Early-season thrips (Thysanoptera:Thripidae) control and soybean yield in North Texas
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Large numbers of thrips (Thysanoptera:Thripidae) can infest soybean (Glycine max L. Merr.) and cotton (Gossypium hirsutum L.) during the seedling stage in the southwestern USA. Although much is known about the consequences of control for cotton, there are few data on whether control measures are economically justified in soybean. Field studies testing the effects of early-season insecticide application on soybean growth and yield were performed at Prosper, TX, in 2000 and 2001. Tests were planted on 28 April 2000, 16 May 2001, and 17 May 2001 with the cultivar Garst D421 STS. Treatments were: (A) an untreated check (B) two foliar applications of acephate (automatic spray regime), (C) one foliar application of acephate (threshold spray regime), and (D) in-furrow aldicarb at planting. Thrips and several seedling traits were sampled three times during the first six weeks of growth and midseason pests were sampled in June 2000 and July 2001. Densities of thrips in the in-furrow aldicarb treatment were less than one per plant except when populations reached five per plant or greater at 31 days after planting (DAP) in 2000. Foliar acephate applications decreased thrips populations to levels similar to that of aldicarb. Mean thrips densities (per plant) in the untreated check were 4.0, 8.6, and 8.5 at 18, 24, and 31 DAP, respectively, in 2000; whereas, densities were 0, 4.9, and 1.6 at 15, 21, and 26 DAP, respectively, in 2001. Insecticide treatments did not substantially alter seedling dry weight, leaf area, or leaf chlorophyll. Mid-season populations of other insects were not affected by the early-season treatment. Grain yields were low because of severe drought in both years and were not affected by the treatments.
