The influence of farming practices on slugs and their predators in reduced-tillage field crops in Pennsylvania
Open Access
- Author:
- Douglas, Margaret Rose
- Graduate Program:
- Entomology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 29, 2012
- Committee Members:
- John Frazier Tooker, Thesis Advisor/Co-Advisor
Mary Ellen Barbercheck, Thesis Advisor/Co-Advisor
Heather D Karsten, Thesis Advisor/Co-Advisor - Keywords:
- slugs
Deroceras reticulatum
conservation tillage
no-till
biological control
Carabidae
sustainable agriculture - Abstract:
- Slugs are a destructive pest of myriad field crops in reduced-tillage settings, particularly in the mid-Atlantic and Northeastern United States. Current management options are limited and farmers have expressed a need for improved slug control; however, basic aspects of slug ecology in the region remain obscure. My thesis begins with a review of existing knowledge on slug ecology, natural history, scouting, and management. Through this review, I identified research areas in need of attention for improving integrated management of slugs. In the remaining chapters, I attempt to address several of these needs through laboratory and field experiments. In preliminary laboratory experiments, I explored the potential for common generalist predators to contribute to slug suppression in Pennsylvania. Wolf spiders and cantharid larvae were disinclined to eat slugs; however, two common ground beetle species, Chlaenius tricolor and Pterostichus melanarius, preyed on slugs and protected soybean seedlings from damage, indicating a potentially important role for them in biological control. Next, I examined how crop management decisions influence slugs, insect pests, and predators in reduced-tillage maize systems, in field studies spanning two years. Weed and manure management had few effects on pest activity, crop damage, or predator activity in either year, although cultivation reduced late-season slug activity in 2011. Low-external-input crop rotations using cover crops were somewhat more vulnerable to slugs and European corn borer compared to a control rotation using pre-emptive insect management; however, damage from these pests was likely sub-economic in all rotations. Furthermore, in the second year of the study, the low-external-input rotations supported higher levels of predation on sentinel caterpillars, and comparable or lower levels of slug activity late in the season compared to the higher-input control rotation. Overall the low-external-input rotations were competitive with the more conventional, pre-emptive approach. Finally, I examined the influence of the common seed treatment, thiamethoxam, on slug damage to soybeans in a tritrophic context. In laboratory experiments, thiamethoxam did not significantly influence slug survival or feeding behavior on soybean. However, slugs that were fed for one week on thiamethoxam-infused soybean seedlings were poisonous to the ground beetle, Chlaenius tricolor. My results suggest that neonicotinoid seed treatments do not prevent slug damage to soybean, and in fact may exacerbate slug damage if slugs pass these insecticides to their predators. This possibility bears further evaluation in field studies.