Field experiments were conducted near Marianna, Trenton, and Archer, FL in 1990 and 1991 to investigate the effect of nicosulfuron mixtures and time of application on five peanut cultivars. Nicosulfuron at 54 g ai/ha was applied alone or in mixture with 2,4-DB at 280 g ai/ha 5 weeks after planting (WAP), 9 WAP, or 5 plus 9 WAP. Injury was greater from early and sequential nicosulfuron applications while a single application 9 WAP typically did not cause significant injury or reduce peanut yield. The 5 WAP and 5 plus 9 WAP applications often caused early visible injury and sometimes reduced peanut yield. When peanut yields were compared, ‘Florigiant’ was the most sensitive cultivar while ‘Southern Runner’ and ‘Valencia’ were more tolerant to nicosulfuron. ‘Sunrunner’ and ‘NC-7’ were intermediate in tolerance to nicosulfuron. In several instances, the addition of 2,4-DB to nicosulfuron reduced initial crop injury and ameliorated yield losses resulting from nicosulfuron applied alone.

A three-year field study in west-central Kansas investigated the effects of combinations of spray carrier, nonionic surfactant (NIS), triasulfuron, and/or 2,4-D on winter wheat foliar injury and grain yield. Herbicides applied in water without NIS caused little or no foliar injury in two of three years. Urea-ammonium nitrate (UAN) at 112 L/ha (40 kg N/ha) alone or as a carrier for herbicides caused moderate to severe foliar injury in all three years. Adding NIS to UAN spray solutions increased foliar injury, especially with the tank mixture of triasulfuron + 2,4-D. Effects of triasulfuron + NIS or 2,4-D applied in UAN were additive. Foliar injury was related inversely to temperature following application. Foliar injury was most evident 4 to 7 d after application and disappeared within 2 to 3 wk. Diluting UAN 50% with water lessened foliar injury in two of three years, especially in the presence of NIS, regardless of whether herbicides were in the spray solution. Treatments did not reduce wheat grain yield in any year despite estimates of up to 53% foliar injury one year.

Research was initiated to determine (a) whether a common waterhemp population was resistant to acetolactate synthase (ALS) inhibiting herbicides, (b) the percentage of the population that was ALS-inhibitor resistant, (c) the resistance mechanism, and (d) the effectiveness of a whole plant assay to detect ALS-inhibitor resistance. ALS-inhibitor resistance was confirmed in a common waterhemp population near Davis City, IA. The Davis City common waterhemp population was cross resistant to both imidazolinone and sulfonylurea herbicides, but not to lactofen. Approximately 10% of the Davis City common waterhemp population was sensitive to a rate of imazaquin 4 times the normal field rate. Davis City common waterhemp isolated ALS was much less sensitive to imazaquin and primisulfuron inhibition than was grain amaranth or an ALS-sensitive common waterhemp isolated ALS. Imazaquin I50 values were 366.4 and 3.4 μM for ALS isolated from Davis City common waterhemp and grain amaranth, respectively. Primisulfuron I50 values were 3.6 and 0.007 μM for ALS isolated from Davis City common waterhemp and grain amaranth, respectively. A whole plant ALS assay was developed that allowed for much more rapid detection of an ALS-resistant species and used less plant material than a conventional ALS assay.

Hemp sesbania control by chlorimuron applied with crop oil concentrate at 1.0% v/v, BCH 815 at 1.0% v/v, methylated seed oil at 1.0% v/v, a blend of methylated seed oil and organosilicone surfactant at 0.5% v/v, organosilicone-based surfactant at 0.125% v/v, and nonionic surfactant at 0.25% v/v was evaluated in field studies in 1994 and 1995. Control by chlorimuron at 4.5 g ae/ha was greater when applied with BCH 815, organosilicone-based surfactant, and nonionic surfactant than with crop oil concentrate, methylated seed oil, and a blend of methylated seed oil and organosilicone surfactant. When chlorimuron was applied at 4.5 g/ha with BCH 815 or nonionic surfactant, hemp sesbania control was similar to that by chlorimuron at 9 g/ha applied with methylated seed oil, the blend of methylated seed oil and organosilicone surfactant, or organosilicone-based surfactant.

Overseeding established kikuyugrass swards with tall fescue or perennial ryegrass reduced kikuyugrass cover. Renovation prior to seeding did not aid in the establishment of these two species. Increasing the seeding rate from 79 to 157 kg/ha improved the establishment of perennial ryegrass but not tall fescue. When kikuyugrass plugs were introduced into established turf, tall fescue reduced the invasion of kikuyugrass stolons more than perennial ryegrass. Tall fescue reduced percent kikuyugrass cover, number and spread of stolons, and biomass (compared to perennial ryegrass). The newer turf-type tall fescue cultivars ‘Bonsai,’ ‘Falcon,’ and ‘Olympic’ were more effective than the older tall fescue cultivar ‘Fawn’ in reducing kikuyugrass invasion by reducing stolon number, stolon length, and biomass.

Seven field experiments were conducted in Oklahoma to compare efficacy and wheat response to currently registered cheat suppression or control herbicide treatments. Chlorsulfuron + metsulfuron premix (5:1 w/w) at 26 g ai/ha applied PRE controlled cheat 20 to 61%, increased wheat grain yields at two of seven locations, and decreased dockage due to cheat at five of seven locations. Chlorsulfuron + metsulfuron at 21 g/ha tank-mixed with metribuzin at 210 g/ha, applied early fall POST, controlled cheat 36 to 98% and increased wheat yield at four of seven locations. Metribuzin applied POST in the fall at 420 g/ha controlled cheat 56 to 98% and increased wheat yields at five of seven locations. Both POST treatments decreased dockage at all locations.

Diclofop at 840 g ai/ha, fenoxaprop at 90 g ai/ha, and imazamethabenz at 530 g ai/ha fall-applied controlled wild oat 96, 99, and 95% and increased wheat grain yields 26, 29, and 24%, respectively. These herbicides controlled wild oat over a wider range of growth stages than current labels indicate. The same treatments applied in March were less effective for wild oat control and did not increase wheat yield.

Field studies were conducted between 1990 and 1992 to determine tolerance of English pea at different growth stages to bentazon (0.56 kg ai/ha) and paraquat (0.14 kg ai/ha), applied alone and in combination. Initial crop injury with paraquat and paraquat plus bentazon averaged 37 and 21%, respectively. Crop injury dissipated by 21 d after treatment. Foliar injury at the different growth stages was equivalent but yields of peas treated at the six-node stage were reduced in two of four trials. Applying paraquat plus bentazon at the earlier growth stages consistently resulted in pea yields equivalent to those of plots receiving trifluralin plus handweeding or bentazon alone. Greenhouse studies were conducted to determine the effect of paraquat plus bentazon on control of selected weeds common to pea production fields. Redroot pigweed, common purslane, and common lambsquarters mortalities were 100, 100, and 90%, respectively, with the bentazon plus paraquat combination. However, barnyardgrass and large crabgrass mortalities decreased 88 and 91%, respectively, when bentazon was added, compared to paraquat alone.

Field experiments were conducted at Kalispell, MT, to determine the optimum adjuvant combination for wild oat control in peppermint with quizalofop. Quizalofop was applied to four- and eight-leaf wild oat plants at 20 and 50 g ai/ha with either a nonionic surfactant (NIS) or methylated seed oil (MSO) alone or in combination with 28% urea ammonium nitrate (UAN) liquid fertilizer. Differences among adjuvants were most apparent when quizalofop was applied at the lowest rate. MSO was more effective than NIS for enhancing quizalofop activity. Quizalofop efficacy with both adjuvants increased when applied with UAN. Greater than 90% wild oat control was obtained with the lowest rate when applied with MSO plus UAN to four-leaf wild oat plants. These results demonstrate the potential to improve the consistency of weed control as well as reduce postemergence herbicide rates when applied with the proper adjuvant combination.

Field experiments were conducted at Jay and Marianna, FL in 1988 and 1989 to determine the effects of sicklepod, Florida beggarweed, and common cocklebur density on chlorothalonil deposition to peanut foliage, peanut foliar disease incidence, and peanut yield. At a density of four weed plants per 8 m of row, Florida beggarweed and sicklepod reduced chlorothalonil deposition on peanut foliage by 20%, while common cocklebur reduced fungicide deposition by 34%. At the same density, incidence of the foliar diseases early leaf spot and late leaf spot increased 10% with Florida beggarweed, 14% with sicklepod, and 20% with common cocklebur compared with weed-free peanut. The predicted peanut yield loss from a weed density of four plants per 8 m was 16 to 19% for Florida beggarweed, 23 to 25% for sicklepod, and 31 to 39% for common cocklebur. Weed biomass increased with increasing weed density.

Field experiments were conducted in 1991 and 1992 near Stoneville, MS and Greenville, MS, to determine the impact of pyrithiobac on cotton fruiting, maturity, and yield. Trials were conducted in areas maintained weed-free with standard production practices to optimize yields. Pyrithiobac was applied at 105 or 210 g ae/ha either PRE or POST to cotton in the cotyledon to 2-leaf, 5- to 7-leaf, and matchhead-square (MHS) stages of growth. At one location, monosodium salt of methylarsonic acid (MSMA) and fluometuron plus MSMA were applied as standard comparisons. At the Stoneville location, injury 1 wk after treatment (WAT) with pyrithiobac ranged from 2.5% with 105 g/ha applied at cotyledon to 2-leaf to 26% with 210 g/ha applied at MHS. Injury was transient in nature and was rarely detectable 4 wk after treatment in either year. Injury was not evaluated at the Greenville location. At Stoneville, a reduction in height occurred with MHS applications of pyrithiobac and MSMA. There was no reduction in yield for any treatment compared to the untreated check in 1991 at Stoneville and in both years at Greenville. In 1992 at Stoneville, treatments of 210 g/ha pyrithiobac, MSMA, and fluometuron plus MSMA at all application timings reduced yield. Pyrithiobac at 105 g/ha applied PRE also reduced yield. Greatest yield loss occurred with treatments of MSMA applied at MHS. There were no yield reductions at either location with postemergence application of 105 g/ha pyrithiobac.

Integration of a fungal pathogen with herbicides may enhance melaleuca control efforts in South Florida. Hyphal inoculum of four Botryosphaeria ribis Gross & Duggar isolates were evaluated in vitro for compatibility with imazapyr, glyphosate, and a surfactant. Imazapyr at 12 to 60 mg ai/ml did not cause significant loss of inoculum viability in all four isolates within 2 h after mixing. After 24 h, inoculum viability of isolate BR-4 remained unchanged at these imazapyr concentrations, but viability of BR-1 through BR-3 was reduced. Glyphosate at the lowest concentration (32 mg ai/ml) significantly reduced inoculum viability of all isolates within 2 h. Initially, the inoculum viability of all isolates remained unaffected by 1, 5, and 10% (v/v) surfactant concentrations. After 24 h, the surfactant reduced inoculum viability of BR-2, BR-3, and BR-4 inconsistently between experiments, while the inoculum viability of BR-1 was reduced significantly at all concentrations. Mixing of the lowest concentrations of imazapyr, glyphosate, and surfactant significantly reduced inoculum viability within 2 h. This corresponded to the results obtained for glyphosate alone. These results show that hyphal inoculum of B. ribis may be mixed with imazapyr and surfactant for field applications, but mixing the fungus with glyphosate may not be as efficacious.

Glufosinate at 1.1 and 2.2 kg/ha injured ‘Koshihikari’ rice lines that were transformed with the BAR gene from 0 to 53%. However, transgenic ‘Gulfmont’ rice was not injured. Rice yields of transgenic ‘Gulfmont’ lines and six of nine ‘Koshihikari’ lines were not affected by 2.2 kg/ha glufosinate. In field studies, flooding reduced the efficacy of glufosinate in controlling red rice, and greenhouse tests determined that glufosinate efficacy was reduced when red rice was submerged between 25 and 50% of its height. Plant heights and dry weights of red rice increased as flood water depth increased at all rates of glufosinate.

Field experiments were conducted to evaluate various herbicides and application technologies for the control of cogongrass. Imazapyr at 0.8 kg ae/ha provided the highest cogongrass control, followed by glyphosate (3.4 kg ae/ha) and sulfometuron (1.1 kg ai/ha) when applied as a single application. When sequential applications were evaluated, glyphosate plus imazapyr provided the best control. Sulfometuron could be applied sequentially after imazapyr or glyphosate with no loss of control, but control was less if sulfometuron was the initial herbicide. Tank mix combinations of glyphosate and imazapyr (100% rate at 3.4 and 1.1 kg ae/ha, and subsequent rates of 0 + 100, 25 + 75, 50 + 50, 75 + 25, and 100 + 0% of each herbicide, respectively) provided similar cogongrass control regardless of rate. Control using imazapyr improved from 20 to 40% with 234 L/ha diluent volume when compared to 46 L/ha. Glyphosate at either of these volumes provided from 0 to 21% inhibition of cogongrass. A 50% concentration of imazapyr applied twice with a ropewick provided greater control than a 33% concentration with one pass or either concentration of glyphosate with one or two passes. Efficacy with glyphosate applied using a ropewick was not affected by concentration or number of passes.

Greenhouse and field studies were conducted in 1991 and 1992 to determine the potential for interaction among pyridate (0.5, 1.0 kg ai/ha), sethoxydim (0.22 kg ai/ha), and crop oil concentrate (COC) (1.25% v/v) applied alone or in two- and three-way combinations to transplanted cabbage. Additionally, the effect of applying sethoxydim and COC 1 and 2 d before and after application of pyridate was investigated. In greenhouse-grown cabbage, injury increased twofold and dry weight was reduced 15% when pyridate dose was doubled. Sethoxydim increased pyridate injury significantly, reducing dry weight 31%. When COC was applied with pyridate, injury increased and dry weight decreased linearly. Despite substantial crop injury 7 d after treatment with pyridate alone, pyridate + sethoxydim, and pyridate + COC, yields of field-grown cabbage were reduced significantly in 1 yr only when the three materials were combined. Pyridate injury decreased as time between sethoxydim + COC applications, before and after pyridate was applied, increased.

Field experiments conducted in 1992 and 1993 evaluated transplanted watermelon tolerance to ethalfluralin applied PPI, PRE (before transplanting), and POST (immediately after transplanting) at 1.2 or 2.4 kg ai/ha. Other treatments for comparison included the registered herbicides ethalfluralin POST-directed spray (PDS), ethalfluralin PDS followed by (fb) naptalam POST, bensulide plus naptalam PPI, and a nontreated check. All treatments controlled common lambsquarters and goosegrass 83 to 100% 2 and 6 weeks after treatment (WAT). Watermelon was injured 30 to 77% in 1992 and 14 to 83% in 1993 by ethalfluralin PPI or PRE at 1.2 or 2.4 kg/ha. Ethalfluralin POST was not injurious to watermelon. In 1992, watermelon treated with ethalfluralin POST at 1.2 and 2.4 kg/ha yielded 52 to 62% more fruit than watermelon from the nontreated check. In 1993, yield of transplanted watermelon treated with ethalfluralin POST was similar to that in the nontreated check.

Eleven sweet corn hybrids representing a wide range of injury with imazethapyr in a greenhouse study were evaluated in simulated imazethapyr carryover field studies conducted at Arlington, WI. Imazethapyr at 0, 11, 22, and 44 g ai/ha was applied and incorporated 15 d prior to planting sweet corn. The greatest injury occurred 28 d after planting, with reductions in height ranging from 0 to 25%. Reductions in corn ear yields were similar all years for 10 of the 11 hybrids. Reductions in corn ear yield for ‘Crisp N’ Sweet 710,’ ‘Cornucopia,’ ‘Super Sweet Jubilee,’ ‘Excellency,’ and ‘DMC 20–35′ were less than for ‘Natural Sweet 9000,’ ‘Jubilee,’ ‘Zenith,’ ‘Green Giant 40,’ and ‘Green Giant 97.’ In 1992, plots were prepared for an actual imazethapyr carryover study by applying imazethapyr PPI at 70 and 140 g/ha and planting soybean. In 1993, four sweet corn hybrids were planted. Corn ear yield of Green Giant 97 was reduced following previous-year applications of 140 g/ha imazethapyr. Corn ear yields of Excellency, Super Sweet Jubilee, and Jubilee were not reduced at either actual carryover rate. These studies indicate variability among sweet corn hybrids in susceptibility to imazethapyr. Greenhouse results were indicative of field responses and may be useful as a rapid test to determine hybrid susceptibility.

Pesticide leaching experiments using widely spaced sampling sites may not adequately characterize chemical leaching behavior such as nonuniform flow between sampling points. We conducted this study to determine the three-dimensional variability of atrazine and chloride movement within a small volume of soil (2,700 cm1) under field conditions. A 1-m2area of Williamson silt loam (coarse-silty, mixed, mesic, Typic Fragiochrept) was sprayed uniformly with atrazine (1.1 kg ai/ha) and chloride (80 kg/ha). We used the Leaching Estimation and Chemistry Model (LEACHM) to simulate chemical movement. After 6.5 cm of rainfall during a 29-d period, we sampled 36 squares (5 by 5 cm) in the central 30- by 30-cm portion of the treated area at six depth increments (0 to 2, 2 to 5, 5 to 10, 10 to 15, 15 to 21, and 21 to 30 cm) and determined atrazine and Cl−concentrations. We recovered 26% of the applied atrazine and 138% of the applied chloride. Low atrazine recovery may have been due to leaching beyond 30 cm and/or degradation while excess chloride recovery is attributed to high background concentrations. Coefficients of variation (CVs) for atrazine significantly increased with depth and ranged from 26 to 353%, while CVs for Cl−were independent of depth and ranged from 32 to 66%. Derived atrazine concentration isograms illustrated highly nonuniform herbicide transport. Although LEACHM overestimated atrazine movement in the upper 15 cm, it was fairly accurate in the lower 15 cm. The overall trend in Cl−flow was adequately predicted, even though the predicted Cl−concentrations were underestimated. LEACHM could not accurately predict nonuniform flow or the variability in solute concentrations between points. However, its prediction of the atrazine center of mass (about 4.7 cm) agreed well with the derived isograms. These findings demonstrate that localized nonideal solute transport may be missed in larger sampling schemes and in simulation models.

Field studies conducted in 1991 to 1993 evaluated the efficacy of clomazone applied at various timings for weed control in soybean. Clomazone applied 45, 30, 15, or 0 days prior to planting (DPP) provided season-long control of velvetleaf and giant foxtail. In 1991 and 1992 clomazone alone 30 and 45 DPP failed to control redroot pigweed. Clomazone alone 45 DPP failed to control common lambsquarters. In 1991 and 1992 clomazone at 0.84 kg/ha plus metribuzin applied 45 DPP failed to control redroot pigweed. The addition of metribuzin plus chlorimuron to the above clomazone treatments resolved these weed control deficiencies. Weed control in 1993 was nearly complete across all clomazone treatments. In 1993 clomazone treatments which included metribuzin or metribuzin plus chlorimuron applied PPI or PRE reduced yield. Herbicide injury is the likely cause of this reduction because most treatments in 1993 provided 99% control of all weed species.

Farmers need information on herbicide technology and crop performance to assess the profitability of new herbicide-resistant crop technologies. First-generation imazethapyr-resistant corn hybrids evaluated at the University of Wisconsin yielded less than other commercial hybrids. To determine if this resistance trait affected yield or agronomic traits, 10 near-isogenic pairs of imazethapyr-resistant and -susceptible corn hybrids were compared. Whether treated with imazethapyr or not, imazethapyr-resistant hybrids yielded the same when averaged across hybrids, although yield varied among a few individual hybrids within single experiments. Seven of the imazethaypr-resistant hybrids yielded the same, two yield more, and one yielded less than their susceptible near-isogenic counterpart during eight site-years. Grain moisture was not affected, but imazethapyr-resistant hybrids had fewer broken stalks than did susceptible hybrids. The imazethapyr resistance trait does not appear to affect yield potential, but the backcrossing procedure may have caused early resistant hybrids to lag behind in yield compared to other new hybrids.