Annual bluegrass is one of the most difficult-to-control weeds in creeping bentgrass putting greens. Field trials were conducted in 2003 and 2005 to evaluate bispyribac-sodium for annual bluegrass management in creeping bentgrass greens maintained at a 3 mm mowing height. Bispyribac-sodium applied weekly at 12 or 24 g ai/ha controlled annual bluegrass 86% 12 wk after initial treatment (WAIT). In 2003, bispyribac-sodium applied at 12 and 24 g/ha/wk injured creeping bentgrass approximately 15 and 50% by 4 WAIT, respectively. However, injury was transient and was not evident by 12 WAIT. In 2005, the 12 and 24 g/ha/wk injured creeping bentgrass 15 and 85% by 8 WAIT, respectively, and was still evident throughout the trial. Putting green quality was reduced when compared to nontreated creeping bentgrass by the same treatments. The removal of annual bluegrass caused soil exposure until creeping bentgrass grew over the bare areas, contributing to decreased quality evaluations. Management of annual bluegrass in creeping bentgrass putting greens is possible with bispyribac-sodium. However, these results indicate bispyribac-sodium can cause excessive injury when applied to creeping bentgrass mowed at 3 mm.

Field studies were conducted during the 2002 thru 2004 growing seasons at two locations in the south-central Texas cotton-production region to evaluate trifloxysulfuron and trifloxysulfuron plus prometryn in combination with either S-metolachlor or glyphosate or both for weed control and cotton response. Cotton leaf burn (13 to 19%) was noted in 2002 at one location with trifloxysulfuron plus prometryn applied late POST-directed (LPDIR). Herbicide combinations that included trifloxysulfuron controlled barnyardgrass, hemp sesbania, yellow nutsedge, Palmer amaranth, smooth pigweed, ivyleaf morningglory, pitted morningglory, and smellmelon at least 80% in most instances. Glyphosate applied early POST over-the-top (EPOTT) and mid-POST over-the-top (MPOTT) at 0.84 kg ai/ha followed by trifloxysulfuron plus prometryn at 1.1 kg ai/ha applied LPDIR controlled the above-mentioned weeds plus Texas panicum at least 94%. No other herbicide systems provided effective control (greater than 79%) of Texas panicum. Higher cotton yields in 2002 were obtained with herbicide systems that included glyphosate alone or glyphosate plus S-metolachlor applied EPOTT or LPOTT followed by trifloxysulfuron plus prometryn applied LPDIR, whereas in 2003, none of the herbicide systems increased yield over the nontreated check.

Bioassay experiments were conducted to determine the phytotoxicity of methanol and ethyl acetate extracts of hairy vetch and cowpea residues on the germination and radicle elongation of three vegetable crops and three weed species. The species tested included common chickweed, redroot pigweed, wild carrot, tomato, corn, and cucumber. The extracts of both species were dissolved in methanol to yield seven concentrations ranging from 0 to 8 g/L. Germination was significantly reduced by methanol and ethyl acetate extracts of hairy vetch extracts except for corn and tomato. Common chickweed and wild carrot were the only species that showed consistent reduction in germination with the methanol and ethyl acetate cowpea extracts. The radicle growth of most species, with the exception of corn and cucumber, was reduced by the extracts of both cover crops. Corn and cucumber radicle elongation was stimulated at low concentrations of the extracts; however, these observations were not significantly different among treatments. This study demonstrated that methanol and ethyl acetate extracts of hairy vetch and cowpea contained allelopathic compounds and that their phytotoxicity is likely species specific. Future studies should focus on the identification and isolation of the allelochemical(s) found in the methanol and ethyl acetate extracts of the hairy vetch and cowpea residues.

A callus induction and plantlet regeneration system for croftonweed was developed by studying the influence of explant type (leaf, stem, and nodal segment) and different concentrations of plant growth regulators. The leaf was a better explant for callogenesis compared to the stem. The highest callus induction frequency (87.2%) was obtained from leaf segments on Murashige and Skoog's medium (MS medium) supplemented with 0.5 mg/L (2,4-dichlorophenoxy)acetic acid and 2.0 mg/L 6-benzylaminopurine (BA), and 71.6% differentiation along with a multiplication rate of 4.1 adventitious shoots per callus was achieved with a combination of 0.5 mg/L 1-naphthaleneacetic acid (NAA) and 1.0 mg/L BA. In addition, MS medium supplemented with 0.5 mg/L NAA and 1.0 mg/L BA was the best medium for axillary shoot regeneration from nodal segments. Rhizogenesis of cultured shoots was satisfactorily obtained in half-strength MS without any growth regulators. The regenerated rooted plantlets were successfully acclimatized in soil where they grew normally without showing any morphological variation. These studies provide the prerequisite system for the development of genetic engineering in the future and propagating croftonweed rapidly for further study.

Foramsulfuron has recently been registered for weed control in corn in Ontario, but there is very little information on the rate of foramsulfuron required to obtain at least 90% weed control. Our objective was to determine the foramsulfuron rates giving at least 90% weed control while maintaining crop yield loss due to weed interference and injury at less than 5%. Ten field trials were conducted at five Ontario locations (Exeter, Harrow, Ridgetown, Woodslee, and Woodstock) in 2001 and 2002 to evaluate the effectiveness of foramsulfuron at rates ranging from 8.75 to 140 g ai/ha. To obtain a reduction in biomass of 90% (I90) at 78 d after treatment (DAT), foramsulfuron must be applied to common lambsquarters at 68 g/ha and to common ragweed at 86 g/ha, respectively. For green foxtail a foramsulfuron rate of 25 g/ha was required to achieve 90% control. The application of foramsulfuron caused injury to corn at 7 DAT at Ridgetown and Woodstock only, but did not exceed a rating of 10%; by 14 and 28 DAT no corn injury was recorded at any location. Corn yield of at least 95% of a weed-free check was obtained at Woodstock when foramsulfuron was applied at 70 g/ha. At Exeter and Woodslee yield was 90% of the weed-free check at a foramsulfuron rate of 35 g/ha. Finally, at Harrow and Ridgetown, corn yield was lowered at all foramsulfuron rates because of broadleaved weed interference. Tank-mixing foramsulfuron with dicamba plus prosulfuron improved common lambsquarters and common ragweed control and final corn yield was improved by more than 20% when compared with an application of foramsulfuron alone. Thus, these results show that weed control with foramsulfuron is species specific and that tank mixtures with a broadleaf herbicide may be required for broad-spectrum weed control and to protect the full yield potential of corn.

Studies were conducted to evaluate absorption and translocation of 14C-glyphosate in glyphosate-resistant (GR) cotton. Both commercial GR cotton events [glyphosate-resistant event 1, marketed as Roundup Ready®, released 1997 (GRE1), and glyphosate-resistant event 2, marketed as Roundup Ready Flex®, released 2006 (GRE2)] were evaluated at the four-leaf and eight-leaf growth stages. Plants were harvested at 1, 3, 5, and 7 d after treatment (DAT). Glyphosate absorption, as a percentage of applied, increased over time with 29 and 36% absorption at 7 DAT in four-leaf GRE1 and GRE2 cotton, respectively. In eight-leaf cotton, glyphosate absorption (33% at 7 DAT) was not different between events. Glyphosate translocation patterns were not different between events or harvest timings and exhibited a source–sink relation. Observed translocation differences between cotton growth stages were probably due to reduced glyphosate export from the treated leaf of eight-leaf cotton. An additional study compared absorption and translocation of 14C-glyphosate and 14C-sucrose in 5- and 10-leaf GRE2 cotton. Averaged over trials, 14C compounds, and growth stages, cotton absorbed 28% of the applied dose at 14 DAT. On the basis of the percentage of 14C exported out of the treated leaf, glyphosate and sucrose translocation patterns were similar, indicating that glyphosate may be used as a photoassimilate model in GRE2 cotton.

Weed control and potato response to halosulfuron applied alone POST and with rimsulfuron or S-ethyl dipropyl carbamothioate (EPTC) were evaluated in 2004 and 2005 near Paterson, WA. Potatoes were injured and exhibited chlorosis and stunted growth after halosulfuron applications of 18, 26, and 35 g/ha. Potato height was reduced 33 and 20% in late May by halosulfuron at 18 or 26 g/ha in 2004 and 2005, respectively. Halosulfuron applied alone failed to control hairy nightshade and large crabgrass. Total tuber yield and U.S. no. 1 yield were reduced 10% in halosulfuron-treated plots because of poor weed control and possibly herbicide injury. Tank-mixing rimsulfuron with halosulfuron improved control of hairy nightshade and large crabgrass and increased potato yield. Tank-mixing EPTC at 2 kg/ha with halosulfuron improved early-season hairy nightshade control, but weed control was poor at row closure. Rimsulfuron applied alone at 18 or 26 g/ha controlled hairy nightshade and large crabgrass without potato injury and resulted in the greatest potato yields.

Meadow foxtail is a rhizomatous grass widely grown for hay and pasture in wet meadows of the western United States and Canada. Two sulfonylurea herbicides, chlorsulfuron and metsulfuron-methyl, were evaluated for their effects on meadow foxtail biomass. Both herbicides were applied at four doses, 0.035, 0.070, 0.105, and 0.140 kg ai/ha, together with a control at each of two sites in October 2003. Treatments were replicated four times at each site and arranged in a randomized complete block design and sampled in July 2004 and 2005. Meadow foxtail biomass depended on site (P = 0.001) or year (P = 0.001), but not herbicide treatment (P = 0.182). No biomass production losses resulted from applying up to 0.14 kg/ha of either chlorsulfuron or metsulfuron-methyl on meadow foxtail, even in relatively high-pH soils.

Studies were conducted to determine injury potential to rotational crops from carryover of herbicides used in watermelon production. Treatments included halosulfuron, ethalfluralin, and sulfentrazone alone; halosulfuron in tank mixtures with bensulide, clomazone, ethalfluralin, and naptalam; and a tank mixture of naptalam and bensulide. Sulfentrazone applied at 224 g ai/ha to watermelon severely reduced spinach emergence, but did not reduce emergence of broccoli, cabbage, or wheat. Residues of sulfentrazone applied to watermelon at 450 g/ha stunted growth of broccoli and cabbage and was the only treatment that reduced wheat stand. Injury to broccoli, cabbage, and spinach increased as the halosulfuron rate increased. Ethalfluralin did not reduce stand or cause injury to any of the four rotational crops. Naptalam plus bensulide did not reduce stand of the four crops and caused either slight or no injury. Residues of sulfentrazone and halosulfuron can injure vegetables following crops in which these herbicides are used, and caution should be taken particularly with spinach, broccoli, and cabbage in this respect.

Two Italian ryegrass populations from Mississippi, Tribbett and Fratesi, were suspected to be tolerant to glyphosate. A third population from Mississippi, Elizabeth, known to be susceptible to glyphosate, was included for comparison. Plants were treated with the isopropylamine salt of glyphosate at 0, 0.11, 0.21, 0.42, 0.84, 1.68, 3.36, and 6.72 kg ae/ha. GR50 (herbicide dose required to cause a 50% reduction in plant growth) values for the Tribbett, Fratesi, and Elizabeth populations were 0.66, 0.66, and 0.22 kg/ha, respectively, indicating that the Tribbett and Fratesi populations were threefold more tolerant to glyphosate compared with the Elizabeth population. These three populations were also treated with diclofop at 0, 0.13, 0.25, 0.5, 0.75, 1, and 2 kg ai/ha. Diclofop GR50 values for the Tribbett, Fratesi, and Elizabeth populations were 0.25, 0.28, 0.21 kg/ha, respectively, indicating similar tolerance to diclofop in the three populations. Response of all three populations to clethodim rate (0, 0.02, 0.03, 0.05, 0.06, 0.08, 0.09, and 0.13 kg ai/ha) was measured. Clethodim GR50 values for the Tribbett, Fratesi, and Elizabeth populations at the small growth stages were 0.016, 0.023, 0.014 kg/ha, respectively, and at the large growth stage were 0.04, 0.034, 0.02 kg/ha, respectively.

Quinoclamine has been evaluated for POST control of liverwort in nursery crop production. Nearly all previous research has assumed that high spray volumes (e.g., > 935 L/ha) were required for quinoclamine to be effective. To test this assumption, quinoclamine was applied to liverwort in a factorial treatment arrangement of three rates (1.4, 1.9, and 3.8 kg ai/ha), three spray volumes (374, 1,112, and 1,871 L/ha), and two spray pressures (276 and 414 kPa). Control was influenced primarily by quinoclamine rate, although there was a trend for greater control with higher spray pressure. Absorption and translocation studies using 14C-quinoclamine established that 14C absorption into liverwort thalli approached 70% of the amount applied within 9 h after application. Although liverwort lacks vascular tissue, 14C is readily translocated away from the site of entry and tended to accumulate at thallus margins. Neither absorption nor translocation was influenced by spray volume. The perceived requirement for high spray volume may be a misdirected assumption on the basis of the high proportion of inert ingredients within the current formulation. Conversely, this assumption has no basis within liverwort biology or quinoclamine behavior.

Transgenic, herbicide-resistant cultivars and equipment to spindle-pick 38-cm rows has renewed interest in narrow-row cotton production. Field experiments were conducted at four locations in North Carolina during 2004 and 2005 to evaluate weed management systems in glufosinate-resistant cotton planted in 38- and 97-cm rows. Weeds included broadleaf signalgrass, goosegrass, fall panicum, large crabgrass, Palmer amaranth, smooth pigweed, pitted morningglory, and tall morningglory. Greater than 90% control of annual grasses and Amaranthus spp. in 2004 and Ipomoea spp. in both years was obtained in narrow-row cotton with glufosinate applied early POST (EPOST) and mid-POST (MPOST) to two- and six-leaf cotton, respectively. With good early-season control by glufosinate and rapid canopy closure, there was little benefit from pendimethalin, fluometuron, or pyrithiobac applied PRE, S-metolachlor or pyrithiobac mixed with glufosinate applied MPOST, or trifloxysulfuron applied late POST (LPOST) to 11-leaf cotton in 2004. In 2005, with larger weeds at initial application, glufosinate EPOST and MPOST did not adequately control annual grasses and Amaranthus spp. Pendimethalin PRE increased control to greater than 90% and increased yields 59 to 75%. Pendimethalin PRE followed by S-metolachlor or pyrithiobac mixed with glufosinate at MPOST was no more effective than pendimethalin alone. Without PRE herbicides, trifloxysulfuron applied LPOST increased Amaranthus but not annual grass control. Cotton row spacing had no effect on cotton yield and little effect on weed control.

Field studies were conducted in 2002 and 2005 to evaluate autumn vegetable tolerance to residual herbicides applied the previous spring under low-density polyethylene (LDPE) mulch. Spring applications of 1.12 kg/ha S-metolachlor, 0.027 kg/ha halosulfuron, 0.28 kg/ha sulfentrazone, and 1.12 kg/ha S-metolachlor plus 0.027 kg/ha halosulfuron were made under LDPE mulch in March of each year and included a nontreated control. After removal of the spring crop, vegetables were planted the following August. Seeded and transplanted squash, seeded cucumber, transplanted eggplant, and transplanted cabbage were evaluated. Injury to eggplant, cucumber, and transplanted and seeded squash ranged from 8 to 16% for halosulfuron, sulfentrazone, and S-metolachlor plus halosulfuron in 2002, but no injury was observed in 2005. Cabbage injury was less than 5% for any herbicide treatment either year. There were no differences for cabbage biomass for three harvests for any herbicide treatment relative to the nontreated control. Vine length for cucumber and transplanted squash was significantly reduced by sulfentrazone relative to the nontreated control. Eggplant yield for the first harvest was significantly reduced by sulfentrazone as compared with the nontreated control in 2002 but not in 2005. To avoid injury to rotational crops, growers should read all herbicide labels when considering spring herbicide applications under LDPE mulch when autumn vegetable plantings are part of their production scheme to ensure successful crop production.

Viable horseradish roots of various sizes remain in the soil after harvest and can develop into volunteer plants in subsequent crops. Experiments were conducted to evaluate POST herbicides on volunteer horseradish control and to determine if efficacy is dependent upon horseradish root segment size, herbicide rate, horseradish cultivar, or horseradish shoot size at application. In the greenhouse, horseradish root segment size did not affect herbicide efficacy. Chlorimuron, cloransulam, imazamox, (2,4-dichlorophenoxy)acetic acid (2,4-D) amine, halosulfuron, and imazethapyr plus imazapyr provided greater than 95% foliar control of volunteer horseradish. Chlorimuron, halosulfuron, and 2,4-D amine were also among the herbicides that provided the greatest reduction in horseradish root biomass (69% or greater). Glyphosate provided little foliar control (76%) and root biomass reduction (57%) after one application. The efficacy of 2,4-D amine on horseradish foliage and root biomass increased with increasing herbicide rate; however, the response of horseradish to halosulfuron was similar for all rates evaluated. Root biomass reduction of the horseradish cultivar ‘1573’ was less responsive to 2,4-D amine and halosulfuron applications compared with ‘1038’ and ‘1722’. However, foliar injury from 2,4-D amine and halosulfuron was less for the horseradish cultivar ‘1038’ compared with ‘1573’ and ‘1722’. In field studies, 2,4-D amine applied to 15- and 30-cm-tall horseradish and halosulfuron applied to 15-cm-tall horseradish resulted in the greatest foliar and root biomass reduction. This study indicated that in-season control of volunteer horseradish in rotational crops may be achieved through proper herbicide selection.

Conservation tillage systems, used successfully by cotton producers on the Texas southern High Plains, have facilitated the development of new weed problems including horseweed (Conyza canadensis) and Russian thistle (Salsola iberica). Studies were conducted in 2004 and 2005 near Lubbock, TX to evaluate winter weed control with (2,4-dichlorophenoxy)acetic acid (2,4-D), dicamba, and diflufenzopyr plus dicamba. All of these herbicides have current registration restrictions limiting their use in cotton. Cotton response studies were initiated in 2003 and repeated in 2004 and 2005 to evaluate cotton injury and yield from dicamba (0.14 and 0.28 kg ai/ha), diflufenzopyr plus dicamba (0.10 and 0.20 kg/ha), and 2,4-D (0.56 and 1.12 kg/ha) applied 4, 2, and 1 wk before planting (WBP); and to determine the minimum interval between application of these herbicides and cotton planting without affecting yield. 2,4-D controlled both horseweed and Russian thistle, and could be applied as close as 2 WBP without injuring cotton. However, dicamba as well as diflufenzopyr plus dicamba were less effective on horseweed and Russian thistle as size increased and both injured cotton regardless of interval between application and planting.

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.

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.

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.

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.

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.