Management of European red mite populations on apple and plum trees with soybean oil

Degummed soybean oil emulsions were compared to a standard petroleum oil emulsion for efficacy against overwintering and summer populations of European red mite, (ERM), Panonychus ulmi Koch, on apple and plum trees in a commercial orchard, Russellville, TN, in 1994 and 1995. Oils were applied with a handgun sprayer to dormant and delayed-dormant bud stage trees to kill overwintering ERM eggs and suppress mite populations. Summer oil applications were tested on apple for their effect on motile ERM and predatory mites.

A dormant application of 5.0% soybean oil plus a delayed-dormant application of 2.0% soybean oil significantly reduced ERM populations in April, May, and June on apple. A summer spray of 0.5% soybean oil reduced ERM densities below densities on the control trees or the 0.25% soybean oil-treated trees. ERM densities were lower on plum trees treated with a dormant application of 5.0% soybean oil plus a delayed-dormant application of 2.0% soybean than densities on control trees in June 1994. The use of soybean oil emulsions has potential as a management practice for winter and summer ERM populations on apple and plum trees.

ERM larvae appeared on apple trees in early April. In eastern Tennessee, oil sprays should be most effective when applied just prior to the hatching of overwintering eggs, in late March. Approximately eight generations of ERM were observed on apple in 1994.