Effect of Potato Aphid (Homoptera: Aphididae) on Yield, Quality, and Economics of Staked-Tomato Production

Abstract

Field studies were conducted in 1990 and 1992 to measure the impact of potato aphid, Macrosiphum euphorbiae (Thomas), infestations on the yield, quality, and economics of staked, fresh-market tomato production. Treatments consisted of a nontreated control and applications of the experimental aphicide RH7988 at threshold levels of 10, 25, 50, 65, and 100% infested leaves. Although total yield did not vary significantly among treatments, yields were consistently lower in the control, 65, and 100% threshold treatments. However, fruit quality, as measured by percentage of fruit graded as combination grade (U.S. No. 1 and 2), U.S. No. 3, and culls, was statistically highest in the 10 and 25% threshold treatments in 1990, and the 10, 25, and 50% threshold treatments in 1992. Reductions in fruit quality were related to higher levels of hemipterous-damaged fruit and fruit affected by weather-related physiological disorders (sunscald and weathercheck). The larger aphid populations in the high threshold treatments were presumably attractive to stink bugs and leaffooted bugs, which fed on aphids as well as tomato fruit. The higher levels of sunscald and weathercheck were because of stunted foliage and higher levels of foliar early blight, which decreased leaf area and exposed fruit to these disorders. Reductions in fruit quality were most apparent during the late season harvests. When yields were adjusted for hemipterous damage and physiological disorders, net profits increased and, in 1990, only the control exhibited a significant reduction in net profits compared with the low aphid threshold treatment, indicating that reduction in fruit quality was the primary cause of profit loss in the high threshold treatments. However, in 1992, significant reductions in net profits were observed at thresholds of >50% for both nonadjusted and adjusted yields. Recommended potato aphid threshold levels for vine-ripe harvested tomatoes are 50% infested leaves when using broad-spectrum insecticides, but only 25% when using narrow-spectrum aphicides. The higher threshold when using broad-spectrum insecticides is recommended because damage caused by hemipterous insects would be averted.