Sweetpotato [Ipomoea batatas (L.) Lam.] is a staple crop that provides nutritional benefits to humans globally, but it is subject to yield loss when competing with weeds, especially during the early stage of establishment. Yield loss can vary widely based on the cultivar, production environment, weed species, and management techniques. To address this challenge, we conducted field research at the Samuel G. Meigs Horticulture Research Farm, Lafayette, IN, and at the Southwest Purdue Agricultural Center, Vincennes, IN, in 2022 to determine the effect of sweetpotato cultivar on the critical weed-free period. The experiment was a split-plot design, with weed-free interval treatments as the main plot factor and cultivar as the subplot factor. The three cultivars used were ‘Covington’, ‘Monaco’, and ‘Murasaki’. Weeds were removed by hand and allowed to establish and compete with the crop beginning at 0, 14, 21, 28, 35, or 42 d after transplanting (DAP). As the weed-free interval increased from 0 to 42 DAP, predicted total yield increased from 19 kg ha−1 to 20,540 kg ha−1 for Covington, 3 kg ha−1 to 11,407 kg ha−1 for Monaco, and 125 kg ha−1 to 13,460 kg ha−1 for Murasaki at the Lafayette location. At Vincennes, as the weed-free interval increased from 0 to 42 DAP, predicted total yield increased from 14,664 kg ha−1 to 33,905 kg ha−1 for Covington, 4,817 kg ha−1 to 18,059 kg ha−1 for Monaco, and 12,735 kg ha−1 to 21,105 kg ha−1 for Murasaki. A threshold of ≤10% total yield reduction was achieved by maintaining sweetpotatoes weed-free 24 DAP for Covington, 20 DAP for Murasaki, and 33 DAP for Monaco.

Infestations of common milkweed (Asclepias syriaca L.), in descending order of incidence in Nebraska, occurred on areas occupied by soybean [Glycine max (L.) Merr.], oats (Avena sativa L.), sorghum [Sorghum bicolor (L.) Moench.], railroad rights-of-way, fallow land, roadsides, corn (Zea mays L.), winter wheat (Triticum aestivum L.), pasture, and alfalfa (Medicago sativa L.). Average crop yield reductions, within common milkweed communities of 11100 to 45 200 plants/ha, ranged from 2 to 10% for corn, 4 to 29% for sorghum, and 12 to 19% for soybeans. Reductions in crop yields tended to increase with increasing common milkweed populations. Germination percentage of common milkweed and sorghum were not significantly affected by growing medium conductivities below 7 and 13 mmho/cm2, respectively. Growth media at pH 2 significantly reduced germination percentage, hypocotyl length, and radicle length of both common milkweed and sorghum as compared with pH 4 to 10. Undiluted aqueous extracts of common milkweed shoot and root material significantly reduced germination percentage, hypocotyl length, and radicle length of sorghum.

Studies were conducted at Grand Rapids, MN, to determine the effect of giant burreed (Sparganium eurycarpum Engelm. # SPGEU) planted at 6, 12, and 24 corms/m2 on wild rice (Zizania palustris L. ‘K2′) growth and yield. Giant burreed, a spreading perennial, had shoot densities of 21, 29, and 42/m2 at harvest for the 6, 12, and 24 corms/m2 treatments, respectively. Wild rice yield and panicle number were reduced approximately 60% when giant burreed shoot density was 40/m2 or higher when compared to the weed-free control. Giant burreed did not interfere with nutrient uptake of wild rice on a whole-plant basis, and increased N fertilizer application did not reduce losses in dry weight. Giant burreed reduced penetration of photosynthetically active radiation (PAR) from 2 to 35% in the wild rice canopy from the early tillering to the anthesis stage of wild rice development. In growth chamber studies, wild rice dry weight and panicle number were reduced by 46 and 65%, respectively, when wild rice was shaded for 12 weeks and compared to a full light treatment. Reduction of PAR penetration into the wild rice canopy appears to be the major mechanism of giant burreed interference with wild rice.

Field studies were conducted in 1991 and 1992 to determine potential soybean injury due to 2,4-D ester at 560, 1120, and 1680 g ai/ha applied 0, 7, and 14 d before planting (DBP). Delayed emergence and increased injury of soybean were observed as 2,4-D rate increased and interval between application and planting decreased. Delay in emergence ranged from 0 to 67% and 0 to 50% in 1991 and 1992, respectively. Injury at 15 days after planting (DAP) combined over years ranged from 0 to 61%. Minimal (0 to 8%) delay in emergence and minimal (0 to 5%) injury at 15, 30, 45, and 60 DAP occurred when 2,4-D at 560 or 1120 g/ha was applied 7 or 14 DBP. No significant yield reduction occurred due to 2,4-D rate, application timing, or their interaction.

Field studies were conducted in 1993 and 1994 to evaluate the tolerance of 16 sweet corn cultivars, representing a range of genotypes, to rimsulfuron applied postemergence (POST) at 12.5 and 25 g ai/ha. There was a significant cultivar by herbicide interaction for visual plant injury, plant height, and yield. ‘Merit’ and ‘Silver Extra Sweet’ were the most sensitive cultivars, with rimsulfuron resulting in complete plant mortality regardless of application dose. ‘Golden Jubilee,’ ‘King Arthur,’ ‘Ivanhoe,’ and ‘Zenith’ were less sensitive. Ten cultivars were tolerant to applications of rimsulfuron at 12.5 g/ha. Sensitivity to rimsulfuron increased as application dose increased.

Removal and plant-back studies were conducted in North Carolina in 1991 and 1992 to determine the critical period of large crabgrass competition in transplanted triploid (seedless) watermelon. For every week that large crabgrass remained in watermelon, medium (3.6 to 7.3 kg) melon yield decreased 3,996 kg and 716 fruit ha−1. For every week that large crabgrass emergence was delayed, yield increased by 814 kg and 142 fruit ha−1. Likewise, for every week that large crabgrass remained in watermelon, marketable (3.6 kg and over) yield decreased 5,582 kg and 911 fruit ha−1. For every week that large crabgrass emergence was delayed, yield was increased 881 kg and 151 fruit ha−1. Large crabgrass emerging after 6 wk had no effect on marketable fruit or number of watermelon. To achieve the greatest quality or quantity of medium or marketable fruit, a large crabgrass-free period between 0 and 6 wk after transplanting was necessary.

The effects of common cocklebur (Xanthium pensylvanicum Wallr.) on soybean [Glycine max (L.) Merr. ‘Wells′] development and seed yield were investigated at Urbana, Illinois, from 1974 through 1977. Increased densities of common cocklebur reduced soybean seed yield, total dry weight, and number of pods per plant. Under full-season competition, one common cocklebur/3 m of row reduced soybean seed yield by 3 to 12%. Soybean seed yield, total dry weight, and number of pods per plant increased as the length of time from soybean emergence to common cocklebur emergence increased. Common cocklebur emerging 4 weeks after soybean emergence reduced soybean seed yield by 7%. As duration of competition with common cocklebur increased, soybean seed yield, total dry weight, and number of pods per plant decreased. The reduction in soybean seed yield was less than 10% when common cocklebur was removed 6 weeks after soybean emergence. Effects of common cocklebur competition with soybeans in Illinois were similar to those observed in the southern United States.

Field experiments were conducted at Frederick, MD, in 1985 and 1986 to determine effects of weed-interference periods and insects on bell peppers. Weed-interference periods of approximately 40 and 60 d reduced both bell pepper fruit number and weight 10 and 50%, respectively. Bell pepper foliage weight was reduced 10 and 50% with approximately 20- and 50-day weed-interference periods. In 1985 and 1986, insect populations were low with an average of 10 and 3% of the pepper fruit infested, respectively. Most infested fruit was damaged by European corn borer. No significant differences in insect infestation of fruit as related to time of weed-interference periods were noted.

Field studies were conducted to determine the response of sublethal glyphosate and dicamba doses to processing tomato flowering loss and marketable yield. Dose–response studies for both herbicides were conducted on four commercial processing tomato lines (two different lines within each study) and plants were sprayed at either the vegetative stage or the early bloom stage. Both glyphosate and dicamba caused higher yield losses when sprayed at the early bloom stage. A 25% yield loss was observed with 8.5 and 7.5 g ae ha−1 for glyphosate and dicamba, respectively, at the early bloom stage and 43.9 and 11.9 g ae ha−1 for glyphosate and dicamba, respectively, at the early vegetative stage. Overall, these tomato cultivars were more sensitive to dicamba than to glyphosate. We conclude that glyphosate and dicamba drift could have serious implications on tomato yields especially if the drift occurs during flowering.

Field experiments were conducted at Hays and Manhattan, KS, in 2002 and 2003 to determine winter wheat response to simulated drift rates of glyphosate and imazamox. Glyphosate and imazamox at 1/100×, 1/33×, 1/10×, and 1/3× of usage rates of 840 g ae/ha glyphosate and 35 g/ha imzamox were applied individually to wheat in the early jointing or the early flower stages of growth. Wheat injury and yield loss increased as herbicide rate was increased, with minimal effect from either herbicide at the 1/100× rate, and nearly complete kill and yield loss of wheat from both herbicides applied at the 1/3× rate, regardless of growth stage at application. In general, wheat injury and yield reduction were greater from glyphosate than from imazamox. In addition, wheat injury and yield loss were greater from herbicide treatment at the jointing stage than at the flowering stage of development. Correlation analysis suggests that visual injury is an accurate indicator of yield reductions. Germination tests of harvested grain showed that the viability of the wheat seed was not reduced if plants survived the herbicide treatment and produced a harvestable seed.

Field experiments were conducted at Wooster, OH, in 2010 and 2011 to evaluate the effect of simulated drift rates of 2,4-D, dicamba, and 2,4-D plus glyphosate on processing broccoli and bell pepper. Treatments were made in July of each year when bell pepper and broccoli were at the 10- and eight-leaf stage, respectively, and included five 2,4-D rates (1/50, 1/100, 1/150, 1/200, and 1/400 of the recommended field rate of 840 g ae ha−1), five dicamba rates (1/50, 1/100, 1/150, 1/200, and 1/400 of the recommended field rate of 560 g ae ha−1), and three rates of 2,4-D plus glyphosate (1/100, 1/200, and 1/400 of the recommended field rates). Crop injury was recorded at 7 and 28 d after treatment (DAT). Broccoli and bell pepper responded differently to simulated drift rates each year with higher initial injury ratings observed in 2010, and more persistent symptoms in 2011. 2,4-D at the 1/50 rate reduced broccoli yield by approximately 50% in 2010. Simulated drift rates of 2,4-D did not cause broccoli yield reduction in 2011, nor did simulated drift rates of dicamba, or 2,4-D plus glyphosate reduce yield either year. Although simulated drift treatments did not reduce total yield of bell pepper, the timing of fruit maturity was affected. Yield at first harvest was reduced by high simulated drift rates of each herbicide and by the herbicide tank mix. These results indicate that broccoli and bell pepper are sensitive to very low doses of 2,4-D and dicamba that are typical of those encountered in drift events. The impact of actual drift on delayed maturity and total yield of these crops is likely to be costly for the farmer.

Field studies were conducted from 2000 through 2002 to evaluate the effects of atrazine, pendimethalin, and trifluralin applied alone or in combination followed by cultivation when weeds and grain sorghum were less than 7 cm tall (early postemergence [EPOST]) or when weeds and grain sorghum were 10 to 15 cm tall (late postemergence [LPOST]). Atrazine plus pendimethalin applied EPOST caused 9 to 14% sorghum stunting all 3 yr while atrazine plus trifluralin applied EPOST caused 1 to 4% grain sorghum stunting. When applied LPOST, atrazine plus pendimethalin or trifluralin resulted in no greater than 3% stunting. Tumble pigweed was controlled at least 99% with atrazine plus pendimethalin or trifluralin applied EPOST or LPOST, whereas Texas panicum was controlled at least 97% with atrazine plus pendimethalin or trifluralin applied EPOST, and 76 to 100% with LPOST application. Sorghum yields were reduced with atrazine plus pendimethalin applied EPOST when compared with all herbicide combinations in one of 3 yr.

Field studies were conducted in 2005 and 2006 to determine the most effective chemical options within three individual herbicide-based burndown programs, glyphosate, paraquat and glufosinate, for controlling glyphosate-resistant horseweed in Mississippi. Burndown treatments were applied April 5, 2005 and March 15, 2006 to horseweed plants 15 to 30 cm in height. Glyphosate at 0.86 kg ae/ha alone provided 60 to 65% horseweed control 4 wk after treatment (WAT). Control 4 WAT ranged from 73 to 74% when the glyphosate rate was increased to 1.25 kg/ha. Glyphosate at 0.86 kg/ha applied in combination with 2,4-D at 0.84 kg ae/ha or dicamba at 0.28 ae/ha maximized control of horseweed (≥ 90%) 4 WAT and soybean yield. Horseweed control 4 WAT with paraquat alone at 0.84 kg ai/ha ranged from 55 to 63% and control did not improve by increasing the rate to 0.98 kg/ha. Addition of 2,4-D or dicamba to paraquat maximized horseweed control both years (78 to 89%), whereas soybean yield was maximized with addition of dicamba or metribuzin at 0.42 kg ai/ha. Glufosinate applied alone at 0.47 kg ai/ha resulted in at least 88% control of horseweed and maximized soybean yield. Results indicate that effective management of glyphosate-resistant horseweed can be obtained in glyphosate-resistant soybean in glyphosate-, paraquat-, and glufosinate-based preplant weed control programs.

Feeding trials were conducted on three (young, mid-fill and mature) developmental stages of cowpea Vigna unguiculata ssp. unguiculata pods in the screenhouse using fourth instar nymphs and adults of Anoplocnemis curvipes (Fabricius), Riptortus dentipes (Fabricius), Mirperus jaculus (Thunberg), Clavigralla tomentosicollis Stål and C. shadabi Dolling. Anoplocnemis curvipes was observed to be the most damaging coreoid species causing a yield reduction of 26.4–51.7% followed by R. dentipes (24.4–29.4%), M. jaculus (21.9–26.9%), C. tomentosicollis (17.9–22.4%) and C. shadabi (15.9–20.4%). The fourth instar nymphs of each pod-sucking bug species caused a significantly higher cowpea yield reduction than their respective adults. Similarly, infestation on young pods compared to mid-fill and mature stages resulted in significantly higher yield reduction. The results suggest that infestation levels of two fourth instar nymphs of A. curvipes or three fourth instar nymphs of the other four pod-sucking bug species per young pod should be adequate for screening of cowpea varieties for resistance to the coreoid bugs.