Twelve replicated soybean field trials were conducted in 1993–1997 to evaluate the effects of a foliar application of the insect growth regulator Dimilin® (0.07 or 0.035 kg Al/ha) and the plant nutrient boron (0.28 kg nutrient/ha) on the incidence of insect pests and the enhancement of yield and quality. Dimilin (diflurbenzuron) was very effective at all test locations in controlling velvetbean caterpillars, Anticarsia gemmatalis Hübner, for the remainder of the season once the foliar application was made on soybeans in the R2 (full bloom) to R5 (pods filling with seeds) growth stage. Six of the test sites had significant yield increases in the Dimilin plots due to protection from economic crop injury from this pest. Dimilin was not effective in controlling stink bugs, primarily Nezara viridula (L.) and Euschistus servus (Say), and Mexican bean beetles, Epilachna varivestis Mulsant. Scout® (tralomethrin) and MVP® (Bacillus thuringiensis Berliner) did not provide adequate residual pest control when combined with the boron treatment. Yield enhancements from boron (Solubor®, soluble disodium octaborate tetrahydrate) were observed in seven tests, but yields were significantly higher than the no boron treatments in only three experiments. The nutrient applications did not influence the abundance of arthropod pests at any test location. The overall soybean yield enhancement of around 440 kg/ha (6.5 bu/a) above the untreated plots represents a positive net economic return for the total investment of around $55 per ha. Dimilin accounted for most of the yield increase due to effective pest control, but the addition of boron costs very little ($3.00/ha) with a return of about 35 kg/ha across all soil types (higher response in sandy soils). It appears that a dimilin/boron foliar application around R3 stage soybeans (small pods forming) can be a profitable strategy in south Georgia, especially in areas where velvetbean caterpillars are annual economic pests and the fields contain sandy soil with low levels of available boron.
2Department of Entomology
3Department of Crop & Soil Sciences