Group Title: Environmental Entomology, 34 (4). pp. 857-865.
Title: Effects of living and synthetic mulch on the population dynamics of Whiteflies and Aphids, their associated natural enemies, and insect-transmitted plant diseases in Zucchini.
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Title: Effects of living and synthetic mulch on the population dynamics of Whiteflies and Aphids, their associated natural enemies, and insect-transmitted plant diseases in Zucchini.
Series Title: Environmental Entomology, 34 (4). pp. 857-865.
Physical Description: Book
Creator: Frank, Daniel L.
Liburd, Oscar E.
Affiliation: University of Florida -- Entomology and Nematology Department
Publication Date: 2005
Subject: Homoptera   ( lcsh )
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Bibliographic ID: UF00083961
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.


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Effects of Living and Synthetic Mulch on the Population Dynamics of
Whiteflies and Aphids, Their Associated Natural Enemies, and
Insect-Transmitted Plant Diseases in Zucchini


Department i i ..... .. and Nematology, University of Florida, Gainesville, FL 32611

Environ. Entomol. 34(4): 857-865 (2005)
ABSTRACT Living and synthetic mulches were evaluated for control of the silverleaf :,,. :I,
Benisia ._. .**.. : Bellows and .. .... and aphids in zucchini plantings. Two living mulches,
buckwheat, Fagopyrmn esculentum Moench, and white clover, Trifolium repens L., and two synthetic
mulches 11 .... i white) were evaluated during the fall of 2002 and 2003. Results from pan-traps,
II sticky traps, and foliar counts showed that .. i. i and buckwheat mulches consistently had
fewer numbers of adult I ..;. I.. and aphids compared with the standard white mulch treatments.
In 2003, a significant increase in the abundance of natural enemies was recorded in all treatments.
living mulch treatments had higher natural enemy populations than synthetic mulch and bare-ground
treatments. However, there were no differences in the species diversity of natural enemies found
between treatments. The effectiveness of mulchesfor. ..-, ii, ..... .., .. i: 1.. i ..i the
incidence of squash silverleaf disorder were inconsistent between years. Additional data taken at the
end of the 2003 season revealed that two viral strains (PRSV-W and WMV-2) were present in the field.
However, visual symptoms associated with these viral diseases did not occur until the end of the season.

KEY WORDS rnulch, I..:. :. aphid, zucchini,

ida. During the 2002 2003 field season, Florida grow-
ers harvested >18,000 ha of cucurbits, valued at more
than $170 ...1.=: .. (NASS 2004). Despite these num-
bers, rising costs associated with preventing insect
related problems, combined with cheaper imports
from Mexico, have threatened the production and
value of many Florida cucurbits. Currently, crop
plant physiological disorders and insect-transmitted
diseases have become serious problems for many
growers around the state.
One of the most damaging plant physiological dis-
orders in cucurbits is squash silverleaf (SSL) disorder.
SSL is associated with the feeding of immature white-
flies, Bemisia ..,. .^ Bellows and Perring, and is
characterized by silvering of the adaxial leaf surface
and blanching of fruit (Yokomi et al. 1990, Costa et al.
1993. Jim6nez et al. ). Variations in the feeding
densities of immature i1. I. have been shown to
affect the severity of SSL symptoms, which can de-
velop in as little as 14 d (Yokomi et al. 1990, Schuster
et al. 1991, Costa et al. 1993).
The most important vectors of plant viruses include
aphids, which have been known to transmit 275 dif-
ferent viral diseases (Nault 1997). Crops in the Cu-

SCorresponding author: Entomology and Nematology, Bldg- 970,
Natural Area Drive, Gainesville, F. 32611 (e-mail: oeliburd@

natural enemies

curbitaceae are highly susceptible to several of these
insect-trarnsmitted viruses. Important viruses affecting
cucurbits in Florida include zucchini 1:. mosaic
virus (ZYMV), watermelon mosaic virus-2 (WMV-2),
cucumber mosaic virus (CMV), and papaya ringspot
virus-watermelon strain (PRSV-W) (Adlerz 1978,
Provvidenti et al. 1984, Purcifull et al. 1988). Symp-
toms of these viruses include pronounced reduction in
growth; the oc .... .i '. mosaic, and blis-
tering of leaves; and reduced fruit set (Demski and
S1 .11 I 1974, Lisa et al. 1981). In addition, the fruits
harvested from infected plants are often malformed
and distorted, rendering them unmarketable (Blua
and Perring 1989).
Several aphid species have been associated with
transmitting these viruses in a stylet-borne nonpersis-
tent manner (Coudriet 1962, Lisa et al. 1981, Adlerz
1987. Castle et al. 1992). Stylet-borne viruses are char-
acterized by having no latent period within the vector
and having an infectivity time of a few hours or days.
This, coupled with the rapid ...:.: and inocula-
tion of the virus during brief test probes into the plant
epidermis, can .I. rapid spread throughout a given
In addition to transmitting viruses and causing plant
disorders, heavy infestations of 1i. ,, :i.. and aphids
generally cause a reduction in plant vigor (Barlow et
al. 1977, Buntin et al. 1993). The excretion of honey-
dew by these insects can serve as an important me-

0046-225X/05/0857-0865$04.00/0 d 2005 Entomological Society of America


dium for promoting growth of sooty mold fungi (Cap-
nodium spp.), which can further reduce plant vigor
and yield (Byrne .. I t-1. 1990, Palumbo etal. 2000).
The unpredictability and severity of these cucurbit
pests and associated diseases in conjunction with in-
jury from secondary pests makes efficient manage-
ment strategies necessary in a cucurbit production
Currently, pesticides play a major role in the pest
management of cucurbits. However, this control strat-
egy can become problematic, because frequent use of
insecticides can ,.,:.:. .11i, increase production
costs as I1 as increase the potential for resistance. In
addition, a heightened awareness of the .' .... ,i ef-
fects of pesticides to nontarget organisms and the
environment has led many to search for alternative
methods to regulate pests in cucurbits.
Several studies have evaluated both living and syn-
thetic mulches independently for control i..i Ii.
(B. argeontifolii) or aphids. These studies have shown
successful reduction in population densities of white-
flies and .Ji1... i, 1.1. i ..- the onset and spread of
associated insect-borne diseases (Brown et al. 1993,
Summers et al. 1995, Hooks et al. 1998, Summers and
:; : .. .. 2002). Hooks et al. (1998) found that living
mulches were effective in reducing multiple pest com-
plexes and the incidence of associated diseases. Re-
cently, Surmmers et al. (2004) found that colonization
by B. -:^ t.. and the incidence of aphid-transmit-
ted diseases were reduced i I. muulch com-
pared with unmulched plots.
Some debate exists as to which mulching system
(i.e., living mulch or synthetic 11. ,. ) offers the
best potential for management of i, i. and
aphids. Our hypothesis was that the use of living and
synthetic (reflective) mulches would suppress the ac-
tivity of i1,.. li, and aphids, thus reducing viral
infection and the occurrence of plant disorders. The
specific objective for this research was to study the
effects of living and synthetic (reflective) mulch on
the population dynamics of I .... i. and aphids,
their associated natural enemies, and insect-transrmit-
ted plant diseases. Also, identifying which mulching
system offers the best habitat for these beneficial
could help shape production practices in the future.

Materials and Methods
Field research was conducted at the University of
Florida, Plant Science Research and Education Unit
located in Citra, FL. during the fall growing season.
Trials were conducted using standard production
practices. Zucchini, Cucurbita pepo L., cultivar Arm-
bassador, were planted from seeds on raised beds
spaced 1.2 m apart. Mulches used during these studies
included two synthetic mulches (white and .. i. -
tive), two living mulches (buckwheat and white clo-
ver), and a bare ground (control). Buckwheat, Fago-
pyrujm esculentum Moench, and white clover,
T.. .'" :. repens L., mulches were seeded by hand. In
2002. individual plot size was i 14 m and sown with
eight rows. Living mulches were planted 1 d after

zucchini seeding on top of rows. In 2003, because of
time constraints and labor reduction, individual plot
size was reduced to 14 by 12 m and sown with seven
rows. Living mulches were seeded 1 wk before zuc-
chini planting between rows to .11 a greater estab-
lishment period and to reduce competition between
the living mulch and zucchini plants. Treatments were
replicated four times in a randomized complete block
design, with blocks spaced 15 m apart.
Trap Sampling. Adult I.... II. were monitored
using unbaited Pherocon AM traps (Y ii -.: I YS:
Great Lakes Integrated Pest Management [IPMj,
Vestaburg, MI) placed within interior zucchini rows.
Trap heights were adjusted relative to plant height.
Each treatment plot contained a total of three YS traps.
One trap was placed in the center of the treatment
plot, and two others were placed at -t... ;I ends of
the treatment plot forming a diagonal line All YS traps
were placed in the field 2 wk after zucchini planting.
YS traps were left in the field for a 24-h duration once
per week until final harvest.
Alate aphids were monitored using blue water pan-
traps (Packer Ware Bowls, Gainesville, FL). Pan-traps
had a diameter of 15.5 cm and contained .250 ml of
5% detergent solution (Colgate-Palmolive Co., New
York, NY). Traps were placed at mid-plant height
within interior zucchini rows. Three water pan-traps
were used per plot. Traps were placed in the field 2 wk
after zucchini planting. The arrangement of the water
pan-traps and the time period in which they were
exposed in the treatment plots were similar to YS traps.
In 2003, clear water pan-traps (Pioneer/Tri-State Plas-
tics, Dickson, KY) were used in addition to blue pan-
traps. Clear pan-traps were square, with a diameter of
15.5 cm. One clear water pan-trap was placed in the
center of each plot and treated in a similar manner as
the blue pan-traps.
Foliar Sampling. Nine plants from each plot were
randomly selected for counting adult i.... Ii, and
aphids (apterae and alate). Foliar .,..1;I. was initi-
ated 4 wk after planting and conducted weekly until
final harvest. One leaf was sampled per zucchini plant,
which was partitioned according to plant stratum (up-
per, n = 3; medium, n = 3; lower, n = 3 leaves),
.II .1 i of9 leaves sampled per plot (36 leaves/
treatment). If aphid densities were high (>100 per
leaf), counts were taken from one-half of the leaf and
used to estimate the number on the whole leaf All
:.,1 iH adults, aphids, and other pest species encoun-
tered on the leaf surfaces were recorded.
To estimate the number of i.,. :i nymphs, 1-in-
diameter circular leaf disks were removed using a cork
borer from nine leaves (selected from foliar counts).
Leaves were stored in plastic bags and transported to
the laboratory in an ice chest. Leaf disks were re-
moved from oneside ofs i. i i.t i I .. theleaf
tip and petiole and halfway between the mid-vein and
leaf edge (Gould and Naranjo 1999). Leaf disks were
removed in the Fruit and Vegetable IPM laboratory,
and examined under a X40-dissecting microscope. All
i,,. li nymphs encountered on the leaf surfaces
were recorded.

Vol. 34, no. 4


Natural Enemy -. , Natural enemies were
sampled using in situ counts. Leaves from six plants in
each plot were randomly selected. In 2002, nine leaves
from each plant were randomly selected, and in 2003,
six leaves from each plant were randomly selected for
visual identification of beneficial arthropods. Sam-
:i.._ was initiated 4 wk after planting and conducted
weekly until the end of the season.
Physiological Disorder Evaluation. Visual observa-
lions for symptoms of squash silverleaf disorder were
recorded weekly from 10 randomly selected zucchini
plants within the interior rows of each treatment plot.
The percentage of plants displaying visual symptoms
of silverleaf (silvering on adaxial leaf surface) was
taken until the end of the season. Silverleaf symptoms
were rated on the new leaf growth, with the severity
rated on a scale of 0-5 as indicated by Paris et al.
Disease Identification. Leaves from four randomly
selected plants exhibiting virus infection (i.e., I II .
ing, mosaic, blistering) were collected from each plot
(16 leaves per treatment), and taken to the University
of Florida, Vegetable Entomrology Laboratory for dis-
ease identification. Each sample was tested for eight
viral diseases using enzyme-linked immunosorbent as-
say (ELISA) procedures specific for each virus. The
viral diseases that plants were tested for included
CMV, PRSV-W, squash mosaic virus (SMV), tobacco
streak virus (TSV), tomato spotted wilt virus (TSWV),
watermelon leaf mottle virus (WMV), WMV-2, and
ZYMV. All plates containing samples were marked for
visual positives and read on an ELISA plate reader
(Bio-Tek, Winooski, VT).
Statistical Analyses. Data from arlhropod counts
and physiological disorder and disease ....: .
analyzed by repeated measures analysis of variance
(ANOVA) using the SAS GLM procedure. All data
were square root transformed to stabilize variances,
and means were separated with least significant dif-
ference test (LSD) a = 0.05 (SAS Institute 2002). In
addition, predators and parasitoids were visually re-
corded and identify ed to order in the field. The number
of insects identified in each order is presented as
percentage ofthe totalnumber, I t. I.. 1. :. it ,
the year. Similarly, pest individuals were recorded in
the same manner with aphids and io 1l.. .replacing
the title Heteroptera.

Trap 5- 2n.l i- In 2002, YS traps within plots
containing white mrulch had ,i, ..... ... white-
fly adults, B. argentifolii, than the bare ground (con-
trol), .. Il.. :. clover, and buckwheat treatments
(Table 1). Traps within buckwheat mulch plots had
... i;:.ii fewer adult i.,. 1i,. compared with all
other treatments. Similarly in 2003, YS traps within
buckwheat mulch had significantly fewer adult white-
flies than white, clover, and bare-ground treatments
(Table 1). Throughout the 2003 season, traps within
reflective mulch had ...-. ...-ii fewer .-I 11i
adults compared with all other treatments.

Table 1. Mean SEM no. adult whitellies per YS trap in
zucchini at Citra, FL. for all sampling dates

2002 2003
White 15.4 1.8a 3.6 0.5a
Reflective 9.8 1.2e 1.1 0.2c
Buckwheat 7.7 1. d 1.8 0.2b
Clover 10.3 1.5be 4.6 0.7a
Bare ground (control) 13.4 1.8b 4.3 + 0.6a

Means followed by the same letter are not significantly different
(F 0.05, LSD test).
For 2002, F 5.75; df 4,84; P < 0.0004; for 2003, F 13.21; df
4,72; P < 0.0001.

During 2002, blue pan-traps within white mulch
treatments caught ,..i... 'i more alate aphids
compared with each of the other treatments, which
did : : .. ... : ...i (Table2). ..... i ... ') 03,
more alate aphids were caught over white mulch com-
pared with all other treatments (Table 2). Unlike in
2002, blue pan-traps within reflective mulch had sig-
nificantly fewer alate aphids than white, buckwheat,
and clover, but was borderline insignificant with the
bare-ground treatment. J ..... the number of alate
aphids trapped in clear pan-traps was also ..i. .
less in reflective than white, bare ground, and clover
but was similar to the buckwheat mulch treatment
(Table 2). In 2003, the total number of alate aphids
captured in clear pan-traps compared with the num-
ber captured in blue pan-traps was not ., ,
1,11 .. .: (F = 3.6; df = 1,4; P = 0.0573). However,
when comparing these traps by treatment, significant
differences were found between trap types in bare
ground using the LSD test for pairwise comparison
(t = -2.76, Pr > t = 0.0060).
..,i 1, '-- iu n2002, plantswithin white mulch
had .: more adult N i,,L. :,. than buck-
wheat and clover but had similar numbers to reflective
mulch and bare-ground treatments (Table 3). The
number of apterous and alate aphids did not differ
significantly between treatments (Table 3). In 2003,
the number. I I... : I..:. :i. o i apterous aphids did
not differ ._e... ...i between treatments (Table 3).
However, i,_.,, ... 1 fewer alate aphids were re-
corded on plants in reflective mulch compared with
white, clover, and bare-ground treatments but had
similar numbers to buckwheat (Table 3). Data col-

Table 2. Mean SEM no. alate aphids per pan-trap in zucchini
at Citra, FL, for all sampling dates

2002 2003 2003
(clear pan-traps)
White 15 0.2a 0.8 1.2 0.3a
Reflective 0.3 O.0.l .2 0 O.l 0.2 O.le
Buckwheat 0.5 0.4 0.b 0.3 i .lbe
Clover 0.5 0.1b 0.4 0.1b 0.8 0.3ab
Bare ground (control) 0.5 0.3 0.1bc 0.9 0.2a

Means followed by the same letter are not significantly different
(F 0.05, LSD test)
For 2002, blue pan-traps, F = 27.82; df 1= 4,84: P < 0.0001; for 2003,
blue pan-traps. F 9.12; df 4,72; P < 0.0001: for 2003, clear-pan traps,
F 4.3, df 4,72: P 0.0036.

August 2005


Table 3. Mean SEM no. aphids and whiteflies per zucchini
leaf in Citra, FL. for all sampling dates

Whiteflies Aphids Aphids
(adult) (apterous) alatee)
White 12.6 2.3a 0.5 0.3 02 0.1
Reflective 12.3 3.1 a 0.2 01 0. 0.1
Buckwheat 5.9 1 1.6b 0.6 1 0.4 0.1 1 0.1
Clover 5.7 1 1.7b 0.2 7 0.2 0.4 0.1
Bare ground (control) 8.9 1 1.8ab 0.5 0.2 0.3 0.1
White 4.1 0.9 8.5 3.4 1.0 o0.2b
Reflective 2.6 1 0.7 2.1 0.9 0.1 0O.Oc
Buckwheat 2.9 0.8 4.4 1.7 0.7 1 0.2be
Clover 4.5 1 0.9 11.7 3.9 2.0 1 0.7a
Bare ground (control) 7.1 1.5 7.3 2.2 1.8 0.5a

Means followed by the same letter are not significantly different
(P 0.05, LSD test).
For adult whiteflies in 2002, F 4.37; df = 4,72; P < 0.0032; for
apterous aphids in 2002, F = 0.90; df 4,72; P = 0.4705: for alate
aphids in 2002, F = 1.45 df = 4,7: = 0.2265; for adult whiteflies in
2003. F 2.47; df 14,32; P 0.0(l 1; for apterous aphids in 2003, F
2(08; df 4,32; P 0 1064; for alate aphids in 2003, F 7.95: df = 4,32:
p < 0.0001

elected from both field seasons revealed that aphids and
.. ii. were the dominant pests recorded in the
field. In 2002, i .-; I. comprised the majority (85%)
of pest individuals sampled (Fig. 1 a), whereas in 2003,
aphids comprised the i- ..: (63%) of pest individ-
uals (Fig. lb). In addition, leaf-mininig flies (Diptera:
Agromyzidae) were a minor pest in 2003 but were
never recorded in 2002 (Fig. la and b).
In 2002, there were no significant differences in the
number of immature I-.. !:i found between treat-
ments (F = 1.81; df = 4,312; P = 0.1262). Similarly, in
2003, there were no si .. ..... .1:1 .. .. .in the num-
ber of immature 1-... :i.. found between treatments
(F = 1.20; df = 4,208; P = 0.3101). However, signifi-
cantly more immature i,.,. :i1 were recorded on
the lower plant stratum of zucchini plants compared
with the middle or top plant strata for all treatments
in 2002 (F = 75.39; df = 2,6; P < 0.0001; Fig. 2a) and
2003 (F = 26.6; df = 2,6; P = 0.0010; Fig. 2b).
Natural Enemies. In 2002, there were no significant
differences in the number of natural enemies found
between treatments (Table 4). In 2003, clover mulch
had significantly higher numbers of natural enemies
than white, 1 i I and bare groundbut had similar
numbers to buckwheat mulch (Table 4). Data col-
lected from both field seasons showed that arthropods
in the order Araneae were the dominant natural en-
emy (Fig. 3a and b). These representations of the
percentage of natural enemies found within the field
showed more arthropod abundance in 2003.
Physiological Disorder Evaluation, In 2002, signif-
icantly more symptoms of SSL were recorded in plants
grown on bare ground than in white, reflective, and
clover but had similar scores to buckwheeat mulch
(Table 5). Throughout the season, plants on reflective
mulch had significantly less severe symptoms of sil-
verleaf than all other mulch treatments with the ex-
ception of clover (Table 5). During 2003, plants on

white and reflective mulches had significantly more
severe symptoms of SSL than all other treatments,
whereas plants on bare ground and clover mulch had
significantly less symptoms (Table 5).
Disease Identification. Data taken at the end of
the 2003 season revealed that two viruses, PRSV-W
and WMV-2, were present in the field. ELISA tests
found four cases of PRSV-W within plants on the bare
ground and clover mulch treatments, and one case of
PRSV-W was found in the white, ii : and buck-
wheat mulch (Fig. 4). Two cases of WMV-2 were
found within plants on the bare-ground treatments,
and one case (WMV-2) was found in the clover mulch
(Fig. 4). There were no significant ,1i, .. in the
number of virus-infected plants between treatments
(F = 1.37; df = 7,19; P = 0.3007).

Insect Response to Mulches. During the 2002 field
season, results from trap catches showed that white
mulch consistently had higher populations of adult
' :.,. :!:. and alate aphids compared with the other
mulch treatments, including bare ground (control).
However, the 2003 field season revealed no significant
.Irt ..... .. between white mulch, clover, and bare-
ground (control) treatments with respect to YS and
clear pan-trap catches. These results are consistent
with Adlerz and Everett (1968), who showed that
white (polyethylene) mulches had higher populations
of aphids compared with reflective mulch and bare
ground. T. I ... -I: ., farmers have used white or
white on black mulches in Florida for fall cucurbit
production. Itis unclear why ,. 1I.I .. I ... i ...I alate
aphids responded strongly to white mulch, because
previous research has shown that they are attracted to
. i: colors in the visible light spectra (' ......
C0 I llI both trap and foliar counts showed that
plants grown on .. II. and buckwheat mulches
consistently had fewer adult ',,l. i-, and aphids
compared with the other mulch treatments, including
bare ground. The suppression of, i..: 11. and aphids
by i J1. i mulch was not surprising. There have
been several reports of the use of reflective mulches
to suppress I.I I. and aphid activities (Adlerz and
Everett 1968, 'I\ I '1 .. and Moore 1968, Csizin-
szky et al. 1995, Summers et al. 2004). Reflective mulch
is currently being suggested as an alternative to con-
ventional pesticides and white or black synthetic
mulches to suppress I. 11 and aphid activities in
selected vegetable crops. The suppression of adult
: and aphids on zucchini plants with buck-
wheat mulch has also been observed in Hawaii (Hooks
et al. 1998). However, information on whether or not
their findings were applicable to north Florida situa-
tions was unavailable. Buckwheat is an annual plant
that completes its life cycle in Florida in 6 wk. It
:! .. profusely and attracts beneficial insects to the
cucurbit crop. Buckwheat may have potential in sus-
tainable (organic) cucurbit production in Florida in
the future as more research is conducted. Clover

Vol. 34, no. 4



SAphids 6%

* Whiteflies 85%

O Lepidopterans 9%

1% _1

SAphids 63%
* Whiteflies 32%
o Lepidopterans 1%
* Dipterans 4%

Fig. 1. (a) Percentage of total pest individuals sampled in zucchini at Citra, FL, categorized by taxon (2002). (b)
Percentage of total pest individuals sampled in zucchini at Citra, FL, categorized by taxon (2003).

mulch was difficult to establish and does not seem to
be suitably adapted to north Florida conditions. As a
result, its use is not appropriate in north Florida cu-
curbit production systems.
The effectiveness of mulches for controlling imma-
ture whitefly numbers and the incidence of SSL were
inconsistent between years. This may be a function of
differences in population pressure caused by environ-
mental conditions. The total average whitefly adult
and nymph populations were higher in 2002 than in
2003. Similarly, silverleaf severity was higher in 2002
compared with 2003.
Plant Strata. Plant strata played an important role in
feeding location of immature ~1, ii... II. During 2002

and 2003, it was clear that the location of immature
\ i,,-. I i. was restricted to the lower plant strata for
all treatments. These results are consistent with Sim-
mons (1994), who saw 90 95% of Bemisia tabaci eggs
and nymphs on the lower plant strata of various crops.
Higher nitrogen content in older leaves (Bentz et al.
1995) or increased protection from pesticides, natural
enemies, and environmental factors offered by leaves
located on the lower plant strata (Chu et al. 1995, Liu
and Stansly 1995) may have played a role in the lo-
cation of nymphal \vi. I 1i. .i. Similarly, older zucchini
leaves have less dense trichomes, which can allow for
easier oviposition of eggs and attachment by nymphs
(Butler et al. 1986, Kishaba et al. 1992, McAuslane

August 2005



S 45
4. 40
'S 35
S 30
S 20
E 15
o 10
: 0

White Reflective Buckwheat



White Reflective Buckwheat Clover


Fig. 2. (a) Populations of immature whiteflies on zucchini plant strata in Citra, FL (2002). (b) Populations of immature
whiteflies on zucchini plant strata in Citra, FL (2003).

1996). In either case, more research must be con-
ducted so that efficient sampling and control of
nymphal B. argentifolii populations can occur in zuc-
chini and other cucurbit crops. Management tactics
involving monitoring or chemical controls should be
directed to the lower leaves because the majority of
immature \.ih. i .. are restricted to this area.

Table 4. Mean SEM no. natural enemies per zucchini leaf in
Citra, FL, for all sampling dates
2002 2003
White 0.04 1 0.02 0.33 1 O.Obc
Reflective 0.04 1 0.02 0.26 1 O.Oc
Buckwheat 0.02 1 0.01 0.41 1 0.lab
Clover 0.01 0.01 0.48 1 0.1a
Bare ground (control) 0.06 0.02 0.28 1 O.Obe
Means followed by the same letter are not significantly different
(P = 0.05, LSD test).
For2002,F =2.13; df 4,72; P 0.0852; for2003, F 2.72; df 4,60;
P 0.0377.

Natural Enemies. In 2003, a significant increase in
the abundance of natural enemy species was seen
throughout all treatments. The reasons why such a
high abundance was seen in 2003 is unknown, but
differences in ambient temperature and rainfall may
account for some of the variations observed. Living
mulch treatments had higher natural enemy popula-
tions than the synthetic mulch and bare-ground treat-
ments. These results support the natural enemy hy-
pothesis proposed by Root (1973) that increased plant
diversity leads to increased natural enemy densities.
However, there were no differences in the diversity of
natural enemies found between treatments (data not
shown). Understanding which natural enemies are
present with respect to the various mulch treatments
allow for future research to be conducted on the
efficiency of these insects with appropriate mulch
treatments for control of zucchini pests and prevents
unnecessary efforts to introduce natural enemies that
are already present.


* Top
* Middle
* Bottom


* 2.5

0) 2
EE 1

t 0.5

I 0

* Middle
* Bottom


Vol. 34, no. 4



*Araneae 89%
* Coleoptera 8%
* Hymenoptera 3%


SAraneae 39%
Coleoptera 29%
390% 0 Heteroptera 12%
O Diptera 8%
U Hymenoptera 7%
Neuroptera 3%
Other- 2%

Fig. 3. (a) Percentage of total natural enemies sampled in Citra, FL, categorized by order (2002). (b) Percentage of total
natural enemies sampled in Citra, FL, categorized by order (2003).

Physiological Disorder and Plant Disease. The in-
cidence of SSL disorder was inconsistent between

Table 5. Mean + SEM silverleaf score per treatment in zuc-
chini at Citra, FL, for all sampling dates

2002 2003
White 4.1 O0.1b 1.5 O.1la
Reflective 3.7 O.le 1.4
Buckwheat 4.2 O.lab 1.1
Clover 3.9 0.1 1.0 0.1be
Bare ground (control) 4.4 0.1a 1.0 0.1e

Means followed by the same letter are not significantly different
(P = 0.05, LSD test).
For 2002, F = 12.19; df = 4,48; P < 0.0001; for 2003, F = 11.50;
df = 4,72; P < 0.0001.

years. These inconsistencies may have been influ-
enced by a number of factors, such as the variability
of insect numbers between years and weather. The
fact that relatively few nymphal iN i. i1i. are needed
to induce SSL may have also compounded the prob-
lem. Additionally, throughout the 2002 and 2003 field
seasons, no detrimental effects on plant growth were
observed from SSL symptoms. It is unclear why SSL
disorder never became a problem because a number
of negative physiological factors are known to occur.
In 2002, zucchini plants never exhibited visual
symptoms associated with viral diseases. This may
have been caused in part by the low incidence of
aphids seen within the field for that year. Despite high
aphid numbers and the occurrences of two associated

August 2005


U) 7
a 6

r 1





Fig. 4. Mean number of virus infected plants per treatment in Citra, FL (2003).

viral diseases in 2003, visual symptoms of WMV-2 and
PRSV-W did not occur until zucchini matured and did
not seem to have an effect on plant growth. Although
white mulch had a greater incidence of pests, it had
only one case of PRSV-W. Adlerz and Everett (1968)
noted that, although more aphids were caught over
white mulch compared with reflective and bare
ground, the incidence of viral diseases was signifi-
cantly less than the bare ground. They believed that
this occurred because one or more of the aphid species
attracted to white mulch were not effective in virus
transmission. Overall, no significant differences were
found between the different mulch treatments.
Economics. Ease of incorporation can play a central
role for whether or not a particular tactic is incorpo-
rated into an IPM program. The cost of buckwheat
seeds used for both field seasons was $74. Although
buckwheat is an annual, it can be managed so that it
produces seed throughout the year and does not re-
quire subsequent planting later in the season. White
clover, a perennial, plus innoculant cost $68 for both
field seasons. Alternately, white mulch cost $120, and
reflective mulch was $145 for both field seasons.
Although the costs of living mulches were less than
synthetic mulches, they required additional upkeep
and management. For instance, living mulches re-
quired additional water and had to be maintained so
that they did not become a weed problem later in the
year. Overall, synthetic mulches were easier to main-
tain and required no establishment period before zuc-
chini were planted. In addition, no special watering
features or additional drip lines were needed in plots
treated with synthetic mulch.
In our experiments, it seems that the net gains with
respect to the suppression of \.ii.i. i.. and aphids
with living mulches were erased when the additional
upkeep and management were taken into consider-
ation. More research is needed on potential choice of
living mulch suited for Florida conditions before living
mulches are recommended. It seems for now that
reflective mulch in combination with a reduced-risk

insecticide may offer a better alternative to manage
i. i, 11.. and aphids in northcentral Florida zucchini

We thank S. Webb for the use of laboratory equipment
and assistance in editing the first draft of this manuscript,
F. Slansky for assistance in editing the first draft of this
manuscript, S. Legaspi for help in id.-iint llf% whitefly
nymphs and natural enemies, S. Taylor and staff at the Citra
Plant Science Research and Education Unit located in Citra,
FL, A. Ar6valo for help with statistics, and everyone at the
University of Florida Fruit and Vegetable IPM laboratory in
Gainesville, FL. Funding was provided by USDA T-STAR-C
Grant 721498712. This is Florida Experiment station publi-
cation article R-10531.

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Received for publication 25 November 2004, accepted 2 June

August 2005

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