A damage index for estimating yield loss in sunflowers caused by sunflower midge

Abstract

A description of six categories of damage to sunflower heads by sunflower midge, Contarinia schultzi Gagne, is presented based on visual estimates of the relative area of seed destroyed as well as the degree of head cupping expressed as the ratio of the length of the thickened receptacle to the head diameter. Fractional yields of the six damage classes (0–5), determined from heads collected in commercial fields, were 1.0, 0.82, 0.69, 0.41, 0.15 and 0. Head diameter was significantly associated with midge damage and accounted for more variation than the damage rating in regressions of the two factors on yield. Ratings by observers with varying degrees of experience using the damage descriptions agreed significantly in evaluating the same group of heads. The sunflower midge index provides a simple and standard method for comparing varietal reactions to midge and for estimating commercial losses. Key words: Sunflower, Contarinia schultzi Gagne