EFFECTS OF THE POTATO APHID MACROSIPHUM EUPHORBIAE (THOMAS) (HOMOPTERA: APHIDIDAE) ON OILSEED FLAX, AND STAGE-SPECIFIC THRESHOLDS FOR CONTROL

Abstract

AbstractThe potato aphid, Macrosiphum euphorbiae (Thomas), infests oilseed flax, Linum usitatissimum L., when the crop is flowering and developing seeds. Field studies in cages, open plots, and commercial fields showed that the aphid can cause yield losses of 20% or more, but reduces the weight of individual seeds only slightly and has no effect on oil quality. A single application of a foliar insecticide at full bloom or the green boll stage will control the potato aphid until harvest. The yield loss of flax is 0.021 t/ha per aphid per plant for crops sampled at full bloom and 0.008 t/ha per aphid per plant for crops sampled at the green boll stage. The economic threshold for the potato aphid in flax is three aphids per plant at full bloom and eight aphids per plant at the green boll stage, based on crop prices and control costs from 1990 to 1992. Aphids should be controlled as soon as the economic threshold is exceeded. If control is not warranted at full bloom, aphid densities should be assessed again at the green boll stage. The effective use of growth-stage-specific sampling and economic thresholds will maximize the benefits of insecticide use for producers and minimize unnecessary or ineffectively timed applications.