A native fungus, Botryosphaeria ribis, was evaluated under field conditions to determine its potential to control melaleuca. Applications consisted of either wound inoculations of trees with B. ribis or fresh stump treatments with B. ribis alone or mixed with imazapyr herbicide. There was no mortality among nondefoliated trees inoculated with B. ribis. Mortality of B. ribis-inoculated trees was increased by three complete defoliation cycles. Defoliated trees inoculated with isolate BR-5 exhibited 100% mortality compared to 17% for defoliated but noninoculated trees. Wounds inoculated with B. ribis during winter produced longer cankers than did noninoculated wounds. Stump regrowth reduction by treatment with B. ribis alone was less effective than treatment with imazapyr alone. Mixtures of B. ribis with imazapyr or imazapyr alone at comparable concentrations did not differ in stump regrowth control.

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.

Greenhouse and field experiments were conducted to determine the response of corn (Zea mays), barnyardgrass (Echinochloa crus-galli), common lambsquarters (Chenopodium album), large crabgrass (Digitaria sanguinalis), velvetleaf (Abutilon theophrasti), and yellow foxtail (Setaria lutescence) to RPA 201772. Barnyardgrass, large crabgrass, velvetleaf, and common lambsquarters were more susceptible than yellow foxtail to RPA 201772. Velvetleaf was the most susceptible species and rates above 18 g ai/ha of RPA 201772 controlled 100% of the population 4 wk after treatment (WAT). Percent control of all the weed species increased with increased RPA 201772 rates. In the field, the dry weights of yellow foxtail decreased as the rate of RPA 201772 increased from 0 to 210 g/ha. However, a 60% reduction of dry weight of yellow foxtail was recorded at 140 g/ha of RPA 201772 compared to the untreated check 6 WAT, whereas at 12 WAT the dry weight of yellow foxtail was reduced to only 15% because of intraspecific competition. Yellow foxtail was moderately susceptible to RPA 201772. Corn was tolerant to RPA 201772; the GR80 value was 435 g/ha in the greenhouse. The bleaching injury to corn in the field was less than 10%, and it was found only with the 210 g/ha rate of RPA 201772. This injury was temporary and the plants recovered within 2 to 3 wk. Based on the GR80 values, velvetleaf was the most susceptible, followed by common lambsquarters, large crabgrass, barnyardgrass, and yellow foxtail.

Field research was conducted to evaluate the response of soybean to various herbicides applied at rates to simulate drift damage. Dicamba, glyphosate, glufosinate, and the sulfonylurea herbicides CGA-152005, primisulfuron, nicosulfuron, rimsulfuron plus thifensulfuron, and CGA-152005 plus primisulfuron were applied to soybean at the two to three trifoliolate leaf stage in 1997 and 1998 at and ⅓ of the recommended use rates. The order of yield reduction after herbicide treatment was CGA-152005 > dicamba > CGA-152005 plus primisulfuron > rimsulfuron plus thifensulfuron > primisulfuron. Soybean yields were not reduced by glyphosate, glufosinate, and nicosulfuron. Applications of all herbicides at rates higher than of the use rate caused injury symptoms within 30 d after treatment. However, soybean plants had partially or fully recovered by the end of the growing season. Therefore, early-season injury symptoms from herbicide drift are not reliable indicators for soybean yield reduction.

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.

Soil-applied herbicides alone or followed by postemergence (POST) applications of CGA-277476 were evaluated for season-long weed control in soybean. Common cocklebur, hemp sesbania, and pitted morningglory control was not consistently improved with a soil-applied herbicide followed by a POST application of 79 g ai/ha CGA-277476. However, in locations with heavy weed pressure, a tank-mix of chlorimuron + metribuzin + trifluralin or imazaquin + pendimethalin followed by CGA-277476 improved common cocklebur, hemp sesbania, and pitted morningglory over CGA-277476 alone. Sequential application of CGA-277476 following SAN 582 improved weed control over SAN 582 alone. When weed pressure was not severe, there were no differences in control from CGA-277476 alone or following soil-applied herbicides. A POST application of CGA-277476 following soil-applied herbicides did not consistently improve soybean yield over CGA-277476 alone. Yield from soybean treated with SAN 582 was improved when CGA-277476 was applied. In contrast, when chlorimuron + metribuzin + trifluralin or imazaquin + pendimethalin were applied at planting, yield was similar with or without POST application of CGA-277476.

Propanil and carbaryl mixtures, propanil formulated with carbaryl, the package mixture of propanil plus molinate (alone and plus pendimethalin), propanil plus quinclorac, and propanil plus pendimethalin were evaluated in field experiments for control of propanil-resistant and -susceptible barnyardgrass in 1995 and 1996 in Arkansas. Propanil alone at 3.3 kg ai/ha did not control propanil-resistant barnyardgrass when applied to two-leaf and repeated at four-leaf barnyardgrass. Propanil at 3.3 kg/ha with carbaryl at 0.1 to 0.3 kg ai/ha controlled propanil-resistant barnyardgrass at least 90% when applied at the two-leaf stage with no rice yield reduction. Applications repeated at the four-leaf stage also controlled propanil-resistant barnyardgrass, but rice injury was 66% with 0.3 kg/ha carbaryl in 1 of 2 yr, and rice yield was reduced. Control of resistant barnyardgrass with the commercial formulation of propanil plus carbaryl and propanil plus molinate was lower with a single application than with repeat applications. Propanil plus quinclorac, propanil plus pendimethalin, and propanil plus molinate plus pendimethalin controlled resistant barnyardgrass with one application at the two-leaf stage.

Imazethapyr resistance in common sunflower (Helianthus annuus) was confirmed in 1996 in a field near Rossville, KS. In 1997, common sunflower achenes were collected within a 20-km radius of the field with known resistance to determine if resistance was present in nearby fields or if resistance had spread to the native population on the roadside. Collections were made from 14 soybean (Glycine max) fields, one corn (Zea mays) field, and 11 roadsides. Achenes from Konza Prairie Research Natural Area, a prairie that had received no herbicide applications in the past 25 yr, served as the susceptible control. Common sunflower seedlings were treated in a greenhouse with 71 g ai/ha imazethapyr and 11 g ai/ha chlorimuron. In all 15 fields sampled, at least 1% of the common sunflower exhibited an intermediate response to imazethapyr or chlorimuron. In 13 fields, at least 1% of the plants were resistant to imazethapyr, and in all 15 fields, at least 1% of the plants were resistant to chlorimuron. Ten roadsides had common sunflower that showed intermediate response to imazethapyr or chlorimuron. At least 1% of the plants from seven roadsides were resistant to imazethapyr or chlorimuron. Common sunflower collected from fields with repeated applications of imazethapyr showed more resistance to imazethapyr than to chlorimuron.

Antagonism of quizalofop-P efficacy on annual grasses by bromoxynil has been noted in both the field and greenhouse. Laboratory experiments were conducted on yellow foxtail (Setaria glauca) to determine the effect of mixing bromoxynil with the ethyl ester of quizalofop-P on absorption, translocation, and metabolism of 14C-quizalofop-P Applying bromoxynil in mixture with quizalofop-P reduced 14C-label absorption from 63 to 51%, 73 to 52%, 77 to 68%, and 90 to 80% at 4, 8, 24, and 96 h after treatment, respectively. Translocation of 14C-label from the treated leaf into the shoot above or shoot below was unaffected by bromoxynil. However, translocation into the roots was reduced from 0.9 to 0.4% and 1.0 to 0.5% at 4 and 8 h after treatment, respectively, but differences were not noted at 0.5, 1, 24, and 96 h after treatment. Bromoxynil increased deesterification of quizalofop-P-ethyl into quizalofop-P acid from 45 to 60% in the shoot above the treated leaf. However, bromoxynil did not affect metabolism of quizalofop-P in the treated leaf or shoot below the treated leaf. These results suggest that antagonism of quizalofop-P activity by bromoxynil is primarily due to decreased absorption of quizalofop-P, whereas effects on translocation and metabolism were minor.

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.

Cloransulam-methyl applied postemergence (POST) following various preplant-incorporated (PPI) herbicides was evaluated in four experiments for weed control in North Carolina soybean over a 2-yr period at three locations. Acifluorfen plus bentazon or chlorimuron alone applied POST injured soybean more than cloransulam-methyl when following any soil-applied herbicide. When following trifluralin PPI, cloransulam-methyl controlled common ragweed, entireleaf morningglory, and pitted morningglory comparable to acifluorfen plus bentazon or chlorimuron. Common lambsquarters and prickly sida control was higher when acifluorfen plus bentazon was applied POST following trifluralin PPI compared to trifluralin PPI followed by cloransulam-methyl or chlorimuron. Acifluorfen plus bentazon or chlorimuron POST controlled yellow nutsedge and smooth pigweed more than cloransulam-methyl POST when following trifluralin PPI. When trifluralin was applied PPI in mixtures with chlorimuron plus metribuzin, flumetsulam, or imazaquin, control of most species was similar regardless of POST treatment used. Soybean treated with cloransulam-methyl yielded 250 kg/ha more than treatments with chlorimuron when these herbicides followed trifluralin plus flumetsulam or trifluralin plus imazaquin. Net returns with different herbicide systems followed trends similar to soybean yield.

Field studies were conducted to examine weed control efficacy and crop injury with SAN 582 (proposed name, dimethenamid) in irrigated ‘Russet Burbank’ potato. SAN 582 applied preemergence (PRE) at 1.1 to 1.7 kg ai/ha controlled light to moderate infestations of redroot pigweed, common lambsquarters, and hairy nightshade > 90%. Season-long control of these species with mixtures of SAN 582 plus metribuzin or rimsulfuron was > 98% and was similar to or better than registered mixtures. Green foxtail control with SAN 582 alone ranged from 83 to 100%, depending on rate and year. SAN 582 mixtures with metribuzin or rimsulfuron usually controlled green foxtail > 90%. In weed-free plots, SAN 582 was applied alone PRE or early postemergence (EPOST) at rates up to 3.4 kg/ha. SAN 582 applied EPOST usually caused 10 to 30% more potato injury than when applied PRE, but U.S. No. 1 yield was not reduced by SAN 582 applied either PRE or EPOST. SAN 582 shows good potential for PRE use in irrigated potato.

Field experiments were conducted in 1996 and 1997 at five locations in southwestern Ontario to develop dose-response curves for SAN 1269H (SAN 835H plus dicamba) for weed control and crop tolerance in corn. SAN 1269H controlled wild buckwheat (Polygonum convolvulus L.), common ragweed (Ambrosia artemisiifolia L.), common lambsquarters (Chenopodium album L.), pigweeds (Amaranthus retroflexus L. and A. powellii S. Wats.), barnyardgrass [Echinochloa crus-galli (L.) Beauv.], and yellow foxtail [Setaria glauca (L.) Beauv.]. Biologically effective doses of SAN 1269H (BAS 662H) were 440, 430, 180, and 40 g/ha for yellow foxtail, barnyard grass, wild buckwheat, and common ragweed, respectively. The biologically effective dose (that which provides 90% reduction in weed dry matter) for common lambsquarters was 560 g/ha when SAN 1269H was applied preemergence (PRE) and 110 g/ha when applied postemergence (POST). When applied PRE at a rate of 420 g/ha, pigweed was controlled, whereas only 85 g/ha was required when applied POST. Grain yield increased with dose of SAN 1269H and did not differ with time of application. Temporary crop injury was observed when SAN 1269H was applied at the four- to six-leaf growth stage. Optimum corn yields were achieved with doses of 100 to 250 g/ha.

Jointed goatgrass (Aegilops cylindrica) is a serious problem for winter wheat producers throughout the western U.S. Interference from this weed can severely reduce grain yield and contaminate harvested grain, resulting in dockage losses. There are currently no selective herbicides registered for controlling jointed goatgrass in wheat. Imazamox, an imidazolinone herbicide, was applied to an imidazolinone herbicide-resistant (IMI) wheat mutant of the winter wheat cultivar ‘Fidel.’ Jointed goatgrass control from spring postemergence application of imazamox ranged from 61 to 97% when applied at 36 g/ha. Negligible crop injury from imazamox treatment was observed at 36 g/ha at several locations under dryland environments in the U.S. Pacific Northwest. Wheat yield was increased 19 to 41% by imazamox treatment in three of four experiments. Percent dockage resulting from jointed goatgrass spikelet contamination of harvested wheat grain was eliminated by imazamox treatment. Introduction of the IMI trait into commercial wheat cultivars could provide an effective method for selective control of jointed goatgrass in winter wheat.

A postemergence (POST) timing study was conducted on established populations of burcucumber (Sicyos angulatus) in corn (Zea mays), and a second study examined the residual activity of several herbicides for burcucumber control under greenhouse conditions. In the field study, flumiclorac, halosulfuron, primisulfuron, CGA 152005, and CGA 152005 + primisulfuron (45, 71, 40, 40, and 20 + 20 g ai/ha, respectively) were applied at two POST timings. CGA 152005, primisulfuron, and the combination provided greater than 85% control of burcucumber 14 wk after planting (WAP). Flumiclorac and halosulfuron provided 60% control or less by 8 WAP. Timing of the POST applications did not influence burcucumber control by 11 WAP with any herbicide. In the greenhouse, germinated burcucumber seeds were placed in soil treated with atrazine, chlorimuron, primisulfuron, or CGA 152005 at normal field use rates. All treatments provided similar residual control early; however by 4 wk after treatment (WAT), control from atrazine was less than 10% compared to 69% for chlorimuron and about 50% for primisulfuron and CGA 152005. This research suggests that CGA 152005 and primisulfuron can both be effective for managing burcucumber in corn, whereas flumiclorac and halosulfuron proved ineffective.

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.

An experiment was conducted near Scottsbluff, NE, to assess three techniques for establishing perennial grasses in pasture sites and to evaluate the effectiveness of five perennial grasses compared with herbicide or mowing for Canada thistle control. Perennial grass density 9 mo after seeding and perennial grass biomass 12 mo after seeding both followed the same trend, indicating that preplant rototilling improved perennial grass establishment. After 3 yr, Canada thistle control was greater than 90% in plots where perennial grasses had been established utilizing preplant rototilling, and competitive grasses were as effective as yearly applications of clopyralid at 0.55 kg/ha for controlling Canada thistle. Averaged across two studies conducted for 3 yr, hybrid wheatgrass, intermediate wheatgrass, Russian wildrye, tall fescue, and western wheatgrass provided 85, 74, 76, 78, and 66% Canada thistle control, respectively.

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.

Studies were conducted to observe the effect of full and reduced rates of postemergence (POST) herbicides on seedling and rhizome johnsongrass (Sorghum halepense) at different growth stages. Herbicides and labeled rates included primisulfuron at 40 g/ha, nicosulfuron at 35 g/ha, fluazifop-P at 210 g/ha, and clethodim at 140 g/ha. Contour graphs to predict johnsongrass control at different growth stages and herbicide rates were developed. Excellent seedling and rhizome johnsongrass control was obtained with reduced rates of herbicides applied at the three- to five-leaf stages. Primisulfuron at 20 g/ha resulted in 90% or greater control of seedling johnsongrass in the three- to four-leaf stage. Rhizome johnsongrass at this growth stage required 30 g/ha of primisulfuron for the same level of control. Nicosulfuron at 17.5 and 26.3 g/ha provided 90% or greater control up to the four-leaf stage of seedling and rhizome johnsongrass, respectively. Fluazifop-P and clethodim were more effective than primisulfuron and nicosulfuron. Fluazifop-P at 105 g/ha resulted in 90% or greater control of seedling and rhizome johnsongrass up to the seven- and five-leaf stages, respectively. Clethodim at 35 g/ha controlled seedling johnsongrass at least 90% up to the eight-leaf stage. Clethodim at 70 g/ha provided 90% or greater control of rhizome johnsongrass if applied at the three- to four-leaf stages.

Field trials were conducted to evaluate weed control and crop safety with postemergence-applied herbicides in two cultivars of low-tannin seedling sericea lespedeza (Lespedeza cuneata). Two applications of either 2,4-D amine at 0.28 kg ae/ha or 2,4-DB amine at 0.56 kg ae/ha controlled sicklepod (Senna obtusifolia) ≥ 90%. Equivalent control of smallflower morningglory (Jacquemontia tamnifolia) required either two applications of 2,4-D or three of 2,4-DB. Three applications of either herbicide were required for comparable spotted spurge (Euphorbia maculata) control. Sericea lespedeza was not adversely affected when either herbicide was applied up to three times per season over two consecutive seasons. Tolerance to 2,4-D and 2,4-DB was equal between two sericea lespedeza cultivars. Absorption of foliar-applied 14C-2,4-D was greater in sicklepod and smallflower morningglory than in sericea lespedeza. Translocation of absorbed 14C-2,4-D was equivalent between sicklepod and sericea lespedeza but greater in smallflower morningglory than in sericea lespedeza. Absorption and translocation of foliar-applied 14C-2,4-DB was equivalent between sicklepod and sericea lespedeza. Furthermore, 14C-2,4-DB absorption was less in smallflower morningglory than in sericea lespedeza.