Timothy Grey and Eric P. Prostko. Univ of Georgia, Crop and Soil Science Dept, 115 Coastal Way, P.O. Box 748, Tifton, GA 31794
In Georgia, late season peanut weed control depends on chlorimuron,, bentazon, and 2,4-DB. Economically, chlorimuron is applied to approximately 18% of the crop, costing farmers at least $1.5 million. Producers have complained of inconsistent Florida beggarweed control with chlorimuron and increased incidence of peanut injury from spotted wilt virus, bentazon provides only topical control, and 2,4-DB drift can damage cotton. These concerns force growers to choose between potential crop losses with respect to investment in weed control versus other cropping issues. Additionally, increased miss-applications of glyphosate to peanut by either tank contamination or glyphosate accidentally put into a spray tank when confused for crop oil occur. Growers then ask how much yield loss can occur and if they should continue to apply fungicides to injured peanut. Glyphosate as a late season postemergence herbicide could offer growers control options for Florida beggarweed and sicklepod as these two species are very sensitive. However, peanut research data, with respect to tolerance, yield, and quality, is unavailable for late season applications. Field studies were used to determine peanut response to glyphosate applied at 75, 90, and 105 days after planting (DAP) at Plains and Tifton. Rates were 2, 4, 6, 8, and 12 oz/acre of Roundup Original-max. Data indicated that peanut was tolerant to glyphosate at low doses early in the season and actually increased yield at 2 oz/acre acre. At 75 DAP peanut was susceptible 6 oz/acre and greater. At 90 and 105 DAP peanut was tolerant to rates of 6 oz/acre and less. Injury to peanut included leaf drop, chlorosis, and some stand loss at rates of 8 and 12 oz/acre. Peanut yield was reduced reflecting injury. Peanut seed size was reduced by 75 DAP 8 and 12 oz/acre treatments to 609 and 558 mg/seed, respectively. The nontreated control weighted 685 mg/seed.
See more of Posters--Crops
See more of The 2007 SAAS Convention
