Influence of irrigation and fungicide sprays on prevalence of Erynia neoaphidis (Entomophthorales : Entomophthoraceae) infections of green peach aphid (Homoptera : Aphididae) on spinach

Infections from Erynia neoaphidis (Remaudiere & Hennebert) have often resul ted in epizootics in green peach aphid, Myzus persicae (Sulzer), population s on spinach, Spinacia oleracea L., produced for processing in the Arkansas River Valley of Arkansas and Oklahoma. Use of this fungal pathogen as an a phid management tool has been unsuccessful because of poor timing, i.e., ep izootic occurrence generally occurs at or after harvest. In the study repor ted herein, attempts at manipulating disease occurrence with overhead irrig ation and fungicide applications were made. In samples 16- to 35-d after ir rigation was initiated, the percentage of aphids infected with E. neoaphidi s was significantly greater than in aphids from plots not receiving irrigat ion. The percentage of infection in the 35 d sample was twice as great in i rrigated plots as in those not irrigated. In subsequent samples, however, s ignificant differences were not detected and peak epizootic did not differ between the irrigation treatments. M. persicae populations were eliminated in both blocks 63 d after sampling was initiated. The fungicide, manganese ethylenebisdithiocarbamate, initially had little detectable effect on disea se prevalence; however, in samples taken 21- and 41- d after the initial ap plication, percentage of aphids infected with E. neoaphidis was significant ly reduced.