Seed shattering phenology at soybean harvest of economically important weeds in multiple regions of the United States. Part 3: Drivers of seed shatter

Authors: SCHWARTZ-LAZARO, LAUREN - Louisiana State University; SHERGILL, LOVREET - Montana State University; EVANS, JEFF - University Of Illinois; BAGAVATHIANNAN, MUTHU - Texas A&M University; BEAM, SHAWN - Virginia Tech; BISH, MANDY - University Of Missouri; BOND, JASON - Mississippi State University; BRADLEY, KEVIN - University Of Missouri; CURRAN, WILLIAM - Pennsylvania State University; Mirsky, Steven; DAVIS, ADAM - University Of Illinois; EVERMAN, WESLEY - North Carolina State University; FLESSNER, MICHAEL - Virginia Tech; HARING, STEVEN - Virginia Tech; JORDAN, NICHOLAS - University Of Minnesota; KORRES, NICHOLAS - Oak Ridge Institute For Science And Education (ORISE); LINDQUIST, JOHN - University Of Nebraska; NORSWORTHY, JASON - University Of Arkansas; SANDERS, TAMEKA - Mississippi State University; STECKEL, LARRY - University Of Tennessee; VANGESSEL, MARK - University Of Delaware; YOUNG, BLAKE - Texas A&M University

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2021
Publication Date: 11/15/2021
Citation: Schwartz-Lazaro, L.M., Shergill, L.S., Evans, J.A., Bagavathiannan, M.V., Beam, S.C., Bish, M., Bond, J.A., Bradley, K.W., Curran, W.S., Mirsky, S.B., Davis, A.S., Everman, W.J., Flessner, M.L., Haring, S.C., Jordan, N.R., Korres, N.E., Lindquist, J.L., Norsworthy, J.K., Sanders, T.L., Steckel, L.E., Vangessel, M.J., Young, B. 2021. Seed shattering phenology at soybean harvest of economically important weeds in multiple regions of the United States. Part 3: Drivers of seed shatter. Weed Science.70:79-86. https://doi.org/10.1017/wsc.2021.74.
DOI: https://doi.org/10.1017/wsc.2021.74

Interpretive Summary: The rise of weeds developing resistance to herbicides has greatly complicated weed management. One way to decrease the creation and growth of herbicide-resistant weed populations is through the use of harvest weed seed control (HWSC). In HWSC, modified harvest combines gather weeds along with the cash crop during harvest; seeds are then disposed of in set areas in the field for further control (as with chaff lining) or destroyed (as with impact mills attached to combines). HWSC prevents the seeds of weeds that have "escaped" control during the growing season from joining the weed seedbank to sprout in future years. However, in order to be effective HWSC relies on seeds actually being attached to the weed plants at the time of harvest. This study investigated weed seed retention and shatter (i.e. loss from the parent plant) for 22 weed species across multiple soybean grain-producing regions of the US. This study also evaluated whether plant biomass (i.e. size), weather conditions such as wind, and growing degree days (i.e. amount of heat accumulated over growing season) affected seed retention. Weather had no consistent impact. However, larger weed plants held on to their seeds more than smaller weeds and thus were the best target for HWSC. This work will guide recommendations to farmers as to the usefulness of HWSC in their systems depending on end-of-season weed size, allowing them to increase the efficiency of their weed control efforts.

Technical Abstract: Seed retention, and ultimately seed shatter, are extremely important for the efficacy of harvest weed seed control (HWSC) and likely influenced by various agro-ecological and environmental factors. Field studies investigated seed shattering phenology of 22 weed species across three soybean [Glycine max (L.) Merr.] producing regions in the US. We further evaluated the potential drivers of seed shatter in terms of weather conditions, growing degree days, and plant biomass. Based on our results, weather conditions had no consistent impact on weed seed shatter. However, there was a positive correlation between individual weed plant biomass and delayed weed-seed shattering rates during harvest. Our work demonstrates that HWSC can potentially reduce weed seedbank inputs of plants that have escaped early season management practices and retained seed through harvest. However, smaller individuals of plants within the same population that shatter seed before harvest pose a risk of escaping early season management and HWSC.