In previous research, use of PRE soil residual herbicides was reduced 50% in no-till corn and soybean by banding herbicides over crop rows followed by mowing weeds growing between rows two times. The research goals were (1) to determine whether such between-row mowing systems adequately controlled weeds and prevented grain yield loss in other competitive field crops, such as no-till grain sorghum, and (2) to compare broadcast herbicide treatments with between-row mowing systems. PRE atrazine plus dimethenamid at relative rates of 0.75× and 1× (where 1× = 1.7 plus 1.3 kg ai/ha, respectively) were band-applied over rows shortly after planting followed by two between-row mowings close to the soil surface. In 2 of 3 yr in Missouri, this system controlled giant foxtail and common waterhemp as well as broadcast herbicides in no-till sorghum. In 2 of 3 yr, between-row mowing systems also prevented yield loss in no-till sorghum as well as both broadcast herbicides at the same rates and the weed-free check.

The effect of N levels, weed control treatments, and their interaction on maize yield and weed growth in sandy soils is not completely understood. Therefore, field experiments were conducted during 2005 and 2006 to determine if management can improve maize competitiveness with weeds, and thus achieve the yield potential of maize in sandy soils. The experiment included three N levels (300, 338, and 375 kg/ha) and five weed control treatments, e.g., hand hoeing twice, hand hoeing three times, fluroxypr + hoeing once, hoeing once + bispyribac-Na, and a nonweeded check. N rates affected dry weight of weeds growing with maize except with large crabgrass. Biomass of common purslane, considered a nitrophilous species, was increased by all N levels. Weeds were controlled by all treatments compared with the nontreated check; however, herbicide treatments were not superior to hand-hoeing treatments. Using more N favored growth and yield of maize more than weeds. Adding N fertilizer also improved most yield parameters. Highest grain yield of maize resulted at 375 kg/ha N. All weed control treatments improved grain yield two- to threefold compared with the nonweeded check. The interaction between N rates and weed control treatments had significant effects on dry biomass of common purslane and barnyardgrass, as well as grain index and biological yield parameters of maize. Grain yields were improved with fluroxypyr applied 2 wk after sowing (WAS) maize followed by one hand hoeing 6 WAS or hoeing at 3 WAS followed by bispyribac-Na applied 6 WAS. However, highest yields were obtained by hoeing early during the growing season.

Experiments were conducted in 2005 and 2006 near Huntley, Montana to evaluate two formulations of mesosulfuron-methyl for the control of wild oat in malt barley. The two formulations differed due to the amount of safener, mefenpyr-diethyl, that each contained. Formulation 1 and 2 contained mesosulfuron-methyl and mefenpyr-diethyl at a 1 : 2 and 1 : 6 ratio, respectively. The two formulations were applied alone at two rates or in combination with other small grain herbicides that are typically used for broadleaf weed control. The low and high rate of formulation 1 contained 7.8 and 10.1 g ai/ha of mesosulfuron-methyl and 15.6 and 20.2 g ai/ha of mefenpyr-diethyl, respectively. The low and high rate of formulation 2 contained 2.5 and 3.1 g ai/ha of mesosulfuron-methyl and 15 and 18.6 g ai/ha of mefenpyr-diethyl, respectively. These treatments were compared to a standard treatment of fenoxaprop and a nontreated control. In 2005, formulation 2 applied alone at the low and high rates caused barley injury of 7 and 11% at 21 days after treatment (DAT) and 4 and 7% at 56 DAT, respectively. Applications of formulation 1 caused barley injury that was 9 and 17 percentage points greater at 21 DAT and 12 and 18 percentage points greater at 56 DAT than barley injury from applications of formulation 2 when these herbicides were applied alone at the low and high rate, respectively, in 2005. In both years, formulation 1 applied alone at either rate injured barley more than fenoxaprop at 21 and 56 DAT. In both years, formulation 1 and 2 applied alone controlled wild oat between 85 and 96% at 21 DAT and between 92 and 98% at 56 DAT. Regardless of rate, wild oat control with either formulation was similar to that provided by fenoxaprop at 56 DAT. In 2005 and 2006, barley yield was equivalent between treatments of formulation 1 or 2 and that produced by barley treated with fenoxaprop. No difference in the percentage of plump kernels occurred between treatments of formulation 2 and fenoxaprop. The percentage of plump kernels was reduced 6 to 7 percentage points with treatments containing formulation 1 compared to treatments containing formulation 2. Overall, formulation 2 was effective for the control of wild oat in malt barley. Low levels of malt barley injury occurred with this treatment; however, barley successfully recovered by harvest, and yield and kernel size were equivalent to barley treated with fenoxaprop.

The manufacturer's recommended rate for fomesafen in snap beans, dry beans, and soybeans may cause carryover injury in sweet corn. A field experiment, a survey, and multiple greenhouse experiments were conducted to (1) estimate the fomesafen residue concentrations in the soil that might result from use of lower than registered rates, (2) estimate fomesafen residue concentrations in growers' fields and evaluate grower practices for their effects on carryover potential, and (3) investigate the effects of soil type and sweet corn variety on the potential for fomesafen to cause injury to sweet corn. Results of the dissipation study predicted average soil concentrations to be approximately 0.019 mg fomesafen/kg soil at the start of the sweet corn planting season. Half-life values ranged between 28 and 66 d, with an average of 50 d. Residues in grower fields were slightly less than those found in the dissipation study. Injury from fomesafen varied significantly by sweet corn variety and by soil type. Sweet corn grown in soils with high organic matter and low pH were most susceptible to injury from fomesafen. At high rates of fomesafen (0.12 mg/kg), reductions in dry weight of sweet corn varieties ranged from 5 to 60%. At rates of fomesafen slightly higher than those detected in field soils at the time of sweet corn planting (0.03 mg/kg), dry weight either increased slightly (variety trial) or decreased by 6 to 12% (soil-effect trial) depending on soil type. The risk of sweet corn yield losses because of fomesafen carryover appear relatively low. Growers can reduce the risk of carryover injury by planting tolerant varieties in fields where fomesafen was applied the preceding year.

Estimates of seed viability using the imbibed seed crush test, a method performed by applying pressure to imbibed seeds, were compared with estimates obtained from using the imbibed seed crush test supplemented with tetrazolium staining. The seeds of three weed species, giant foxtail, green foxtail, and yellow foxtail, were collected from three different crops and tested by each method. The results from the two approaches were strongly and significantly correlated. The imbibed seed crush test requires considerably less skill and time to perform and is a reasonable alternative to tetrazolium staining to test the seed viability of newly produced foxtail seeds.

A field study was conducted at Vezaiciai branch of the Lithuanian Institute of Agriculture from 1998 to 2000 to determine weed emergence dynamics in potato and to estimate the effect of different intervals of weed crop competition on potato tuber yield. Treatments varying in intervals of weed-free conditions and competition were laid out in a randomized complete block design with six replications. The greatest emergence of annual broadleaf weeds (62 to 86% of the season total) in the crop was observed in the period from potato planting until flowering. Emergence of winter annuals such as field violet and scentless mayweed was greatest in the period from the 20-cm potato plant height until harvesting. Competition was most detrimental to potato tuber yield in the periods from planting until flowering, from planting until 25 d after flowering, or for the entire growing season. Potato tuber yield decreased by 8.1, 8.4, and 6.4%, respectively, during these competition intervals compared to the weed-free treatment. The results indicated that the critical weed-free period, when weed competition was detrimental to yield, started from planting until 25 d after flowering if regular interrow cultivation was applied.

Field studies were conducted during the 2004 and 2005 growing seasons to evaluate the effects of various herbicides on smellmelon control and soybean yield response. Pendimethalin applied pre-emergence (PRE) alone controlled smellmelon no better than 70%, whereas pendimethalin plus imazethapyr, flumioxazin, or cloransulam applied PRE provided almost complete smellmelon control (99%). Pendimethalin applied PRE followed by acifluorfen applied early postemergence (EPOST) provided similar control. Glyphosate alone applied late postemergence (LPOST) provided complete control (100%), and pendimethalin followed by glyphosate applied EPOST controlled smellmelon at least 95%. Most herbicides increased soybean yield over the nontreated check.

Field trials were conducted in East Lansing, MI in 2004 and 2005 and in St. Charles, MI in 2004, 2005, and 2006 to compare weed control and sugarbeet tolerance from microrate herbicide treatments that included s-metolachlor and dimethenamid-P. Treatments included the base microrate treatment alone and with full- and split-application rates of s-metolachlor at 1.4 kg/ha or dimethenamid-P at 0.84 kg/ha at the various microrate application timings. All treatments injured sugarbeet. In 2004 and 2006, full rates of both s-metolachlor and dimethenamid-P applied PRE or in the first microrate application injured sugarbeet more than the base microrate treatment. When s-metolachlor or dimethenamid-P were split-applied between PRE and the third microrate application or between the first and the third microrate applications, injury was still greater than from the base microrate treatment. Furthermore, applying dimethenamid-P at one-fourth the full rate in all four microrate applications injured sugarbeet more than the base microrate treatment. A full rate of s-metolachlor or dimethenamid-P applied in either the third or fourth microrate applications or splitting the applications between the second and fourth microrate treatments did not increase sugarbeet injury compared with the base microrate treatment. Control of common lambsquarters and giant foxtail from all treatments containing s-metolachlor or dimethenamid-P, regardless of the time of application, was greater than from the base microrate treatment at all locations. Pigweed spp. control was 94% or greater from all treatments. In 2004, late-season control of giant foxtail was greater from all treatments that included s-metolachlor or dimethenamid-P compared with the base microrate treatment. In 2005, the only treatments that did not improve late-season giant foxtail control compared with the base microrate treatment were the treatments that included a full rate of s-metolachlor or dimethenamid-P applied in the fourth microrate application. Even though some herbicide treatments that included s-metolachlor or dimethenamid-P injured sugarbeet more than the base microrate treatment, recoverable sucrose per hectare was similar among treatments.

Guar production in the United States is limited to a relatively small region in the semiarid southern Great Plains of Texas and Oklahoma. The lack of POST broadleaf herbicides is a potential limiting factor to increased production. A greenhouse study was initiated in 2001 at the Texas A&M Research Center near Vernon, TX to evaluate guar tolerance to 10 POST herbicides typically used in soybean or cotton. Guar seedlings were grown in pots, and herbicides with appropriate adjuvants were applied to 3-wk-old seedlings at the registered rate (1×) and twice (2×) the registered rate for soybean or cotton. The study was repeated twice, with six replications in each run. Twenty-eight d after treatment (DAT), visual injury and aboveground dry weight of viable biomass were recorded for each plant. Significant differences (P = 0.05) were noted among herbicides for visual injury and viable biomass. Little or no differences in visual injury and aboveground dry weight were observed between the control (no herbicide applied) and the 1× rate of 4-(2,4-dichlorophenoxy)butanoic acid, bentazon, or imazethapyr 28 DAT. A 1× application rate of acifluorfen, imazamox, thifensulfuron, or bromoxynil caused minor visual injury of 7 to 9% and a reduction in dry weight of 8 to 23%. Pyrithiobac and chlorimuron caused 38 and 47% visible injury and a 35 and 58% reduction in dry weight, respectively. Guar was most sensitive to lactofen, with the 1× rate causing 100% visual injury and no recoverable aboveground biomass. This greenhouse study identified three POST herbicide candidates with potential to control broadleaf weeds in guar without noticeable plant injury, and offers data to support herbicide registrations for this minor crop.

A survey of seven production fields in Indiana, Illinois, and Ohio was conducted to assess henbit and purple deadnettle growth and soybean cyst nematode (SCN) development and reproduction on these weeds. Autumn and spring growth of purple deadnettle and henbit was influenced by location within each state. In general, winter annual weeds were larger in size and reached maturity earlier in the spring at the southern sample sites than those in the north. All growth stages of SCN were found to be associated with henbit and purple deadnettle at both autumn and spring sample timings. SCN juveniles were generally found infecting roots at highest abundance in the spring. SCN cyst and egg production also were widespread and occurred to a much higher degree during the autumn than the spring developmental period. The results of this survey indicate that management tactics designed to minimize the potential for SCN reproduction on winter annual weeds would probably be most effective if conducted in the autumn, when the majority of SCN reproduction occurred. However, spring populations of winter annual weeds that harbor SCN juveniles might facilitate additional SCN reproduction and population increase if the weeds are not controlled in a timely manner prior to planting.

Field experiments were conducted in 2003 and 2004 to evaluate the effects of reduced rates of glufosinate on development and yield of three nonglufosinate-resistant cotton varieties. The varieties evaluated were selected on their relative maturity with PayMaster (PM) 1218, early maturity; FiberMax (FM) 960, medium maturity; and Delta and Pine Land (DP) 555, late maturity. Rates of 47, 23, and 4.7 g ai/ha were applied, representing 10, 5, and 1% of the typical use rate per application of 467 g ai/ha, respectively. As might be expected, when averaged over varieties, the 10% rate showed more injury than the 5%, and the 5% rate caused more visual injury than the 1% rate. Pooled over timing and rate, PM1218 showed more injury (18%) than FM960 (7%), which showed more injury than DP555 (1%) 7 days after application (DAA) at the 10% rate. However, although PM1218 showed the most visual injury, this did not translate into delay in maturity or loss of lint yield. DP555 showed 70 kg ai/ha and 50 kg ai/ha lint yield loss when glufosinate was applied at the 10% rate on the fifth and eighth node stage, respectively. DP555 was delayed in maturity when glufosinate was applied at the 10% rate on the eighth node stage. FM960 showed 30 kg/ha lint yield loss when glufosinate was applied at the 10 and 5% rates at the fifth node stage. Maturity of FM960 was delayed with the 10 and 5% rates applied at the fifth node stage.

The ability to accurately estimate herbicide efficacy is critical for any decision-support system used in weed management. Recent efforts by weed scientists in the North Central United States to adopt WeedSOFT across a broad region have resulted in a number of regional research projects designed to assess and improve the predictive capability of WeedSOFT. Field studies were conducted from 2000 to 2002 in Nebraska, Missouri, and Illinois to evaluate herbicide-efficacy predictions made by WeedSOFT in two corn-row spacings. Following crop and weed emergence, input variables, such as weed densities and heights, were entered into WeedSOFT to generate a list of treatments ranked by predicted crop yields. The five treatments evaluated included those predicting highest crop-yield potential (recommended control treatment 1), a 10% yield reduction, a 20% yield reduction, a 10% yield reduction plus cultivation, and cultivation alone. These treatments were applied to corn grown in 38- and 76-cm rows. Generally, treatments applied in 38-cm rows had more accurate herbicide-efficacy predictions compared with 76-cm rows. WeedSOFT provided better control predictions for broadleaf than grass species. WeedSOFT provided excellent herbicide-efficacy predictions for the highest crop-yield potential, which indicates a good potential for practical use of this software for herbicide recommendations.

The efficacy of metolachlor on rigid ryegrass was determined under a no-till seeding system in an experiment conducted in 2004 and 2005 in South Australia. Metolachlor at a rate of 0.48 and 0.96 kg ai/ha was applied at 40 or 46 d (very early preplant, VEPP) and 20 or 23 d before crop sowing (early preplant, EPP), and at sowing (preplant, PP) in 2004 and 2005; the herbicide was incorporated by sowing. The control of rigid ryegrass was greater than 80% when metolachlor was applied PP; however, that application resulted in phytotoxic effects on emergence and yield of wheat; metolachlor was more phytotoxic when applied at 0.96 kg/ha than at 0.48 kg/ha. Metolachlor applied EPP provided 71 to 83% rigid ryegrass control, whereas VEPP application provided only 33 to 49% control. Reduction in wheat grain yield was not observed at these application times. This study indicates that metolachlor at 0.48 kg/ha could be safely applied around 20 d before crop sowing to selectively control rigid ryegrass in wheat.

Medusahead is an introduced, winter-annual grass covering millions of hectares of the semiarid West. It forms exclusive stands and has a dense thatch cover that resists the establishment of desirable species. Prescribed fire can remove medusahead litter and improve plant establishment. Medusahead control is fundamental to establishing desirable species that will, in turn, resist further invasion. Imazapic is an effective herbicide for control of medusahead, but more information is needed on its effects on desirable species. Our objectives were to test how imazapic application rate and timing affected medusahead, seeded desirable species, and other nontarget vegetation on burned and unburned rangeland in southeast Oregon. We burned existing medusahead infestations at two different sites in June 2003. Following the burn, imazapic was applied at rates of 0, 35, 70, 105, 140, 175, and 210 g ai/ha between July and October of 2003 in a randomized strip-plot design. In November 2003, monocultures of seven desirable species were drill-seeded across the imazapic treated areas. Data on cover and density of medusahead and seeded species were collected in 2004 and 2005. Cover data of nontarget species were collected in the summer of 2005. Medusahead cover was highest in control plots and lowest in plots that received the highest herbicide application rates. Medusahead cover was lower in burned plots. The effect of imazapic on nontarget vegetation was less clear. Seeded species established in the study plots, but their response to herbicide rate showed few consistent patterns; some of the seeded species showed little response to herbicide, whereas others appeared to establish best at different herbicide rates, depending on site and whether the plots were burned or unburned. Site and burn treatment also affected how imazapic rate or application month influenced cover of perennial or annual grasses or forbs.

A study was established to evaluate herbicides registered for barnyardgrass control in rice for activity on creeping rivergrass. Treatments included 208 g ai/ha cyhalofop early POST (EPOST) followed by (fb) 315 g/ha cyhalofop late POST (LPOST), 22 g ai/ha bispyribac EPOST fb 22 g/ha bispyribac LPOST, 66 g ai/ha fenoxaprop EPOST fb 86 g/ha fenoxaprop LPOST, 70 g ai/ha imazethapyr EPOST fb 70 g/ha imazethapyr LPOST and 50 g ai/ha penoxsulam mid-POST (MPOST). Each POST program was evaluated with and without 448 g ai/ha clomazone PRE. Barnyardgrass control, averaged over days after treatment (DAT), was 88 to 92% with the addition of clomazone PRE. Clomazone applied PRE followed by two applications of cyhalofop controlled creeping rivergrass at 91%. Creeping rivergrass control was less than 75% at 35 to 49 DAT. This response indicates only suppression of creeping rivergrass is achieved with the herbicide programs evaluated in this study.

Field surveys were conducted to evaluate the prevalence of stalk-boring insects in giant ragweed in Indiana and Michigan soybean fields. Greenhouse studies were also conducted to determine whether stalk-boring insects had a negative impact on control of giant ragweed with glyphosate. In the June 2005 field surveys, 18 to 30% of all giant ragweed plants sampled contained stalk-boring insects or insect tunnels. Languriidae, Noctuidae, Pyralidae, and Tortricidae families were found most often at the time glyphosate was being applied to soybean fields to control giant ragweed. Cerambycidae and Curculionidae families were typically found later in the season after herbicide applications were completed. In the August field surveys in Indiana, 28 to 62% of the giant ragweed plants that showed evidence of stalk-boring insects were not controlled by POST herbicide applications suggesting that control was compromised by the presence of stalk-boring insects. In greenhouse studies, glyphosate efficacy on 15-cm-tall giant ragweed was enhanced by the presence of stalk-boring insects; however, glyphosate efficacy on 45-cm plants was reduced by the presence of stalk-boring insects. Overall, this research suggests that there is a possibility that stalk-boring insects could reduce glyphosate efficacy on giant ragweed.

Field and greenhouse studies were conducted from 1996 to 2000 to determine tropical soda apple fruit size required for mature seed, overwintering survival potential of seeds, and growth and fruit production in a containment area near Stoneville, MS (latitude 33°25′N). Seedling emergence was ≥ 50% from tropical soda apple fruit > 1.8 cm in diameter. Tropical soda apple overwintering emergence was 14, 10, 48, 42, and 13% from seed alone and 86, 83, 48, 41, and 18% for seeds in tropical soda apple fruit overwintering at 100, 0, −5, −10, and −15 cm from the soil surface, respectively. Before frost (early November), average tropical soda apple plant heights were 0.8, 0.6, and 0.7 m; plant diameters were 2.6, 1.7, and 2 m; fruit produced per tropical soda apple plant were 415, 342, 128; and plant weights were 9.9, 9.5, and 4.9 kg at 27 wk after transplanting (WATP) for 1996, 1997, and 1998, respectively. Regeneration from overwintering tropical soda apple roots varied depending on the winter conditions. These results suggest that tropical soda apple plants can survive mild winters.

Growers and certified crop advisors (CCAs) across Indiana were surveyed during the winter of 2003 to 2004 to assess their perceptions about soybean cyst nematode (SCN) and use of SCN management practices. Most farmers (57%) and CCAs (72%) surveyed reported a moderate to high level of concern regarding SCN and its potential impact on soybean yield. The majority of those surveyed were also aware that some winter annual weeds can serve as hosts for SCN. Crop management practices specifically aimed at managing the impact of SCN were employed by 55 and 78% of growers and CCAs, respectively. However, only 21% percent of growers said that they had sampled a field for nematodes within the last two years. Growers from eastern and southern Indiana were less likely to be concerned about SCN, to implement SCN management strategies, and to have the soil tested for SCN than growers throughout the rest of the state. In addition, smaller farmers appear to be less concerned and knowledgeable about SCN than those who operate larger farms. The results of this survey suggest that the majority of Indiana growers would likely adopt winter weed control to manage SCN. Also, with respect to winter weed control, future Extension efforts should be focused on southern Indiana where both the risk for SCN reproduction on winter annuals and the need for education on SCN appear to be highest.

Three field trials were conducted over a 2-yr period (2004 and 2005) at Exeter and Ridgetown, Ontario to evaluate the tolerance of eight market classes of dry beans to KIH-485 applied PRE at 210 and 420 g ai/ha. KIH-485 PRE caused as much as 67% visual injury in small-seeded and 44% visual injury in large-seeded dry beans. KIH-485 applied PRE at 420 g/ha reduced plant height up to 47% at Ridgetown and 8% at Exeter in 2004, and reduced height of brown and white bean by 15 and 19%, respectively, but had no effect on the height of the other beans in 2005. Shoot dry weight was not affected at Exeter in 2004 but was reduced by 46% at Ridgetown in 2004 and 14% at Exeter in 2005. In 2004, seed moisture content increased by 5, 6, and 12% in black, otebo, and pinto beans, respectively. Seed yield was reduced up to 27% at Ridgetown and 11% at Exeter in 2004 but was not affected at Exeter in 2005. On the basis of this research, KIH-485 PRE causes unacceptable injury in some dry bean market classes.

Field studies were conducted in 2005 at five locations throughout Illinois to determine the effect of maturity date and canopy width characteristics of selected glyphosate-resistant soybean cultivars on competitive ability against weeds. Natural weed populations at all sites were allowed to compete with the soybean cultivars until the V1, V3, V5, or V7 growth stage and then removed with an application of glyphosate. Light-interception readings, weed control ratings, and soybean yield were all measured to compare cultivars. Cultivars of later maturities tended to withstand early season weed competition better and attained higher yields when weeds were removed at later timings than those of earlier maturity. Although canopy width differed moderately among cultivars in some cases, canopy width had no effect on the ability of soybeans to compete with weeds. Thus, choosing soybean cultivars of later maturity might provide more flexibility in weed management and might reduce losses due to weeds, but that benefit needs to be balanced with yield potential.