Critical Timing of Weed Removal in Dry Bean as Influenced by the Use of Preemergence Herbicides

The critical timing of weed removal (CTWR) is the point in crop development when weed control must be initiated to prevent crop yield loss due to weed competition. A field study was conducted in 2018 and 2020 near Scottsbluff, NE to determine how the use of preemergence herbicides impacts the CTWR in dry bean. The experiment was arranged as a split-plot, with herbicide treatment and weed removal timing as main and sub plot factors, respectively. Herbicide treatment consisted of no-preemergence, or pendimethalin (1070 g ai ha–1) + dimethenamid-P (790 g ai ha–1) applied preemergence. Sub-plot treatments included season-long weed-free, weed removal at: V1, V3, V6, R2, and R5 dry bean growth stages, and a season-long weedy control. A four-parameter logistic model was used to estimate the impact of time of weed removal, for all response variables including dry bean yield, dry bean plants m–1 row, pods plant–1, seeds pod–1, and seed weight. The CTWR based on 5% yield reduction was estimated to range from the V1 growth stage [(16 d after emergence (DAE)] to the R1 growth stage (39 DAE) in the no-PRE herbicide treatment. In the PRE-applied treatment, the CTWR began at the R2 growth stage (47 DAE). Dry bean plants m–1 row was reduced in the no-preemergence treatment when weed removal was delayed beyond the R2 growth stage in the 2020 field season. The use of preemergence-applied herbicides prevented a reduction in the number of pods plant–1 in 2020, and the number of seeds pod–1 in 2018 and 2020. In 2018, the number of pods plant–1 was reduced by 73% when no-preemergence was applied, compared to 26% in the preemergence-applied treatment. The use of preemergence-applied soil active herbicides in dry bean delayed the CTWR and preserved yield potential.

Biodegradable mulch controls weeds and increases water use efficiency in lettuce crops

ABSTRACT Vegetable cultivation requires high water use and weed control. Soil cover using recycled paper, can be an alternative to polyethylene film to reduce weed incidence, soil temperature and increase water use efficiency beyond reduces costs and environmental pollutions. The objective of this study was to evaluate the use of biodegradable mulch in weed management and water use efficiency (WUE) in lettuce crop. The treatments were composed of brown recycled paper (RP), black polyethylene film (PF) and soil without cover with weed removal (WR) and without weed removal (WW). RP and PF were efficient to control weeds. The soil temperature with RP was 8.2 and 2.1ºC lower than with PF and WR, respectively. The lettuce yield with RP was 14.5 and 28.3% higher than WR, and with PF, respectively. The water volume applied with RP was 26.5% lower, and WUE was 55.6% higher compared to WR. Soil cover with recycled paper controlled weeds, reduced soil temperature and water consumption and increased yield and water use efficiency in lettuce crop.

Critical Time for Weed Removal in Corn as Influenced by Planting Pattern and PRE Herbicides

Determining the critical time for weed removal (CTWR) is essential for the development of an integrated weed management plan. Therefore, field experiments were conducted to evaluate the effects of two planting patterns (standard and twin-row) with and without PRE-applied herbicides on CTWR in corn. Experiments were laid out in a split-plot arrangement with two main plots: (i) standard row planting (SRP) that is 70 cm wide, and (ii) twin-row planting (TRP) with 50 cm distance between each set of double rows. Each main plot was divided into two sub-plots (with and without PRE herbicides). The sub-sub-plots consisted of seven weed removal timings for PRE herbicides, and tank mixes were utilized (S-metolachlor (1.44 kg a.i. ha−1) + terbutylazine (0.75 kg a.i. ha−1)). The CTWR without PRE herbicides was similar in both the SRP and TRP systems, where it was around the V1 to V2 (16 to 19 d after emergence (DAE)) growth stages. The use of PRE-applied herbicides delayed CTWR in SRP to the V4 to V10 (25 to 58 DAE) stages and up to the V11 (60 DAE) stage in TRP. These results clearly indicate that PRE herbicides are important for protecting corn yields regardless of the planting pattern. In more meteorologically favorable seasons (sufficient heat and precipitation) in both sowing systems, corn plants produce their biological maximum with the fact that over the number of plants per unit area (SRP = 80,000 plants ha−1, TRP = 93,900 plants ha−1) provide higher yields in variants with PRE herbicides, and thus the advantage of the TRP system can be justified.

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

Residual herbicides applied PRE provide early season weed control, potentially avoid the need for multiple POST herbicides, and can provide additional control of herbicide-resistant weeds. Thus, field studies were conducted in 2017 and 2018 at Concord, NE, to evaluate the influence of PRE herbicides on critical time for postemergence weed removal (CTWR) in corn. The studies were arranged in a split-plot design that consisted of three herbicide regimes as main plot treatments and seven weed removal timings as subplot treatments in four replications. The herbicide regimes included no PRE herbicide, atrazine, and a premix of saflufenacil/dimethenamid-P mixed with pyroxasulfone. The weed removal timings were at V3, V6, V9, V12, and V15 corn growth stages and then plots were kept weed-free until harvest. A weed-free and nontreated control were included for comparison. The relationship between corn growth or yield, and weed removal timings in growing degree days (GDD) was described by a four-parameter log-logistic model. This model was used to estimate the critical time for weed removal based on 5% crop yield loss threshold. A delay in weed removal until the V2 to V3 corn growth stage (91 to 126 GDD) reduced corn biomass by 5% without PRE herbicide application. The CTWR started at V3 without PRE herbicide in both years. Atrazine delayed the CTWR up to V5 in both years, whereas saflufenacil/dimethenamid-P plus pyroxasulfone further delayed the CTWR up to the V10 and V8 corn growth stages in 2017 and 2018, respectively. Herbicide applied PRE particularly with multiple sites of action can delay the CTWR in corn up to a maximum growth stage of V10, and delay or reduce the need for POST weed management.

Critical time for weed removal in dicamba tolerant soybean as influenced by pre emergence herbicides

Field experiment was conducted in 2019 at Haskell Agriculture Laboratory, Concord, NE, USA. Goal of the study was to test the influence of PRE-EM herbicides on the Critical Time for Weed Removal (CTWR) in dicamba-tolerant soybean. The study was arranged in a split-plot design which consisted of four herbicide regimes as main plot treatments and seven weed removal timings as subplot treatments, with four replications. The herbicide regimes included: (1) no PRE and glyphosate, (2) acetochlor and dicamba as PRE and glyphosate as POST, (3) acetochlor and dicamba as PRE and glyphosate and dicamba as POST, and (4) acetochlor and fomesafen as PRE and acetochlor, glyphosate and dicamba as POST. The five weed removal times included the V1, V3, V6, R2 and R5, and there were also weedy and weed-free season long plots. By utilizing herbicide regimes, the CTWR was delayed to 632 GDD (until V4 soybean growth stage, 28 days after emergence) for acetochlor and dicamba as PRE and glyphosate as POST, 861 GDD (until V6 soybean growth stage, 32 days after emergence) for acetochlor and dicamba as PRE and glyphosate and dicamba as POST, and 1060 GDD (until R1 soybean growth stage, 42 days after emergence) for acetochlor and fomesafen as PRE and acetochlor, glyphosate and dicamba as POST.