The effect of season-long interference by bands of weeds growing only between rows (BR) on field corn yields has not been reported before or compared with weedy and weed-free (i.e., weeded) plots or bands of weeds growing only in row (IR). The null hypothesis of this research was that field corn yields would be ranked as weed-free > BR weedy only > IR weedy only > weedy (IR + BR weedy) in response to season-long weed interference by these four treatments. Weeds growing as bands closest to field corn were expected to reduce field corn yields more than those growing as bands further away between field corn rows. Field corn yield response to these four weed interference treatments was studied in Missouri for 4 yr. In late summer, most weed ground cover consisted of giant foxtail, the chief weed present, and common waterhemp, a lesser weed. Observed field corn yields averaged for 4 yr were ranked as weed-free > IR weedy only > BR weedy only > weedy. Field corn yields of the IR weedy only, BR weedy only, and weedy treatments averaged 76, 63, and 41%, respectively, of the weed-free treatment (=7,820 kg/ha). In two of the 4 yr, field corn yield of the IR weedy treatment exceeded that of the BR weedy treatment, whereas these treatments could not be statistically distinguished from one another in the other 2 yr. These research results refute the null hypothesis and demonstrate that it may be more critical to control BR than IR weeds, although controlling both BR and IR weeds maximized field corn yields.

Velvetleaf plants have diurnal leaf movements, which may result in decreased interception of herbicides when applications are made near sunset. However, it is not known if leaf angle alone accounts for diurnal fluctuations in efficacy. Greenhouse experiments were conducted to determine the effect of time of day (TOD) of application and velvetleaf leaf angle on glufosinate efficacy and spray interception. Glufosinate at 90, 180, and 360 g ai/ha was applied to 10-cm-tall plants at 4:00, 6:00, 7:00, 7:30, and 8:00 P.M., respectively. Leaf angles were either manipulated physically to −90° or the plant's natural 2:00 P.M. leaf angle (approximately −10°) or were allowed to exhibit their natural leaf movements. Plant dry weight 3 wk after treatment revealed that TOD effects were observed for all leaf angle treatments after glufosinate application at 90 g/ha. At 180 g/ha glufosinate, there was no TOD effect for plants with 2 P.M. leaf angles, whereas there was a TOD effect for plants with −90° and natural leaf angles. At 360 g/ha glufosinate, biomass for the −90° leaf angle plants was similar to that for the natural and the 2:00 P.M. leaf angle plants when glufosinate was applied at 4:00 P.M. but was significantly different at or after 6:00 P.M. This suggests that at least 4 h of light is needed to provide optimum herbicide activity when spray interception is reduced as a result of leaf movements. Leaf angle decreased by as much as 70% from 4:00 to 8:00 P.M., which resulted in approximately 50% less spray interception at 8:00 P.M. than at 4:00 P.M. These data provide evidence that leaf angle plays a pivotal role in reducing glufosinate efficacy when applications are made near sundown. However, leaf angle is not the sole reason for reduced efficacy because TOD effects were observed at different leaf angles with 4 h of light, after an application of 360 g/ha glufosinate.

Effective, long-term wild oat management requires an integrated approach that uses management techniques beyond simple herbicide application. A 5-yr (1996 to 2000) zero tillage study was conducted to assess the influence of barley harvest timing on wild oat densities in subsequent years at Lacombe, AB, Canada and Melfort, SK, Canada. Harvest timings included barley harvested 1 wk after heading (early), approximately 14 to 16 d later at the soft dough stage (normal), and at maturity (grain). In the absence of herbicides, wild oat densities decreased in silage plots harvested early and increased in grain plots. Reductions were more distinct at Lacombe where barley phenological differences and whole plant moisture contents between early and normal silage harvests were greater than at Melfort. Half rates of wild oat herbicides (ICIA 0604 and imazamethabenz) did not augment reductions in wild oat densities after early silage harvest, but did improve wild oat management after normal silage harvest, and in grain production. At Lacombe, early silage harvest reduced wild oat densities more than did herbicides in grain production. Similar trends were apparent at Melfort but were not statistically significant. Early barley silage harvests may be an effective integrated weed management tool for wild oat.

Field experiments were conducted in Virginia in 2000 and 2001 to determine the response of wheat and Italian ryegrass biotypes to postemergence applications of diclofop-methyl compared with several experimental and registered herbicides. Control of diclofop-methyl–sensitive Italian ryegrass by AE F130060 03 was similar to control by diclofop-methyl and was greater than that by chlorsulfuron plus metsulfuron, chlorsulfuron plus metribuzin, MON 37560, ICIA 0604, and CGA 184927. AE F130060 03 also controlled diclofop-methyl–resistant Italian ryegrass better than the other herbicides. Late-season spike density of diclofop-methyl–resistant Italian ryegrass was reduced 91 to 98% by AE F130060 03. Despite injury ranging from 10 to 24%, grain yield from wheat treated with AE F130060 03 was similar to or greater than yield from wheat treated with the other herbicides. Italian ryegrass control, spike density, and grain yield were not influenced by AE F130060 03 rate or addition of methylated seed oil.

The allelopathic potential of wild radish was evaluated in controlled environments by determining if an aqueous extract from oven-dried wild radish shoots suppressed germination and radicle growth of some crops and weeds common to the southeastern United States. In addition, phytotoxicity from topical applications of the aqueous extract was assessed, along with crop and weed suppression by soil incorporated, air-dried wild radish residues. Germination and radicle growth of all species were reduced by the extract compared with distilled water. However, topical applications of the aqueous extract failed to induce injury on any species by 7 d after treatment. Emergence and shoot fresh weight of the bioassay plants were reduced by wild radish residue incorporated into soil, with the level of suppression dependent on the quantity of residue incorporated. Sicklepod and prickly sida were extremely sensitive to incorporated wild radish residues, with > 95% fresh weight reduction at 0.5% (wt/wt) residue, compared with an untreated control. Conversely, yellow nutsedge showed a high degree of tolerance in all trials. Of the crops evaluated, cotton emergence and growth were most sensitive to incorporated wild radish residues. These data indicate that wild radish aqueous extract or incorporated residues (or both) suppress seed germination, radicle growth, seedling emergence, and seedling growth of certain crops and weeds and these responses are attributed to an allelochemical effect.

Field studies were conducted in 1999, 2000, and 2001 to determine the effectiveness of mesotrione applied preemergence (PRE) or postemergence (POST) in no-till corn. Also, a proposed prepackage mix of mesotrione plus acetochlor (1:11 ratio of mesotrione–acetochlor) in combinations with the trimethylsulfonium salt of glyphosate (glyphosate-TMS), paraquat, and 2,4-D was investigated. Mesotrione PRE at 235 g ai/ha or greater controlled common lambsquarters, smooth pigweed, and common ragweed at least 80%. POST mesotrione at 35 g/ha and higher controlled common lambsquarters 91% or greater. Mesotrione applied POST at 140 g/ha controlled smooth pigweed greater than 97%. Common ragweed control from POST mesotrione was inconsistent, ranging from 56 to 97%. PRE and POST applications of mesotrione did not adequately control goosegrass, giant foxtail, fall panicum, johnsongrass, or cutleaf eveningprimrose. The mesotrione plus acetochlor prepackage mix plus glyphosate-TMS or paraquat controlled field pansy and ivyleaf morningglory similar to or better than did the prepackage mixture of the isopropylamine salt of glyphosate (glyphosate-IPA) plus atrazine plus acetochlor. But common ragweed control by mesotrione plus acetochlor plus glyphosate-TMS or paraquat was occasionally lower than control by the prepackage mixture of glyphosate-IPA plus atrazine plus acetochlor. Corn injury was generally less than 10% with PRE and POST mesotrione applications.

Yellow nutsedge, a weed commonly present in Florida vegetable fields, may substantially reduce crop yields when not controlled. Soil fumigation with methyl bromide effectively controls nutsedges, but methyl bromide is being phased out of production and use in the United States. Therefore, nutsedge management in bell pepper is a cause for concern. An experiment was conducted during four seasons (spring and fall of 1999 and 2000) to determine the tolerance of bell pepper grown at two in-row spacings (23 and 31 cm) to interference resulting from planted yellow nutsedge tuber densities (0 to 120 tubers/m2). Relative to yields with no nutsedge, pepper fruit yields in each season were reduced 10% with fewer than 5 planted tubers/m2. Yield losses increased more rapidly with an increase in initial nutsedge density from 0 to 30 than from 30 to 120 tubers/m2. With 30 nutsedge tubers/m2, large fruit yield was reduced 54 to 74% compared to that with no nutsedge. Nutsedge shoots overtopped the pepper plants as early as 6 wk after treatment when, with 15 planted tubers/m2, nutsedge interference reduced pepper plant biomass by 10 to 47%. In the absence of methyl bromide, weed control strategies with high efficacy against yellow nutsedge will be needed for bell pepper production.

Common management alternatives were compared in a factorial arrangement for 2 yr to determine their effects on green foxtail and yellow foxtail seed production in spring wheat in the Northern Great Plains of the United States. Seed production was measured twice, at wheat harvest (in August) and postharvest (after first lethal frost in autumn). Management alternatives were early, middle, and late crop-sowing dates; no-till, chisel, and moldboard plow tillage systems; and broadleaf herbicide only and broadleaf herbicide plus fenoxaprop applications. Fenoxaprop reduced foxtail seed production at wheat harvest but not at postharvest. Early sowing also decreased seed production at wheat harvest but increased postharvest seed production. Tillage system had no consistent effects on foxtail seed production. Postharvest seed production often was greater than or equal to that at wheat harvest regardless of management system. These results indicate that in-crop management alternatives, such as postemergence grass herbicide and early crop sowing, may lower the number of foxtail seeds at harvest substantially, but they must be accompanied by postharvest weed control to reduce overall seed production.

Field and laboratory studies were conducted from 1993 to 1997 to determine the feasibility of controlling nodding broomrape in sunflower by treating crop seeds with pronamide. Soaking sunflower seeds for 5 min in 50% pronamide solution or coating at the equivalent of 2 kg/ha with pronamide did not impair seed germination or seedling growth, and controlled nodding broomrape 49 to 68% and 51 to 77%, respectively, up to 105 d after planting. Studies of the effect of treated sunflower seeds on germination and seedling growth, at several time intervals after the herbicide application (0, 30, 60, and 90 d after treatment [DAT]), were conducted. Soaking with 50% solution or coating at 2 kg/ha reduced seedling growth by 20 and 24% 60 DAT, respectively, compared with the control.

Studies on weed management systems with bromoxynil-resistant, glyphosate-resistant, and nontransgenic cotton cultivars in a no-tillage environment were evaluated in North Carolina and Tennessee in 1997 and 1998. All weed management systems in nontransgenic and bromoxynil-resistant cotton controlled sicklepod 72 to 78%, whereas sicklepod was controlled at least 94% in glyphosate-resistant cotton. Entireleaf and pitted morningglory, smooth pigweed, and common cocklebur were controlled at least 92% with all management systems. Fiber quality was also measured in Tennessee. Micronaire and fiber strength ranged from 4.35 to 4.55 units and 28.6 to 30.1 g/tex, respectively, in bromoxynil-resistant and glyphosate-resistant cultivars that received postemergence over-the-top (POT) herbicides. Harvest trash content ranged from 0.80 to 1.15% in systems where POT and late postemergence–directed (LAYBY) herbicides were used and was 1.65% where multiple glyphosate applications were used with no LAYBY herbicides. Cotton lint yield and net returns were generally highest in systems that included bromoxynil or pyrithiobac POT followed by cyanazine plus MSMA LAYBY or multiple glyphosate treatments where no LAYBY herbicides were used.

Bahiagrass is used for roadsides, pastures, and lawns in the southeastern United States mainly because of drought and nematode tolerance. Metsulfuron is a sulfonylurea herbicide, which selectively controls bahiagrass in bermudagrass. Certain cultivars of bahiagrass were observed to be tolerant to recommended rates of metsulfuron. Therefore, research was conducted to investigate the susceptibility of five major bahiagrass cultivars to metsulfuron applied at increasing rates to 42 g ai/ha. Five bahiagrass cultivars were evaluated: ‘Pensacola’, ‘Tifton-9’, ‘Argentine’, ‘Common’, and ‘Paraguayan’. Argentine, Common, and Paraguayan cultivars showed a four- to fivefold increased tolerance to metsulfuron compared with Pensacola. Because of yearly inconsistencies, results for Tifton-9 were inconclusive.

The postemergence herbicide ethofumesate and the plant growth regulator paclobutrazol were evaluated for annual bluegrass control in creeping bentgrass turf managed as golf fairways. Both products were applied under several different timing regimes relative to the time of the year. Paclobutrazol treatments provided significantly greater annual bluegrass control than ethofumesate. There were no differences between rates of paclobutrazol (0.28 and 0.14 kg ai/ha) when applied from spring through summer. Annual bluegrass control after spring and summer applications of paclobutrazol was 85% or more. Clipping weight data indicated that paclobutrazol suppressed growth in annual bluegrass longer than in creeping bentgrass. It was concluded that prolonged suppression of annual bluegrass by paclobutrazol resulted in creeping bentgrass dominance and subsequent annual bluegrass control. Additionally, applications of ethofumesate in autumn–winter, followed by paclobutrazol applied in spring–summer, provided significant control of annual bluegrass in 1 yr of the study.

Eight sweet corn cultivars were evaluated for tolerance to AE F130360 in five field experiments conducted over 2 yr in Ontario. AE F130360 was applied postemergence at 70 and 140 g ai/ha, the latter rate representing a spray overlap in the field. Response to AE F130360 varied with respect to sweet corn cultivar and herbicide rate. Minimal crop injury was observed in seven of the eight cultivars. One cultivar, ‘DelMonte 2038’, was extremely sensitive, showing 94% or more injury for all site-years. Plant height of most cultivars was not negatively affected by AE F130360 treatments, with the exception of DelMonte 2038, which sustained height reductions of 78% or greater compared with the untreated control. The crop injury and height reductions that were observed in DelMonte 2038 were reflected in the marketable yields, which were reduced by 92% or more as a result of the AE F130360 treatments. Marketable yields also tended to be reduced in ‘Calico Belle’ and ‘Rival’. On the basis of marketable yields, it was concluded that ‘CNS 710’, ‘GG 222’, ‘GG 246’, ‘GH 2684’, and ‘Reveille’ have full tolerance to AE F130360, Calico Belle and Rival tend to have moderate tolerance, and DelMonte 2038 has zero tolerance to AE F130360.

Field research was conducted to test a method of herbicide application in which chemical is placed directly onto cut surfaces of plants during a mowing operation. Specially designed mowers equipped with a fluid application system allow for low-volume herbicide application from the cutting blades during the mowing process (wet blade). Two prototype wet-blade machines, including a sickle bar cutter and a Burch Wet-Blade rotary mower, were used to apply triclopyr, clopyralid, and 2,4-D at various rates and combinations using a total carrier volume of 25 L/ha. Weed management studies were conducted on dogfennel, annual lespedeza, and clovers during a 2-yr period. Wet-blade herbicide applications were effective and performed as well as or better than comparative rates applied using a foliar spray technique. Triclopyr at 2.24 kg ae/ha controlled dogfennel when applied with either the rotary mower or the sickle bar cutter (94 and 77%, respectively). Rotary mower applications of 0.20 kg ae triclopyr + 0.07 kg ae clopyralid per hectare in rough turf achieved 90% control of annual lespedeza and 95% control of red and white clovers.

Nonfungicidal effects of agricultural fungicides on crop plants have been reported previously; however, there are few reports of nontarget effects of fungicides on weedy species. Field research trials in Oregon demonstrated that the growth of several broadleaf weeds was reduced after multiple applications of the fungicide propiconazole. Greenhouse experiments confirmed that preemergence applications of propiconazole reduced the biomass accumulation of several common broadleaf and grass weeds 15 to 63%. Laboratory experiments were performed on redroot pigweed, the most sensitive species, to examine the effects of propiconazole on germination and early seedling growth. Redroot pigweed germination and total seedling length (root plus shoot) were reduced at propiconazole concentrations above 37 and 0.36 mg/L, respectively. Growth-regulating effects of fungicides such as propiconazole on the germination and early growth of weeds may contribute to integrated weed management, especially when adequate moisture ensures the presence of germinating seeds and small seedlings throughout the growing season.

Greenhouse studies were conducted to evaluate shoot number, shoot weight, and root weight reduction of yellow and purple nutsedge to three placement levels (soil, foliar, and soil + foliar applied) and four herbicide treatments (CGA-362622, imazaquin, MSMA, and imazaquin + MSMA). Soil-applied CGA-362622 reduced shoot number, shoot weight, and root weight greater than foliar-applied CGA-362622. Foliar-applied imazaquin and soil-applied MSMA achieved little reduction in measured variables compared with the nontreated control. Foliar-applied imazaquin and soil-applied MSMA reduced shoot number, shoot weight, and root weight less than imazaquin + MSMA applied in a similar manner. Averaged over placement levels, imazaquin reduced shoot weight of yellow nutsedge greater than purple nutsedge. Averaged over herbicide treatments, soil-applied treatments were more effective in reducing purple nutsedge shoot number, whereas foliar-applied treatments were more effective in reducing yellow nutsedge shoot number.

Diminishing availability and increasing costs of herbicides cause strawberry growers to seek both chemical and nonchemical alternatives, especially for within-row weed control soon after strawberries are transplanted. Several weed control treatments for strawberry establishment were examined during 2 yr in Minnesota. Treatments included: woolen landscaping fabric centered over the crop row; as above, but 2-ply fabric; spring canola incorporated into soil when 30 cm tall; as above, but canola killed with burndown herbicide and left as mulch; standard herbicide, DCPA; hand weeded; and no weed control. Areas between all strawberry rows were cultivated. Measurements included weed densities and weights, numbers of strawberry daughter plants, and fruit yield 1 yr after transplantation. The best alternative treatment was the 1-ply woolen fabric. It nearly eliminated weeds from rows, promoted daughter plant rooting, and allowed maximum fruit yields, equivalent to those of the DCPA and hand-weeded treatments. Canola mulch controlled weeds inconsistently and achieved only modest to low production of daughter plants and fruit. Weed control and fruit yield with incorporated canola were similar to the weedy check treatment.

There are few efficient and cost-effective methods for controlling weeds in processing tomatoes. Sulfosulfuron is a sulfonylurea herbicide developed for controlling weeds in wheat. In previous studies, we have demonstrated the efficacy of sulfosulfuron in selectively controlling Orobanche aegyptiaca in tomato. The objective of the present study was to elucidate the potential of sulfosulfuron to selectively control troublesome, nonparasitic weeds in tomato. In the greenhouse, sulfosulfuron efficacy at 37.5, 75.0, and 112.5 g ai/ha applied preplant incorporated (PPI), preemergence (PRE), and postemergence (POST) was tested. Sulfosulfuron when applied PPI and POST was highly selective in controlling weeds without causing injury to tomato. The weeds that were efficiently controlled, even at low rates of application, included purple nutsedge, black nightshade, mustard, pigweed, and bindweed. PRE application resulted in the most efficient weed control but was phytotoxic to tomato at high rates.

Studies were conducted in 2000 and 2001 to investigate responses of glyphosate-resistant cotton, glyphosate-resistant soybean, and selected weed species to postemergence applications of isopropylamine (Ipa) and diammonium (Dia) salts of glyphosate at selected rates ranging from 0.42 to 3.36 kg ae/ha. No differences were detected between either glyphosate salts or application timings for cotton injury, cotton lint yield, micronaire, fiber length, fiber strength, or fiber uniformity. In a weed-free soybean study, no differences in soybean injury occurred between early-postemergence treatments of the two glyphosate salts. Injury from late-postemergence treatments did not exceed 12% with glyphosate-Ipa or 9% with glyphosate-Dia at 3.36 kg/ha. Soybean treated with glyphosate-Ipa yielded 3,050 kg/ha, whereas soybean treated with glyphosate-Dia yielded 2,880 kg/ha, when averaged over glyphosate rate and application timing. In a soybean study that included weed control as a variable, weed control at 14 d after treatment (DAT), and soybean yield was independent of glyphosate salt. Control of common ragweed, ivyleaf morningglory, pitted morningglory, and large crabgrass at 28 DAT was similar at 0.84 kg/ha of either glyphosate salt.

Field studies were conducted at Yoakum and Stephenville, TX; Jay, FL; and Midville and Plains, GA, to determine the persistence of imazapic applied to peanuts at 0, 70, 140, and 210 g ai/ha. The following year, cotton, sorghum, and corn were planted in the treated plots in Texas, cotton was planted in Florida, and corn and cotton were planted in Georgia and evaluated for carryover injury. Data collected to determine injury included plant heights and weights. In 1999 in Texas and in Florida and Georgia, there was no significant carryover injury to rotational crops from any of the imazapic rates. Data on cotton and sorghum plant height from Texas in 2000 showed height reductions for the 210-g/ha rate on cotton and the 140- and 210-g/ha rates on sorghum. These data showed no significant carryover effects to rotational crops from the 70-g/ha rate of imazapic applied to peanuts the previous year.