Utah Pests News Winter 2007-08

Woolly apple aphid root galls (top); twig colony (middle); twig gall (bottom).   


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Woolly Apple Aphid Suppression on Apple Roots


The decrease in use of broad-spectrum insecticides in apple orchards in Utah and the western U.S. appears to be correlated to an increase in some insects that were secondary problems in the past. Woolly apple aphid is one of these secondary pests that are more common today. Woolly apple aphids feed in the phloem of limbs and roots and cause galls that decrease the efficiency of nutrient uptake and fluid transport. The aphids are covered with a grayish-white waxy material that protects them from the environment, natural enemies, and insecticides. Recent research in Utah has evaluated the efficacy of a still unregistered systemic insecticide, spirotetramat (Bayer CropScience). Spirotetramat has demonstrated good suppression of woolly apple aphids on tree limbs. In 2007 the opportunity arose to evaluate suppression of aphids and galling on roots.

Eighteen-year-old apple trees were pulled from the ground and the roots of root suckers evaluated for galls. As compared to untreated trees, there was a significant reduction in root gall ratings (Fig. 1, below) and numbers of galls (Fig. 2, below) on trees that were sprayed with spirotetramat (8 or 12 oz per acre + 1% horticultural mineral oil) either once at petal fall (May 9) or twice (May 9 and June 11). Bayer CropScience is pursuing registration of spirotetramat on apple. These results are encouraging that an effective product may soon be available to assist apple producers with managing this challenging pest.

-Diane Alston, Extension Entomologist