Effects of production practices on soil-borne entomopathogens in Western North Carolina vegetable systems

Populations of endemic soil entomopathogens (nematodes and fungi) were monitored in vegetable production systems incorporating varying degrees of sustainable practices in Fletcher, NC. Two tillage types (conventional plow and disk versus conservation tillage), two input approaches (chemically versus biologically based), and two cropping schedules (continuous tomato versus 3-yr rotation of corn, cucumber, cabbage, and tomato) were employed in large plots from 1995 to 1998. A Galleria mellonella (L.) trap bioassay was used to identify and monitor activity of Steinernema carpocapsae, Heterorhabditis bacteriophora, Beauveria bassiana, and Metarhizium anisopliae populations during the vegetable growing season (April-September). Seasonal detection of entomopathogens was significantly higher in conservation compared with conventional tillage systems. The strip-till operation did not affect levels of detection of S. carpocapsae. Pesticide use significantly reduced detection of entomopathogenic fungi. Type of ground cover significantly affected temperature in the upper 12 cm of soil; highest soil temperatures were observed under black plastic mulch and bare ground, whereas lowest temperatures were observed under rye mulch and clover intercrop. The high soil temperatures associated with certain ground covers may have reduced entomopathogen detection or survival. Although type of tillage appeared to be the primary factor affecting survival of endemic soil entomopathogens in our system, other factors, such as pesticide use and type of ground cover, can negate the positive effects of strip-tillage.