture. In some
cases, Crimson Sweet can suffer very severe losses to wilt.
Laboratory and greenhouse studies of the soil from the Crimson Sweet plots
indicated that Crimson Sweet was uniquely able to promote the buildup of a
biological control agent in the soil. We believe that the biocontrol agent is a
soil fungus that is antagonistic to the Fusarium wilt fungus. We currently are
studying methods to use this soilborne fungus to develop biological control
procedures for Fusarium wilt to watermelon and other crops, if possible. We are
also attempting to determine the mechanism of promotion of the biocontrol fungus by
Crimson Sweet so that it might be incorporated into other watermelon cultivars.
CANTALOUPE FUNGICIDE TEST
Date of Planting: March 14, 1990
Variety: Gold Star
Procedure: Sprays are applied weekly (Bayleton is applied on 14-day schedule) in
100 gallons of dilute spray per acre at a pressure of 180 psi, using a boom sprayer.
(L) Aliette 80W + Bayleton 50W + Triton
(M) Rovral 4SC + Bayleton 50W + Triton
(N) Aliette 80W + Rovral 4SC + Bayleton
50W + Triton CS-7
(0) Ridomil/Bravo 81W + Bayleton 50W
Rate (Amt. Product/Acre)
2.0 Ibs + 0.125 lb + 1.0 pt
1.0 pt + 0.125 Ib + 1.0 pt
2.0 lbs + 1.0 pt + 0.125 lb + 1.0 pt
2.0 Ibs + 0.125 lb
Results: Not complete.
WATERMELON FUNGICIDE TEST
Date of Planting: March 14, 1990
Variety: Crimson Sweet
Procedure: Sprays are applied weekly in 100 gallons of dilute spray per acre at a
pressure of 180 psi, using a boom sprayer.
Treatment Rate (Amt. Product/acre)
(J) Ziram 3.0 lbs
(K) Thiram 3.0 lbs
(L) Unsprayed ---
(M) Bravo 720 + Benlate 50DF 1.5 pts + 0.25 lb
(N) Bravo 720 1.5 pts
(0) Bravo 90DG 1.25 lbs
(P) Bravo 720 1.5 pts to 2.4 pts
(R) Bravo 90DG 1.25 lbs to 2.0 lbs
Results: Not complete.
FUNGICIDES FOR WATERMELON DISEASE CONTROL
Fungicidel Rate/Acre GSB DM PM Alt. LS
Benlate lb ++ 0 -- 0
Bravo 720 1 3 pts ++ ++ -- +
Ridomil/Bravo 81W 1 h 2 lbs + ++ -- +
Kocide 101 1 3 lbs 0 + -- 0
Kocide 606 2 4 pts 0 + -- +
Bravo 90DG 1 2 h lbs ++ ++ -- +
Benlate Ib ++ 0 ++ 0
Bravo 720 1 3 pts ++ ++ + +
Bravo 90DG 1 2 Ibs ++ ++ + +
Bayleton 50WP 2 4 oz 0 0 ++ 0
Topsin M Ib ++ 0 ++ 0
Ridomil/Bravo 81W 1 2 lbs + ++ + +
10ther formulations of these products may be available. Read the label for
directions and rates.
2GSB = gummy stem blight, DM = downy mildew, PM = powdery mildew, ALS = Alternaria
leafspot; ++ = most effective, + = effective, 0 = not effective.
BACTERIAL FRUIT BLOTCH OF WATERMELON
In the 1989 watermelon season, a new bacterial fruit rot of watermelon was
observed in commercial fields in Florida and many other states in the Eastern U.S. :
The disease was devastating in several fields, especially in Florida and South
Carolina. In some fields, as large as 10 acres, very few fruit were marketable.
Symptoms. Symptoms on the fruit begin as small, greasy-looking, water-soaked
areas of a few millimeters diameter and enlarge to dark-green, water-soaked lesions
of several centimeters diameter with irregular margins. Lesions originate on the
upper surface of the fruit and often cover a large percentage of the surface. At
first, the lesions do not extend into the flesh of the melon, but are primarily
surface lesions. As he lesions age, the melon surface often cracks and bacterial
ooze can be seen on the fruit. Fruit decay follows in many of the melons and can be
a problem in post harvest shipments. These symptoms are very similar to those first
observed in 1967 and 1968 on the research farm to Leesburg, but they did not occur
again after 1968. Similar symptoms have been observed in Australia and Guam, where
the disease is called 'fruit blotch'.
The fruit blotch bacterium also produces foliar symptoms on watermelon
seedlings. Initial symptoms consist of water-soaking of the lower surface of
cotyledons and leaves, followed by necrotic lesions frequently with chlorotic halos.
The fruit blotch bacterium is very similar to a bacterium originally obtained from a
watermelon seedling disease in Georgia in 1965.
Epidemiology. Since watermelon fruit blotch is a new problem, very little is
known about the ecology and epidemiology of the causal bacterium. The bacterium
from seedlings in Georgia and fruit blotch in Guam was reported to be seedborne.
However, the evidence for seed transmission was based primarily on seed inoculation
by vacuum infiltration, or by immersion in a bacterial suspension. Seed
transmission of the bacterium could not be demonstrated with commercial seed in
Guam. The fruit blotch bacterium in Guam has been shown to survive in soil for 1-2
weeks and infect seedlings grown in the soil, but there is no information on
survival from season to season in the soil or on weed hosts.
With harvested watermelon fruit in laboratory or greenhouse inoculation
experiments, wounding of the melon surface was necessary for symptom development.
However, in a field experiment, symptoms developed 48-72 hours after inoculum was
sprayed on the nonwounded melon surface. Wounding does not seem to be necessary for
disease development under field conditions. Stomates on the fruit surface may serve
as the port of entry for the bacteria.
Control. Since the disease has occurred for only one year and so little is
known about the epidemiology, it is very difficult to develop control strategies for
watermelon fruit blotch. We can assume that some of the control measures employed
for other diseases would also serve to reduce the risk from bacterial fruit rot for
growers that had the disease last year. I would recommend plowing under debris from
last year's field and planting this year's crop as far away from last year's field
as possible. With direct seeded watermelon, remove any seedlings that have water-
soaked of necrotic lesions during thinning and, with transplants, use only disease-
free plants. Weed control, especially of volunteer cucurbits, may also be
beneficial for fruit blotch control.
Based on field observations, fruit of some cultivars, Crimson Sweet for example,
appeared to be less susceptible to fruit blotch than fruit of other cultivars. In a
field test at the research center in Leesburg, 21 cultivars were evaluated for
susceptibility to fruit blotch. Watermelon fruit, ranging in age from 14 days post
pollination to maturity, were inoculated by spraying the melon surface with inoculum
consisting of approximately 5 x 105 bacterial cells per ml. The fruit were left on
the vine and evaluated for symptoms at one and three weeks after inoculation.
Water-soaked symptoms were first observed 48-72 hrs after inoculation. Differences
in watermelon cultivar resistance to the bacterium were observed. The more
resistant cultivars were Sangria, Sugar Baby, Crimson Sweet and Early Jubilee.
Comparison of watermelon cultivars for susceptibility to bacterial fruit blotch in
a field test at Leesburg.
Fruit blotch severity Percentage of fruit with
Cultivar rating (0-5)z severe symptoms
Sangria 0.0 0
Crimson Sweet (A)
Crimson Sweet (P)
Charleston Gray (A)
Charleston Gray (P)
Jubilee (P) 1.9 27
Prince Charles 2.3 44
Charleston Gray 133 2.4 58
Mickylee 2.5 50
ZRating on arbitrary scale where 0 = no symptoms, 3 = small, greasy areas <3 cm
diameter, 5 = entire upper surface covered by lesion.
As a note of caution, these are the results of only one field test and cultivars
that did not develop symptoms in this test could be susceptible under other
conditions. However, growers that plan to plant watermelons near an area that had
fruit blotch last year may want to consider, a less susceptible cultivar.
CUCURBIT INSECT CONTROL
S. E. Webb, Entomologist
WILL STYLET OIL REDUCE THE SPREAD OF MOSAIC VIRUS IN WATERMELON?
In north central Florida, watermelon mosaic virus is a consistent and serious
problem. Because the disease is spread rapidly by many different kinds of aphids
(not just those that actually reproduce on watermelon), it is extremely difficult to
control. One possible way to reduce virus spread is to somehow discourage-aphids
from even the short test feedings that can lead to infection or to somehow interfere
with the actual process of acquiring and transmitting the virus. One material that
seems to do this is a special mineral oil formulation which has been used to protect
peppers and squash from similar aphid-transmitted viruses in Florida. Several
growers in Marion County have been using this oil (JMS Stylet Oil) on watermelon.
Other growers continue to use insecticides, hoping to reduce virus spread by killing
To see if oil could really delay virus spread in a fast-growing vine crop we
used stylet oil alone and in combination with endosulfan (Thiodan), a commonly used
insecticide, in large plots of watermelon ('Charlee') and monitored the spread of
virus every three days. Plots consisted of 10 rows of watermelon, 117 feet long
with plants spaced eight feet apart within the rows to make it easier to keep track
of individual plants. Oil was applied at four and five day intervals at 400 psi,
using a boom sprayer with TX55 nozzles spaced eight inches apart. Endosulfan (2 pts
per acre) was applied at approximately two week intervals, a total of seven
applications in the fall of 1988 and a total of six applications in the spring of
1989. This spring, endosulfan applications were reduced to conform to the product
label, i.e., no more than three applications per season. We trapped aphids in green
tile traps, designed to sample aphids that would actually be landing in the crop.
We also counted leaves and measured leaf area for the early stages of plant growth
(up to 700 leaves per plant). In the spring of 1989, as part of a regular survey of
local watermelon fields, we recorded virus incidence in eight areas of two adjacent
fields located in Weirsdale; one field was being treated with stylet oil and the
other was not.
In the fall of 1988, virus symptoms appeared in the crop one month after
planting. Actual infection must then have occurred only two weeks after planting
(symptoms develop approximately 10 days to two weeks after infection). Figure 1
shows the development of disease. Even though aphid numbers were not high until
late in the fall, many virus-infected weeds (and even some late-planted spring
watermelon) were available as sources of virus. Plots not being treated and those
treated with only endosulfan rapidly became infected. Oil-treated plots (with and
without endosulfan) lagged behind by approximately one week (to 50% infection) but
were eventually overwhelmed. Total weight of harvested melons did not differ among
the treatments and quality was generally poor because of the earliness of infection.
In the spring of 1989 virus appeared much later, almost two months after
planting (Figure 2) and corresponded to a large flight of aphids. Sources of virus
in the spring (as yet unknown) are much less common than in the fall. Oil again
gave us a week to ten day delay in reaching 50% infection which resulted in a lower
incidence of disease at harvest (approximately 65% vs 95%). More melons in the
check and endosulfan-treated plots showed symptoms of virus infection but no
significant differences in yield were found. This spring, we planted late
(March 17) and virus appeared early, one month after planting. In addition, a large
source of virus had built up two weeks prior to this, in the squash planting east of
our watermelon plots. Again, oil-treated plots reached 50% infection one week later
than plots not receiving oil, but this time, because of the earliness of infection,
all plots will be 100% infected by harvest. As of this writing we have not yet
begun to harvest and compare fruit damage.
Although a one week delay is not impressive, that we could achieve this in a
small plot situation is significant. Oil-treated plots were constantly exposed to
aphids that picked up virus in adjacent untreated plots. In a large field
situation, when the entire field is being treated, much longer delays should be
possible, especially if oil is applied consistently right from the beginning of the
spring growing season. The two fields we compared in Weirsdale showed vast
differences in the amount of final disease. During the fall, however, there may be
too many sources of virus for oil to be highly effective. The fall situation may be
comparable to the situation in our small plots where virus built up in untreated
plots next to treated plots.
Endosulfan, although it did control melon aphids in the fall of 1988 (the only
time we had problems with aphids attacking the crop), had little effect on virus
spread, and in fact may have slightly increased the rate of spread, perhaps by
irritating the aphids and causing them to move more rapidly from plant to plant. We
saw little difference between the check and the insecticide-treated plots this year
when we reduced the number of endosulfan applications from six to two. Thus, the
use of insecticides in the spring crop does not seem justified unless insects
causing direct damage to the plants are present, such as rindworms.
The rapid growth and large surface area of watermelon plants make it difficult
to protect them with anything that must be applied to leaves. Even young watermelon
plants (prior to fruit set) have up to 45 square feet of leaf surface area (one
surface only). Stylet oil, if used properly however, may delay the onset of virus
epidemics, particularly in the spring when sources of virus are not as abundant as
in the fall. The extra cost may be justified only when virus has consistently been
a problem. We are trying to identify, through our surveys, the characteristics of
virus-prone areas and are also attempting to correlate the first incidence of
disease and peak aphid flights with winter and early spring weather conditions.
This would allow a grower to better assess his or her risks of suffering a serious
disease problem and thus provide a better basis for making a decision to use a
costly control measure.
Note: One recent problem with using stylet oil has been the loss of the EDBC
fungicides for cucurbits. The remaining broad spectrum fungicide is not compatible
(although Benlate and Ridomil are) with oil and should not be applied within two
weeks of an oil treatment. In this part of the state, fungicides are not usually
needed early in the season when stylet oil would be most useful so there may still
be a way to obtain the benefits of both if the weather is cooperative.
S) 0.8 oil -endosulfan
.S 0.6 endosulfan
31 37 42 48 54 60 66
days after planting
Figure 1. Progress of mosaic virus in watermelon fall 1988.
65 75 85
days after planting
Figure 2. Progress of mosaic virus in watermelon spring 1989.
D. J. Gray, Developmental Biologist
Tissue and cell culture research combined with molecular genetics research is
designed to accelerate development of virus resistant seedless varieties.
ACCELERATED DEVELOPMENT OF SEEDLESS VARIETIES
A tissue culture cloning system has been developed for rapid propagation of
plants from selected individuals. Plants of diploid, triploid and tetraploid
varieties produced with this cloning system have been grown to fruit in field tests.
This technique allows newly developed tetraploids to be rapidly increased to the
number of plants needed for triploid seed production. The time normally needed to
increase tetraploid seed by conventional selling in order to provide plants for
triploid seed production is circumvented.
DEVELOPMENT OF VIRUS RESISTANT SEEDLESS WATERMELON
Research to regenerate watermelon plants from cell cultures is being initiated
at Leesburg in conjunction with molecular genetic research conducted by E. Hiebert
at the Gainesville campus. This project seeks to use genetic engineering technology
to place genes for a high degree of virus resistance into seedless watermelon. The
rationale for this project rests on the facts that: 1) seedless watermelon will
continue to fruit and produce up to triple the yield of seeded varieties if
conditions for growth remain favorable and 2) endemic virus diseases cannot be
adequately controlled and their presence causes fruiting to cease. Thus, with
proper management of other diseases, higher yields should be obtainable from virus
resistant seedless varieties than from seeded varieties.
Collaborators to this project, Drs. G. E. Elmstrom, D. E. Purcifull and S. E. Webb,
will be responsible for evaluating the resulting germplasm in the laboratory,
greenhouse and field.
Combination of tissue culture cloning and genetic engineering technology has
potential to exploit the superior quality and yield characteristics of seedless
watermelon. This will be accomplished by accelerating the normal method of variety
improvement and by inducing viral disease resistance.
IF j. SAC f i1O
0 The Institute of Food and Agricultural Sciences
O The statewide agricultural arm of the University of
Florida dedicated to Teaching, Research and Extension.
O A faculty team located at the University of Florida, and
at 22 research centers and 67 county Extension offices
throughout the state.
o A partnership in research and education, funded by state,
federal and local government, and with gifts and grants
from individuals, foundations and industry.
O An organization whose mission is -- to educate students
in agriculture and related sciences, to strengthen Florida's
agricultural industry through research, to improve the
quality of life for all Floridians through IFAS Extension