Field experiments were conducted in Auburn, AL in 2008 and 2009 to assess new aryloxyphenoxypropionate (AOPP) herbicides applied alone and tank-mixed with triclopyr for Tifway bermudagrass control in Zorro zoysiagrass. Treatments included three sequential applications of clodinafop (0.07 kg ai ha−1); triclopyr (1.12 kg ae ha−1); clodinafop + triclopyr (0.07 + 1.12 kg ha−1); fenoxaprop (0.10 kg ai ha−1); fenoxaprop + triclopyr (0.10 + 1.12 kg ha−1); metamifop (0.40 kg ai ha−1); and metamifop + triclopyr (0.40 + 1.12 kg ha−1). Clodinafop, fenoxaprop, and metamifop applied alone controlled Tifway bermudagrass 32 to 65% when rated 3 wk after the final application; however, the addition of triclopyr to these AOPP herbicides increased bermudagrass control to ≥ 89%. All AOPP herbicides applied alone caused unacceptable injury to Zorro zoysiagrass (20 to 42%) 3 wk after the final application. Clodinafop resulted in the greatest zoysiagrass injury (42%), whereas metamifop caused moderate injury (20%). Zorro zoysiagrass exhibited less injury (< 3%) and greater turf coverage (≥ 95%) when AOPP herbicides were tank-mixed with triclopyr. Of the three AOPP herbicides evaluated in this study, only fenoxaprop is currently labeled for use on turfgrass. However, the nonlabeled herbicides (clodinafop and metamifop) provided bermudagrass control and zoysiagrass safety equal to the commercial standard (fenoxaprop) 3 wk after the final application when tank-mixed with triclopyr. Where zoysiagrass is contaminated with bermudagrass, turf managers will likely have to make applications of AOPP herbicides tank-mixed with triclopyr over multiple years to control bermudagrass as it will continue to regrow from deep rhizomes.

Studies were conducted under greenhouse conditions at Michigan State University and Texas Tech University to investigate the tolerance of Miscanthus × giganteus and Miscanthus sinensis to POST herbicides. Miscanthus sinensis and M. × giganteus were treated with 10 and 18 POST herbicide treatments, respectively. Plants were evaluated for injury as well as dry aboveground and belowground biomass production 28 days after treatment. Imazethapyr at 0.069 kg ai ha−1 caused 5% injury to M. sinensis, which was greater than the nontreated check. Imazethapyr, imazamox at 0.044 kg ai ha−1, and rimsulfuron at 0.017 kg ai ha−1 reduced aboveground biomass of M. sinensis compared with the nontreated check. Dicamba at 0.56 kg ai ha−1 and halosulfuron at 0.035 kg ai ha−1 resulted in M. sinensis aboveground biomass similar to the nontreated check. Injury exhibited by M. × giganteus was greater than the nontreated check with glyphosate at 0.84 kg ae ha−1 (54%), foramsulfuron at 0.037 kg ai ha−1 (32%), nicosulfuron at 0.035 kg ai ha−1 (28%), and imazamox at 0.044 kg ai ha−1 (10%). These treatments also yielded the lowest aboveground biomass values. The results of this study demonstrate that M. sinensis is more tolerant of the POST herbicides tested here than M.×x. giganteus. Several herbicide options may be available for weed management in M. sinensis and M. × giganteus stands following additional field trials to validate initial findings.

Weeds are one of the main limiting factors in crop production, causing billions of dollars in annual global losses through degraded agricultural and silvicultural productivity. Weeds also reduce access to land and water, impair aesthetics, and disrupt human activities and well-being. The number of positions devoted to weed science teaching, research, and extension at 76 land-grant institutions across the United States and its territories was determined and compared with that for plant pathology and entomology. The number of classes and graduate students in these disciplines at those institutions was also determined. There are more than four times as many entomologists and more than three times as many plant pathologists as weed scientists at land-grant institutions. There are approximately five times as many graduate students currently in entomology and almost three times as many in plant pathology compared with weed science. There are approximately five times as many entomology and two and a half times as many plant pathology undergraduate classes compared with weed science classes. These differences increase when graduate courses are considered. Most land-grant universities have either none or few graduate classes in weed science. There are more than six times as many graduate entomology courses and more than five times as many plant pathology courses compared with weed science graduate classes. There are no departments devoted solely to weed science, whereas entomology and plant pathology departments are both common. Most universities have little to no faculty assigned to ornamental, fruit, aquatic, or forestry weed control. Number of faculty assigned to vegetable, turf, non-crop, ecology, and basic/laboratory studies in weed science are also limited. Additional university resources are needed if weed science research, teaching, and extension efforts are to meet the priority needs for the management of weeds in the agricultural, natural resources, and urban ecosystems.

The use of aminopyralid combined with metsulfuron for western snowberry control was evaluated with field trials conducted near Rushville, NE. Herbicides treatments consisted of aminopyralid plus metsulfuron, aminopyralid plus metsulfuron plus 2,4-D, 2,4-D alone, and metsulfuron plus chlorsulfuron plus 2,4-D plus dicamba. All treatments were applied in May and June. Sixty days after treatment (DAT) western snowberry control with aminopyralid plus metsulfuron at 0.073 + 0.012 kg ai ha−1 applied in May was 64%, whereas when applied in June, control was 97%. Meanwhile control with 2,4-D was 99 and 78% for the May and June applications, respectively. No major differences between application timings were observed 60 DAT for the rest of the treatments, with control levels ranging from 85 to 99%. One year after application, differences in control between application timings only persisted for 2,4-D. At 365 DAT, western snowberry control with aminopyralid plus metsulfuron at 0.073 + 0.012 kg ai ha−1 was 76 and 78% for May and June applications, respectively. The addition of 2,4-D at 1.1 kg ai ha−1 to aminopyralid plus metsulfuron provided excellent control and was similar to the combination of metsulfuron, chlorsulfuron, 2,4-D, and dicamba for both May and June applications. Grass production and animal carrying capacity were higher after western snowberry control with the majority of the treatments. Aminopyralid plus metsulfuron applied at the lower rate was the exception. The increase in the carrying capacity after western snowberry control ranged from 2.2 to 4.5 animal unit month (AUM). The control of western snowberry resulted in an increase in net income per hectare when compared with the untreated checks, ranging from $4 to $47.9 ha−1. Several options are available for effective western snowberry control during a broader time of application with increased grass production.

Conventional lentil, because it is relatively noncompetitive, requires effective weed control. In conventional lentil, metribuzin should be applied by the four-node stage to avoid crop injury. This is earlier than the critical period of weed control (CPWC) of lentil, which is between the five- and 10-node stage. However, imidazolinone herbicides potentially can be applied later in imidazolinone-resistant lentil, which might allow lentil to be kept weed-free for the CPWC. The objective of this experiment was to determine the best herbicide choice and application timing necessary to achieve the CPWC in lentil. To do this we tested herbicides differing in efficacy and residual control. The herbicides imazethapyr/imazamox, imazamox, and metribuzin + sethoxydim were applied at the two- and six-node lentil stage. Of the three herbicide treatments, metribuzin + sethoxydim resulted in grain yield that was on average 31% lower than the other herbicides. This occurred because of greater broadleaf biomass (composed primarily of wild mustard) in lentils treated with these herbicides regardless of application timing. Because of this, the CPWC was not attained with metribuzin + sethoxydim. Late applications of imazethapyr/imazamox or imazamox resulted in grain yields 30% higher than with early application of these herbicides. Early applications of the imidazolinone herbicides gave poor control of grass weeds (wild oat and green foxtail), but late applications resulted in grass weed control equivalent to metribuzin + sethoxydim. Imazethapyr/imazamox or imazamox should be applied at the five- to six-node stage of lentil to achieve the CPWC.

Kochia poses a challenge to vegetation management in both agricultural and noncrop areas. This species has developed widespread resistance to several herbicides with differing modes of action, including acetolactate synthase inhibitors and photosynthesis inhibitors. Resistance is also beginning to appear against the synthetic auxins and glycines. Therefore, alternative PRE and POST herbicides are needed for effective kochia management, especially in roadside bare-ground zones. Both PRE and POST herbicides were screened on rights-of-way in Pennsylvania. Mixtures containing diuron, flumioxazin, sulfentrazone, pendimethalin, prodiamine, and bromacil were evaluated for PRE activity in combination with glyphosate. POST kochia control was assessed for 15 noncrop herbicides. Results from all trials varied with kochia size and vigor at time of treatment. Although diuron is the current industry standard for PRE control in tank mixes, sulfentrazone appeared to have the most POST activity against vigorously growing kochia. All PRE herbicides evaluated performed better than the standard, sulfometuron plus chlorsulfuron alone. Dicamba, dicamba plus diflufenzopyr, fluroxypyr, and glyphosate performed best against kochia when applied POST. The recently available chemistries saflufenacil and aminocyclopyrachlor require further evaluation of application timing and use rates, respectively, for POST activity on kochia.

Options for suppressing bermudagrass seedheads in managed turfgrass systems are limited. Experiments were conducted in 2009 and 2010 evaluating the use of fenoxaprop (25, 50, 75, and 100 g ha−1) for ‘Riviera’ bermudagrass seedhead suppression and growth regulation compared to imazapic (52 g ha−1), trinexapac-ethyl (91 g ha−1) and mefluidide (561 g ha−1). In field experiments, seedhead suppression ranged from 77 to 100% for fenoxaprop and imazapic at 35 d after treatment (DAT). Comparatively, seedhead suppression was < 25% for either trinexapac-ethyl or mefluidide at 35 DAT. Seedhead suppression was > 90% from 7 to 35 DAT for fenoxaprop applied at ≥ 50 g ha−1. Injury, determined visually, from fenoxaprop and imazapic in both the field and greenhouse measured < 25% on all rating dates, with no significant injury present after 21 DAT. In greenhouse experiments, fenoxaprop and trinexapac-ethyl showed similar reductions of bermudagrass growth; no differences in aboveground biomass were detected between these treatments at 42 DAT. Results of the current study illustrate that fenoxaprop and imazapic can be applied for bermudagrass seedhead suppression and growth regulation if moderate (< 25%) injury can be tolerated up to 21 DAT. Additional research is needed to evaluate the use of fenoxaprop and imazapic for seedhead suppression on other common and hybrid bermudagrasses.

Continuous planting of lettuce from December to September each year in the Salinas Valley of California requires preparation of raised fallow beds ready for planting. Application of soil residual herbicides during winter fallow periods controls weeds but must be used with caution because germinating lettuce seedlings are very sensitive to herbicide soil residues. Three herbicides were applied to fallow beds at about 90, 60, and 30 d before lettuce was seeded. Herbicides tested were flumioxazin at 71, 105, and 211 g ai ha−1, two formulations of oxyfluorfen each at 280 and 560 g ha−1, and carfentrazone at 36 g ha−1. Herbicide injury to lettuce was assessed by visual estimates, crop stand, and number and weight of marketable lettuce heads. The 71 g ha−1 rate of flumioxazin, both oxyfluorfen formulations, and carfentrazone did not injure seeded lettuce or reduce the number or weight of lettuce heads. Flumioxazin at 211 g ha−1 injured lettuce, reducing the number of marketable heads, and should not be used within 90 d of lettuce planting.

Catbriar can be problematic to ranchers who graze rangeland. Five field studies of 2 yr duration were conducted during the 2007 to 2010 growing seasons to evaluate the effects of mowing and foliar-applied herbicides on the control of catbriar in Oklahoma rangeland. Without mowing, a formulated mixture of triclopyr and fluroxypyr (2.7 and 0.9 g ae L−1) and triclopyr alone (2.4 g ae L−1) applied at a volume of approximately 720 L ha−1 twice over 2 yr consecutively controlled catbriar 69 and 71% (visual rating), respectively. Relative to the untreated control, these two treatments reduced the number of live catbriar stems 53 and 64% at the final evaluation, respectively. Mowing without herbicide was equally as effective as any herbicide treatment in reducing the catbriar population. The effects of herbicide were independent of mowing (i.e., the two experimental variables were noninteractive). If infested areas can be mowed, adding herbicide is not necessary to reduce catbriar population.

Field trials were established in 2005 and continued in 2006 to evaluate a conventional broadcast herbicide sprayer compared to a variable spray (sensor-activated) weed-sensing sprayer (WSS). The computer-based Herbicide Application Decision Support System (WebHADSS™) was used to determine a portion of the herbicides applied (based on herbicide efficacy and economics). Weed control, herbicide usage, crop yield, and net returns were compared across treatments. The broadcast applications were usually the most effective at controlling weeds. A PPI herbicide did not always improve weed control compared to treatments in which no PPI herbicide was applied. Variable treatments used less herbicide than the broadcast system in both years. Cotton lint yields in broadcast applications were similar to the weed-free check in both years of the study. Variable treatments often provided equivalent net returns (gross yield revenue less weed control cost) to the broadcast treatments. Although herbicide savings were observed in the variable treatments when compared to a broadcast system, a reduction in weed control was observed, indicating the need for future improvements of this system. A site-specific weed management program used in conjunction with WebHADSS™ may have potential in cotton production systems in the Texas Southern High Plains where weed densities are low.

Growth of vegetation in curbside cracks causes deterioration of asphalt and curbs, reducing road longevity and safety capabilities. Road managers spend a considerable amount of time and money on roadside vegetation management every year. The vegetation in curbside cracks in these study regions is managed approximately once a year by mowing and road sweeping using street-sweeper trucks. Nevertheless, ideal management practices of roadside vegetation have not yet been established partly due to insufficient knowledge of the ecological strategies of plants invading roadsides, especially curbside cracks. Although establishment of plants in the cracks might be restricted due to severe anthropogenic road disturbances, the cracks could be habitats for species with specific ecological traits. The objective of this study was to clarify the floristic and functional characteristics of roadside weeds, particularly species invading curbside cracks, to provide information for effective road management. The species composition of plants invading the cracks was surveyed along Route 3 (southern Japan) and Route 4 (eastern Japan) in different climatic zones, based on 108 floristic inventories. We compared species occurrence and composition to characterize the dominant ecomorphological traits of the species. In total, 163 species occurred in curbside cracks along both routes. Species composition of vegetation in curbside cracks was more variable between the routes than between land-use types. Of the 54 species, more than 5% occurred in all plots, and only three had differences in occurrence among land-use types. Ecomorphological trait composition patterns of the species were similar across land-use types. From these results, we found that regardless of differences in species composition among regions, climatic conditions, and surrounding land-use type, there were some dominant ecomorphological traits of roadside vegetation with plants in curbside cracks, such as ephemeral monophytes that are barochorous or anemochorous. By contrast, rhizomatous perennials, which cause greater deterioration of asphalt than ephemeral monophytes, were rare along the cracks. Although vegetation composition and structure generally depend on land-use types and disturbance regimes, linear landscape elements such as curbsides might be habitats for plants adapted to road disturbances. Roadside vegetation management, such as mowing and road sweeping once a year, seems sufficient to restrict establishment of rhizomatous perennials around Japan.

Field experiments were established near Casselton and Fargo, ND, to evaluate the effect of aminopyralid soil residue on alfalfa, corn, soybean, and sunflower planted one or two growing seasons after treatment. At Fargo, ND, aminopyralid caused no injury or yield reduction to alfalfa, corn, and sunflower seeded 20 or 23 mo after treatment (MAT) in a silty clay soil. However, soybean yield was reduced when aminopyralid at 120 or 240 g ae ha−1 was fall- or spring-applied 20 or 23 mo before seeding. At Casselton, ND, aminopyralid injured alfalfa, soybean, and sunflower planted 8 and 11 MAT. Injury and yield reduction were less from treatments spring-applied than from those that were fall-applied. For example, aminopyralid at 120 g ha−1 applied in September caused 95, 94, and 100% injury to alfalfa, sunflower, and soybean, respectively, 8 MAT, whereas the same treatment applied in June caused 10, 8, and 44% injury 11 MAT. Aminopyralid at 120 g ha−1 continued to reduce soybean yield by an average of 45% at 20 MAT (fall-applied), but yield was similar to the control when aminopyralid was applied 23 mo before seeding (spring-applied). Warm soil with moderate moisture during the summer months appeared to be very important for degradation of aminopyralid. Corn was not affected by aminopyralid when seeded 8 or 11 MAT and appeared to be the best cropping option for land recently treated with aminopyralid. Aminopyralid applied at spot-treatment rates of 240 g ha−1 had long-term soil activity similar to picloram at 560 g ha−1.

The utility of solaria (1 by 1-m plastic sheets) to predict densities of a few weed species in summer crops has been demonstrated previously, but needed further research to be adopted by farmers and advisors. We tested the method to detect important weeds in Argentina and Minnesota, and determined the minimum number of solaria required to predict the presence of emerged weed seedlings in the forthcoming growing season. Three experiments were performed in Buenos Aires Province, Argentina, and one in Minnesota. Solaria were placed in fields with different previous crops and soil management: no tillage (two fields) and conventional tillage (two fields). Preceding crops were corn (one field), wheat (one field), and double-cropped wheat/soybean (two fields). After weeds were enumerated, solaria were removed, sunflower (one field) and soybean (three fields) were planted, and weeds later assessed in each crop. Results indicate that one solarium per 1.9 ha can detect common lambsquarters with 95% confidence within the next summer crop. For other species, one solarium per 4.2, 1.2, 1.0, and 1.8 to 2.7 ha (depending upon field site) for large crabgrass, prostrate knotweed, wild buckwheat, and green foxtail, respectively, was required. The low cost and simplicity of assessment make this technique more suitable than that of soil seed-bank samples to predict weed emergence. The number of solaria required to forecast weed infestation levels confidently is sufficiently low that their use may be justified, especially in small fields of high-value crops.

Field experiments were conducted to evaluate the efficacy of herbicides and soil sterilants for the fairway conversion of ‘Tifway’ bermudagrass to ‘Zorro’ zoysiagrass. Treatments included glyphosate (4.48 kg ae ha−1), EPTC (7.84 kg ai ha−1), dazomet (338 kg ai ha−1), siduron (13.4 kg ai ha−1), glyphosate plus ETPC (4.48 + 7.84 kg ha−1), glyphosate plus dazomet (4.48 + 338 kg ha−1), EPTC plus siduron (7.84 + 13.4 kg ha−1), and dazomet plus siduron (338 + 13.4 kg ha−1). Glyphosate treatments were applied 5 wk prior to establishment (WPE), dazomet and EPTC treatments were applied 3 WPE, and siduron was applied at establishment. Dazomet and EPTC treatments were incorporated to a depth of 10 to 15 cm with a rotary tiller and rolled with a weighted roller to reduce losses from volatilization after application. Zorro zoysiagrass was established in June 2008 and 2009 using a mixture of rhizomes and stolons at a rate of 76 cm3 m−2. Results indicate that glyphosate + dazomet, glyphosate + EPTC, dazomet + siduron, and EPTC + siduron were equally effective at controlling Tifway bermudagrass. EPTC and dazomet controlled bermudagrass more effectively when used in combination with glyphosate or siduron. There were no significant differences in bermudagrass cover between the EPTC combinations with glyphosate or siduron and dazomet applied with glyphosate or siduron. Comparing EPTC- and dazomet-alone, EPTC yielded less bermudagrass cover (32%) than dazomet (71%). At present, research is limited on using EPTC for controlling perennial grasses in turfgrass systems. Data from these studies demonstrate the potential use of EPTC as a preplant soil herbicide to control hybrid bermudagrass during zoysiagrass renovation.

Glyphosate-resistant giant ragweed in Arkansas was reported in 2005. A study was conducted to (1) confirm and characterize the glyphosate resistance in giant ragweed, (2) determine if reduced absorption or translocation is the mechanism of glyphosate resistance in giant ragweed, and (3) evaluate the efficacy of nine POST-applied soybean herbicides to control glyphosate-resistant and -susceptible giant ragweed. Based on the rate required to kill 50% of plants (LD50 values), resistant giant ragweed biotypes from Greene and Jefferson counties were 2.3- to 7.2-fold less sensitive to glyphosate compared to susceptible biotypes. Glyphosate absorption and translocation for glyphosate-resistant and -susceptible biotypes was similar at 24 and 72 h after treatment. Thus, differential absorption or translocation is not a mechanism of glyphosate resistance in this resistant giant ragweed biotype. Control of resistant giant ragweed biotypes with glyphosate at a labeled field application rate of 840 g ha−1 was only 60% or less compared to complete control of a susceptible giant ragweed biotype. However, bentazon, carfentrazone, cloransulam, and fomesafen controlled both biotypes more than 95%.

Field studies were conducted in 2008 in Ontario, OR and Paterson, WA to determine the effect of simulated glyphosate drift on ‘Ranger Russet’ potato, including visual injury, shikimic acid accumulation, and tuber yield. Glyphosate was applied at 8.5, 54, 107, 215, and 423 g ae ha−1; which corresponds to 0.01, 0.064, 0.126, 0.254, and 0.5 of the lowest recommended (846 g ha−1) single application dose for glyphosate-resistant corn and sugar beet. Glyphosate was applied when potato plants were at 10-cm height, stolon hooking, tuber initiation, or bulking stage. The greatest visual foliar injury was observed when glyphosate was applied at a dose of 54 g ha−1 or greater and potato plants were at the hooking stage. The lowest foliar injury was observed when glyphosate was applied to potato plants at the bulking stage. The I50 glyphosate dose at 42 d after treatment (DAT) was estimated to be 167 g ha−1 for potatoes sprayed at the hooking stage. The corresponding glyphosate dose to result in 50% injury for potatoes sprayed at tuber initiation, 10-cm height, and bulking stages were 129%, 338%, and 438%, respectively, greater than hooking stage. The U.S. No.1 potato yield was inversely related to vine injury and shikimic acid accumulation. Shikimic acid accumulation increased when glyphosate was applied at 107 g ha−1 or greater. U.S. No.1 potato yield was reduced by 46% and 84% relative to the untreated control (55 and 76 T/ha) when glyphosate was applied at 107 g ha−1 to plants in the hooking stage at Ontario and Paterson, respectively. Tuber yields at both sites were lowest when glyphosate was applied at hooking and tuber initiation stages.

Direct-seeding of cover crops is often promoted to reduce potential soil loss during the winter, enhance soil fertility, and reduce energy use and equipment traffic on fields. The impact of direct-seeding of cover crops on wild-proso millet seedling emergence in subsequent crops is unknown. In this study, a pulse–chase experiment determined the effect of five fall soil management strategies, two spring primary tillage levels, and two herbicide programs on wild-proso millet emergence in a subsequent crop of snap beans. Wild-proso millet seeds were sown following sweet corn harvest in two commercial production fields to simulate seed rain at a density of 500 and 1,000 seeds m−2 in the fall of 2004 and 2005, respectively. The experimental design was a split–split plot. Five fall treatments were applied to main plots and included direct drilling of cover crops, conventionally tilled and drilled cover crops, a winter fallow treatment, and two additional treatments that were direct-drilled and conventionally tilled in the fall but that were not seeded with cover crops to separate the effects of tillage and cover crops on wild-proso millet emergence. Main plots were split in the spring and snap beans planted without primary tillage or conventionally planted after the soil was tilled. Tillage and cover crop treatments applied in the fall influenced emergence in the spring but with slightly different outcomes at the two sites. Direct drilling without a cover crop produced more wild-proso millet seedlings in snap beans than the winter fallow plot; tillage before cover crop planting in the fall produced recruitment levels less than or equal to densities in the winter fallow plots, with one exception. At one site, cover crops increased emergence compared to plots without cover crops. Spring tillage did not alter the affect of the five fall management treatments on wild-proso millet emergence. Direct-seeding of cover crops should be done with equipment or methods that minimize soil disturbance to prevent movement of wild-proso millet seeds into protected and favorable zones of emergence in the soil.

The need for sustainable agricultural-production systems has generated demand for effective, nonsynthetic, alternative weed-control strategies. For some vegetable crops there are few herbicide options available, and there is little prospect of new herbicides being registered for vegetable crops. Brassicaceae seed meal, a residue product of the seed oil extraction process, can provide a resource for supplemental nutrients, disease control, and weed suppression. The objective of this study was to evaluate the effect of different Brassicaceae seed meals and application rates on the emergence of wild oat, Italian ryegrass, prickly lettuce, and redroot pigweed, which are some of the major weeds in vegetable production systems. White mustard seed, Indian mustard seed, and rapeseed meals were used with (intact) or without a functional myrosinase enzyme (denatured). Intact white mustard seed meals applied at a rate of 2000 kg ha−1 significantly reduced weed seedling emergence and weed dry biomass compared with intact rapeseed-meal–amended treatments. Indian mustard showed significantly better herbicidal efficacy on the grassy weeds than did white mustard, which was most effective in controlling broadleaf weeds. In all instances, a 1000 kg ha−1 application rate of either Indian mustard or white mustard exhibited greater herbicidal effect than did the 2000 kg ha−1 application rate of rapeseed meal. These results demonstrate that all glucosinolates are not equal in herbicidal effects. The herbicidal effects of the mustard seed meal could offer vegetable growers a new option for weed control, particularly in organic production systems. In practice, it would seem feasible to treat soils with a blend of Indian mustard and white mustard seed meals so that both grass and broadleaf weeds could be effectively controlled.

The feasibility of visual detection of weeds for map-based patch spraying systems needs to be assessed for use in large-scale cropping systems. The main objective of this research was to evaluate the reliability and profitability of using maps of Johnsongrass patches constructed at harvest to predict spatial distribution of weeds during the next cropping season. Johnsongrass patches visually were assessed from the cabin of a combine harvester in three corn fields and were compared with maps obtained in the subsequent year prior to postemergence herbicide application. There was a good correlation (71% on average) between the position of Johnsongrass patches on the two maps (fall vs. spring). The highest correlation (82%) was obtained with relatively large infestations, whereas the lowest (58%) was obtained when the infested area was smaller. Although the relative positions of the patches remained almost unchanged from 1 yr to the next, the infested area increased in all fields during the 4-yr experimental period. According to our estimates, using a strategy based on spraying full rates of herbicides to patches recorded in the map generated in the previous fall resulted in higher net returns than spraying the whole field, either at full or half rate. This site-specific strategy resulted in an average 65% reduction in the volume of herbicide applied to control this weed.