'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.

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.

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.

In response to concerns about acetolactate synthase (ALS) inhibitor–resistant weeds in wheat production systems, we explored the efficacy of managing Bromus spp., downy and Japanese bromes, in a winter wheat system using alternative herbicide treatments applied in either fall or spring. Trials were established at Lethbridge and Kipp, Alberta, and Scott, Saskatchewan, Canada over three growing seasons (2012–2014) to compare the efficacy of pyroxasulfone (a soil-applied very-long-chain fatty acid elongase inhibitor; WSSA Group 15) and flumioxazin (a protoporphyrinogen oxidase inhibitor; WSSA Group 14) against industry-standard ALS-inhibiting herbicides for downy and Japanese brome control. Winter wheat injury from herbicide application was minor, with the exception of flucarbazone application at Scott. Bromus spp. control was greatest with pyroxsulam and all herbicide treatments containing pyroxasulfone. Downy and Japanese bromes were controlled least by thiencarbazone and flumioxazin, respectively, whereas Bromus spp. had intermediate responses to the other herbicides tested. Herbicides applied in fall resulted in reduced winter wheat yield relative to the spring applications. Overall, pyroxasulfone or pyroxsulam provided the most efficacious Bromus spp. control compared with the other herbicides and consistently maintained optimal winter wheat yields. Therefore, pyroxasulfone could facilitate management of Bromus spp. resistant to ALS inhibitors in winter wheat in the southern growing regions of western Canada. Improved weed control and delayed herbicide resistance may be achieved when pyroxasulfone is applied in combination with flumioxazin.

Experiments were conducted in 1988, 1989, and 1990 at two locations in Missouri to study the influence of fall tillage on the soil persistence of several soybean herbicides and subsequent injury to the rotational crops winter wheat, corn, cotton, and grain sorghum. Chlorimuron, clomazone, imazaquin, imazethapyr, and metribuzin plus chlorimuron were applied at their label and double label rate (2X) in soybean. Fall chisel plowing did not influence the carryover potential of these herbicides on any of the crops, in any year, or at either location of the research. However, herbicides injured several of these rotational crops. The 2X-label rate of clomazone reduced winter wheat grain yield at both locations. None of the herbicide treatments at either location reduced corn yield. Imazaquin applied at the 2X rate caused greater than 30% visible injury to cotton in 1989; however, cotton yield was not affected. The 2X rate of chlorimuron caused a reduction of grain sorghum yield in 1989, but not in 1990 or 1991 at Novelty.

Experiments were conducted to determine the influence of spray carrier salts, UV light, and temperature on sethoxydim phytotoxicity to oat or yellow foxtail. Spray solution pH and ions present were both important to sethoxydim phytotoxicity to oat. Sodium and calcium salts were antagonistic to sethoxydim phytotoxicity only when the spray carrier pH exceeded 7. Ammonium salts and ammonium hydroxide were synergistic with sethoxydim, and the synergism was independent of spray solution pH. Ammonium sulfate, but not ammonium hydroxide, overcame sodium bicarbonate antagonism of sethoxydim. The antagonism of sethoxydim phytotoxicity by sodium bicarbonate was greatest in the presence of UV light and most pronounced when treated plants were exposed to mid-day sunlight. Sodium bicarbonate or low temperature may reduce the speed of sethoxydim absorption allowing for greater UV degradation of unabsorbed sethoxydim on the leaf surface.

Volatility and drift are problems commonly associated with auxin-like herbicides. Field and greenhouse studies were conducted at Texas A & M University to develop a method of quantifying volatility and subsequent off-target movement of 2,4-D, dicamba, and triclopyr. Rate–response curves were established by applying reduced rates ranging from 4 × 10−1 to 1 × 10−5 times the normal use rates of the herbicides to cotton and soybean and recording injury for 14 d after treatment (DAT) using a rating scale designed to quantify auxin-like herbicide injury. Injury from herbicide volatility was then produced on additional cotton and soybean plants through exposure to vapors of the dimethylamine salt of 2,4-D, diglycolamine salt of dicamba, and butoxyethyl ester of triclopyr using air chambers inside a greenhouse and volatility plots in the field. Injury resulting from this exposure was evaluated for 14 d using the same injury-evaluation scale that was used to produce the rate–response curves. Volatility-injury data were then applied to the rate–response curves so that herbicide rates corresponding with observed injury could be calculated. Using this method, herbicide volatility rates estimated from greenhouse-cotton injury were determined to be 3.0 × 10−3, 1.0 × 10−3, and 4.9 × 10−2 times the use rates of 2,4-D, dicamba, and triclopyr, respectively. Greenhouse-grown soybean developed injury consistent with 1.4 × 10−2, 1.0 × 10−3, and 2.5 × 10−2 times the normal use rate of 2,4-D, dicamba, and triclopyr, respectively. Under field conditions, cotton developed injury symptoms that were consistent with 4.0 × 10−3, 2.0 × 10−3, and 1.25 × 10−1 times the recommended use rates of 2,4-D, dicamba, and triclopyr, respectively. Field soybean displayed injury symptomology concordant with 1.6 × 10−1, 1.0 × 10−2, and 1.1 × 10−1 times the normal use rates of 2,4-D, dicamba, and triclopyr, respectively. This procedure provided herbicide volatility rate estimates that were consistent with rates and injury from the rate–response injury curves. Additional research is needed to ascertain its usefulness in determining long-term effects of drift injury on crop variables such as yield.

Four experiments (three in Macedonia, Greece and one in Holtville, CA) were conducted in 1988 and 1989 to evaluate foliar applications of picloram, glyphosate alone and with adjuvant, and triclopyr for the control of established silverleaf nightshade. Silverleaf nightshade control was determined by comparing stem population at the time of herbicide application to stem population 6 to 11 mo after application. Picloram, averaged over rate and location, controlled silverleaf nightshade consistently, restricting regrowth to less than 5%. Silverleaf nightshade control with glyphosate alone or with adjuvant varied with location, regrowth ranged from 0 to 69%. Regrowth of silverleaf nightshade treated with triclopyr approached that of the untreated control.

A 2-yr experiment evaluated the effect of spring soil disturbance on the periodicity of weed emergence. At four locations across the northeastern United States, emerged weeds, by species, were monitored every 2 wk in both undisturbed plots and plots tilled in the spring with a rotary cultivator. Eight weed species including large crabgrass, giant and yellow foxtail, common lambsquarters, smooth pigweed, eastern black nightshade, common ragweed, and velvetleaf occurred at three or more site-years. Spring soil disturbance either had no effect or reduced total seedling emergence compared with undisturbed soils. Total seedling emergence for large crabgrass, giant foxtail, smooth pigweed, and common ragweed were on average, 1.4 to 2.6 times less with spring soil disturbance, whereas eastern black nightshade and velvetleaf were mostly unaffected by the soil disturbance. The influence of soil disturbance on yellow foxtail and common lambsquarters emergence varied between seasons and locations. Although the total number of emerged seedlings was often affected by the soil disturbance, with the exception of yellow foxtail and common ragweed, the periodicity of emergence was similar across disturbed and undisturbed treatments.

Field experiments were conducted to compare large crabgrass control by clethodim or sethoxydim applied alone and with selected fungicides registered for use in peanut. Fluazinam, propiconazole plus trifloxystrobin, or tebuconazole did not affect efficacy of clethodim or sethoxydim. Azoxystrobin, boscalid, chlorothalonil, and pyraclostrobin reduced efficacy of clethodim and sethoxydim in some experiments. Increasing the herbicide rate increased large crabgrass control regardless of the addition of chlorothalonil. In laboratory experiments, 14C absorption was less when 14C-clethodim or 14C-sethoxydim was applied with chlorothalonil. Pyraclostrobin and tebuconazole did not affect absorption of 14C-clethodim or 14C-sethoxydim.

Studies were conducted at one location in 1997 (W97) and in two locations in 1998 (E98 and W98) near Garden City, KS, to evaluate the impact of Palmer amaranth at densities of 0, 0.5, 1, 2, 4, and 8 plants/m of row on forage yield and quality of irrigated corn and to determine if harvesting Palmer amaranth–infested corn for forage rather than for grain would reduce losses. Weed-free corn, Palmer amaranth alone, and corn–Palmer amaranth harvested together were evaluated for forage yield and quality. Forage quality was determined by evaluating in vitro dry matter digestibility (IVDMD), acid detergent fiber (ADF), neutral detergent fiber (NDF), and crude protein (CP). Corn grain and forage yield declined with increasing Palmer amaranth density. However, decline in forage yield ranged from 1 to 44% of the weed-free yield at Palmer amaranth densities of 0.5 and 8 plants/m of row, whereas decline in grain yield ranged from 11 to 74% of the weed-free yield at the same densities. Digestibility of weed-free corn forage, expressed as IVDMD, was significantly higher than that of Palmer amaranth alone at W97 and W98. The CP of weed-free corn forage was similar to that of Palmer amaranth forage at W98, but it was lower at the other two locations. In contrast, CP did not differ between corn–Palmer amaranth harvested together and weed-free corn. The IVDMD of weed-free corn forage was greater than that of corn–Palmer amaranth mixture at W98, but no differences were observed at the other two locations. The relative feeding values of weed-free corn and corn–Palmer amaranth mixture were similar, and greater than that of Palmer amaranth in monoculture. These results indicate that Palmer amaranth interference in corn may not affect forage quality but can cause a decline in yield. This decline in yield is less when harvesting corn and Palmer amaranth together for forage rather than for harvesting corn grain alone.

Field observations in 1986 indicated that increased injury to soybean could occur from clomazone plus metribuzin and clomazone plus linuron compared with metribuzin or linuron alone. Field experiments to measure this response were conducted in 1988, 1989, and 1990 at two locations in Michigan. Atrazine at 0, 1120, 2240, and 3360 g ha-1 was applied the year previous to soybean planting to determine if atrazine residues in the soil influenced soybean response. Herbicide treatments in soybean included clomazone, metribuzin, linuron, alachlor, clomazone plus metribuzin or linuron, alachlor plus metribuzin or linuron, and an untreated control. Additive and synergistic responses in soybean to clomazone plus linuron and clomazone plus metribuzin, regardless of atrazine application rate, occurred in some field environments. Experiments in the greenhouse demonstrated that soybean shoot weight was reduced synergistically from clomazone plus metribuzin compared with either herbicide alone, and the response was greater on a soil with 2.5% organic matter compared with a soil with 4.4% organic matter. Clomazone plus metribuzin reduced leaf area and shoot dry weight, regardless of placement, while leaf area and shoot dry weight were reduced more when clomazone plus linuron- and atrazine plus metribuzin-treated soil was placed in the same zone as the soybean seed. The synergistic interaction in soybean to clomazone plus metribuzin occurred under both cool and warm temperature regimes in growth chamber studies.

“Cool white, and intricate, Queen Anne's lace hedges our summer highways with spendthrift loveliness. But who of us can imagine the full beauty and wonder of this plant as we speed by?”—Green Immigrants by Claire Shaver Haughton.

Machine-vision cultivator guidance systems are commercially available to growers, but little work has been done to determine if these guidance systems can improve integrated weed management systems in vegetable crops. Studies were conducted in 2005 and 2006 in broccoli and lettuce to evaluate band-applied DCPA or pronamide, respectively, and four noncultivated bands ranging from 5.1 to 12.7 cm. DCPA or pronamide were applied in bands centered on the seed line at 0, 7.6 or 12.7 cm wide. A commercial machine-vision system was used to guide a commercial cultivator. Generally, weed densities and hand-weeding times were less where the DCPA band in broccoli or the pronamide band in lettuce were 7.6 or 12.7 cm wide compared to no herbicide. Weed densities were lowest in both crops where the noncultivated band width was 5.1 cm compared to 12.7-cm noncultivated bands. For broccoli in both 2005 and 2006, net returns above production costs were generally higher in the 7.6- and 12.7-cm-wide DCPA bands compared with the no-herbicide band. In lettuce in both years, the no-pronamide treatment had higher net returns, when compared with the 7.6- and 12.7-cm pronamide bands. Lettuce yields and higher net returns in the no-pronamide treatment compared to the 7.6- and 12.7-cm pronamide bands may be due to slight yield reduction from pronamide. Results suggest that pronamide was not needed during the dry months of the year when weed management tools such as hand-weeding and cultivation work very well. However, in periods of rainy weather when cultivation and hand-weeding are not possible, then pronamide would likely provide the greatest economic benefit. Given the large impact of cultivation on vegetable weed management programs, the greatest potential benefit of machine-vision guided cultivators is if they facilitate more timely and effective cultivation.

Reduced-tillage systems including no-tillage and striptillage have well-known benefits for conserving and improving soils, protecting vulnerable crops from extreme weather events, and reducing labor and fuel costs associated with full-width inversion tillage (Franzluebbers 2002, 2005; Parsch et al. 2001; Pesant et al. 1987; Spargo et al. 2008). Despite these benefits, reduced-tillage has not been widely adopted in many cropping systems due in part to the increased difficulty of managing weeds when tillage is not used. Not surprisingly, adoption of reduced-tillage has occurred primarily in crops for which low-cost, effective herbicides are available, including glyphosate-resistant soybean [Glycine max (L.) Merr.], corn (Zea mays L.), cotton (Gossypium hirsutum L.), and sugarbeets (Beta vulgaris L.) (Horowitz et al. 2010; Tarkalson et al. 2012). Increased use of a narrow range of herbicides in these cropping systems has exacerbated problems of herbicide resistance (Duke and Powles 2009; Heap 2012). Conversely, adoption of reduced-tillage has been limited in crops where effective herbicides are not available (e.g. in “minor crops” like vegetables) or prohibited (e.g. in organic production systems). Research aimed at identifying nonchemical approaches to managing weeds in reduced-tillage production systems has the potential to increase adoption of reducedtillage while minimizing herbicide use and selection pressure for herbicide resistance in production systems currently using reduced tillage (Figure 1).

The challenges associated with the adoption of conservation tillage and/or low-input cropping systems, whether organic or herbicide-free, across Canada are shaped by scale, environment, and local practices. A study in eastern Canada captured the challenges of introducing low-input cropping systems in mature (20+ yr) tillage treatments in a barley/red clover/corn/soybean rotation. Each mature tillage system came with its own weed problems, but this did not affect crops such as barley and red clover, which produced similar yields across high and low input systems. However, some form of primary tillage was needed to achieve adequate weed control and yield in organic (ORG) and herbicide-free (HF) systems. The HF and ORG systems with no-till actually failed to produce a corn crop but produced soybean yields that were half or less than that for other treatments. The successful combination of conservation tillage practices and low-input systems in eastern Canada would thus appear to be crop-specific, being easier to achieve in competitive cereal crops. In western Canadian organic agriculture, tillage is practiced with low-disturbance chisel plows instead of inversion plows. However, green manure crops (summer cover crops) are often terminated with tandem discs. Both roller crimpers and mowing can successfully kill annual green manure crops such as field pea and rye, and usually result in reduced weed growth following termination. However, the lack of tillage can result in lower crop yields in wheat following green manure terminated by roller crimping compared to tillage. Challenges for no-till organic practices include perennial weed control and soil fertility. Overall, flexible crop production programs such as the former Manitoba Pesticide Free Production program and the “Agriculture raisonnéeTM” program in Québec are more likely to promote sustained environmental, economic, and social prosperity than rigid adherence to organic or no-till practices.

Combinations of thifensulfuron with carbaryl, chlorpyrifos, malathion, and methomyl caused soybean injury that exceeded the expected injury based on effects of herbicide and synergists applied alone. Thifensulfuron-induced injury and growth reductions generally increased as insecticide rates increased from 140 to 560 g ai ha-1. TBPT and fenarimol also synergistically enhanced thifensulfuron injury in soybeans. Yellow foxtail control by thifensulfuron was enhanced slightly by all insecticides except carbaryl. Insecticides did not enhance kochia control by thifensulfuron.

Experiments were conducted in 1989 and 1990 to study the effects of 220 g ai ha-1 AC 263,222, 840 g ai ha-1 glufosinate, 560 g ai ha-1 glyphosate, and 840 g ai ha-1 paraquat on sicklepod seed production and quality when applied at R5, R6, R7, and R8 growth stages of sicklepod. No seed were produced on plants treated at R5 with paraquat and glufosinate; glyphosate was the least effective herbicide at this growth stage. Although sicklepod seed germinated after AC 263,222 application at R5, no seedling emergence occurred. Normal seedlings, seedling emergence, and seedling radicle length were reduced by all herbicides applied to parent plants at R5, R6, and R7 growth stages. AC 263,222 applied at R7 reduced normal seedlings and seedling emergence more than any other herbicide. No effects were observed on any of the variables investigated when herbicides were applied at R8.

Studies were conducted at two sites in South Dakota in 1992 and at one site in 1993 to measure the effect of velvetleaf on corn growth and yield. Velvetleaf was overseeded in corn rows and thinned to densities of 0, 1.3, 4, 12, and 24 plants/m2. Velvetleaf leaf area index and total biomass were positively correlated with velvetleaf density. Biomass per velvetleaf plant and corn biomass were correlated negatively with velvetleaf density. The percent corn yield reduction was similar for locations and years in spite of large yield differences. Maximum yield loss estimated by a hyperbolic yield reduction model was 37.2% with a loss of 4.4% per unit velvetleaf density.

Interactions of fluazifop-P, sethoxydim, clethodim, and quizalofop-P with DPX-PE350 were evaluated. DPX-PE350 at 110 g ae ha−1 reduced control of large crabgrass when mixed with all graminicides and control of broadleaf signalgrass when mixed with fluazifop-P or quizalofop-P. Increasing the rate of graminicide reduced or eliminated antagonism. Applying sethoxydim and DPX-PE350 sequentially eliminated antagonism on large crabgrass. Control of seedling johnsongrass by the graminicides was not reduced by DPX-PE350. DPX-PE350 reduced control of rhizomatous johnsongrass by sethoxydim. Graminicides had no effect on entireleaf morningglory control with DPX-PE350.