Critical time for weed removal in glyphosate-resistant soybean as influenced by preemergence herbicides

Abstract

Widespread and repeated use of glyphosate resulted in an increase in glyphosate-resistant (GR) weeds. This led to an urgent need for diversification of weed control programs and use of PRE herbicides with alternative sites of action. Field experiments were conducted over a 4-yr period (2015 to 2018) across three locations in Nebraska to evaluate the effects of PRE-applied herbicides on critical time for weed removal (CTWR) in GR soybean. The studies were laid out in a split-plot arrangement with herbicide regime as the main plot and weed removal timing as the subplot. The herbicide regimes used were either no PRE or premix of either sulfentrazone plus imazethapyr (350 + 70 g ai ha−1) or saflufenacil plus imazethapyr plus pyroxasulfone (26 + 70 + 120 g ai ha−1). The weed removal timings were at V1, V3, V6, R2, and R5 soybean stages, with weed-free and weedy season-long checks. Weeds were removed by application of glyphosate (1,400 g ae ha−1) or by hoeing. The results across all years and locations suggested that the use of PRE herbicides delayed CTWR in soybean. In particular, the CTWR without PRE herbicides was determined to be around the V1 to V2 (14 to 21 d after emergence [DAE]) growth stage, depending on the location and weed pressure. The use of PRE-applied herbicides delayed CTWR from about the V4 (28 DAE) stage up to the R5 (66 DAE) stage. These results suggest that the use of PRE herbicides in GR soybean could delay the need for POST application of glyphosate by 2 to 5 wk, thereby reducing the need for multiple applications of glyphosate during the growing season. Additionally, the use of PRE herbicides could provide additional modes of action needed to manage GR weeds in GR soybean.

PRE herbicides influence critical time of weed removal in glyphosate-resistant corn

“…Corn at the V10 growth stage is near canopy closure depending on the row spacing and thus would substantially reduce the competitive impact of emerging weeds on grain yield (Knezevic et al 2003;Tursun et al 2016). Results from previous studies suggested that the CTWR varied with season, crop type, agronomic practice, and environmental factors (Adigun et al 2014;Evans et al 2003;Hall et al 1992;Knezevic et al 2019b;Norsworthy and Oliveira 2004; (Barnes et al 2019).…”

“…Previous studies estimating CTWR in crops have demonstrated that the CTWR is location specific and can be influenced by crop type, weed composition and density, agronomic practices, and environmental conditions (Adigun et al 2014;Evans et al 2003;Knezevic et al 2019b;Osipitan et al 2016;Teasdale 1995;Tursun et al 2016). Limited studies have demonstrated how preplant and PRE herbicides could influence the CTWR and delay the need for POST weed control input in popcorn, soybean, and sunflower (Barnes et al 2019;Elezovic et al 2012;Knezevic et al 2019b). Barnes et al (2019) reported that CTWR started at the V10 or V15 stage with a PRE application of atrazine/S-metolachlor, compared to a CTWR at V4 when no PRE herbicide was used in popcorn.…”

Residual herbicides affect critical time of Palmer amaranth removal in soybean

“…In absence of a PRE herbicide, the ED 50 occurred at 205 GDDc, and it was delayed to 304 and 328 GDDc, respectively, with flumioxazin and flumioxazin/metribuzin/pyroxasulfone. Similarly, Knezevic et al (2019) reported that saflufenacil/imazethapyr/pyroxasulfone and sulfentrazone/imazethapyr applied PRE delayed the ED 50 to 699 and 850 GDDc, respectively, compared with 222 GDDc when no PRE herbicide was applied, with common weed species across the research sites being common lambsquarters (Chenopodium album L.), velvetleaf (Abutilon theophrasti Medik. ), and waterhemp [Amaranthus tuberculatus (Moq.)…”

“…where Y is the response variable (yield [kg ha -1 ], plants m -1 row, pods plant -1 , seeds pod -1 , or yield loss [YL]), c is the lower limit, d is the upper limit, x is the duration of weed removal timing in GDDc, e is the ED 50 (GDDc where 50% response between lower and upper limit occurs; inflection point), and b is the slope of the line at the inflection point. The CTWR in this study was determined based on an arbitrary 5% yield loss threshold (Knezevic et al, 2003(Knezevic et al, , 2019. Root mean square error and modeling efficiency (ME) were calculated to evaluate goodness of fit for soybean yield and yield loss (Barnes et al, 2018;Roman et al, 2000;Sarangi & Jhala, 2018b).…”

“…A recent multilocation study in Nebraska reported that use of a PRE herbicide in soybean reduced early‐season weed competition and delayed the CTWR (Knezevic et al., 2019). The CTWR in soybean across three locations in Nebraska has been reported from V1 to V2 without PRE herbicide and was delayed 2–5 wk depending on PRE herbicide used and the field location (Knezevic et al., 2019).…”