Suraj Kar, Thayne Montague,* Kyle Lauterbach, Trey Ruland, Pierre Helwi, and Edward Hellman
*Texas Tech University and Texas A&M University AgriLife Research and Extension Center, Department of Plant and Soil Science, Texas Tech University, Bayer Plant Science Building, Room 103, 2911 15th Street Mail Stop 2122 , Lubbock, TX 79409 (thayne.montague@ttu.edu)

With more than 500 wineries, the state of Texas is the fifth-largest wine-producing state within the United States. The Texas High Plains American Viticulture Area (AVA) produces nearly 80% of all winegrapes (Vitis vinifera L.) in Texas. However, this same area is a major cotton-producing region where new formulations of auxin-based herbicides are being used by the agriculture industry with increasing regularity. It is thought synthetic auxin herbicides (predominantly 2,4-D and dicamba) are applied to nearly 90% of cotton grown on the Texas High Plains. Grapevines are among the most sensitive species to synthetic auxin herbicides, and concentrations lower than 100 times the recommended rate can cause vine injury. Close proximity to cotton fields and climate factors (hot, dry, and windy conditions) found within the AVA have made vineyards particularly vulnerable to herbicide volatilization and drift injury. Multiple injury events, causing as much as 85% reduction in grape yield, have been reported within the Texas High Plains AVA. To evaluate the extent and risk frequency of off-target movement of auxin-based herbicide, a field survey was conducted during the 2020 grapegrowing season within six Texas High Plains AVA vineyards through monthly leaf tissue sampling. Results indicated a single volatilization and drift event occurring early in the growing season, with concentrations ranging between 3.75 to 13.70 ng/g, and 80.41 to 266.55 ng/g for 2,4-D and dicamba, respectively. Although the effect on yield reduction in these vineyards were not studied, a visual appraisal indicated damage to vegetative tissues of vines, including decreased shoot growth, leaf area, internode length, and pruning weight. This survey is a first of its kind study and gives growers crucial field-level information on the extent and frequency of off-target movement of synthetic auxin herbicide within Texas High Plains AVA vineyards.

Funding Support: State of Texas Viticulture and Enology Research Funds, Department of Plant and Soil Science