Seed-shattering phenology at soybean harvest of economically important weeds in multiple regions of the United States. Part 2: Grass species

Abstract

Seed shatter is an important weediness trait on which the efficacy of harvest weed seed control (HWSC) depends. The level of seed shatter in a species is likely influenced by agroecological and environmental factors. In 2016 and 2017, we assessed seed shatter of eight economically important grass weed species in soybean [Glycine max (L.) Merr.] from crop physiological maturity to four weeks after maturity at multiple sites spread across eleven states in the southern, northern, and mid-Atlantic U.S. From soybean maturity to four weeks after maturity, cumulative percent seed shatter was lowest in the southern U.S. regions and increased as the states moved further north. At soybean maturity, the percent of seed shatter ranged from 1 to 70%. That range had shifted to 5 to 100% (mean: 42%) by 25 days after soybean maturity. There were considerable differences in seed shatter onset and rate of progression between sites and years in some species that could impact their susceptibility to HWSC. Our results suggest that many summer annual grass species are likely not ideal candidates for HWSC, although HWSC could substantially reduce their seed output at during certain years.

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

“…For most species, the significant negative slope relationship, regardless of weed type, showed that plants with smaller relative biomass shattered more seeds than larger plants (Table 2). This was more apparent for the grass species, possibly because these species shatter their seeds earlier in the season than the broadleaf weeds (Schwartz-Lazaro et al 2021b). Moreover, it has been reported that weed seed shatter varies across climatic conditions and agroecosystems, which was also apparent in this experiment (Taghizadeh et al 2012).…”

“…These field studies investigated the potential for HWSC to be implemented across several major crop-producing regions in the US as an additional IWM tool (Schwartz-Lazaro et al 2021a, 2021b. In general, annual broadleaf weeds are better suited to HWSC, based on the fact that these species retain their seeds for longer into the season in comparison to the annual grasses.…”

“…However, little research has been conducted to evaluate seed retention of various economically important weeds in three major U.S. grain-producing regions that currently face multiple herbicide resistant weed invasions: the north-central region, the south-central region, and the mid-Atlantic region. To help address this, studies were conducted to determine the seed-shattering phenology of 22 economically important weeds across these three regions (Schwartz-Lazaro et al 2021a, 2021b. These studies aid in determining the potential for successful use of HWSC in grain production systems.…”

“…Many annual weed species retain a majority of seed before harvest, thus allowing the seeds to be collected by harvesting equipment that then spreads the seeds out of the rear of the combine, facilitating population dispersal and persistence and enabling weeds to persist in the seedbank (Forcella et al 1996;Goplen et al 2016;Schwartz et al 2016;Schwartz-Lazaro et al 2017, 2021a, 2021bSoni et al 2020;Walsh et al 2013). The lack of weed seed shattering before harvest can be beneficial to newer integrated weed management (IWM) practices such as the use of harvest weed seed control (HWSC) tactics.…”

Effects of Narrow-Windrow Burning on Weed Dynamics in Soybean in Louisiana

“…For example, weed seed retention was greater than 90% for Palmer amaranth, smooth pigweed (Amaranthus hybridus L.), common lambsquarters (Chenopodium album L.), jimsonweed (Datura stramonium), common cocklebur (Xanthium strumarium L.), and johnsongrass up to 3 weeks after soybean maturity across the majority of states (Schwartz-Lazaro et al, 2021a). Barnyardgrass and junglerice (Echinochloa colona L.) also retained greater than 80% of seed up to 2 weeks after soybean maturity (Schwartz-Lazaro et al, 2021b). Modeling studies (Shergill et al, 2020) report greater than 80% seed retention is needed for HWSC to be viable.…”