The Influence of European Red Mites on Intensity of Alternaria Blotch of Apple and Fruit Quality and Yield

Two levels of Alternaria blotch (Alternaria mali) intensity and three levels of European red mite (Panonychus ulmi) populations were established to study the possible effect of an interaction between mite feeding and fungal infection on disease intensity and fruit quality and yield of apples (Malus x domestica cv. Delicious). The effect of mite feeding on disease and yield was most apparent in 1991, when disease severity and levels of mite infestations were higher than in 1992 and 1993. Disease severity was increased with increased mite densities in more instances than it was with defoliation and fruit drop. Fruit quality characteristics such as diameter, weight, firmness, commercial color, and soluble solids content were not affected to a great extent by increased mite densities although soluble solids content was reduced in about one-half of the tests with a high intensity of Alternaria blotch.