Alton N. Sparks, Jr., University of Georgia Cooperative Extension, Department of Entomology
Tifton, GA 31793, asparks@uga.edu
Introduction
The sweetpotato whitefly (a.k.a. silverleaf whitefly) can be a severe pest in Fall vegetable production in some areas of south Georgia. This pest is of particular concern in squash, where even low populations cause silverleaf symptoms.
Neonicotinoid insecticides play a key role in managing this problem. Recent registration of
‘new’ neonicotinoid insecticides has increased efficacy of foliar applications. This test was conducted to evaluate the efficacy of foliar applied neonicotinoid insecticides for management of silverleaf in squash.
Materials and Methods
A small plot trial was conducted at the
University of Georgia Horticulture Farm in
Tifton, Georgia. Squash, var. Destiny III, was direct seeded in single rows on six foot beds for this test on 7 Aug., 2006. Drip tape was immediately set on the rows to maintain adequate moisture for plant establishment and for irrigation during the season. After plant establishment, experimental plots measuring one row (assumed
36 inch for treatment calculations) by 35 feet were established in a randomized complete block design..
Treatments evaluated in the test were V-
10170 50 WD at 1.5 and 2.0 oz/ac, Venom 70SG at 3 oz/ac, and combination treatments of Venom at 3 oz/ac plus V-10170 at 1.5 and 2.0 oz/ac.
These treatments were compared with Assail
30WDG at 4 oz/ac and a non-treated control.
backpack sprayer (60 PSI) in a total volume of 40 gpa with three hollow-cone nozzles per row (one over-the-top, 2 on drops). Applications were initiated at the two-leaf stage. Silverleaf symptoms were not present at this time, although pest pressure was severe. Application dates were
19, 26 and 31 Aug.
Treatment efficacy was evaluated by rating of silverleaf symptoms and yield. Plots were visually examined and rated on the amount and distribution of silverleaf symptoms as follows:
0 = no silverleaf
1 = light symptoms and spotty distribution within the plot
2 = light symptoms throughout the plot, or moderate symptoms and spotty
3 = moderate symptoms and even distribution
4 = heavy symptoms and spotty distribution
5 = heavy symptoms throughout the plot
On each harvest date, each plot was hand picked, with the entire plot picked. Fruit were counted and weighed. Fruit were visually examined and an average rating for fruit color was assigned for the harvest from each plot. The color scale ranged from 1(white) to 5 (bright yellow of a typical yellow squash). Ratings generally ranged from a
2 (near white) to 3 (cream colored) or 4 (near yellow). All 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).
Results and Discussion
All treatments significantly reduced silverleaf ratings, as compared to the non-treated check (Table 1). Treatment with Assail and treatments containing Venom provided the greatest suppression. However, silverleaf ratings increased dramatically in the 5 days between the
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two ratings, and during foliar application, within all treatments. This is of concern, as it was entirely unexpected with both the Assail and
Venom treatments. Treatments containing Venom or Assail also provided the ‘best’ fruit color in the test; however, none of the treatments averaged over a three (Table 1).
Yield data followed similar trends to the silverleaf ratings (Tables 2 and 3), with the exception that the numerical trend for improvement over the check with both V-10170 treatments was not significant. Assail and treatments containing Venom provided the greatest yields. Addition of V-10170 did not improve performance over Venom alone.
Overall, Assail and Venom provided the greatest suppression of silverleaf symptoms and highest yields in this test. However, the increase in silverleaf symptoms in these two treatments, during the period of weekly foliar applications, is of concern. Based on similar experiments over the last few years, this would not be expected.
Potential resistance to the neonicotinoid insecticides is of concern.
Table 1. Silverleaf ratings (0 to 5) and fruit color evaluations, squash foliar insecticide efficacy test,
UGA Horticulture Farm, Tifton, Georgia, 2006.
Silverleaf Ratings Fruit Color Ratings
Treatment
24 Aug.
29 Aug.
6 Sept.
8 Sept.
Check
V-10170 1.5oz
2.75 a
2.00 b
5.00 a
4.25 b
2.00 c
2.06 c
2.38 b
2.13 b
V-10170 2.0oz
Venom
Venom+
V-10170 1.5oz
Venom
+V-10170 2.0oz
Assail
1.50 b
0.00 c
0.25 c
0.00 c
0.00 c
4.00 b
3.00 d
3.50 c
3.25 cd
3.00 d
2.00 c
2.50 ab
2.63 a
2.44 b
2.56 ab
2.13 b
2.88 a
2.94 a
2.88 a
2.88 a
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Table 2. Average number of fruit harvested per plot, squash foliar insecticide efficacy test, UGA
Horticulture Farm, Tifton, Georgia, 2006.
Number of fruit harvested per plot
Treatment
6 Sept.
8 Sept.
11 Sept.
Total
Check 2.00 d 1.50 c 0.00 c 3.50 c
V-10170 1.5oz
V-10170 2.0oz
7.25 d
12.25 cd
7.25 bc
5.25 c
0.25 c
1.25 c
14.75 c
18.75 c
Venom
Venom+
V-10170 1.5oz
Venom+
V-10170 2.0oz
Assail
29.75 ab
22.25 bc
23.25 bc
37.75 a
20.25 a
25.00 a
18.75 ab
29.75 a
24.00 ab
18.00 b
18.00 b
29.75 a
74.00 ab
65.25 b
60.00 b
97.25 a
Table 3. Average pounds of fruit harvested per plot, squash foliar insecticide efficacy test, UGA
Horticulture Farm, Tifton, Georgia, 2006.
Pounds of fruit harvested per plot
Treatment
6 Sept.
8 Sept.
11 Sept.
Total
Check 0.16 c 0.10 c 0.00 c 0.26 c
V-10170 1.5oz
V-10170 2.0oz
Venom
Venom+
V-10170 1.5oz
0.92 c
1.23 bc
4.49 a
4.38 a
0.69 bc
0.36 c
1.96 ab
2.78 a
0.02 c
0.05 c
2.20 ab
1.62 b
1.62 c
1.64 c
8.64 ab
8.78 ab
Venom+
V-10170 2.0oz
Assail
3.55 ab
5.98 a
1.90 ab
2.94 a
1.41 b
3.10 a
6.85 b
12.01 a
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