Control of woolly aphid, Eriosoma lanigerum (Hausmann) (Hemiptera: Pemphigidae) on mature apple trees using insecticide soil-root drenches

Woolly aphid, Eriosoma lanigerum, is an important pest of apples that infests both the aerial and root parts of the tree. Root colonies are protected from the pesticide sprays applied during the growing season and the climatic effects of winter. Consequently, root colonies are a major source of aerial re-infestation in the following spring. Imidacloprid, the first of a new group of insecticides from the chloronicotinyl family, is known to provide excellent control of woolly aphid on trees up to 7-years-old when applied as a root soil drench. This study compared the effects of a single application of chlorpyrifos, imidacloprid, pirimicarb or vamidothion, applied as a root drench over four growing seasons. A soil wetting agent was added to each chemical to improve soil saturation and penetration. Imidacloprid provided excellent control of woolly aphid on the trees that were 17-years-old at the start of the study and continued to do so for four seasons. Pirimicarb appeared to offer some suppression of woolly aphid during the first season but not in subsequent seasons, while chlorpyrifos and vamidothion failed to control woolly aphid in any season. The potential role for imidacloprid in IPM programs is discussed.