Developing a Risk Index for making BYDV Management Decisions.

D. A. Herbert, Jr., Department of Entomology, Virginia Polytechnic Institute and State University, Tidewater Agricultural Research and Extension Center, 6321 Holland Road, Suffolk, VA 23437, USA, D. W. Johnson, Department of Entomology, University of Kentucky, Research and Education Center, P.O. Box 469, Princeton, KY 42445, USA, K. L. Flanders, Department of Entomology, Auburn University, 208a Extension Hall, Auburn, AL 36849, USA, K. L. Bowen, Department of Plant Pathology, Auburn University, 209 Lifesciences Bldg., Auburn, AL 23849, USA

Barley yellow dwarf is an aphid-vectored luteovirus that can cause significant yield loss in most small grains. New insecticides and/or application strategies are now available to farmers that reduce aphid populations and the impact of BYDV. However, they are costly and due to the sporadic nature of BYDV, it is difficult to predict which fields are at risk and which might benefit from treatment. A group of entomologists and plant pathologists in wheat growing states is currently evaluating the potential for developing a system which combines factors that influence disease incidence and severity to indicate levels of risk and aid framers in making management decisions. Factors included field characteristics - geography (location within the state), history of virus, field size, border types (hedge rows, woods, crops, pasture, etc.), field slope and orientation, previous crop (crop residue); crop management - planting date, tillage method (conventional, minimum), planting method (drilled, broadcast), seed rate, fertilization level (fall and spring - esp. N), variety (level of resistance/tolerance/susceptibility), yield potential, crop value, insecticide usage and timing (seed, at plant, fall or spring foliar), insurance; weather - oversummering weather (wet vs. dry, especially towards summer's end), fall weather (acute frosts vs. warm, heavy rainfall events, etc.), winter weather (aphid mortality, reproduction, spread), spring weather (secondary spread); aphid information - species complex, abundance, % aphids viruliferous, macro movement (e.g., from weather fronts), local movement (from alternative hosts), within field movement; BYDV reservoirs - proximity to crops, proximity to grassy weeds (80 known species, dry down time in relation to crop emergence, indicator plants such as fescue). As efforts continue, factors will be rated as too their importance in influencing BYDV, and to what degree they can be supported by published research findings.

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