EFFICACY OF INSECTICIDES AGAINST
TOBACCO THRIPS ON ONIONS, 2004
Alton N. Sparks, Jr.1, David G. Riley1, and Ronald H. Blackley2
1
University of Georgia
Dept. of Entomology
P.O. Box 1209
Tifton, GA 31793
2
Georgia Cooperative Extension
Courthouse Square
Lyons, GA 30436
Introduction
Thrips are the major arthropod pest of onions in Georgia. Thrips are primarily a
concern as a direct pest of onions, with feeding resulting in loss of effective
photosynthetic leaf area and a reduction in bulb size. More recently, thrips have been
associated with potential introduction and spread of some onion diseases. When thrips
populations increase, generally near the end of the production season, growers rely on
foliar insecticides for control. Insecticidal control options are limited, with few new
insecticides registered on onions and insecticide resistance in thrips. Thus, insecticide
efficacy studies on onions are needed to monitor for insecticide resistance and to identify
new efficacious compounds for potential registration. This study was conducted to verify
the efficacy of currently recommended insecticides and evaluate the efficacy of potential
new insecticides for thrips control on onions. While several thrips species may be found
on onions, the primary species on onions in the Vidalia onion production region in the
past two years and in this study was the tobacco thrips, Frankliniella fusca.
Materials and Methods
Plots were established in a commercial onion field in Toombs County, Georgia.
Samples of thrips adults collected prior to treatment and post-treatment indicated that the
species composition in the test field consisted of almost 100% tobacco thrips.
Experimental plots were 25 feet long by 4 rows (4 rows on one 6 foot bed), with a nontreated bed of onions between plots. Plots were arranged in a randomized complete block
with four replications. Insecticide treatments were applied on 16 April, 2004, with a CO2
pressurized backpack sprayer (60 PSI) in 30 GPA with 4 hollow cone nozzles per bed
(broadcast over-the-top).
Insecticide treatments evaluated were: Lannate LV at 0.9 lb AI/ac (3 pints/ac);
Diazinon AG500 at 0.5 lb AI/ac (1 pint/ac); Warrior T at 0.03 lb AI/ac (3.84 oz/ac);
Mustang Max at 0.025 lb AI/ac (4 oz/ac); Assail 70WP at 0.1 lb AI/ac (2.3 oz/ac); and V10112 20SG at 60 g AI/ac. A non-treated check was included for comparison.
Thrips densities were monitored through visual inspection of plants. All adult thrips
were counted on five randomly selected plants in each plot on each sample date.
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Immature thrips were not counted, but represented a very low percentage of the
population. Thrips counts 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 insecticide treatments significantly reduced thrips populations at three days after
treatment. Lannate, Assail and both Pyrethroids (Mustang Max and Warrior) provided
the greatest reductions at three days after treatment. At 6 days after treatment, thrips had
moved back into the Lannate, Diazinon and V-10112 plots, with less than 40% control in
these treatments. The two pyrethroid treatments and Assail showed longer residual
activity, with the pyrethroid treatments having the lowest numerical densities at 6 days
after treatment. These data support trends seen over the last few years, with the
organophosphate (OPs) insecticides frequently providing less control than the pyrethroid
insecticides. This may well be an indication of increased tolerance to the OPs. The
pyrethroids appear to remain efficacious, but heavy reliance on this chemistry could lead
to rapid development of resistance. Assail does appear to hold promise as a potential
insecticide for control of thrips.
Table 1. Thrips densities, small plot efficacy trial in onions, Toombs County,
Georgia, 2004.
Treatment
Thrips per Plant
3 DAT
Check
6 DAT
11.50 a
11.60 a
Diazinon
6.95 b
10.55 a
Lannate
1.55 d
7.80 b
V-10112
3.80 c
7.10 b
Assail
1.05 d
3.75 c
Mustang Max
1.60 d
2.20 cd
Warrior
1.50 d
1.20 d
Numbers within columns followed by the same letter are not significantly different (LSD;
P=0.05).
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