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1. (Table 1). Symptom development was severe with the un-
sprayed treatments and 69% of the mature fruit had blotch
symptoms. Cupric hydroxide and cupric hydroxide plus
fosetyl-Al provided significant control of the disease, reduc
ing fruit blotch to 10% of the fruit. Streptomycin and
fosetyl-Al alone were not significantly better than the un-
sprayed control.
Yields of marketable fruit were significantly higher with
the treatments that received cupric hydroxide or cupric
hydroxide plus fosety-Al (Table 1). These yields were more
than 5 times the yields with no spray. However, there was
some stunting of vegetative growth with the application of
cupric hydroxide or cupric hydroxide plus fosetyl-Al. Six
applications of cupric hydroxide on watermelon resulted
in severe phytotoxicity in some situations. Therefore,
further experiments were run to determine whether fruit
blotch control was possible with 1 or 2 well-timed applica
tions of cupric hydroxide.
In the fall 1990 test, foliar symptoms of fruit blotch
spread rapidly through the plots after inoculation in Sept.
However, in Oct. and Nov., symptom development and
spread was minimal. Incidence of fruit symptoms was low
regardless of the number of applications of cupric hydro
xide (Table 2). Due to the low incidence of disease, there
were no significant differences among treatments. Plants
that received weekly applications were the only ones that
did not develop fruit blotch. Because of this, 2 additional
treatments that included applications prior to anthesis were
added to the spring 1991 test.
In 1991, foliar symptoms developed on all plants but
the disease stopped spreading 2-3 weeks after inoculation,
despite a very wet spring. Fruit symptoms were very limited
(Table 2). There were no fruit symptoms on plants receiving
weekly applications or on plants receiving 3 applications.
There were also no significant differences in marketable
yields among treatments. The lower yield with the treat
ments receiving weekly applications of cupric hydroxide
probably resulted from the stunted plant growth that oc
curred. No phytotoxicity was observed with any other treat
ment.
Table 2. Number and timing of cupric hydroxide applications for the
control of bacterial fruit blotch of watermelon.
Bactericide
application (no.) and timing7
Seven; weekly from 2 wk prior to
anthesis
Three; 2 wk prior to anthesis, at
anthesis, and 2 wk after anthesis
Two; 2 wk prior to anthesis and
at anthesis
Two; at anthesis and 2 wk after
anthesis
One; at anthesis
One; at first symptoms
Unsprayed
Fruit blotch (%)y
Fall 1990
0
NT
NT
4
10
5
15
Spring 1991
0
0
4
12
4
9
8
1991
Yield
(ton/A)
4.8
8.3
6.5
8.4
8.8
6.5
6.5
7Cupric hydroxide as applied at 1.0 lb/acre in 100 gal of water.
yPercent of the total fruit that have any fruit blotch symptoms. NT means
that the treatment was not tested.
Literature Cited
DeVos, P., M. Goor, M. Gillis, and J. DeLey. 1985. Ribosomal ribonucleic
acid cistron similarities of phytopathogenic Pseudomonas species. Int.
J. Syst. Bacteriol. 35:169-184.
Hopkins, D. L. 1989. Bacterial fruit blotch of watermelon: a new disease
of watermelon, p. 74-75. In: C. E. Thomas (ed.). Proc. cucurbitaceae
89: Evaluation and enhancement of cucurbit germplasm symposium.
29 November - 2 December, 1989, Charleston, SC.
Hopkins, D. L. 1990. Differences in cultivar resistance to bacterial fruit
blotch of watermelon. Phytopathology 80:435 (Abstr.).
Latin, R. X., and K. K. Rane. 1990. Bacterial fruit blotch of watermelon
in Indiana. Plant Dis. 74:331.
Schaad, N. W., G. Sowell, Jr., R. W. Goth, R. R. Colwell, and R. E. Webb.
1978. Pseudomonas pseudoalcaligenes subsp. citrulli subsp. nov. Int. J.
Syst. Bacteriol. 28:117-125.
Somodi, G. C., J. B. Jones, D. L. Hopkins, R. E. Stall, T. A. Kucharek,
N. C. Hodge, J. C. Watterson, and D. Randleas. 1991. Occurrence of
a bacterial watermelon fruit blotch in Florida. Plant Dis. 75:1053-1056.
Wall, G. C., and V. M. Santos. 1988. A new bacterial disease of watermelon
in the Mariana Islands. Phytopathology 78:1605 (Abstr.).
Webb, R. E., and R. W. Goth. 1965. A seedborne bacterium isolated from
watermelon. Plant Dis. Reptr. 49:818-821.
Proc. Fla. State Hort. Soc. 104:272-275. 1991.
FLOATING ROW COVERS EXCLUDE INSECTS
AFFECTING FALL-GROWN SQUASH IN CENTRAL FLORIDA
Susan E. Webb
Central Florida Research and Education Center
IFAS, University of Florida
5336 University Avenue
Leesburg, FL 34748-8203
Additional index words, aphids, sweetpotato whitefly, Bemisia
tabaci, pickleworm, melonworm, Cucurbita pepo, Diaphania
spp.
Florida Agricultural Experiment Station Journal Series No. N-00504.
I thank American Agrifabrics and April Corporation for donations of
material and D. Yadon and K. Kelley for technical assistance.
272
Abstract. Spunbonded polyethylene floating row covers were
evaluated for effectiveness in excluding aphid-vectored vir
uses, whiteflies, (Bemisia tabaci [Gennadius]), pickleworm,
(Diphania nitidalis Stoll), and melonworm, (D. hyalinata L.)
from zucchini squash {Cucurbita pepo L.) In 1989 and 1990,
a lightweight cover (Agryl P10, American Agrifabrics, Al
pharetta, Georgia) and white on black polyethylene mulch
were used alone and in combination. The effect of the date
of cover removal on yield was also determined. In 1990, a
heavier material (Agryl PI 7) was tested only in combination
with mulch. Both materials effectively excluded insects. Mosaic
viruses vectored by aphids were rarely found when plants
were first uncovered, although most plants developed virus
symptoms within 2 or 3 weeks after uncovering. In 1989, more
Diaphania larvae and, in 1990, more whiteflies were found
Proc. Fla. State Hort. Soc. 104: 1991.

2. on plants with mulch but no cover than on plants that were
untreated, perhaps because plants with mulch were more vig
orous. Yields were significantly higher with both mulch and
covers, even when covers were left in place up to 2 weeks
after the beginning of flowering.
Cucurbits grown in Florida are severely damaged by
several mosaic viruses, all transmitted nonpersistently by
aphids (Purcifull et al., 1988). In addition, insect pests such
as pickleworm (Diaphania nitidalis), melonworm (D.
hyalinata), and several aphid species can cause severe dam
age, particularly in the fall. In recent years a new pest, the
sweetpotato whitefly, Bemisia tabaci, has caused additional
problems, including a disorder characterized by leaf silver
ing. Silverleaf, particularly a problem on squash, can be
induced byjust a few feeding nymphs (Yokomi et al., 1990).
A potential danger associated with high whitefly popula
tions is the introduction of whitefly-vectored viruses which
have caused severe losses in squash and muskmelon in the
southwestern United States (Duffus and Flock, 1982). Al
though direct damage to squash from aphids and Diaphania
spp. can be prevented by timely applications of insecticides,
damage from silverleaf and insect-vectored viruses cannot.
In the past few years, lightweight floating row covers
(lighter versions of the spunbonded polyethylene or polyes
ter that is used for frost protection) have been used to
protect cucurbits from viruses transmitted by aphids and
whiteflies (Natwicketal., 1988; Perringetal., 1989; Conway
et al., 1989) and from pests causing direct feeding damage,
such as cucumber and flea beetles (Adams et al., 1990) and
squash bugs (Cartwright et al., 1990). The purpose of this
study was to determine if row covers could be used to pro
tect squash under the hot, humid conditions of the fall
growing season in Florida and to determine the best time
to remove covers to allow pollination.
Materials and Methods
Floating row cover material (Agryl P10) and white-on-
black polyethylene mulch (RDT-502, April Corp., Sanibel,
FL) were used alone and in combination in the fall of 1989.
The experiment was designed as a split-plot with factors
of cover and mulch as main plot treatments and time of
uncovering as the subplot treatment. Zucchini squash,
Cucurbita pepo L. cv. 'Seneca' was planted 2.5 ft apart in
raised beds that were 5 ft apart, in plots consisting of 8
rows, 25 ft long. Treatments were replicated 4 times. Mulch
was applied shortly before planting and row covers were
put in place immediately after planting. All plots had re
ceived preplant applications of herbicides and were side-
dressed with fertilizer, treated with fungicide and irrigated
(overhead) as necessary.
Within each main plot, 1 randomly chosen row (subplot)
was uncovered on each of 3 dates: 10 Oct., several days
before flowering; 18 Oct., 6 to 7 days after the beginning
of flowering; 24 Oct., 12 to 13 days after the beginning of
flowering. Immediately after uncovering the row, all insects
were counted on 5 plants in each plot, including those plots
that were mulched but not covered and the untreated check
plots. Plants were also rated for virus symptoms. After the
first sample date (10 Oct.), only 4 plants were examined in
each plot; only 3 of 4 blocks were examined on the third
date.
Proc. Fla. State Hort. Soc. 104: 1991.
Fruit from all plants in sampled rows (1 row for each
of 3 uncovering dates in each main plot) was harvested at
a commercially acceptable size (6 to 8 inches long), at 2 and
3 day intervals from 21 Oct. to 13 Nov. Squash was sepa
rated into marketable and unmarketable categories based
on the presence or absence of virus symptoms. Yields from
all dates for each row were summed and divided by the
number of plants per row.
Because of problems with the disintegration of cover
material when used over mulch in 1989, a heavier material
(Agryl PI7) was included in the experiment in 1990 but
was tested only in combination with mulch. Squash was
planted on 25 Sept., at the same spacing as the previous
year. Main plots consisted of 6 rows and subplots consisted
of 2 rows uncovered on each of the first 2 uncovering dates
and 1 row on the third date.
Treatments were evaluated as before for insects, dam
age and virus infection. The first date, 30 Oct., was approx
imately 5 to 7 days after first bloom, the second, 3 Nov.,
was approximately 9 to 11 days after flowering began and
the third, 8 Nov., was approximately 14 to 16 days after
first bloom. Subplots were harvested from 2 Nov. until 21
Nov. Squash was considered marketable if it was not dam
aged by pickleworm nor showing symptoms of virus infec
tion.
A square root transformation was used for all insect
counts and yield data to stabilize variance. An arcsine trans
formation was used for proportions of plants infected with
viruses. Analysis of variance was used to analyze all data.
Contrasts were used to examine the effects of uncovering
date on yield.
Results and Discussion
1989. In 1989 row cover material over plants that were
mulched began to break down 3 weeks after planting. In
contrast, covers over plants that were not mulched did not
begin to tear until late in the season. No virus symptoms
were observed on plants when first uncovered, except for
those in 1 row with a badly damaged cover. Almost all
plants in plots without covers showed symptoms of infection
before 10 Oct. Two weeks after uncovering, however, al
most all plants showed mosaic symptoms.
Figure 1 shows the mean number of Diaphania spp.
(pickleworm and melonworm), whitefly adults, and the level
of aphid infestation per plant on each sample date. New
rows were examined on each occasion. All main effects and
interactions reported below were significant at P = 0.05.
Aphid numbers are shown as infestation levels in Fig.
1A. Aphids were counted individually until numbers ex
ceeded 150. Each level, from 1 to 11, represents an addi
tional 15 aphids, i.e., 1 = 1 to 15 aphids, 2 = 16 to 30, 3
= 31 to 45, etc. On the first sample date there was an
interaction of mulch and cover. Covers excluded aphids
and mulch alone had a slight repellant effect. On the last
2 dates, only covers affected aphid numbers (even though
covers over mulch were torn) and the effect of mulch dis
appeared.
Sweetpotato whitefly adults rapidly appeared on newly
uncovered plants, often within the time needed to examine
plants that had just been uncovered (Fig. IB). Covers af
fected whitefly numbers on the first 2 sample dates and an
interaction of cover and mulch occurred on the last date
when covers over mulch were badly damaged.
273

3. 0
□ Mulch ED Mulch+cover
1989
Check
Mulch
Cover
Mulch+Cover
CD
Q_
5
<D
C/)
c
5
d
c
CO
CD
10Oct 18Oct 24Oct
Date row covers removed
10-
■ Check
□ Mulch
Cover
□ Mulch+Cover
Check
Mulch
Cover
Mulch+Cover
10 Oct. 18 Oct. 24 Oct.
Date of cover removal
Fig. 1. Mean number of insects per plant on 20 (10 Oct.), 16 (18 Oct.)
and 12 (24 Oct.) plants per treatment in 1989. (A) aphid infestation level
(see text for explanation of level), (B) sweetpotato whitefly adults, (C)
pickleworm and melonworm larvae. Plants in all treatments were evaluated
on dates when covers were removed from row cover treatments.
Pickleworm and melonworm (Fig. 1C) were excluded
by intact covers. There was an interaction of mulch and
cover on the first sample date. Larvae were found in greater
numbers on mulched plants without covers than on plants
without mulch but were absent from covered plants regard
less of mulch. Once covers were no longer intact, the in
teraction disappeared (more larvae were found on mulched
plants regardless of cover).
In 1989 plants uncovered a week or more after initial
flowering produced more marketable fruit than plants un
covered before flowering (Fig. 2). Both cover and mulch
significantly affected yields when plants were uncovered
on the first date. For plants uncovered on the second and
third dates there was an interaction of mulch and cover,
274
30 Oct 3 Nov 8 Nov
Date row covers removed
Fig. 2. Yield (bushels per acre) of zucchini squash uncovered on differ
ent dates in 1989 and 1990. On each date that covers were removed,
corresponding plants in rows without covers were evaluated for insect
damage. The same rows were used later for comparing yields.
mainly because of the damaged covers over mulched rows.
Plants in these rows became infected with virus sooner than
those in rows with intact covers and thus yields were re
duced. In contrast, plants with mulch alone had higher
yields than plants with no mulch or covers.
1990. In 1990 both the lightweight and the heavier row
cover material lasted through the growing season. There
were no significant differences in yield or insect numbers
related to cover weight so the treatment that received PI7
was not included in the final analysis.
Very few plants with mosaic symptoms were found in
covered plots when covers were first removed and then
only in plots having covers that had torn or come loose.
Virus symptoms appeared somewhat later in 1990 than in
1989; 85% of plants with no treatment exhibited symptoms
on the first sample date as did 57% of those in plots with
only mulch. Almost all plants exhibited signs of infection
18 days after covers were removed.
Covered plants were protected from aphids, whiteflies
and Diaphania spp., even more so than in 1989, because
covers remained intact for a longer period of time (Fig. 3).
Only covers had a significant effect on insect numbers,
Proc. Fla. State Hort. Soc. 104: 1991.

4. V)
;
60
50
40.
30-
20
10
■
□
m
u
Check m A
Mulch I
Cover H
Mulch+Cover H
ii 1
Check
Mulch
Cover
0 Mulch+cover
■
10.
0-
■
D
m
_n
I
c
Check
Mulch
Cover H
Mulch+Cover H—
^—i I
LJLi
E
i
30 Oct. 3 Nov. 8 Nov.
Date of cover removal
Fig. 3. Mean number of insects per plant (20 plants per treatment) in
1990. (A) aphids, (B) sweetpotato whitefly adults, (C) pickleworm and
melonworm larvae. Plants in all treatments were evaluated on dates when
covers were removed from row cover treatements.
except for sweetpotato whitefly adults (Fig. 3B), which were
also affected by mulch. Whiteflies were found in greater
numbers on plants with mulch possibly because these plants
were more vigorous and perhaps more attractive to the
whitefly.
Yields were much lower in 1990, possibly because of
the later planting date (Fig. 2). There were significant ef
fects of both cover and mulch (increased yields) when rows
were uncovered on either the first or second date and an
effect of cover on the last date. Yields were significantly
higher in covered plots for each date. Yields declined
linearly as covers were removed at later dates. Yields from
plants with only row covers, however, did not decrease
significantly until the last uncovering date.
In both years, plants grew well under covers even under
conditions of high heat and humidity. Covers allowed water,
fungicide, and adequate light to reach the plants but effec
tively excluded insects and insect-vectored diseases. Mulch
also affected insect behavior. Aphids numbers were lower
on plants in mulched plots, especially in 1990 when overall
populations were lower than in 1989. Effects on virus inci
dence, however, were only apparent on the first sample
date. Once foliage covers the mulch, the repellant effect
may no longer be great enough to prevent virus vectors
from landing and probing (Adlerz and Everett, 1968;
Wyman et al., 1979).
Diaphania spp. were also affected by mulch, although
perhaps indirectly. In 1989 pickleworm and melonworm
larvae were always found in greater numbers on plants in
mulched versus bare ground plots. It is possible that the
greater vigor of the mulched plants made them more attrac
tive to egg-laying females. In 1990, however, these differ
ences were not seen. The later appearance of severe virus
symptoms in 1990 may have reduced the difference in at
tractiveness of plants in mulched and bare ground plots.
It is not clear why sweetpotato whitefly was found in greater
numbers on mulched plants in 1990 than in 1989.
In the fall in Florida, the high level of virus inoculum
present in weeds and the high numbers of Diaphania spp.
make it almost impossible to grow cucurbits. Currently the
cost of row cover material is probably too high to justify its
routine use in production of summer squash. Higher value
cucurbits may benefit, however, especially if the costs and
risks of insecticide use are weighed. If sweetpotato whitefly
becomes resistant to chemicals now used for its control,
covers may be a reasonable alternative.
Literature Cited
Adams, R. G., R. A. Ashley, and M. J. Brennan. 1990. Row covers for
excluding insect pests from broccoli and summer squash plantings. J.
Econ. Entomol. 83:948-954.
Adlerz, W. C. and H. P. Everett. 1968. Aluminum foil and white
polyethylene mulches to repel aphids and control watermelon mosaic.
J. Econ. Entomol. 61:1276-1279.
Cartwright, B., J. C. Palumbo, and W. S. Fargo. 1990. Influence of crop
mulches and row covers on the population dynamics of the squash
bug (Heteroptera:Coreidae) on summer squash. J. Econ. Entomol.
83:1988-1993.
Conway, K. E., B. D. McCraw, J. E. Motes, and J. L. Sherwood. 1989.
Evaluations of mulches and row covers to delay virus diseases and
their effects on yields of yellow squash. Applied Agricultural Research
4:201-207.
Duffus, J. E. and R. A. Flock. 1982. Whitefly-transmitted disease complex
of the desert southwest. Calif. Agric. 36(11-12):4-6.
Natwick, E., A. Durazo III, and F. Laemmlen. 1988. Direct row covers
for insects and virus diseases protection in desert agriculture. Plasticul-
ture 78:35-46.
Perring, T. M., R. N. Royalty, and C. A. Farrar. 1989. Floating row covers
for the exclusion of virus vectors and the effect on disease incidence
and yield of cantaloupe. J. Econ. Entomol. 82:1709-1715.
Purcifull, D. E., G. W. Simone, C. A. Baker, and E. Hiebert. 1988. Im-
munodiffusion tests for six viruses that infect cucurbits in Florida.
Proc. Fla. State Hort. Soc. 101:401-403.
Wyman, J. A., N. C. Toscano, K. Kido, H.Johnson, and K. S. Mayberry.
1979. Effects of mulching on the spread of aphid-transmitted water
melon mosaic virus of summer squash. J. Econ. Entomol. 72:139-143.
Yokomi, R. K., K. A. Hoelmer, and L. S. Osborne. 1990. Relationships
between the sweetpotato whitefly and the squash silverleaf disorder.
Phytopathology 80:895-900.
Proc. Fla. State Hort. Soc. 104: 1991. 275