Laboratory and field assays with entomopathogenic nematodes for the management of oblique banded leafroller Choristoneura rosaceana (Harris) (Tortricidae)

The activity of steinernematid entomopathogenic nematodes against Choriston eura rosaceana was evaluated under laboratory and field conditions. In petr i dish trials, all instars were susceptible to Steinernema carpocapsae AII strain with LD50 values of 13, 5, 3, and 2 infective juveniles for the thir d-, fourth-, fifth-, and sixth-stage larvae, respectively. Steinernema riob rave 335, S. feltiae UK, S. carpocapsae AII, and S. glaseri 326 caused 85, 55, 45, and 8% mortality of third instars when exposed to the concentration of 25 infective juveniles per dish. When third instars were exposed to S, carpocapsae AII for 0, 1, 4, 8, 12, and 24 hours, larval mortality was 12, 13, 21, 47, 64, and 87%, respectively. At least 8 hours' exposure was requi red to cause a significant increase in mortality when compared with the con trol (water) and the 1 and 4-hour exposures. None of the tested adjuvants p rovided a significant improvement in the average total number and the avera ge number of living S, carpocapsae AII per unit leaf area when compared to the water control. Under field conditions, foliar applications of S. carpoc apsae AII at the rate of 2 x 10(9) infective juveniles/ha provided 37, 19, and 13% larval control. At present, efficacy level and treatment cost precl ude nematode applications as a sole treatment against this pest.