Tillage, insecticide inputs, crop rotation and intercropping: Factors that affect insect pests and natural enemies in vegetable systems in western North Carolina

Populations of foliar insect pests and natural enemies were monitored in vegetable production systems incorporating varying degrees of sustainable practices in Fletcher, NC. Two types of tillage (conventional plow and disk, strip-tillage), two input approaches (chemically based, biologically based) and two cropping schedules (continuous tomato, 3-year rotation of corn, cucumber and tomato) were employed in large plots 1995–1998. Tomato pest pressure was relatively low in all years, resulting in a limited evaluation of the impact of production systems on potato aphid, Macrosiphum euphorbiae (Thomas), and its associated parasitoids and predators. Thrips ( Frankliniella spp.) populations were significantly higher in the biological input treatments in three of four years. Lepidopterous (primarily Helicoverpa zea Boddie) tomato damage was significantly higher in biological treatments in all years, and damage by thrips and pentatomids increased each year in the continuous tomato crop schedule. The majority of insect population measurements were significantly influenced by type of insecticide input or type of ground cover. Few population measurements were affected by tillage type. In the short term, foliar insect problems in commercial vegetable production may be associated predominantly with insecticide input (i.e. more damage with use of biologically based insecticides) and use of intercropping (i.e. more damage in systems with living mulch); however, the long term effects of tillage and crop rotation remain to be seen. In addition to the study described previously, a small-plot study was established in 1997–1998 to separate effects of pesticide use, intercropping and herbicide application on selected epigeal arthropods. Adult carabid beetles and lycosid spiders appeared to be more active in systems with ground cover. Trap catches of carabid species were not significantly affected by insecticide input, but trap catches of lycosids were lower in plots with conventional insecticide use. No consistent effect of tillage was found over time, although Scarites spp. were more active in minimally disturbed habitats in 1998. Two distinct patterns of seasonal activity were observed for carabid beetles and lycosid spiders. Ground cover, via intercropping, generally enhanced abundance of carabids and lycosids, while tillage type, pesticide use and crop rotation had different effects on different species. A Galleria mellonella (L.) trap bioassay was used to detect the presence of Steinernema carpocapsae, Heterorhabditis bacteriophora, Beauveria bassiana and Metarhizium anisopliae populations during the vegetable growing season (April–September). Seasonal entomopathogen activity was significantly higher in strip-tilled compared to conventional-tilled plots. The strip-till operation did not appear to affect 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, lowest temperatures were observed under rye mulch and clover intercrop. The high soil temperatures associated with certain ground covers may have reduced entomopathogen activity or survival. Although type of tillage appears to be the primary factor affecting survival and activity of endemic soil entomopathogens in our system, other factors, such as pesticide use and type of ground cover, may negate the positive effects of strip-tillage.