Alton N. Sparks, Jr.1 and David G. Riley2
University of Georgia
Dept. of Entomology
P.O. Box 1209
Tifton, Georgia 31793
P.O. Box 748
Tifton, GA 31793
The silverleaf whitefly is a key pest of many vegetable crops grown in south
Georgia. Its populations are somewhat sporadic with the most severe infestations
occurring in susceptible vegetables grown in the fall. In areas with consistent fall pest
pressure producers of higher value susceptible crops rely heavily on neonicotinoid
insecticides applied in a preventative manner. Producers of lower value crops or in areas
with inconsistent pest pressure need highly efficacious foliar insecticides for control of
whitefly in a more curative approach. This test was conducted to evaluate selected foliar
insecticides for control of silverleaf whitefly on snap beans.
Materials and Methods
A small plot trial was conducted in a planting of snap beans at the University of
Georgia’s Horticulture Hill Farm in Tifton, Georgia. Snap beans (var. zodiac) were direct
seeded on 2 Aug., 2004, with two rows planted on six foot beds (rows on 3 foot centers).
Experimental plots were 2 rows (one bed) wide by 20 feet, with 3 foot allies down the
row and a fallow six foot bed between planted beds. Plots were arranged in a randomized
complete block with 4 replications. Treatments were applied on 23 and 31 August with a
CO2 pressurized backpack sprayer (60 PSI) in 30 GPA with three hollow cone nozzles
per row (one over-the-top, 2 on drops).
Insecticides evaluated were: Knack 0.86EC at 8 and 10 oz/ac; Oberon 2SC at 8.5
oz/ac; Assail 30WDG at 4 oz/ac; Rimon (novaluron) 0.83EC at 9 oz/ac; and a rotation of
Danitol 2.4EC at 0.2 lb AI/ac tank mixed with Orthene 97 at 0.5 lb AI/ac in rotation with
Knack 0.86EC at 8 oz/ac. A non-treated control was included for comparison.
SLWF adults were sampled the day after each foliar application. Adults were
counted on one leaf from five randomly selected plants per plot. The leaf was gently
turned over and all adults counted. The test was terminated at 3 days after the second
application because of poor plant stand and overall plant health (disease and hurricanes
had greatly reduced plant stand). To estimate control levels at termination of the test,
three plants were randomly selected from each plot. All leaves on each plant were
examined for SLWF nymphs and infested leaves were placed into a one pint ice cream
container (all infested leaves from one plot were placed into a single container). The
leaves were held in the laboratory at room temperature for about one month to allow
older nymphs to complete development, adult emergence and mortality. All adults which
emerged from the leaves were counted. Data were analyzed with the PROC ANOVA
procedure of PS-SAS. Where significant differences were detected (P<0.05), means were
separated with LSD (P=0.05).
Results and Discussion
The only treatment that showed significant reductions in whitefly adults in the
field counts was the Danitol+Orthene treatment (reduction on 24 Aug. following the
Danitol+Orthene application; no reduction on 1 Sept. following the Knack application).
Given the mode of action of most of the other insecticides tested, the lack of activity on
adults (or lack of detection in a small plot situation) was expected.
Adult emergence from nymph infested leaves was lowest in all three treatments
containing Knack. Rimon also showed good to excellent reductions in adult emergence.
The lack of performance with Oberon and Assail are difficult to explain at this time.
Assail has provided excellent control of whiteflies in fall squash tests, included a test
adjacent to this bean trial.
Table 1. Silverleaf whitefly densities and adult emergence, snap bean efficacy study,
Tifton, Georgia, 2004.
Number of SLWF adults per leaf
Number of adults
emerged per three
24 Aug.
1 Sept.
25.1 a
45.0 a
268.8 a
22.8 a
47.2 a
292.0 a
22.4 a
50.1 a
188.0 ab
28.8 a
56.9 a
46.0 bc
8.3 b
58.9 a
6.8 c
26.6 a
51.4 a
0.0 c
Knack 8 oz
Knack 10 oz
32.7 a
56.9 a
0.3 c
Numbers within columns followed by the same letter are not significantly different (LSD;