Development and Estimation of Aphid Populations Infesting Annual Winter Plantings of Strawberries in California

Abstract

Temporal occurrence and sampling of aphids infesting fresh market strawberries were investigated in two successive annual winter plantings in Orange County, Calif. Chaetosiphon fragaefolii (Cockerell) was the dominant species as well as the primary cause of contamination. Aphis gossypii Glover was also a contaminant, but did not reach population densities as high as C. fragaefolii. Myzus persicae (Sulzer) and Macrosiphum euphorbiae (Thomas) were less common and were of minor importance. Aphid densities in excess of a log (x + 1) value of 1.5 (30.6 aphids) per plant resulted in contaminated fruit. Populations of C. fragaefolii on the youngest or oldest leaves co-varied with total populations, but this technique was not reliable for the other species. A binomial sampling plan based on the presence or absence of aphid infestations on the oldest trifoliate leaf per plant provided an efficient and conservative estimate for determining when pesticide applications are necessary.