Drip irrigation and mulching were tested to minimize unproductive water loss through evaporation and weed interference. A field experiment was conducted during spring season of 2020 and 2021 in split plot design with three replications. The study includes six treatment combinations of drip irrigation methods (surface drip and subsurface drip irrigation) and mulching (black plastic, paddy straw and no mulch) along with one conventional furrow irrigation without mulching (as control) in main plots. Four weed control treatments (atrazine 1000 g a.i./ha as pre-emergence, two hand weedings at 30 and 60 days after sowing [DAS], weed free and weedy for whole crop growth period) were kept in the subplots. The combination of drip irrigation and mulches significantly enhanced leaf area index and crop biomass at 60 DAS than furrow irrigation. Integration of subsurface drip irrigation with plastic mulching resulted in the lowest weed density and biomass among main plots. Drip irrigation coupled with plastic and straw mulching resulted in 86 and 50% reduction in weed density and biomass, respectively, as compared to no mulching. Integration of subsurface drip with paddy straw mulch and black plastic mulch resulted in 17.1 and 15.5% higher maize grain yield, respectively, as compared to furrow irrigation. The highest irrigation water productivity (3.58 kg/m3) was observed in combination of subsurface drip and paddy straw mulch followed by combination of subsurface drip and black plastic mulch (3.51 kg/m3). Overall, straw mulching in drip irrigation system proved economical in terms of maize productivity.

While much research has focused on crop damage following foliar exposure to auxin herbicides, reports documenting the risk posed by exposure via root uptake of irrigation water are lacking. Herbicide residues circulated in tailwater recovery systems may pose threats of cross-crop impacts to nonresistant cultivars with known sensitivity to auxins. An auxin-susceptible soybean [Glycine max (L.) Merr.] cultivar was grown in a controlled growth chamber environment and exposed to dicamba dissolved in irrigation water applied to the soil surface, simulating furrow irrigation. Five herbicide treatment concentrations, ranging from 0.05 to 5.0 mg L−1 and encompassing estimated field doses of 3.1 to 310g ha−1, were applied to the soil of potted soybean plants at V3/V4 or R1 growth stages. Plant injury (0% to 100%), dry mass, height, number of pods, and number of pod-bearing nodes were measured. Kruskal-Wallis and logistic regression analyses were performed to determine treatment differences and examine dose effects. Yield losses were projected using (1) 14 d after treatment plant injury assessments based on injury–yield relationships described for foliar exposures and (2) pod counts. Dicamba concentration was the main significant factor affecting all growth response metrics, and growth stage was a significant explanatory variable only for the height response metric. A nonlinear response to dicamba dose was observed, with the threshold response dose required to affect 50% of plants being three times greater for 40% crop injury compared with 20% injury. Yield projections derived from plant response to root uptake compared with foliar exposure indicate that soybean may express both magnitude of injury and specific symptomology differently when exposure occurs via root uptake. Drift exposure–based models may be incompatible to predict soybean yield loss when injury results from irrigation. Data are needed to develop correlations for predicting yield losses based on field-scale exposure to dicamba in irrigation water, as well as assessment of real-world concentrations of herbicide residues in tailwater recovery systems.

Control of field bindweed (Convolvulus arvensis L.) on irrigated land was studied by application of herbicides once in the fall and then only in the spring for the next 4 yr. Control of field bindweed 8 months after a fall application of 2.2 kg/ha of dicamba (3,6-dichloro-o-anisic acid) or 3.4 kg/ha of 2,4-D [(2,4-dichlorophenoxy)acetic acid] was 90 and 83%, respectively. Spring applications of 0.28 kg/ha of dicamba, 0.56 kg of 2,4-D, or the mixture of these two herbicides suppressed the growth of field bindweed similarly each year. By the fall of the fourth year, field bindweed covered an average of 9% of the soil surface in the plots that received both fall- and spring-applied herbicide treatments, 72% in plots that received only fall-applied herbicide treatments, and 80% in the untreated plots. Yield of corn (Zea mays L. ‘Pioneer 3306’) was significantly higher in all treated plots than in the untreated check plots in 1 out of 2 yr. Yield of sorghum [Sorghum bicolor (L.) Moench ‘Pioneer 833’] was not increased significantly in any treated plots, but in 1 yr the mixture of 0.28 kg/ha of dicamba plus 0.56 kg/ha of 2,4-D reduced yield significantly when this mixture was applied twice at these same rates in the spring.

Yellow nutsedge is an important weed problem in furrow-irrigated fields in the Treasure Valley of eastern Oregon and southwestern Idaho. Field studies were conducted in 2008 and 2009 to evaluate the effect of PPI S-metolachlor or EPTC followed by POST halosulfuron and dicamba plus glyphosate or glyphosate alone on foliar yellow nutsedge control and tuber production in corn. Corn plant height at 8 and 24 d after treatment (DAT) was reduced 20 and 17%, respectively, in POST herbicides alone compared with PPI plus POST herbicide treatments. Yellow nutsedge control at 8 DAT averaged 78% for treatments that included PPI application of EPTC or S-metolachlor 1,600 g ai ha−1 followed by halosulfuron plus dicamba (35 plus 155 g ha−1 or 70 plus 310 g ha−1) plus glyphosate 785 g ha−1 compared with POST treatments alone (49%). The control at 24 DAT was 84% for treatments that contained halosulfuron plus dicamba compared with 73% for POST glyphosate alone. Yellow nutsedge tubers were reduced 56 to 68% among treatments at the end of 2008. Tuber reduction in 2009 was greater with treatments that included PPI herbicides followed by sequential halosulfuron plus dicamba (35 plus 155 g ha−1) plus glyphosate compared with glyphosate alone. Corn yield reflected the level of yellow nutsedge control and early-season weed interference. Treatments that included PPI herbicides had an average yield of 8.2 T ha−1 compared with 6.6 T ha−1 with sequential glyphosate alone. There was a correlation between percent foliar control and the number of yellow nutsedge tubers produced at the end of each year. Application of PPI herbicides followed by POST halosulfuron plus dicamba (35 plus 155 g ha−1 or 70 plus 155 g ha−1) plus glyphosate improved yellow nutsedge control, reduced early corn–weed competition, and produced the highest corn yield under furrow-irrigated conditions.

Weed control in rice is challenging, particularly in light of increased resistance to herbicides in weed populations and diminishing availability of irrigation water. Certain indica rice cultivars can produce high yields and suppress weeds in conventional flood-irrigated, drill-seeded systems in the southern United States under reduced herbicide inputs, but their response to reduced irrigation inputs in these systems in not known. Rice productivity and weed control by weed-suppressive cultivars and conventional nonsuppressive cultivars were evaluated in a nonflooded furrow-irrigated (FU) system and a conventionally flooded (FL) system under three levels of weed management (herbicide inputs) in a 3-yr field study. Rice yields across all weed management levels yielded ∼ 76% less in the FU system than in the FL system. The allelopathic indica cultivar, ‘PI 312777’, and commercial hybrid rice ‘CLXL729’ generally produced the highest grain yields and greatest suppression of barnyardgrass in both irrigation systems. ‘Bengal’ and ‘Wells’ were the top-yielding conventional cultivars whereas ‘Lemont’ and ‘CL171AR’ yielded the least. Weed suppression by PI 312777 and CLXL729 under “medium” weed management was equivalent to that of Lemont and CL171AR at the “high” management level, suggesting that the weed-suppressive cultivars may be able to compensate for suboptimal herbicide inputs or incomplete weed control.