Studies were conducted from 1998 to 2001 in Tifton, GA, on weed management systems in transplanted cantaloupe and watermelon grown on polyethylene-covered seedbeds. Soil fumigants were metham (748 L/ha) and a nonfumigated control. All metham applications were sprayed in a 61-cm band and incorporated with a modified power tiller. Herbicide treatments were ethalfluralin (0.8 kg ai/ha) premergence (PRE), ethalfluralin plus halosulfuron (36 g ai/ha) PRE, ethalfluralin PRE followed by glyphosate (1.1 kg ai/ha) postemergence POST-SHIELDED, ethalfluralin plus halosulfuron PRE followed by glyphosate POST-SHIELDED, and a nontreated control. Premergence herbicides were directed to row middles not covered in polyethylene, without contacting the transplants. Glyphosate was applied to row middles using a hooded sprayer, just before vine running. Overall weed control was not improved with soil fumigation in either cantaloupe or watermelon, and there was no yield response in either crop. There may be minimal benefit in transplanted cantaloupe and watermelon on polyethylene-covered seedbeds from preplant soil fumigation for weed control, in the absence of other pests. Herbicide systems that included halosulfuron PRE or glyphosate applied POST-SHIELDED improved control of yellow nutsedge compared with ethalfluralin alone. Control of Texas panicum, southern crabgrass, Florida pusley, and smooth pigweed was not improved by halosulfuron or glyphosate. Polyethylene-covered seedbeds provide a mechanical barrier to weed infestation for many species. Integration of these weed control practices gives cantaloupe and watermelon growers effective options for weed management, particularly for a troublesome species such as yellow nutsedge.

The absorption and translocation of the isopropylamine salts of 14C-glyphosate and 14C-imazapyr were compared in established terrestrial alligatorweed. Results indicated that more than twice as much imazapyr as glyphosate was absorbed by treated leaves of alligatorweed. In addition, more imazapyr was translocated to the underground storage tissues in alligatorweed than was glyphosate. This difference in translocation to roots and subterranean storage tissues is proposed as a mechanism for tolerance of alligatorweed to glyphosate and susceptibility to imazapyr.

Studies were conducted in 2012 and 2013 to determine the effect of fomesafen based Palmer amaranth control program in ‘Covington' and ‘Evangeline' sweetpotato cultivars. Treatments consisted of fomesafen pretransplant alone at 0.20, 0.28, 0.36, 0.42, 0.56, and 0.84 kg ai ha−1 or followed by (fb) S-metolachlor at 1.12 kg ai ha−1 0 to 7 d after transplanting (DAP), fomesafen at 0.28 kg ha−1 fb S-metolachlor at 1.12 kg ha−114 DAP, flumioxazin pretransplant at 0.105 kg ai ha−1, S-metolachlor at 1.12 kg ha−1 0 to 7 DAP, clomazone at 0.63 kg ha−1 0 to 7 DAP, napropamide at 2.24 kg ha−1 0 to7 DAP, flumioxazin fb S-metolachlor 0 to 7 DAP, and flumioxazin fb clomazone fb S-metolachlor 14 DAP. Fomesafen pretransplant at 0.28 to 0.84 kg ha−1 alone or followed by S-metolachlor at 1.12 kg ha−1 0 to 7 DAP provided 80 to 100% Palmer amaranth control without reduction of yield and significant (< 13%) injury in Covington and Evangeline sweetpotato. Flumioxazin alone or fb S-metolachlor and flumioxazin fb clomazone fb S-metolachlor provided Palmer amaranth control (≥ 95%) with little injury (≤ 5%) and similar yield to the weed-free check. Clomazone alone did not cause injury, but controlled only 24 to 32% of Palmer amaranth at 50 DAP, which resulted in reduced no. 1, marketable, and total sweetpotato yield. Napropamide provided inconsistent control of Palmer amaranth in both years; therefore jumbo and total sweetpotato yield was reduced as compared to the weed-free check in 2012. Palmer amaranth control, sweetpotato cultivar tolerance, and yield in treatments with fomesafen fb S-metolachlor were similar to flumioxazin fb S-metolachlor. In conclusion, a herbicide program consisting of pretransplant fomesafen (0.28 to 0.42 kg ha−1) fb S-metolachlor (1.12 kg ha−1) is a potential option to control Palmer amaranth without causing significant injury and yield reduction in sweetpotato.

Novel forms of selective weed control are needed by many types of growers, but especially by organic growers who are restricted from using synthetic herbicides. Abrasive grit made from corn cobs was expelled from a sand blaster at 517 kPa pressure and aimed at plants of common lambsquarters and corn positioned 300 mm distant. Most small weed plants were killed by one split-second blast of grit, but corn plants suffered little damage by the same treatment. Air-propelled grit made from agricultural residues possibly could be used for selective nonchemical weed control without the need for soil tillage.

Research was conducted in 1997 and 1998 to evaluate narrow row spacing and glufosinate in glufosinate-resistant corn. Glufosinate-resistant corn was planted in 51- and 102-cm row spacings at the same plant populations. Herbicide treatments included glufosinate alone and in different herbicide combinations. Atrazine plus glufosinate enhanced Palmer amaranth control compared to glufosinate alone. Control of johnsongrass, ivyleaf morningglory, entireleaf morningglory, Texas panicum, smellmellon, browntop panicum, and toothed spurge with glufosinate was greater than 82%. Common sunflower control with glufosinate was greater than 95%. Atrazine followed by glufosinate applications provided at least 94% control of all species and was the most consistent herbicide system used. Row spacing had little effect on weed control. Crop injury to glufosinate-resistant corn was minimal with glufosinate and atrazine plus glufosinate combinations.

Field studies were conducted in 1996 and 1997 to evaluate response of eight peanut cultivars to flumioxazin applied preemergence (PRE) at 71 g ai/ha. Peanut cultivars evaluated include ‘NC 12C’, ‘NC 7’, ‘VAC 92R’, ‘NC-V 11’, ‘NC 10C’, ‘AT VC 1’, ‘NC 9’, and the experimental breeding line ‘N9001OE’. Visible injury 3 wk after planting in 1996 was 3% or less regardless of cultivar. In 1997, all cultivars were injured 15 to 28% with flumioxazin PRE, except VC 1, which was injured 45%. No visible injury was observed at 5 and 9 wk after planting. Flumioxazin did not influence the incidence of early leaf spot, late leaf spot, southern stem rot, cylindrocladium black rot, or tomato spotted wilt virus. Flumioxazin did not affect percentage of extra-large kernels, sound mature kernels, other kernels, and total yield.

A practical expert system is needed to handle POST weed control in herbicide-intensive crops such as wheat, barley, oat, rye, sugarbeet, corn, and sorghum. SELOMA is an expert system having a step-by-step problem-solving procedure closely resembling what a weed management expert would follow. It is based on field surveys of weed density, and crop and weed growth stage and height. SELOMA evaluates weed competitiveness and provides weed management advice. It suggests whether or not to intervene, chemical and mechanical weed control treatments, and selects the best herbicides, including commercial formulations, costs, and optimal dosages.

A field study was conducted in 1992 and 1993 to identify the spray volume and droplet size combinations to optimize control of common cocklebur (Xanthium strumarium) from acifluorfen by maximizing target deposition. In many instances, acifluorfen controlled common cocklebur better using either small (250 µm) or large (450 µm) spray droplets when applied at the lower carrier volumes of either 56 or 112 L/ha. When sprays were applied at 169 L/ha, there was little difference in control between droplet sizes. Deposition of acifluorfen was determined in 1993. Stepwise regression indicated that acifluorfen deposition amount is less important than environmental conditions for common cocklebur control. Relative humidity was the most significant variable for determining common cocklebur control with acifluorfen.

Four field experiments were conducted in Louisiana and Mississippi in 2009 and 2010 to evaluate POST herbicides treatments with tembotrione applied alone or as a prepackaged mixture with thiencarbazone for weed control in corn. Treatments included tembotrione at 92 g ai ha−1, thiencarbazone : tembotrione at 15 : 76 g ai ha−1, atrazine at 2,240 g ai ha−1, glufosinate at 450 g ai ha−1, glyphosate at 860 g ae ha−1, and coapplications of tembotrione or thiencarbazone : tembotrione with atrazine, glufosinate, or glyphosate. All treatments were applied to 26-cm corn in the V4 growth stage. Treatments containing thiencarbazone : tembotrione and those with tembotrione controlled barnyardgrass, browntop millet, entireleaf morningglory, hophornbeam copperleaf, johnsongrass, Palmer amaranth, and velvetleaf 85 to 96% and 43 to 97% 28 d after treatment and at corn harvest, respectively. Corn yield ranged from 9,200 to 10,420 kg ha−1 and was greater than the nontreated control following all herbicide treatments, except atrazine alone. Results indicated that thiencarbazone : tembotrione or tembotrione POST is an option for weed management in corn, and applications of thiencarbazone : tembotrione would be strongly encouraged where rhizomatous johnsongrass is problematic.

Kochia is a troublesome weed in the western Great Plains and many accessions have evolved resistance to one or more herbicides. Dicamba-resistant soybean is being developed to provide an additional herbicide mechanism of action for POST weed control in soybean. The objective of this study was to evaluate variation in response to dicamba among kochia accessions collected from across Nebraska. Kochia plants were grown in a greenhouse and treated when they were 8 to 12 cm tall. A discriminating experiment with a single dose of 420 g ae ha−1 of dicamba was conducted on 67 accessions collected in Nebraska in 2010. Visual injury estimates were recorded at 21 d after treatment (DAT) and accessions were ranked from least to most susceptible. Four accessions representing two of the most and least susceptible accessions from this screening were subjected to dose-response experiments using dicamba. At 28 DAT, visible injury estimates were made and plants were harvested to determine dry weight. An 18-fold difference in dicamba dose was necessary to achieve 90% injury (I90) between the least (accession 11) and most susceptible accessions. Approximately 3,500 g ha−1 of dicamba was required in accession 11 to reach a 50% dry weight reduction (GR50). There was less than twofold variation among the three more susceptible accessions for both the I90 and GR90 parameters, suggesting that most kochia accessions will be similarly susceptible to dicamba. At 110 DAT, accession 11 had plants that survived doses of 35,840 g ha−1, and produced seed at doses of 17,420 g ha−1. The identification of one resistant accession among the 67 accessions screened, and the fact that dicamba doses greater than 560 g ha−1 were required to achieve GR80 for all accessions suggest that repeated use of dicamba for weed control in fields where kochia is present may quickly result in the evolution of dicamba-resistant kochia populations.

Field studies were conducted in 1988 and 1989 to examine the interrelations of cultivation and herbicide band width in controlling pitted morningglory and sicklepod in soybean. Alachlor + imazaquin PRE followed by imazaquin + surfactant POST were not applied or were applied on bands 15, 30, 45, 60, 75 cm wide or were broadcast. Plots were cultivated zero, one, two, or three times. Without cultivation, at least a 60-cm wide band was needed to achieve maximum soybean seed yields. A slight linear increase in soybean seed yield in response to increasing band width was observed with one cultivation. With two cultivations, soybean seed yields were similar with and without herbicides, but a 15-cm wide herbicide band was needed to achieve maximum production with three cultivations. Greatest gross returns exclusive of weed management costs were realized with two or three cultivations and a 15-cm wide band.

Laboratory and greenhouse experiments were conducted to determine quinclorac efficacy as influenced by surfactants, methylated seed oil (MSO), basic pH compounds, and salts in the spray carrier water. Quinclorac efficacy for green foxtail control generally increased with an increase in linear alcohol ethoxylate (LAE) surfactant carbon-chain length and percentage of ethoxylation. With LAE surfactants, quinclorac phytotoxicity to green foxtail was nearly doubled (average from 44 to 81%) when triethanolamine (TEA) was included in the spray mixture. Combination of LAE surfactants with TEA also enhanced quinclorac absorption. Enhancement of quinclorac absorption and phytotoxicity by LAE surfactants and TEA was related to spray deposits that had close contact with the cuticle and without apparent quinclorac crystals. Sodium and calcium ions strongly antagonized quinclorac efficacy when applied with a block copolymer surfactant or MSO. Ammonium sulfate or ammonium nitrate adjuvants were more effective than urea–ammonium nitrate liquid fertilizer in overcoming antagonism from salts in spray carrier waters. These results demonstrate the potential for maximizing quinclorac efficacy by careful selection of surfactants, nitrogen fertilizer, and basic pH additives.

A survey was conducted to document the significance of crabgrass species among cropping systems and geographical regions in the continental United States. Surveys were mailed to 117 weed scientists, at least one in each state, including, where possible, extension weed scientists with responsibilities in each of the major agronomic and horticultural crops plus turfgrass systems. A 62% response rate was achieved. Large, smooth, and southern crabgrasses were considered at least occasionally important, with India and blanket crabgrasses considered rarely or not important. Smooth crabgrass and large crabgrass were considered to be important species in most of the latitudinal range, whereas southern crabgrass was considered to be important only in the southern states. Crabgrasses were considered to be more problematic in turf than in other cropping systems. From a regional perspective in turf, large crabgrass was the most important species in the Southeast, followed by southern crabgrass and smooth crabgrass. In the Northeast, smooth crabgrass was perceived as the more important species, but large crabgrass was more important in the north-central states.

A population of buckhorn plantain with suspected resistance to 2,4-D was identified in central Indiana following 30 yr of 2,4-D–containing herbicide applications. Our objectives were to (1) confirm and quantify the level of herbicide resistance in the buckhorn plantain population using dose–response experiments and (2) find alternative herbicides that could be used to control this population. Greenhouse experiments were conducted to quantify the dose–response of resistant (R) and susceptible (S) biotypes of buckhorn plantain to both 2,4-D and triclopyr, two synthetic auxin herbicides from different chemical families. The R biotype was ≥6.2 times less sensitive to 2,4-D than the S biotype. The efficacy of triclopyr was similar on both the R and S biotypes of buckhorn plantain, suggesting the absence of cross-resistance to this herbicide. This is the first report of 2,4-D resistance in buckhorn plantain and the first report of 2,4-D resistance in turf. The resistance mechanism was limited to within a chemical family (phenoxycarboxylic acid) and did not occur across all WSSA Group 4 synthetic auxin herbicides, as the pyridinecarboxylic acid herbicides clopyralid and triclopyr and the arylpicolinate herbicide halauxifen-methyl provided control in our experiments.

Cover crop acreage has substantially increased over the last few years due to the intent of growers to capitalize on federal conservation payments and incorporate sustainable practices into agricultural systems. Despite all the known benefits, widespread adoption of cover crops still remains limited due to potential cost and management requirements. Cover crop termination is crucial, because a poorly controlled cover crop can become a weed and lessen the yield potential of the current cash crop. A field study was conducted in fall 2015 and 2016 at the Arkansas Agricultural Research and Extension Center in Fayetteville to evaluate preplant herbicide options for terminating cover crops. Glyphosate-containing treatments controlled 97% to 100% of cereal rye and wheat, but glyphosate alone controlled less than 57% of legume cover crops. The most effective way to control hairy vetch, Austrian winterpea, and crimson clover with glyphosate resulted from mixtures of glyphosate with glufosinate, 2,4-D, and dicamba. Higher rates of auxin herbicides improved control in these mixtures. Glufosinate alone or in mixture controlled legume cover crops 81% or more. Paraquat plus metribuzin was effective in terminating both cereal and legume cover crops, with control of cereal cover crops ranging from 87% to 97% and control of legumes ranging from 90% to 96%. None of these herbicides or mixtures adequately controlled rapeseed.

A field experiment was conducted in 2009–2010 at Pennsylvania and Maryland locations, and repeated it in 2010–2011 to test the effectiveness of POST-applied herbicides at fall and spring timings on seeded hairy vetch in winter wheat. A total of 16 herbicide treatment combinations was tested that included synthetic auxins, acetolactate synthase (ALS) inhibitors, and a protoporphyrinogen oxidase inhibitor. Spring applications tended to be more effective than fall applications. Among synthetic auxins, clopyralid (105 g ae ha−1) and treatments containing dicamba (140 g ae ha−1) were effective at both timings, resulting in greater than 90% hairy vetch control at wheat harvest. Pyroxsulam and prosulfuron applied at 18 g ai ha−1 provided the most effective hairy vetch control (> 90%) at both application timings among ALS inhibitors. Spring applications of several herbicides provided moderate (> 80%) to high (> 90%) levels of hairy vetch control, including: 2,4-D amine (140 g ae ha−1), mesosulfuron-methyl (15 g ai ha−1), tribenuron-methyl (13 g ai ha−1), and thifensulfuron/tribenuron-methyl treatments (16 and 32 g ai ha−1). Winter wheat injury was evaluated, but symptoms were negligible for most treatments. Winter wheat yields declined with increasing hairy vetch biomass. Fall herbicides may be prioritized to reduce hairy vetch competition during the fall and early spring growing season. Our research has established that several synthetic auxin and ALS-inhibiting herbicides, applied POST in fall or spring, can be safely used in winter wheat to control hairy vetch in an integrated weed management program.

In Australia, widespread evolution of multi-resistant weed populations has driven the development and adoption of harvest weed seed control (HWSC). However, due to incompatibility of commonly used HWSC systems with highly productive conservation cropping systems, better HWSC systems are in demand. This study aimed to evaluate the efficacy of the integrated Harrington Seed Destructor (iHSD) mill on the seeds of Australia’s major crop weeds during wheat chaff processing. Also examined were the impacts of chaff type and moisture content on weed seed destruction efficacy. Initially, the iHSD mill speed of 3,000 rpm was identified as the most effective at destroying rigid ryegrass seeds present in wheat chaff. Subsequent testing determined that the iHSD mill was highly effective (>95% seed kill) on all Australian crop weeds examined. Rigid ryegrass seed kill was found to be highest for lupin chaff and lowest in barley, with wheat and canola chaff intermediate. Similarly, wheat chaff moisture reduced rigid ryegrass seed kill when moisture level exceeded 12%. The broad potential of the iHSD mill was evident, in that the reductions in efficacy due to wide-ranging differences in chaff type and moisture content were relatively small (≤10%). The results from these studies confirm the high efficacy and widespread suitability of the iHSD for use in Australian crop production systems. Additionally, as this system allows the conservation of all harvest residues, it is the best HWSC technique for conservation cropping systems.

Field studies were conducted to evaluate residual herbicides applied alone and with a contact weed control program in peanut in Georgia and Alabama. Residual herbicide treatments included pendimethalin preemergence (PRE) at 924 g ai/ha, diclosulam PRE at 18 and 26 g ai/ha, flumioxazin PRE at 70 and 104 g ai/ha, sulfentrazone PRE at 168 and 280 g ai/ha, and imazapic postemergence (POST) at 71 g ai/ha. All herbicides were applied alone and in combination with an early postemergence (EPOST) application of paraquat plus bentazon. Peanut injury ranged from 0 to 7% for diclosulam, from 0 to 28% for flumioxazin, from 0 to 59% for sulfentrazone, from 0 to 15% for imazapic, and from 4 to 12% for paraquat plus bentazon. Across locations and years, Florida beggarweed control was 92% or greater with flumioxazin PRE at 104 g/ha, 77% or greater with diclosulam PRE at 26 g/ha, 80% or greater with sulfentrazone PRE at 280 g/ha, ranged from 54 to 86% for imazapic POST, and was 68% or less for paraquat plus bentazon EPOST. For diclosulam, sulfentrazone, and imazapic, including paraquat plus bentazon EPOST improved Florida beggarweed control vs. these treatments alone. However, flumioxazin alone provided consistent and season-long Florida beggarweed control without paraquat plus bentazon EPOST. Sicklepod control with imazapic was consistently greater than 90%, but it was 70% or less with diclosulam, flumioxazin, and sulfentrazone. Paraquat plus bentazon EPOST used with the residual herbicide treatments resulted in variable sicklepod control ranging from 40 to 99%. Yellow nutsedge control was 95% or greater with sulfentrazone, varied from 56 to 93% with diclosulam, and was 87% or greater with imazapic. Tall and smallflower morningglory, wild poinsettia, Palmer amaranth, and bristly starbur control varied by residual herbicide treatment. Yields were similar for diclosulam, flumioxazin, sulfentrazone, and imazapic treated peanut.

Dryland rotations are changing in the semiarid Great Plains because of no-till systems. Producers now rotate summer annual crops such as corn with winter wheat and fallow, which can disrupt weed population growth because of diverse life cycles among crops. This study estimated changes in weed populations as affected by rotation design, with the goal of suggesting crop sequences that lower weed community density. We used an empirical life-cycle simulation based on demographics of jointed goatgrass and green foxtail to compare various rotations consisting of winter wheat, corn, proso millet, and fallow across a 12-yr period. The simulation indicated that designing rotations to include a 2-yr interval when seed production of either jointed goatgrass or green foxtail is prevented will drastically reduce weed populations. Arranging four different crops in sequences of two cool-season crops, followed by two warm-season crops was the most beneficial for weed management. Fallow, if used, serves in either life-cycle category. However, if the same crop is grown 2 yr in a row, such as winter wheat, the benefit of rotation design on weed density is reduced considerably. Impact of rotation design on weed density was enhanced by improving crop competitiveness with cultural practices. Rotations with balanced life-cycle intervals not only reduce weed density but enable producers to use alternative weed management strategies, improve effectiveness of herbicides used, and minimize herbicide resistance.

'Silver Xtra Sweet’, ‘How Sweet It Is', ‘Zenith’ and 'Sweetie 76’ were evaluated for response to 0, 35, and 70 g/ha nicosulfuron applied POST at the 5- to 6- or 7- to 8-leaf stages of growth. Nicosulfuron (35 g/ha) caused 60 to 80% visible injury to Silver Xtra Sweet. How Sweet It Is and Zenith were moderately tolerant (< 20% visible injury) and Sweetie 76 was the most tolerant (10% visible injury). All cultivars were less tolerant when nicosulfuron was applied at the 7- to 8-leaf than the 5- to 6-leaf stage. Plant height of Silver Xtra Sweet was reduced 51% by 35 g/ha nicosulfuron applied at the 5- to 6-leaf stage and injury increased when nicosulfuron was applied at the 7- to 8-leaf stage. Yield losses of Silver Xtra Sweet occurred as a result of the nicosulfuron treatments.