Date of Award
Master of Science
Plant, Soil, and Agricultural Systems
Walters, S. Alan
Dicamba drift is a common issue and has been known to cause injury and yield reduction in a wide range of susceptible crops. A study was established to evaluate the effects of a simulated drift on the plant growth and yield of two pumpkin varieties (Cucurbita pepo ‘Magic Wand’ and C. moschata ‘Autumn Buckskin’) during 2019 and 2020 at the Southern Illinois University Horticulture Research Center in Carbondale. Six rates of dicamba were applied to simulate a mid-post-emergence application made in soybean which drifted onto pumpkins at two growth stages, 8-leaf and 12-leaf. These two pumpkin growth stages would be the approximate size of pumpkins when a mid-post-emergence application would typically be made in soybean. The 12-leaf growth stage also corresponds with Simulated drift rates were targeted at 1/1026, 1/513, 1/256, 1/128, 1/64, 1/32 of a 0.56 kg ae ha-1 rate, corresponding to 0.00056, 0.00112, 0.00224, 0.00448, 0.00896, and 0.01792 kg ae ha-1. Actual dicamba deposition was measured used filter papers (surface area = 176.1 cm2) in each treatment and these measured exposure amounts were used in correlational analyses with pumpkin injury, growth, and yield responses. Pumpkin plants did not develop chlorosis or necrosis at any point of the growing season with any of the dicamba application treatments. However, some injury and stunting were observed on pumpkin plants, regardless of drift rate, although pumpkin plant growth and responses were minimal at the drift rates evaluated. Our results indicated that typical dicamba drift rates cause minimal dicamba injury on pumpkin plants at 8- and 12-leaf growth stages with negligible effects on resulting yields. Pumpkin plant injury and stunting would most likely be observed at dicamba drift rates > 1 μg per 176.1 cm2 of leaf area, which converts to 0.62 g per ha. Pumpkins receiving dicamba drift at different growth stages appear to be less sensitive than some other crops, but a drift event at higher rates than those evaluated in this study may impact plant growth and yield. It is important to note that other pumpkin varieties or other Cucurbita species not evaluated in this study may be more susceptible. Producers using dicamba in soybean rotations that are near pumpkin fields should spray under proper wind, temperature, and humidity conditions to best mitigate the occurrence of any drift events. Nomenclature: 3,6-dichloro-2-methloxybenzoic acid, Cucurbita pepo, C. moschata, dicamba, pumpkin.
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