Phoma herbarum was evaluated as a potential biological control agent for dandelion (Taraxacum officinale) in turf. A preliminary controlled environment study identified selected adjuvants that enhanced disease severity by P. herbarum. Subsequently, these adjuvants were evaluated for disease enhancement under field conditions. Adjuvants evaluated included gluten flour, liposome, guar gum from ground guar (Cyamopsis tetragonoloba), durum (Triticum durum), and pectin. Regression analysis revealed a significant (P = 0.05) increase in disease severity by P. herbarum when formulated with gluten Hour, guar gum, or durum semolina compared to treatment with 20% mycelium in potato (Solanum tuberosum) dextrose broth (PDB) alone. No phytotoxicity to dandelion was observed among the adjuvant controls.

Sulfonylurea resistance has been found in Japan, and four of the nine resistant weeds are in the genus Lindernia (Scrophulariaceae). To develop appropriate control methods for these resistant weeds, a rapid method to diagnose sulfonylurea-resistant weeds was improved and applied to common falsepimpernel (L. procumbens), two varieties of low falsepimpernel (L. dubia var. dubia and var. major), and azetogarashi (L. micrantha). Illumination is crucial for diagnosis in Lindernia spp., and treatment with 7.5 or 75 ng ai/ml thifensulfuron-methyl produced clear results.

Hydroponics and sand culture studies evaluated the effects of isoxaben rate (0.84, 1.69, and 3.39 kg/ha) and application type (root only, shoot only, and root plus shoot) on the growth of ajuga, wintercreeper, and dwarf burning bush. Similar responses were exhibited by the three species tested in both hydroponics and sand culture studies. Based on shoot weight reductions, dwarf burning bush was one to three times more sensitive than wintercreeper, which was the most tolerant of the three species, and ajuga was five to 20 times more sensitive than wintercreeper. Isoxaben applied to the root system at all three rates injured ajuga root tips and foliage and reduced root weight by approximately 40% and shoot weight by 20 to 30%. Isoxaben applications to ajuga foliage damaged the roots and leaves and caused over 30% reductions in shoot and root weights at the highest rate tested. Isoxaben applied to dwarf burning bush roots caused less than 20% shoot injury, reduced root weight by 8 to 18%, and reduced shoot weight by less than 10%. Application to dwarf burning bush foliage caused 20 to 30% injury, but only slight reductions in root and shoot weights were observed. No visible injury was observed in wintercreeper from any isoxaben application. However, root treatment reduced wintercreeper root weight by approximately 15%, and shoot treatment reduced shoot weight by 6 to 10% at the highest isoxaben rate tested. Application of isoxaben to both roots and foliage of wintercreeper resulted in similar reductions in shoot and root weights compared to root or shoot exposure alone. Shoot application to wintercreeper affected root growth, and root treatment reduced shoot growth.

Field studies were conducted in 1996 and 1997 at Belleville and Pawnee, IL, to evaluate single and sequential applications of glufosinate on tolerance of glufosinate-resistant corn and annual weed control. Glufosinate caused 0 to 13% corn injury 7 days after treatment (DAT) and 0 to 6% corn injury 28 DAT. Injury was characterized as stunting with glufosinate. Glufosinate at 400 to 1,200 g ai/ha did not reduce final corn height or grain yield. At Pawnee in both years and at Belleville in 1996, a single application of glufosinate at 400 g/ha controlled giant foxtail, velvetleaf, ivyleaf morningglory, and common lambsquarters 85 to 100%. At Belleville in 1997, sequential applications of glufosinate provided greater weed control (87 to 100%) than a single application (0 to 63%) because of weed emergence after application. Weed control with a single application of glufosinate or with nicosulfuron plus bromoxynil was similar at both locations. Height and grain yield of glufosinate-resistant corn were not different from that of glufosinate-susceptible corn (isoline of glufosinate-resistant corn).

Seeds were collected from an imidazolinone-resistant (R) population of smooth pigweed near Marion, MD, and from an imidazolinone-susceptible (S) population near Painter, VA, and grown in the greenhouse. Acetolactate synthase (ALS) enzyme was extracted from both biotypes and assayed in the presence of CGA 152005, chlorimuron, halosulfuron, imazaquin, imazethapyr, nicosulfuron, primisulfuron, pyrithiobac, rimsulfuron, and thifensulfuron to determine if an altered ALS was the mechanism of resistance in the R biotype and to determine if this biotype was cross-resistant to other ALS inhibitor herbicides. The inhibitor concentration required to cause a 50% reduction in ALS activity (I50) was calculated for each herbicide. ALS from the R biotype was approximately 71-, 109,000-, and 9-fold more resistant to imazaquin, imazethapyr, and rimsulfuron, respectively, than that from the S biotype. ALS from the R biotype was approximately threefold more sensitive to pyrithiobac and thifensulfuron than that from the S biotype. R ALS was also slightly more tolerant to CGA 152005 and nicosulfuron and slightly more sensitive to primisulfuron and chlorimuron. ALS from both biotypes generally responded similarly to halosulfuron. Resistance in the R biotype was due to an altered form of ALS that is insensitive to the imidazolinone herbicides and rimsulfuron.

Preemergence herbicides were applied at recommended and three times the recommended rates during 1995, 1996, and 1997 to eight established zoysiagrass (Zoysia spp.) cultivars. Oxadiazon was the only herbicide that did not significantly reduce the quality of any zoysiagrass cultivar. The zoysiagrass cultivars had intermediate tolerance to prodiamine and pendimethalin, while oryzalin, dithiopyr, and benefin plus oryzalin caused the highest injury. ‘Emerald’ and ‘Meyer’ cultivars were least affected by herbicide application. ‘Diamond,’ ‘El Toro,’ ‘Cavalier,’ and ‘Crowne’ showed moderate injury, while ‘Royal' and ‘Palisades’ had the greatest injury. When the performance of zoysiagrass cultivars was averaged across herbicides, turf quality in May was best for Meyer, El Toro, and Crowne. The quality of the majority of cultivars except for Royal improved during the summer and was similar to that of Meyer by late August both years.

Field experiments were conducted in 1996, 1997, and 1998 to evaluate weed control and corn tolerance from soil-applied RPA 201772. Treatments alone and in tank mixtures with other corn herbicides were applied preemergence (PRE) at two locations with conventional tillage and at early preplant (EPP) and PRE application timings in no-tillage corn. RPA 201772 was applied alone and in tank mixtures with one-half the typical field rates of other PRE corn herbicides. In conventional tillage experiments in 1996, 1997, and at one location in 1998, all treatments containing RPA 201772 provided > 90% control of common lambsquarters, redroot pigweed, common ragweed, and velvetleaf. In two no-tillage experiments, common lambsquarters and velvetleaf control was > 90%, regardless of application timing. However, control of redroot pigweed and common ragweed varied among years and application timings. Weed control was more variable from herbicide treatments applied EPP compared with the PRE application timing. Giant foxtail control in both tillage systems was rate, timing, and year dependent. RPA 201772 rates higher than 79 g/ha controlled giant foxtail > 85% at three of five locations. At one location, tank mixtures with RPA 201772 increased giant foxtail control. Corn injury occurred in one of two conventional tillage locations and at the no-tillage location in both 1996 and 1997. Injury was most commonly observed in coarse-textured soils with low clay and organic matter and was more severe with higher rates of RPA 201772. Increased corn injury was also observed when RPA 201772 was combined with acetochlor plus dicloramid or BAYFOE 5043 plus metribuzin. Corn injury from RPA 201772 occurred at application rates above the proposed rate for use on corn. In some cases, severe injury to corn reduced corn yield. Injury to corn from RPA 201772 was not unique to any tillage system and was site, year, and rate dependent.

Growth chamber studies were conducted to investigate the effect of temperature, cultivar, and leaf wax content on the response of broccoli and collard to oxyfluorfen. Broccoli cultivars grown under cool temperatures (15/10 C) were more susceptible to preemergence (PRE) application of oxyfluorfen, and broccoli and collard cultivars grown at cool temperatures were more susceptible to postemergence (POST) application of oxyfluorfen than cultivars grown under warm temperatures (25/20 C). Differences between the tolerant cultivar ‘Pinnacle’ and the susceptible cultivar ‘Packman’ in response to PRE oxyfluorfen application were more distinct at warm temperatures than at cool temperatures. Although the broccoli and collard cultivars used in the POST study varied in leaf wax content, differences in wax content did not appear to be as important as other genetic factors in the differential response to POST oxyfluorfen application between cultivars.

Field studies were conducted in Colorado, Kansas, and Wyoming to compare the use of quinclorac plus 2,4-D with picloram plus 2,4-D, dicamba plus 2,4-D, a glyphosate plus 2,4-D premix, and 2,4-D alone for control of field bindweed (Convolvulus arvensis) in a winter wheat (Triticum aestivum)-fallow rotation. Treatments were applied in late summer or fall each year for two, three, or four consecutive years at the beginning and end of each fallow period. Evaluations were taken 10 to 12 mo after treatment each year. Quinclorac plus 2,4-D and picloram plus 2,4-D consistently performed as well as or better than 2,4-D, dicamba plus 2,4-D, and glyphosate plus 2,4-D. Wheat yields increased when field bindweed was controlled during the fallow period. Strong correlations (r > −0.85) were obtained among visual field bindweed evaluation, biomass, and stand count data.

Certain linear alcohol ethoxylate surfactants with large hydrophobes enhanced nicosulfuron activity on giant foxtail (Setaria faberi) more effectively at low doses than surfactants with small hydrophobes and commercial standards. The most effective surfactants had a C16–18 hydrophobe and 12 to 30 moles of ethoxylation or a C24 hydrophobe with 13 moles of ethoxylation. Response curve analysis showed these linear alcohol ethoxylate surfactants were five- to 20-fold more active on a dose basis than currently used commercial surfactants.

The effects of tracking by tractor wheels on the emergence of common weed species of central Iowa were studied near Ames, IA, in 1996 and 1997. Seedling emergence in tracked and nontracked interrow areas, soil water content, and soil temperature were monitored for 8 to 10 wk after planting of soybean (Glycine max). Compared to nontracked interrow areas, a single wheel-tracking pass at crop planting increased the cumulative number of seedlings of giant (Setaria faberi) and yellow foxtails (S. glauca) by 187%, common waterhemp (Amaranthus rudis) by 102%, and common lambsquarters (Chenopodium album) by 30%. There was little effect of wheel traffic on velvetleaf (Abutilon theophrasti) emergence. After planting, soil water content to a depth of 5 cm was higher in tracked areas than in nontracked areas, but after 6 wk there was no difference. Soil temperature at 4- to 5-cm depth was similar in tracked and nontracked interrows. Compaction from wheel traffic apparently did not create a physical impediment to emergence; rather, it altered micro-environmental conditions in ways that stimulated weed germination and emergence.

Two previously identified triazine-resistant annual bluegrass (Poa annua) biotypes in Mississippi were evaluated to determine the level as well as the mode of resistance compared to a triazine-susceptible biotype. Annual bluegrass seeds were collected at two sites (Meridian and Tupelo, MS) from field plots previously treated with 11.2 kg ai/ha simazine. Seeds were planted on agar containing simazine (0, 0.001, 0.01, 0.1, 1, 10, or 100 mM) or diuron (0, 0.01, 0.1, 1, 10, 100, or 1,000 μM), placed in the growth chamber with an 8 h daylength and alternating temperatures of 15 and 20 C, and allowed to grow for 3 wk, after which fresh weight was determined. Data were subjected to regression analyses and the amount of simazine or diuron required to reduce fresh weight to 50% of the untreated plants was determined. These data indicated a greater than 1,000-fold level of resistance to simazine with either biotype. Diuron concentrations of 5.0, 3.0, and 3.2 μM were required to reduce fresh weight to 50% of the untreated for the triazine-susceptible, Meridian, and Tupelo biotypes, respectively. Sequencing a portion of the chloroplast psbA gene revealed a serine 264 to glycine mutation, which reduced the affinity of the triazine herbicides for the QB-binding niche on the D1 protein in photosystem II.

Field experiments on dry pea (Pisum sativum) were conducted at five locations across the United States in 1995 and 1996 to investigate the effects of low rates of chlorsulfuron, thifensulfuron, and dicamba applied postemergence and of chlorsulfuron, metsulfuron, and clopyralid applied preplant incorporated in the soil on pea plants. Although chlorsulfuron, thifensulfuron, and dicamba caused significant injury symptoms on pea plants, they had little effect on yield. The lowest rates of foliar applications that caused observable symptoms were 0.035, 0.086, and 1.56 g ai/ha for chlorsulfuron, thifensulfuron, and dicamba, respectively, whereas chlorsulfuron, thifensulfuron, and dicamba rates that reduced pea yield by 25% were 0.18, 1.36, and 25 g/ha, respectively. Clopyralid caused more injury symptoms than metsulfuron or chlorsulfuron with soil application. However, the lowest rates of chlorsulfuron, metsulfuron, and clopyralid that caused observable symptoms were lower than the rates that reduced yield. This study showed that pea plants can sustain some level of plant injury without a large reduction in yield.

The absorption, translocation, and metabolism of the ethyl ester of chlorimuron and nicosulfuron in resistant (R) and susceptible (S) smooth pigweed (Amaranthus hybridus) were investigated. R and S smooth pigweed seedlings (5 to 10 cm tall) were treated with foliar-applied 14C-labeled chlorimuron and nicosulfuron and harvested at 3, 6, 24, and 72 h after application. Chlorimuron absorption increased with time in both populations of smooth pigweed and was higher in the R accession only at 6 h after application. Nicosulfuron absorption did not increase with time in the R accession, and after 6 h, there were no differences between the R and S accessions. Absorbed chlorimuron and nicosulfuron were translocated to shoots and leaves above and below the treated leaf, but not into the roots in both accessions. Translocation of chlorimuron and nicosulfuron out of the treated leaf was also similar in the two accessions. Metabolism of 14C-chlorimuron occurred more rapidly in the R accession with approximately 68% remaining as chlorimuron at 3 h after application. At the same time period, 81% of the absorbed radioactivity remained as chlorimuron in the S accession. Metabolism of 14C-chlorimuron at 24 and 72 h after application was greater in the S than the R accession of smooth pigweed. Metabolism of 14C-nicosulfuron was similar in the two accessions and did not increase with time. Rapid herbicide metabolism may explain the twofold level of crossresistance of the R accession of smooth pigweed to chlorimuron at the whole plant level.

Laboratory studies were conducted using a Malvern laser droplet/particle size analyzer to determine the droplet spectra of several venturi-type drift reduction nozzles compared to a standard single, elliptical-orifice flat fan nozzle. Spray solutions of glufosinate, glyphosate, and paraquat were applied through all combinations of five nozzle types (four drift reduction), three tip sizes, and four application pressures. Nozzles were also evaluated for pattern uniformity using water plus surfactant at one pressure. When averaged over herbicide, tip size, and pressure the venturi nozzles collectively produced larger volume median diameter (VMD) droplets than the standard nozzle. The percentage of spray volume in droplets < 205 μm was less for the venturi nozzles (17%) than for the standard nozzle (65%) when averaged across all factors. The order of herbicides producing the largest droplets was paraquat (470 μm) > glyphosate (460 μm) > glufosinate (400 μm), as measured by VMD. The venturi nozzles were more variable in their spray volume distribution than the standard nozzle. Utilization of venturi-type nozzles may minimize the drift potential of the herbicides evaluated but could also lead to uneven herbicide application and subsequent erratic weed control.

Field studies were conducted at five locations in North Carolina and Virginia during 1996 and 1997 to evaluate weed control, peanut (Arachis hypogaea) response, and peanut yield following diclosulam applied preplant incorporated (PPI) and in systems with commercial herbicide standards. All plots received a PPI treatment of ethalfluralin at 840 g ai/ha. Ethalfluralin plus diclosulam controlled entireleaf morningglory (Ipomoea hederacea var. integriuscula), ivyleaf morningglory (I. hederacea), pitted morningglory (I. lacunosa), common lambsquarters (Chenopodium album), eclipta (Eclipta prostrata), and prickly sida (Sida spinosa) as well as and frequently better than ethalfluralin PPI followed by (fb) acifluorfen plus bentazon postemergence (POST), paraquat plus bentazon early postemergence (EPOST) fb imazapic POST, or imazapic POST. Systems with ethalfluralin plus diclosulam PPI at 26 g ai/ha fb acifluorfen plus bentazon POST controlled a broader spectrum of weeds and yielded greater than systems of ethalfluralin PPI fb imazapic POST or ethalfluralin PPI fb acifluorfen plus bentazon POST. Peanut exhibited excellent tolerance to diclosulam PPI at 17, 26, or 35 g/ha.

The effectiveness of preharvest applications of glyphosate on yellow toadflax was evaluated at five sites in Alberta from 1992 to 1994. At each site, glyphosate at 0.9 to 1.8 kg ae/ha was applied with or without nonionic surfactant and/or ammonium sulfate. Glyphosate at 2.7 kg/ha and glufosinate at 0.6 kg ai/ha were applied without additional adjuvants. The treatments were applied 7 to 10 d before crop harvest, when the majority of the yellow toadflax was in a flowering stage. Eleven to 12 mo after glyphosate application, yellow toadflax density was reduced by more than 80%. In most instances, there was no advantage in increasing the glyphosate rate above 0.9 kg/ha. The addition of nonionic surfactant and/or ammonium sulfate did not enhance glyphosate activity. Glufosinate did not control yellow toadflax in the year following treatment. Barley, canola, and flax yields in the year following applications were significantly higher in all preharvest glyphosate-treated plots than in untreated plots.

Adjuvants influence weed control and crop tolerance provided by postemergence (POST) herbicides. Adjuvant effects on weed control and corn and soybean tolerance with CGA-248757 and flumiclorac applied alone and soybean tolerance with CGA-248757 and flumiclorac applied in combination with imazethapyr or CGA-277476 were evaluated. Velvetleaf control in the greenhouse and common lambsquarters, redroot pigweed, and common ragweed control in the greenhouse and field with CGA-248757 and flumiclorac were increased by the addition of an adjuvant. However, corn and soybean tolerance to these herbicides was not affected by adding an adjuvant. Laboratory studies suggest enhanced weed control from the addition of an adjuvant resulted from an increase in CGA-248757 and flumiclorac foliar absorption. In greenhouse studies, velvetleaf, common lambsquarters, and redroot pigweed control with CGA-248757 plus imazethapyr; velvetleaf control with flumiclorac plus imazethapyr; redroot pigweed and common ragweed control with CGA-248757 plus CGA-277476; and velvetleaf, redroot pigweed, and common ragweed control with flumiclorac plus CGA-277476 increased by adding an organosilicone adjuvant when compared with adding a nonionic surfactant (NIS). However, in field evaluations of CGA-248757 or flumiclorac plus imazethapyr, the addition of NIS or an organosilicone adjuvant resulted in equivalent soybean injury, common lambsquarters and redroot pigweed control, and soybean yield. Yet in tank mixtures of CGA-248757 or flumiclorac plus CGA-277476, the addition of an organosilicone adjuvant increased redroot pigweed control and soybean yield compared to adding NIS.

Cloransulam postemergence (POST), diclosulam preemergence (PRE), and flumetsulam preplant incorporated (PPI) and POST were evaluated in six trials at two locations for control of sicklepod and pitted morningglory in soybean. Sicklepod control with cloransulam plus flumetsulam POST was equivalent to chlorimuron POST in seven of eight comparisons both 3 and 6 wk after treatment. Sicklepod control with cloransulam POST was equivalent to chlorimuron in only three of eight comparisons 3 wk after treatment, but late-season control was equivalent in five of six comparisons. Pitted morningglory control with cloransulam alone or in tank-mixture with flumetsulam POST was equivalent to chlorimuron in all comparisons. Control of sicklepod and pitted morningglory was greater in most comparisons when a POST application followed flumetsulam plus trifluralin PPI compared to only trifluralin PPI. In a total PRE stale seedbed system, where all treatments were tank-mixed with pendimethalin plus glyphosate, sicklepod control with all rates of flumetsulam and 26 or 35 g ai/ha diclosulam was equivalent to the standard treatment of imazaquin or metribuzin plus chlorimuron. None of the total PRE programs controlled sicklepod as well as when glyphosate was applied sequentially POST. Pitted morningglory was controlled 83 to 93% with 26 or 35 g/ha diclosulam, equivalent to imazaquin, metribuzin plus chlorimuron, or sequential glyphosate applications 8 wk after the PRE application. Increasing flumetsulam rate increased pitted morningglory control early season, but flumetsulam was not as effective as the other herbicides.

Field trials were conducted to evaluate the influence of three application methods and two types of ground cover on the transport of metolachlor and simazine from container-grown junipers. Application methods used were broadcast spray, broadcast granules, and individual container applications. Woven ground cloth and woven ground cloth plus gravel were used as ground covers. The site received daily irrigation, and surface runoff was sampled and analyzed 0, 1,2, 4, 8, 16, 32, and 56 d after herbicide application. Application method had the greatest effect on herbicide concentrations in runoff. Herbicide application to individual containers resulted in lower simazine and metolachlor concentrations in runoff. Herbicide concentrations took longer to drop below detection levels in surface runoff from broadcast applications.