Managing weeds in watermelon is challenging because of the limited availability of herbicides approved for use in this crop. Field experiments on efficacy and crop tolerance were conducted to determine the potential for halosulfuron use in watermelon in Georgia and North Carolina. Halosulfuron was applied PRE, early POST (EPOST; one-leaf watermelon), and late POST (LPOST; watermelon with 30-cm runners) at 26, 39, and 52 g ai/ha. Under weed-free conditions, PRE treatments did not injure watermelon. EPOST and LPOST treatments caused 45 and 34% injury 2 wk after treatment, respectively, averaged over halosulfuron rate. EPOST treatments reduced watermelon fruit number and total weight by 15 and 22%, respectively, and LPOST treatments reduced total fruit weight 12%. Halosulfuron PRE at 39 or 52 g/ha provided 94% or greater control of carpetweed, Palmer amaranth, and smooth pigweed. EPOST treatments controlled 84 and 88% of yellow nutsedge and smooth pigweed, respectively, but LPOST treatments controlled less than 83% of all weed species. Sequential applications of halosulfuron at 26 g/ha PRE and 26 g/ha LPOST controlled 89 to 99% of carpetweed, coffee senna, Palmer amaranth, smooth pigweed, and yellow nutsedge. Our data suggest growers can effectively use halosulfuron PRE in seeded watermelon. However, POST applications should be made only after watermelon has 30-cm runners and as a salvage spot treatment where previous weed control strategies have failed to provide adequate control.

Experiments were conducted at three locations in Louisiana in 2002 and 2003 to evaluate flumioxazin (36, 72, or 109 g ai/ha) applied pretransplant (PRE) or post-transplant (POST) to sweetpotato. All treatments were applied immediately before or after sweetpotato transplanting to weed-free beds. PRE applications caused 4% or less injury with any rate of flumioxazin at 9 or 18 d after transplanting (DATr) compared with 18 to 20% injury at 9 DATr and 6 to 14% at 18 DATr with 72 or 109 g/ha POST, respectively. Injury from PRE applications of flumioxazin were not different from injury with clomazone (840 g ai/ha) applied POST. Injury at Chase, LA, in 2002 was 8% and less with flumioxazin PRE, but 35 to 83% with flumioxazin POST and appeared to be due to the use of greenhouse-grown cuttings instead of field-grown cuttings, which were used in the other two experiments. There was no interaction between experiments for sweetpotato yield. Plots treated with flumioxazin PRE or 36 g/ha POST yielded greater than sweetpotato treated with clomazone for U.S. No. 1 and 2 grade yield as well as total marketable yield. No differences were observed in yellow nutsedge control with any rate of flumioxazin. At 34 or 50 DATr, flumioxazin controlled yellow nutsedge 73 to 85% with 72 or 109 g/ha applied PRE or POST. Flumioxazin, regardless of application timing or rate, controlled carpetweed and spiny amaranth at least 86%. A similar experiment in Mississippi evaluated tank-mixes of flumioxazin (36, 72, or 109 g/ha) and clomazone (840 g/ha) applied PRE or POST. No sweetpotato injury was observed with flumioxazin PRE. However, injury from flumioxazin POST increased with increased rates (18 to 50% at 18 DATr and 16 to 93% at 25 DATr). Weed control was greater than 80% with all treatments.

Field experiments were established on a loamy fine sand to evaluate weed control in a conservation tillage system where cotton was planted into sorghum stubble. Preemergence herbicides for Palmer amaranth and volunteer sorghum control in cotton included methazole, dipropetryn, prometryn, metolachlor, and metolachlor plus dipropetryn or prometryn. Dipropetryn controlled both weeds without crop injury. Above 1.7 kg ai/ha, methazole provided effective control but injured the crop. Prometryn was less effective than dipropetryn or methazole against Palmer amaranth and controlled <40% volunteer sorghum. Metolachlor unacceptably injured cotton. Cotton yields were excellent when both weeds were controlled.

Glyphosate-based, ready-to-use weed control products often contain pelargonic acid (PA) at a concentration equivalent to that of the glyphosate. It remains unclear what benefit, if any, this combination provides. Greenhouse experiments using large crabgrass, yellow nutsedge, longstalked phyllanthus, and prostrate spurge were conducted to determine whether the addition of PA improved weed control efficacy compared to glyphosate alone. Glyphosate was applied at a series of rates, ranging from 0.11 to 1.12 kg ae/ha, either alone or with an equal rate of PA. Addition of PA to glyphosate was synergistic only in longstalked phyllanthus and yellow nutsedge, and this synergism was manifested only as an increase in the amount of early (i.e., 5 to 7 d after treatment) visual injury. Conversely, longer-term control and control of regrowth was either not affected or reduced by the addition of PA. We conclude that the addition of PA to glyphosate in ready-to-use weed control products is neither warranted nor justified. However, we also note that the increase in early injury that was observed in only two of the four species evaluated could be an important attribute for the consumers for which these products are targeted.

Multilocational characterization of selected herbaceous and shrub legumes was carried out over a 3-yr period at lowland and midlatitude sites in the moist savanna agroecological zone in Nigeria where a south–north gradient exists for rainfall, length of growing season, and insolation. One study site each was located in coastal–derived savanna (DS), southern Guinea savanna (SGS), and northern Guinea savanna (NGS). A fourth site was located in the plateau of the NGS. Only one legume cover crop, lablab, produced adequate ground cover and good weed suppression in three locations irrespective of rainfall amount, duration, and distribution. Velvetbean was superior to other legume cover crops in the lowland savanna locations where rainfall exceeded 1,100 mm/yr but not in the plateau of the NGS where rainfall was less than 1,000 mm. Pigeonpea grew luxuriantly and produced canopy cover that effectively suppressed weeds in the DS where rainfall was high. Centurion grew well and suppressed weeds effectively only in the SGS site where rainfall of 1,120 mm was well distributed over a 5-mo period. Sunnhemp grew well and suppressed weeds only in the NGS study sites where rainfall duration was 4 mo and the length of the growing period was short. Weed density was negatively correlated (P < 0.05) with percentage ground cover of those legume cover crops that were effective in weed suppression in all locations. Redundancy analysis revealed significant associations between weed species and cover crops at each of the locations.

Field research was conducted in 2002 and 2003 to determine the effect of twin- and single-row spacing and POST glyphosate application timing on light interception, weed control, and grain yield of glyphosate-resistant corn and soybean. Row spacing did not affect light interception measured 10 to 11 wk after planting. Corn grain yield in 2002 was 1.0 Mg/ha higher in single rows compared with twin rows when averaged over glyphosate timing, but was unaffected by row spacing in 2003. Soybean grain yield was similar in 19- and 38-cm single rows, and single-row grain yield was 0.2 to 0.4 Mg/ha higher than the twin-row spacing. Corn grain yields were similar to the weed-free control when glyphosate was applied to weeds 10 to 15 cm tall in 2002 and 10 cm tall in 2003. Soybean yield was maximized by application of glyphosate to weeds 15 to 30 cm tall in 2002 and 60 cm tall in 2003.

Imazamox ammonium salt at 53 g ae/ha applied postemergence in the fall to imidazolinone-resistant wheat controlled Italian ryegrass 98 to 100% 10 wk after treatment (WAT). Control 22 WAT was 88 to 98% at two locations and 55% at a third location. Imazamox was more effective applied in fall to three- to four-leaf Italian ryegrass than when applied in spring to one- to three-tiller Italian ryegrass. Split applications, with 27 g/ha applied in fall and spring, were no more effective than 53 g/ha applied in fall. Pendimethalin preemergence in combination with fall-applied imazamox increased control 22 WAT 10 to 33 percentage points at two of three locations. Imazethapyr ammonium salt plus imazapyr isopropylamine salt applied at 47 plus 16 g ae/ha and imazamox at 44 or 53 g/ha were similarly effective, whereas imazethapyr at 70 g/ha was ineffective. Control by imazapic ammonium salt at 70 g ae/ha was equal to or greater than control by imazamox at 44 or 53 g/ha. Imazamox, imazethapyr plus imazapyr, and imazapic controlled diclofop-resistant and -susceptible Italian ryegrass. Thifensulfuron plus tribenuron mixed with imazamox increased Italian ryegrass control in field and greenhouse experiments, whereas dicamba reduced control compared with imazamox applied alone. Control by imazamox plus 2,4-D was similar to or greater than control by imazamox alone.

The critical weed-control period in field seeded cabbage using natural weed stands was 2 wk in 1988 and 4 wk in 1989. Regression analysis showed that the length of weed-free period, weed density, and ambient light reduction by competing weeds were factors affecting cabbage yield. Weeds that emerged after the initial weed-free period shaded the soil and subsequently lowered soil surface temperatures in 1989. Velvetleaf densities of 1.2 and 3.6 plants per m2 that competed all season with cabbage reduced cabbage yields 52% and 71% of the weed-free treatment in 1988 and 76% and 92% in 1989, respectively. Cabbage yields were reduced at all velvetleaf densities seeded 0, 1, and 2 wk after cabbage, but cabbage yield was not reduced when velvetleaf was seeded 4 or 6 wk after cabbage. Cabbage yield was not different between parallel and staggered velvetleaf configurations at 0.6 plants per m2, but was reduced with longer periods of competition. Velvetleaf seed production was prevented with 6 wk weed-free period after cabbage emergence and subsequent destruction of emerging velvetleaf after cabbage harvest.

A field experiment was conducted in 1996 and 1997 to determine snap bean tolerance to halosulfuron based on crop injury, height, and yield. Halosulfuron was applied preemergence (PRE), postemergence (POST), and sequentially PRE followed by (fb) POST at 35, 53, and 70 g ai/ha, respectively. For comparison, a hand-weeded check was included. When data were averaged across years and halosulfuron rates, halosulfuron PRE, POST, and PRE fb POST provided similar yellow nutsedge control (74 to 82%) at snap bean harvest. Halosulfuron PRE resulted in 4% snap bean injury at harvest. Similarly, halosulfuron PRE fb POST resulted in 5% injury, while halosulfuron POST caused the most damage at 8%. Snap bean height at harvest was reduced 14% with halosulfuron POST compared to the weed-free check, with only 5 and 6% reduction caused by halosulfuron PRE and PRE fb POST, respectively. Halosulfuron POST reduced yield 39% compared to the weed-free check, while the PRE and PRE fb POST application timings produced yield similar to the check. When averaged across years and halosulfuron application timings, an increase in halosulfuron rate had no effect on yellow nutsedge control or snap bean yield. A linear trend was found for snap bean injury and plant height at harvest with snap bean injury increasing with an increase in halosulfuron rate while snap bean plant height decreased with an increase in halosulfuron rate. Application of halosulfuron PRE is the safest means to control yellow nutsedge in snap bean in North Carolina.

Metolachlor, applied to the surface of leaching columns as dicalcium phosphate tablets, was recovered over a period of 25 d compared with 2 and 3 d for emulsifiable concentrate and granular formulations, respectively. In similar studies, approximately 27% of napropamide was recovered from tablets during the same period. Adding an adjuvant to the napropamide tablet mixture increased the recovery rate to 55%. Tablet hardness and size had little effect on the release rate of napropamide. Tablets containing 4% ai napropamide released greater amounts of herbicide at a single collection period than did tablets containing 1% ai. Adding an adjuvant to the napropamide tablet mixture significantly improved Italian ryegrass control in the area adjacent to herbicide placement.

Field experiments were conducted at three locations in North Carolina in 1998 and 1999 and one location in Virginia in 1998 to evaluate weed management systems in peanut. Treatments consisted of diclosulam alone preemergence (PRE), or diclosulam plus metolachlor PRE alone or followed by (fb) bentazon plus acifluorfen postemergence (POST). These systems were also compared with commercial standards of metolachlor PRE fb bentazon plus acifluorfen POST or imazapic POST. Our data indicate that diclosulam PRE plus metolachlor PRE in conventional tillage peanut production usually controlled common lambsquarters, common ragweed, prickly sida, and entireleaf morningglory. But control of spurred anoda, goosegrass, ivyleaf morningglory, large crabgrass, and pitted morningglory by this system was inconsistent and may require additional POST herbicide treatments. Systems that included diclosulam plus metolachlor PRE consistently provided high yields and net returns.

Eradication is often stated as an essential element of weed management. Assessing the costs and benefits of eradication programs is often difficult because doing so requires speculation about the impacts and spread of weeds if eradication measures were not undertaken. The objective of this article is to describe and assess the Montana Dyer's Woad Cooperative Project, a program aimed at eradicating dyer's woad from Montana. The Project comprises four key components: early detection, treatment technologies, repeated site visits with monitoring, and education. To evaluate the success of the Montana Dyer's Woad Cooperative Project, we used monitoring data to observe the change in the number of counties where dyer's woad is present, plotted the trend in population size over time, and evaluated change in infestation size. We also predicted population spread based on the 1999 population size and demographic characteristics of dyer's woad. Dyer's woad has been eradicated from 9 of 13 infested counties in Montana, and infestation sizes have decreased in the remaining infested counties. In some counties, a containment effort was needed in conjunction with repeated inventories and treatment applications to prevent spread while depleting the seedbank to the point where eradication is possible. If not for the Project, our analysis suggests that some dyer's woad populations might consist of millions of plants, potentially covering 39,021 ha in Montana and costing $1.9 million/yr to manage. In comparison, the Project has reduced the total area infested in Montana to 2.6 ha and cost the state only $142,000 for the past 7 yr of management. In Montana, dyer's woad eradication from individual counties has been successful because of persistence and ongoing cooperative efforts.

Velvetleaf control and sugarbeet response to POST triflusulfuron applied alone and in combination with desmedipham plus phenmedipham, nonionic surfactant, and urea ammonium nitrate (50:50) were evaluated in the greenhouse (velvetleaf only) and field. In a second field study, the effect of POST applications of triflusulfuron, desmedipham plus phenmedipham, ethofumesate, endothall, or combinations of these herbicides on sugarbeet root yield and quality was determined in the absence of weeds. Triflusulfuron controlled velvetleaf only when nonionic surfactant (NIS) was added to the spray solution. Desmedipham plus phenmedipham plus triflusulfuron gave greater velvetleaf control than triflusulfuron in the absence of NIS in the field. However, adding desmedipham plus phenmedipham to triflusulfuron plus NIS decreased velvetleaf control in the greenhouse. Adding desmedipham plus phenmedipham to triflusulfuron plus NIS increased visible sugarbeet response compared to triflusulfuron plus nonionic surfactant or desmedipham plus phenmedipham 14 d after the last POST application in 1994. In the absence of weeds, POST herbicide applications that included triflusulfuron did not reduce sugarbeet root yield more than other POST herbicides.

Corn inbreds are often more sensitive to herbicides than hybrids. Field experiments were conducted with three corn inbreds to (1) evaluate inbred sensitivity to the acetamide herbicides acetochlor, dimethenamid, flufenacet, and metolachlor, (2) compare the effects of various crop safeners in combination with acetochlor and metolachlor, and (3) measure the effect of herbicide microencapsulation on acetochlor injury. Herbicides were applied preemergence at the registered rate and at two, three, or four times the registered rate in corn. Injury ratings, plant population, and the percentage of plants showing acetamide injury symptoms were used to measure herbicide effect. The inbreds ‘Mo17’ and ‘Great Lakes 15’ (GL15) were sensitive to acetamide injury. Reductions in plant population and increases in the injury rating and the percentage of injured plants were caused by acetochlor, dimethenamid, flufenacet, metolachlor, and flufenacet + metribuzin when applied at three times the registered rate. The inbred ‘B73’ was not injured. The safeners benoxacor and dichlormid reduced injury caused by metolachlor. The percentage of plants injured by metolachlor 15 days after treatment (DAT) was lower when benoxacor was the safener compared to dichlormid. By 28 DAT, plants treated with safeners recovered from injury, and there were no differences between the treatments. The safeners dichlormid and furilazole reduced, but did not always eliminate, injury caused by acetochlor applied at three times the registered rate. Microencapsulation of acetochlor reduced injury to GL15. When the safeners dichlormid or furilazole were included in an acetochlor formulation, microencapsulation did not further reduce corn injury.

Herbicides from several chemical families were evaluated in the greenhouse for preemergence control of perennial weed species emerging from seeds. Weed species were bermudagrass, johnsongrass, Canada thistle, common milkweed, common pokeweed, hemp dogbane, and horsenettle. Atrazine, cloransulam, chlorimuron, clomazone, flumetsulam, imazaquin, linuron, metolachlor, metribuzin, pendimethalin, and sulfentrazone were used representing common preemergence herbicide families used in the mid-Atlantic region for corn and soybean in a sandy loam soil. Hemp dogbane and common pokeweed were controlled (greater than 85%) by eight of the 11 herbicides in this study, indicating they may be the two most susceptible species in the trial. Metolachlor and pendimethalin provided control of only bermudagrass, and linuron controlled only Canada thistle. Cloransulam controlled all species except bermudagrass. Clomazone provided greater than 80% control of all species except horsenettle. Metribuzin alone or in combination with chlorimuron provided the broadest spectrum and highest level of control. Metribuzin provided greater than 85% control of all species except johnsongrass. Soil-applied herbicides can limit the establishment of perennial species from seeds.

A complex coacervate formulation was developed for Colletotrichum truncatum 00-003B1 (Ct), a bioherbicidal fungus against scentless chamomile, and tested in the greenhouse. A two-step process was developed to formulate Ct conidia: (1) invert emulsion preparation—emulsify an aqueous suspension of Ct conidia in nonrefined vegetable oil with the aid of a surfactant, and (2) encapsulate the Ct conidia invert emulsion by complex coacervation. Formulation ingredients, including nonrefined vegetable oils, surfactants, proteins, and carbohydrates, and formulation-processing parameters, including mixing speed and the amount of oil added to invert emulsions, were examined for maximum retention of Ct conidia in the formulation. Most formulation ingredients considered and tested in this study were compatible with Ct, with no significant reduction in conidial germination and mycelial growth. The surfactant soya lecithin promoted the greatest retention of Ct conidia (88%) in the invert emulsion, followed by sorbitan monooleate (82%), glycerol monooleate (70%), and sorbitan trioleate (55%). Optimal retention of Ct conidia in the invert emulsion was observed with a water : oil ratio of 1 : 1.8 to 1 : 3.7, and an overhead paddle stirring speed of 300 rpm when preparing the emulsion. Complex coacervate wall ingredients of 1% gelatin and 2% gum arabic were most effective for Ct conidia retention. In greenhouse studies, scentless chamomile disease rating, following a 24-h dew period, was higher on plants sprayed with the Ct conidia complex coacervate formulation than on plants with Ct conidia suspended in 0.1% Tween 80.

Five herbicides were tested in green pea, and their residual effects on several rotational crops were investigated in northwestern Washington from 1998 through 2000. In both years, imazamox applied postemergence caused 21 and 28% early-season injury at 0.036 and 0.045 kg/ha, respectively, but only in 1999 did early-season injury result in yield loss compared with nontreated, weedy pea. Trifluralin, clomazone, and sulfentrazone caused 15 to 19% injury to pea in 1998 but not in 1999. Although pea treated with sulfentrazone produced more harvestable pods than nontreated pea (5.0 and 4.1 pods/plant, respectively), pod numbers were similar to peas treated with clomazone, pendimethalin, pendimethalin plus imazamox, or trifluralin. All rotationally grown crops were tolerant to herbicides used in green pea, except for strawberry in 1999, in which leaf area was reduced 23% in plots treated with 0.045 kg/ha imazamox compared with nontreated plots. Intensive tillage combined with favorable soil and climatic conditions in this study indicate that western Washington green pea producers may have greater flexibility in their choice of herbicides and rotational crop alternatives than previously believed.

Field experiments were conducted in grain sorghum at five locations in Kansas in 2009 and 2010, to evaluate the efficacy and crop safety of early- to mid-POST (EMPOST) and late-POST (LPOST) applications of premixed pyrasulfotole and bromoxynil (PYRA&BROM) in tank mix combinations with atrazine or atrazine plus 2,4-D ester or dicamba compared to bromoxynil plus atrazine. PYRA&BROM at 244 or 300 g ai ha−1 plus atrazine at 560 g ai ha−1 applied EMPOST controlled pigweed species (Palmer amaranth, tumble pigweed, and redroot pigweed), kochia, velvetleaf, common sunflower, ivyleaf morningglory, and common lambsquarters 93% or greater. Puncturevine control among three locations ranged from 85 to 99%. Control of most weed species was not improved by increasing PYRA&BROM rate from 244 to 300 g ha−1 or by tank mixing 2,4-D or dicamba with PYRA&BROM plus atrazine. However, ivyleaf morningglory control was improved at the LPOST timing by adding 2,4-D or dicamba at 140 g ae ha−1. In no instance did any PYRA&BROM treatment provide greater weed control than bromoxynil plus atrazine at 281 + 560 g ha−1 when applied EMPOST, but in most instances PYRA&BROM treatments were more effective than bromoxynil plus atrazine when applied LPOST. Generally, PYRA&BROM treatments were more effective when applied EMPOST than LPOST, especially when 2,4-D or dicamba was added. PYRA&BROM plus atrazine treatments caused foliar bleaching in sorghum within 7 ± 3 d after treatment, but recovery was complete within 3 to 4 wk and grain yields were not reduced. Tank mixing dicamba with PYRA&BROM and atrazine occasionally reduced visible crop response compared to PYRA&BROM plus atrazine. Our results indicate that PYRA&BROM plus atrazine with or without 2,4-D or dicamba selectively controls several troublesome broadleaf weeds in grain sorghum. Foliar bleaching of sorghum leaves can occur but the symptoms are transient, and grain yields are not likely to be reduced.

Amicarbazone is a photosystem II (PSII) inhibiting herbicide of the triazolinone herbicide family. Greenhouse experiments were conducted to compare the effects of amicarbazone and atrazine on annual bluegrass control and quantum yield (ΦPSII) when applied at three treatment placements (soil-only, foliage-only, and foliage + soil). Herbicide rates for amicarbazone and atrazine were 0.53 and 2.25 kg ha−1, respectively. Amicarbazone applied soil-only and foliage + soil controlled annual bluegrass 57 and 59%, respectively, 1 wk after treatment (WAT). Atrazine applied to foliage + soil controlled annual bluegrass 48% at 1 WAT. All soil-only and foliage + soil treatments were similar 2 WAT. Foliage-only application of amicarbazone provided significantly less control than other amicarbazone treatments throughout the study. Amicarbazone applied soil-only and foliage + soil controlled annual bluegrass 100% at 3 WAT. Soil-only and foliage + soil applications of atrazine and amicarbazone had similar reductions in quantum yield (ΦPSII) at 1 to 3 WAT. Foliar-applied amicarbazone reduced ΦPSII 78, 84, and 86% at 1, 2, and 3 WAT, respectively. The rapid reduction in annual bluegrass ΦPSII and the increase in control resulting from soil contact of amicarbazone indicate root exposure of amicarbazone is beneficial for annual bluegrass control.

In recent years, horseweed has become an increasing problem in Montana. To confirm and characterize the level of glyphosate resistance, seeds were collected from putative glyphosate-resistant (GR) horseweed (GR-MT) plants in a wheat–fallow field in McCone County, MT. Known GR (GR-NE) and glyphosate-susceptible (GS-NE) horseweed accessions from Lincoln, NE, were included for comparison in dose–response and shikimate accumulation studies. Whole-plant glyphosate dose–response experiments conducted at the early- (5- to 8-cm diameter) and late- (12- to 15-cm diameter) rosette stages of horseweed indicated that GR-MT accessions had a 2.5- to 4.0-fold level of resistance to glyphosate relative to the GS-NE accession, on the basis of shoot dry weight (GR50 values). The level of resistance was 3.1- to 7.9-fold on the basis of visually assessed injury estimates (I50 values). At the whole-plant level, about 2.1- to 4.5-fold higher shikimate accumulation was observed in the GS-NE accession compared with the GR-MT and GR-NE accessions over a 10-d period after glyphosate was applied at 1,260 g ae ha−1. In a separate greenhouse study, all three horseweed accessions were also screened with alternate POST herbicides registered for use in wheat–fallow rotations. The majority of the tested herbicides provided ≥90% injury at the field-use rates for all three horseweed accessions 3 wk after treatment. This is the first published report on the occurrence of GR horseweed in Montana cereal production. Increased awareness and adoption of best management practices, including the use of diversified (based on multiple sites of action) herbicide programs highlighted in this study, would aid in mitigating the further spread of GR horseweed in the cereal production fields of the U.S. Great Plains.