Effects of Farm Management Practices on Pest Slugs and Slug Predators in Field Crops
Brichler, Kirsten Nicole
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Mid-Atlantic crop producers are increasingly transitioning to soil conservation methods that include reducing or eliminating tillage and planting high residue cover crops. These practices are associated with an increase in moderate to severe damage to field crops by slugs. Conserving, and even enhancing, natural enemy populations is a desirable way to manage slug infestations because remedial control measures are limited. To better understand how cover crop usage and tillage practices affect slug and natural enemy populations, 43 Virginia fields with different combinations of tillage practices and cover crop use were intensively sampled in 2018 and 2019. Fields were sampled over a six-week period during the early planting season when slugs are most problematic. Shingle traps and pitfall traps were used to sample slugs and natural enemies, respectively. To determine how multiple farming practices, soil composition, landscape features, and field history affect slug feeding injury to seedling plants, over 1,000 hectares of commercial production fields in the Shenandoah Region of Virginia were scouted for slug feeding injury to seedling plants. Corresponding crop producers were then surveyed on management methods. Our goal was to determine if slug feeding risk could be predicted by a single factor and or a combination of factors. Behavioral assays were performed with a common slug pest, Deroceras laeve, to determine if this species prefers feeding on maize, soybean, daikon radish, crimson clover, rye, or hairy vetch leaf tissue. Our sampling study found that cover crop use and conservation tillage type did not affect slug presence and damage, but that these factors affected various slug predators in different ways. We also observed that fields with more Phalangiidae and total predators overall had fewer slugs. Average slug feeding injury in both years was low and no factor or interaction of factors in our broader survey affected slug feeding injury ratings in fields. Behavioral assays indicated that slugs fed more on soybean tissue compared with maize, slugs consumed less maize when it was offered with hairy vetch or crimson clover, and slugs consumed less soybean when it was offered with hairy vetch or daikon radish.
General Audience Abstract
Invasive slug species the gray field slug, Deroceras reticulatum (Muller), and the marsh slug, Deroceras laeve, are major pests of maize and soybean grown in Virginia no-till systems. Slug feeding causes injury to young plants that, when severe, can reduce crop yield and necessitate replanting a field. Chemical control options are limited, and farmers may not be willing to use tillage as a control measure. Conserving arthropod slug predators may suppress pest populations below economic levels. Research is needed to understand how farming methods such as tillage type (e.g., no-till, strip tillage, vertical tillage) and cover crop use affect slugs and their predators. Our study investigated 1) how tillage type and cover crop use affected slug and slug predators, 2) if certain farming practices and field characteristics can be used to predict slug injury, and 3) if slugs preferred feeding on commonly-used cover crop species when offered with maize or soybean seedlings. Commercial production fields with different combinations of no tillage or reduced tillage, and planted with or without cover crops, were sampled to evaluate how these farming practices affect slugs and slug predators. Shingle traps and frames were used before planting and during early plant growth stages to collect and identify slug species; pitfall traps were used throughout the growing season to collect and identify slug predator species. To determine if slug feeding risk could be predicted, a survey of commercial production fields in the Shenandoah area was conducted and used to identify factors, if any, that influence slug feeding. Laboratory assays were used to determine feeding preference by offering slugs opportunity to feed on leaf tissue from a maize or soybean seedling or a mature cover crop species. We found that tillage type and use of cover crops did not affect the abundance of slugs, but that they did influence predator populations. The highest number of total predators were found in fields with reduced tillage, cover crops, and no insecticide use prior to crop emergence. Harvestmen were potentially the most impactful slug predator in the region. Field surveys suggested that no tested factor or interaction of factors affected slug injury to plants in commercial fields. Finally, we observed that slugs fed differently on soybean and maize tissue depending on cover crop species present.
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