Date of Award

12-2005

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Plant, Soil, and Environmental Sciences

Advisor

Chris Reberg-Horton

Second Committee Member

Eric R. Gallandt

Third Committee Member

Francis A. Drummond

Abstract

Cover cropping and soil disturbance are common weed management practices in agroecosystems of the Northeast United States. In addition to their direct impacts on the weed seedbank, these practices secondarily affect weed biocontrol agents. Cover cropping and soil disturbance practices were investigated for their impacts on a promising group of weed biocontrol organisms, the ground beetles, collectively known as carabids (Coleoptera: Carabidae), with particular emphasis on a beneficial carabid species Harpalus rufipes DeGeer. Previous research has identified general habitat characteristics, such as high humidity and vegetative cover, which promote H. rufipes populations. This study investigated some specific characteristics of cover cropping systems and soil disturbance that affect H. rufipes abundance. The impacts of cover crops on H. rufipes movement and abundance were investigated in 2004 and 2005. Using mark-recapture, it was determined that beetles released in fallow plots traveled farther (31.3 m beetle-1) than those released in plots with a pedoat cover crop (25.3 m beetle-1). More marked beetles were recaptured in pealoat plots than fallow plots, thus indicating the potential use of cover crops as refuges. Background populations of H. rufipes were also greater in pea/oat than in fallow plots. These results indicate that H. rufipes will travel to vegetated refuges to avoid fallow areas. The effects of cover crops and corn planting on H. rufipes activity-density were investigated from June to August in 2005. Sweet corn was conventionally planted into soil-incorporated resides or zone till planted into surface residues of five cover crop system treatments that were grown in 2004. H. rufipes abundance was greatest in both zone and conventionally tilled corn planted following a pedoat cover crop and conventionally tilled corn planted following a clover/rye cover crop. There was a significant interaction between cover crop system and corn planting method, thus indicating both carryover and immediate impacts of crop management on H. rufipes abundance. In 2005, the direct impacts of disturbance were investigated on the survival of four species of carabid weed seed predators (H. rufipes, Agonum muelleri Herbst, Anisodactylus merula Germar, and Amara cupreolata Putzeys) , and one arthropod pest predator (Pterostichus melanarius Illiger). Three tillage techniques (moldboard plowing, chisel plowing, and rotary tillage) were compared with an undisturbed control at two sites in Maine. Carabid survival was measured using fenced pitfall traps installed immediately after tillage. More carabids were captured in control and chisel plowed plots than in rotary tilled or moldboard plowed plots. Rotary tillage and moldboard plowing reduced carabid weed seed predator populations by 51% and 54%, respectively. P. melanarius populations, however, were reduced significantly by all disturbance types, indicating greater sensitivity to cultivation than the other four carabid species. From these results, certain cover cropping and soil disturbance regimes conserve weed seed predators. Because these techniques are already used for direct weed management, their use may have the added benefit of promoting weed seed predator populations. Further investigation is needed to determine the long-term impacts of these practices on weed communities and population dynamics of abundant carabid seed predators.

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