Effect of s= eed and foliar insecticide treatments on infestation incidence and yield reduction = by Dectes stem borer (Dectes texanus texanus LeConte (Coleoptera: Cerambycidae)) in Kentucky grown soybean in 2007

Douglas W. = Johnson, Extension Entomologist

Department = of Entomology

College of Agriculture - University of Kentu= cky

WARNING: Data= from non-registered pesticides are included in this report.&nb= sp; In no way should anyone interpret the inclusion of these products as= a recommendation for their use on soybeans. The reader is reminded that the l= abel is a legal document. As always, a pesticide should only be used in strict compliance with the label.

Methods & Procedures

Plots of Asgrow, “AG3906” soybeans were es= tablished on the University of Kentucky Research and Education Center (UK-REC) Princeton, Caldwell Co. KY on 18 May 2007 using a John Deere no-ti= ll planter modified to plant sequential plots. Plots consisted of four 20'-long sections of rows with 30" spacing in a no-tillage seed bed which was seeded at a rate of ten seeds per row-ft. Four non-treatment rows were planted around the complete circumference of the study. Standard agricultural pract= ices for fertility and weed control were used.

The study was planted as a randomized complete block d= esign (Steel and Tory 1960) with four replications. Treatments were assigned rand= omly using SAS AProc = Plan@. Data were analyzed = using “Proc GLM”. If significance was detected, mean separation was d= one using the ”Ryan-Einot-Gabriel-Welsch” multiple-range test (SAS 2000).

Insecticide treatments are listed in Table 1.

Table 1. Insecticide treatments applied to plots of soybean for control of Dectes= stem borer on the UK-REC in 2007.
Insecticide	Application Type/Date
No insecticide	No applic= ation
Regent TS @ 25g ai / 100KG seed	Seed appl= ied
Regent TS @ 49g ai / 100KG seed	Seed appl= ied
Regent TS @ 100g ai / 100KG seed	Seed appl= ied
Cruiser @ 50g ai/ 100KG seed	Seed appl= ied
Warrior (1 foliar app) @ 3.8 fl oz / A	30 July 2= 007
Warrior (2foliar app) @ 3.8 fl oz /A	30 July &= amp; 13 Aug 2007
Regent 4SC (1 foliar app) @ 4.2 floz /A	30 July 2= 007
Regent 4SC (2 foliar app) @ 4.2 floz /A	30 July &= amp; 13 Aug 2007
Regent (fipronil) is a product of BASF. Cruiser (thiamethoxam) and Warri= or (lambda-cyhalothrin) are products of Syngenta.

Seed treatments were made by a commercial treater. Fol= iar sprays were applied using a CO₂ powered, back-pack sprayer calibrated to deliver twenty gallons per= acre at 45 PSI pressure and four miles per ho= ur. The spray boom was fitted with fou= r 8003 nozzles on 18” centers. The single foliar application was made on 30 July, plots receiving two applications were treated on 30 July 07 and again= on 13 Aug 07, based on activity of the De= ctes adult population (Fig. 1.).

The Dectes population was sampled twice weekly with a 15- inch sweep net beginning 14 = June 07; sampling ended on 26 Aug 07, after three successive samples produced no adults. Each sample date consisted of 100 complete figure-eight sweeps. Samples were taken from the non-tr= eatment areas surrounding the study. These samples were used to time the foliar insecticide applications targeting the early instars of the larvae in the plants.

On 17 Sep 07, = Dectes larval infestation data were collected. Five stems were randomly selected f= rom each of the two outer, non-harvest rows of each plot. Each stem was split and examined for larvae or larval damage. The number of damaged and undamaged stems was recorded.

Before harvest the plots were trimmed to fifteen feet = in length. On 24 Sep 07 the two center rows of each plot were harvested using a Winterstiger “delta” plot combine which supplies grain weight (lbs.) percent moisture and test weight for each plot. Plot seed weights we= re standardized to bushels per acre for a 60 lb bushel at 13 % moisture.

Results<= /o:p>

Figure 1. illustrates the number of the Dectes beetles captured on each sampling date. The first beetle was caught on 06 July and = the final capture on 14 Aug. A si= ngle peak capture occurred on 23 J= uly.

There are significant differences among treatments with regard to the level of infestation by Dectes larvae (Table 2.). All Regent treatments produced a significant reduction from the “No Insecticide” plots. The Regent seed applied treatments appear to be superior to the foliar applications. This is quite interesting in that the product is a systemic and appears to be active in a year of low rainfall. T= he Cruiser seed applied treatment and the Warrior foliar treatments were not significantly different from the “No insecticide” check nor from each other.

There were no significant differences in yield among treatments (Table 2.). This is somewhat unexpected given the differences in infestation level among treatments. Though there were some girdled stalks, there was no lodging at harve= st. I expect that the major reason for lack of differences and the overall poor y= ield was lack of adequate rain fall. The 2007 production season progressed from “mild” to “extreme” drought (Agricultural Weathe= r Center. 2007.) from planting to harvest time. At the time of harvest rainfall at these plots wa= s 11.5” below normal for the time interval.

Table 2. Mean yield and infestation incidence in soy= bean plots on the UK-REC treated with various insecticides for control of Dectes stem borer in 2007.
Treatment	n	Yield Bu/Ac ± SE	Mean number (± SE) uninfeste= d stems per 10
Regent TS @ 49g ai / 100KG seed	4	29.5 &plu= smn; 1.4	9.8 ± 0.3 a
Regent TS @ 25g ai / 100KG seed	4	29.8 &plu= smn; 3.1	9.5 ± 0= .3 ab
Regent TS @ 100g ai / 100KG seed	4	30.5 &plu= smn; 1.9	9.5 ± 0= .3 ab
Regent 4SC (1 foliar app) @ 4.2 floz /A	4	25.7 &plu= smn; 1.9	6.= 5 ± 0.5 bc
Regent 4SC (2 foliar app) @ 4.2 floz /A	4	25.7 &plu= smn; 4.9	6.= 3 ± 0.6 c
Warrior foliar (2app) @ 3.8 fl oz /A	4	31.6 &plu= smn; 2.0	3.5 ± 1.3 d<= /p>
No insecticide	4	29.3 &plu= smn; 1.7	3.0 ± 0.7 d<= /p>
Cruiser @ 50g ai/ 100KG seed	4	27.7 &plu= smn; 3.3	2.8 ± 0.8 d<= /p>
Warrior (1 foliar app) @ 3.8 fl oz / A	4	24.0 &plu= smn; 3.3	2.2 ± 0.5 d<= /p>
ANOVA	F(8,27) =3D 0.86; Pr>F=3D0.5631	F(8,27)= =3D22.18; Pr>F=3D<.0001
Means followed by the same letter are not significan= tly different at p=3D0.05 level using Ryan-Einot-Gabriel-Welsch multiple-range test.
Regent TS and Regent 4SC are NOT la= beled for use on soybean.

Summary

The Regent insecticidal treatments appear to have good suppression of Dectes larvae. Conversely, the reduction in Dectes larval infestation by Regen= t did not translate into increased yield. This may have been due to the over-ridi= ng reduction in expected yield by drought conditions.

References

Agricultu= ral Weather Center. 2007. Drought Status For Kent= ucky: 2007. http://www= agwx.ca.uky.edu/latest_drought.shtml

SAS system for Windows V8.1. 2000. SAS Institute, Cary, N= C.

Steel, R. and J. Torrie. 1960. Principles and Procedur= es of Statistics. McGraw-Hill, NY.

Acknowledgements

I wish to acknowledge my colleagues in the Department = of Agronomy for use of their planting equipment and especially Mr. John James = for his help with harvesting. Additionally, I acknowledge the UK-REC farm crew = for making all herbicide applications. Also, I thank the BASF and Syngenta corporations for supplying the insecticides.

University of Kentu= cky, Department of Entomology, Extension Research Reports.

http://pest.ca.uky.edu= /EXT/Res/ResPubs.shtm