Effect of Aphis pomi (Homoptera: Aphididae) Density on Apples

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Abstract
From 1982 to 1984, impact of spray timing on apple aphid, Aphis pomi De Geer, accumulated aphid-days was investigated. Effect of aphid-days on color, diameter, sugar content, firmness of fruit, yield, and shoot growth was also determined. Percentage of infested shoots was regressed with mean densities to evaluate the current estimated economic threshold (50% infested shoots). Varying spray timings had significant effects on accumulated aphid-days. Spray applications made between 450 and 650 degree-days resulted in lower total aphid-days each year. The greatest effect was noted in 1984, when aphid-days were significantly related to yield, shoot growth, and sugar content of fruit on the variety ‘Golden Delicious’. Because no significant relationship between aphid-days, yield, fruit quality, and shoot growth was noted for ‘Red Delicious’, we concluded that the apple aphid did not reduce yield, affect apple quality, or vegetative growth. The current threshold derived from the model for density and percent infested shoots was unsatisfactory for four of six data sets when compared with aphid-day accumulations.

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