Chaff lining: A harvest weed seed control method to manage herbicide-resistant weeds in US soybean production
Date
2021-12
Authors
Bennett, Avery Joel
Major Professor
Advisor
Jha, Prashant
Moore, Kenneth J.
Hodgson, Erin W.
Committee Member
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Abstract
Waterhemp (Amaranthus tuberculatus [Moq.] J. D. Sauer), velvetleaf (Abutilon theophrasti Medik.) and giant foxtail (Setaria faberi Herrm.) are among the most troublesome weeds in corn (Zea mays L.) and soybean (Glycine max [L.] Merr.) production systems of the Midwestern United States. The level of infestation of these weed species are becoming common in soybean fields due to continued rise in herbicide-resistant (HR) populations. In a conventional harvesting system HR weed seeds and crop residue are spread back to the field, increasing the weed seedbank on annual basis. Harvest weed seed control (HWSC) methods such as chaff lining, a non-herbicidal control tactic that targets weed-seed-bearing chaff at the time of crop harvest offers farmer a novel weed management tool. The objectives of this research were: 1) to determine the effect of soybean chaff on emergence dynamics of waterhemp, velvetleaf, and giant foxtail, 2) to determine percent waterhemp seed retention at the time of soybean harvest, 3) to quantify the efficacy of chaff lining in capturing and concentrating waterhemp seeds into a chaff line (30 to 50 cm wide), and 4) to quantify the effect of chaff line on waterhemp emergence and growth in the following corn in-conjunction with herbicides. To accomplish objective 1, greenhouse experiments were conducted in 2019 and 2020 at the Iowa State University (ISU), Ames, IA. Seven soybean chaff rates ranging from 396 to 692 kg ha-1, equivalent to grain yield of 2690 to 4708 kg ha-1 were evaluated. All soybean chaff rates effectively reduced cumulative emergence of waterhemp, velvetleaf, and giant foxtail. At the highest tested rate of soybean chaff (692 kg ha-1) waterhemp emergence was reduced by 97%, velvetleaf emergence by 83%, and giant foxtail emergence by 70% compared to the no-chaff at 6 weeks after treatments. The soybean chaff rate required to reduce emergence by 50% (EC50) was 240 kg ha-1 for waterhemp, 510 kg ha-1 for velvetleaf, and 568 kg ha-1 for giant foxtail. These results indicate that chaff produced by average yielding soybean in Iowa can effectively be used for chaff lining to suppress emergence of these three weed species.
To accomplish objective 2, 3, and 4, field experiments were conducted in 2020 and 2021 in a soybean-corn rotation at ISU Curtiss Farm near Ames, IA and a grower field in Roland, IA. Percent waterhemp seed retention and efficacy of chaff liner were evaluated in 2020 soybean. About 70% of waterhemp seeds were retained on the mother plant at the time of soybean harvest in 2020. The chaff liner concentrated >99% of the waterhemp seeds that entered the combine into the chaff line. The effect of soybean chaff line and corn herbicide programs on waterhemp emergence and growth were evaluated in 2021 corn. Although waterhemp density was 76% higher inside the chaff line than outside the chaff line, aboveground biomass was 63% lower inside the chaff line than outside the chaff-line at 12 weeks after corn planting. Additionally, waterhemp inside the chaff line had a delayed (one week) emergence than waterhemp outside the chaff line. Application of the preemergence herbicides in corn inside the chaff line delayed waterhemp emergence by >2 weeks than outside the chaff-line. A follow-up postemergence herbicide application in corn was needed only inside the chaff line to manage waterhemp, indicating lower overall herbicide use. These results suggest that chaff lining should be implemented in soybean-based cropping systems of the Midwest to target waterhemp seeds at harvest and reduce selection pressure exerted by herbicides, thereby managing herbicide weed seedbanks.
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