2007 Extension Research Report
Insect Management
EFFICACY OF FOLIAR INSECTICIDES FOR CONTROL OF
SILVERLEAF WHITEFLY ON SNAP BEANS
Alton N. Sparks, Jr., University of Georgia Cooperative Extension, Department of Entomology, Tifton,
GA 31793, asparks@uga.edu
most of the dirt, debris and adult whiteflies. The
three plants were placed into a large paper grocery
bag, sealed (folded over twice and stapled) and
labeled. The bags were held to allow for late
instar nymphs to complete development, emerge
as adults and die (bags were held for about 6
weeks before processing). At the end of this
period, the plants were held by the stem and
vigorously shaken inside the bag to dislodge the
dead adult whiteflies. The plants and large debris
were removed from the bag. The bag was then
emptied into a plastic bowl. Whiteflies in the bowl
and whiteflies observed stuck to the bag were
aspirated and placed into glass scintillation vials.
After all the samples were processed, whiteflies
were counted or the numbers estimated based on
volume determination. Where number of
whiteflies was low (less than 500), the sample was
counted with aid of a dissecting microscope.
Samples with obviously high counts were
estimated by aspirating whiteflies into a 1 ml
pipette to determine the volume of whitefly adults
present. Two of these samples with moderate
densities (about 700 each) were also visually
counted. The high density counts samples were
estimated from a published regression equation
and were also calculated based on the whiteflies
per ml in the two moderate density counts. The
published regression equation estimated 9400
whiteflies per ml; whereas, the two moderate
density counts estimated 7725 whiteflies per ml.
Data were analyzed with the PROC
ANOVA procedure of PC-SAS. Where significant
differences were detected (P<0.05), means were
separated with LSD (P=0.05). Data was analyzed
using high density estimates based on the
published regression and based on the calculations
from the moderate counts. Finally, because of
Introduction
The sweetpotato whitefly (aka silverleaf
whitefly), Bemisia tabaci, is a severe pest of a
wide variety of vegetable crops grown in the fall
in some areas of south Georgia. This pest tends to
be most severe in areas with concentrated
production of vegetables and cotton. Legume
crops are a favored host and extremely high
populations can develop on snap beans grown in
the late summer and fall. This test was conducted
at the University of Georgia’s Horticulture Farm
in Tifton, Georgia, to evaluate the efficacy of
foliar applied insecticides for control of silverleaf
whitefly on snap bean.
Materials and Methods
Snap beans, var. Carlo, were direct seeded
on 7 Aug., 2007, with a single row on a six foot
bed. The test was conducted as a randomized
complete block design with four replications.
Individual plot size was one row (36 in. treated)
by 17 feet. Insecticide treatments were applied
with a CO2 pressurized backpack sprayer (60 PSI)
in a total volume of 40 GPA with 3 hollow cone
nozzles per row (one over-the-top, 2 on drops).
Whiteflies were allowed to become well
established in the test prior to initiation of
treatments. Treatments were applied three times
on a weekly schedule (29 Aug., 5 and 12 Sept.).
Insecticide treatments evaluated were: Oberon
2SC at 7 and 8.5 oz/ac; Assail 30 WDG at 4 oz/ac,
with and without DyneAmic at 0.5% v/v; Knack
0.86 EC at 8 oz/ac; and Courier 40SC at 9 oz/ac.
A non-treated control was included for
comparison.
On Sept. 14 (two days after the last
application), three plants were collected from each
plot. Plants were shaken vigorously to remove
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extreme variation in a few treatments, the data
based on the test calculations was also analyzed
after a LOG transformation.
suppress populations but did not statistically
separate from the check. Assail appeared to work
better with addition of DyneAmic, but neither of
these treatments statistically separated from the
check.
Prior similar studies have shown Knack to
work well for control of whiteflies in snap beans.
Oberon and Courier performed better than in prior
studies, however the earlier studies evaluated
efficacy after one or two applications, versus three
applications in this test. Assail has consistently
failed to provide control of whiteflies in snap
bean, however, has also consistently provided
excellent control of the same pest at the same time
in squash.
Results and Discussion
Variation was relatively high in some
treatments, making mean separation less ‘clean’
than the large differences in the means would
indicate. The Check, both Oberon treatments, and
the Assail+DyneAmic treatment showed the
greatest inconsistency.
The trends in the data are relatively
consistent and mean separation after LOG
conversion clearly show the best efficacy with
Knack, followed by Courier and the high rate of
Oberon. The low rate of Oberon appeared to
Table 1. Whitefly adult emergence from insecticide treated snap bean plants, Tifton, Georgia,
2006.
Adults emerged per 3 leaves
Treatment
Published Reg.1
Test Calculation2
Log of Test
Calculation3
Check
1900. a
1592. a
1219. a
Assail
1363. a
1119. a
1041. a
Assail+DyneAmic
802. ab
697. ab
641. a
Oberon 7 oz
757. ab
665. ab
393. a
Oberon 8.5 oz
62. b
62. b
38. b
Courier
48. b
48. b
43. b
Knack
6. b
6. b
6. c
Numbers within columns followed by the same letter are not significantly different (LSD; P=0.05).
1
High density counts (over 500) were estimated based on published regression of volume of whiteflies
against number of whiteflies.
2
High density counts (over 500) were estimated based on numbers of whiteflies per volume in moderate
density counts in this test.
3
Mean separation performed on Log transformed data, with high density estimates based on test data
calculations.
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