Chaff Lines Can Help Control Weeds

Chaff Lines Can Help Control Weeds Herbicide-resistant weeds are still a problem, reducing yield and producing seed for future problem years. Mechanical weed seed control (Vol. 37, No. 6) at the combine can help, but the hammermill add-ons are expensive. A simpler option is chaff lining at harvest. It uses a baffle or chute to concentrate chaff and weed seed from 100% of the field in narrow windrows. “I’ve been working with several colleagues across the U.S. looking at chaff lining, as well as the use of seed mills,” says Jason Norsworthy, University of Arkansas weed scientist and editor of Weed Technology. One of those colleagues, Iowa State University weed science professor Prashant Jha, found that 95% of weed seeds can be concentrated in a chaff line at soybean harvest. While some seed viability is reduced by the natural mulching effect of the chaff line, seed that does germinate usually does so later, making herbicide applications more effective. Another researcher working with the concept is Vipan Kumar, a professor of weed science at Kansas State University. He noted that wheat and sorghum chaff lining was shown to significantly reduce kochia and downy brome emergence. “The mulching effect of chaff lining on weed seed banks further depends on the type of crop being used and the target weed species,” Kumar noted. Norsworthy and others have also explored burning the chaff lines. This practice was once common in Australia but has declined with the adoption of mechanical weed seed destructors. Burning has been considered by weed scientists as far north as Alberta. However, the brief window between harvest and the onset of snow is a problem. Windy days close the window even sooner. Breanne Tidemann, Agriculture Canada weed scientist, Lacombe, Alta., explains that too much wind or wind blowing in the direction of the windrow can negate the effect. If the fire moves too rapidly or isn’t hot enough, the non-seed residue may burn, leaving the seed to germinate in the spring. “Burning is a highly effective option in Arkansas, but it hasn’t been adopted to much extent,” says Norsworthy. He notes that there’s been increased criticism of those who burn stubble, as it creates issues with smoke and carbon dioxide release. Norsworthy’s team tested weed seeds by burning them in a kiln to determine the temperature and duration needed. They discovered that seed size made a difference. Smaller seeds like Palmer amaranth required less heat than larger, hard-coated seeds like pitted morningglory. In a soybean residue burning experiment, all tested weed seeds were killed except for pitted morningglory. However, while the pitted morningglory remained intact, it was nonviable. “When you look at weed management in general, it’s all really centered around soil seed bank management,” said Norsworthy. “If we can drive those soil seedbanks down, it’s going to benefit us in terms of the future populations or densities we have in those fields, as well as lessening the risk of herbicide resistance evolution and spread.” Contact: FARM SHOW Followup, Jason Norsworthy, Crop, Soil, and Environmental Sciences, 115 Plant Sciences Building, University of Arkansas, Fayetteville, Ark. 72701 (ph 479-575-2354; jnorswor@uark.edu; https://crop-soil-environmental-sciences.uark.edu).

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