Weed seed destructor: A harvest weed seed control method to manage waterhemp in soybean

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Meadows, Alexis Linnea
Major Professor
Wiedenhoeft, Mary
Hartzler, Robert G
Licht, Mark
Dentzman, Katie
Committee Member
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Waterhemp (Amaranthus tuberculatus [Moq.] J.D. Sauer) is the most common and troublesome weed in soybean (Glycine max [L.] Merr.) based cropping systems of the Midwestern United States (U.S.). Evolution of multiple herbicide resistance in waterhemp is an increasing concern for soybean producers in Iowa and across the Midwestern states creating an urgent need to develop integrated weed management (IWM) strategies. Harvest weed seed control (HWSC) is one of the potential tools that can be used to limit weed seed inputs into seedbank at the time of crop harvest. Research on the potential of HWSC methods in the U.S. cropping systems is lacking. Objectives of this research were: 1) to quantify waterhemp seed shatter patterns in Iowa soybean production, 2) to quantify waterhemp seed shattering when shaken by the combine header, and 3) to quantify the efficacy of the weed seed destructor in reducing the number of germinable seed returned to the soil seedbank. To accomplish these objectives, field experiments were conducted in 2021 and 2022 in soybean. At the time of soybean harvest, 51% of waterhemp seeds retained on the plant in 2021 which occurred on October 23 compared with 61% in 2022 harvest which occurred on October 7. The timing of waterhemp seed shatter did not affect waterhemp seed viability. In addition to natural waterhemp seed shed, seed shattering occurred when plants were shaken by the combine header during soybean harvest. During this process, waterhemp shattered 15 and 9% of the seeds retained on the plant in 2021 and 2022, respectively. To accomplish objective 3, threshed residue was collected from back of the combine in the presence or absence of seed destructor. Waterhemp seeds passed through the seed destructor were grouped in three categories; no damage (intact), moderate damage, and severe damage. The germinability and viability of intact waterhemp seeds in the presence of weed seed destructor did not differ from those in the absence of weed seed destructor. Waterhemp seeds with moderate damage had 26% lower germination and viability than seeds with no visible damage. No seed germinated or tested viable in severe damage category. Overall, the presence of weed seed destructor reduced number of germinable waterhemp seeds (intact seeds plus seeds tested viable in moderate damage category) by 87% compared to absence of weed seed destructor. Results from this research indicate that a significant portion of waterhemp seeds are likely to enter combine at the time of soybean harvest and therefore, targeting those seeds with a seed destructor will reduce number of germinable seeds returning to the soil seedbank.
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