When spray mixtures were examined using a laser spray droplet analyzer, the new isopropylamine glyphosate formulation produced more small droplets than a previous isopropylamine salt of glyphosate formulation or glyphosate–trimesium plus nonionic surfactant. The use of a pre-orifice flat-fan nozzle and an impact type flat-fan nozzle reduced the amount of small droplets produced compared to an existing extended range flat-fan nozzle, while maintaining a spray droplet distribution that could still provide good weed control. The new nozzle technologies could provide a useful management tool to manage potential drift situations.

Control of downy brome in cool-season perennial grasses grown for seed production must be done prior to seed harvest, because downy brome seeds cannot be separated from cool-season grass seeds. Field experiments were conducted near Powell, WY, and Bridger, MT, to evaluate several herbicides for control of downy brome from 1992 through 1994 in western wheatgrass, slender wheatgrass, beardless wild rye, thickspike wheatgrass, and meadow bromegrass. When fall-applied, only metribuzin at 0.4 kg/ha and oxyfluorfen plus metribuzin at 1.1 plus 0.3 kg/ha controlled 98 and 95% of the downy brome, respectively, without affecting grass seed viability or seed yield. Early spring applications of paraquat at 0.8 kg/ha controlled 100% of the downy brome, but suppressed perennial grasses. Glyphosate applied in early spring at 0.3 kg/ha controlled 48% of the downy brome, but suppressed perennial grasses. Seed yield reductions occurred when thickspike wheatgrass and meadow brome were treated with glyphosate at 0.3 kg/ha.

Research was conducted in 1995 and 1996 to determine the potential for commonly used volunteer corn herbicides to control volunteer sethoxydim-resistant (SR) corn in soybean. Greenhouse studies showed that the SR corn hybrid tolerated 181 times more sethoxydim than the susceptible sister hybrid. SR corn also tolerated other acetyl CoA carboxylase (ACCase) inhibitors including fluazifop-P, quizalofop-P, and clethodim with 30 X, 27 X, and 7 × magnitudes of tolerance, respectively, compared with the susceptible hybrid. SR corn exhibited the least tolerance to clethodim, with a control rating of 50% (CR50) predicted at 28 g ai/ha. Field studies at Dekalb and Urbana, IL, showed that quizalofop-P, fluazifop-P, and fluazifop-P plus fenoxaprop at 62, 140, and 140 + 47 g ai/ha, respectively, controlled 22% or less of volunteer F2 SR corn at 30 days after treatment (DAT). Clethodim at 105, 140, and 210 g/ha consistently suppressed 23 to 70% of the volunteer SR corn. Dry weight reductions at 60 DAT showed the same general trend as the visual estimates of control. The field results confirmed the greenhouse data, which suggested SR corn had the least amount of cross-resistance to clethodim compared to other ACCase-inhibiting herbicides. In 1996, only AC 299,263 and imazethapyr plus imazaquin suppressed volunteer SR corn and prevented soybean yield loss at both locations. However, no system completely controlled volunteer SR corn.

Greenhouse and field experiments were conducted to evaluate herbicidal efficacy on tropical soda apple and bahiagrass. Acifluorfen, clopyralid, dicamba, fluroxypyr, picloram, and triclopyr were the most effective postemergence herbicides, providing > 90% control of tropical soda apple plants with no injury to bahiagrass 145 days after treatment (DAT). Glyphosate and imazapyr resulted in effective (> 90%) control of both seedling and mature tropical soda apple plants. However, these herbicides caused severe (> 90%) damage to bahiagrass. Control of tropical soda apple with 2,4-D, AC-263,222, diuron, fomesafen, lactofen, MSMA, sulfometuron, and triasulfuron was unacceptable (> 90%).

Glufosinate applied postemergence alone and in mixture with pendimethalin, thiobencarb, quinclorac, propanil, bensulfuron, bentazon, acifluorfen, or triclopyr was evaluated on bialaphosresistant (BAR) rice and red rice in field studies. Glufosinate at 2.2 kg ai/ha alone was less phytotoxic (6%) to BAR-transformed rice than when it was applied in combination with 0.4 kg ai/ha triclopyr (59%) or 0.6 kg ai/ha acifluorfen (22%). Rice yield with glufosinate alone was similar to the weed-free check the first year, but 13% less than the weed-free check the second year. For the glufosinate plus triclopyr mixture, rice yield was reduced by 39 and 76% compared with glufosinate alone in 1994 and 1995, respectively. Red rice control was 92% with either 3.4 kg ai/ha propanil or 0.6 kg/ha acifluorfen mixed with 0.6 kg/ha glufosinate, which was greater than for glufosinate alone and the other combinations. Propanil or acifluorfen mixed with glufosinate reduced red rice plant height, panicle maturity, and 100-seed weight 16, 31, and 24%, respectively, compared to glufosinate alone and 30, 48, and 43%, respectively, compared to the nontreated weedy check.

Longspine sandbur is a troublesome weed infesting corn in the Great Plains. However, herbicides are now available to control this species. This study characterized longspine sandbur ecology in irrigated corn to aid producers in integrating herbicides into their production systems. Longspine sandbur began emerging May 25, and by June 15, 84% of the seasonal emergence had occurred. Plant development was related to cumulative growing degree days. Seeds were viable early in longspine sandbur's development, with 20% of seeds viable by heading. Producers can minimize seed production of longspine sandbur in field borders by mowing plants at the boot stage. Bur production per plant was related to time of emergence, with seedlings emerging in late May producing 1,120 burs per plant. Seedlings emerging 4 wk later produced 84% fewer burs. Controlling longspine sandbur before 4 wk of interference prevented loss of corn grain yield.

Additive series experiments were conducted under greenhouse conditions to determine the effect of season-long interference of different initial population densities of purple nutsedge on the shoot dry weight and fruit yield of tomato and bell pepper. Purple nutsedge densities up to 200 plants/m2 linearly reduced shoot dry weight at flowering and fruit yield of both crops as weed density increased. Both variables were directly correlated, and for each percentage unit of tomato shoot dry weight loss at flowering, fruit yield was reduced 1.24 units, whereas for bell pepper this relationship was 1 to 2.01. Total shoot and tuber biomass of purple nutsedge increased as density increased. The presence of either crop caused a decline in the total shoot dry weight accumulation of purple nutsedge, with tomato producing a higher degree of loss than bell pepper to the weed. Fruit yield losses due to purple nutsedge interference reached 44% for tomato and 32% for bell pepper.

Field experiments were conducted in Louisiana to evaluate the effectiveness of tillage, tillage plus herbicide, and herbicide-only fallow programs in controlling bermudagrass. Tillage of fallow fields three times at 3- to 4-wk intervals between row formation in late May and planting in late September or early October reduced bermudagrass infestations in the newly planted crop in December 44 to 51%. When the final tillage operation was replaced by glyphosate postemergence at either 2.24 or 3.36 kg ai/ha in late August, bermudagrass infestation level in December on the surface of the newly planted rows was reduced to below 20%. Two applications of glyphosate at 3.36 kg/ha were more effective than tillage only and as effective as tillage twice followed by glyphosate in reducing bermudagrass infestation levels in the newly planted crop. Application of atrazine at 3.36 kg ai/ha, imazapyr at 0.68 kg ai/ha, metribuzin at 1.68 kg ai/ha, or sulfometuron at 0.14 and 0.28 kg ai/ha to newly formed rows in late May of the fallow period did not reduce the need for tillage or an application of glyphosate during the fallow period to control bermudagrass, but imazapyr at 1.12 kg/ha did. Sugarcane shoot populations in December of the fallow year were similar for the treatment programs despite differences in bermudagrass infestation levels, which ranged from 11 to 94%. However, sugarcane stalk number and height and cane and sugar yield in the plant-cane crop the following year were highest when glyphosate was applied to bermudagrass as two applications either alone or following the application of atrazine or metribuzin, when tillage was followed with one application of glyphosate, and in 1 yr when imazapyr alone was applied to newly formed rows.

Field experiments were conducted from 1989 to 1992 in Balcarce, Tandil, and San Cayetano, all in Buenos Aires province (Argentina), to evaluate clethodim, fenoxaprop-P-ethyl, fluazifop-P, haloxyfop, propaquizafop, and quizalofop-P-ethyl for bermudagrass control in sunflower, soybean, and potato. The highest levels of bermudagrass control 60 days after treatment (DAT) were generally obtained with fenoxaprop-P-ethyl, haloxyfop, propaquizafop, and quizalofop-P-ethyl. Late season bermudagrass control, based on biomass of stolons and rhizomes, suggested that the most consistent treatments in potato and sunflower were haloxyfop at 180 g ai/ha and quizalofop-P-ethyl at 54 g ai/ha. In soybean, clethodim at 336 g ai/ha, haloxyfop at 180 g/ha, propaquizafop at 100 g ai/ha, and quizalofop-P-ethyl at 54 g/ha provided the greatest reductions in bermudagrass biomass. All of the postemergence (POST) graminicide treatments increased crop yields when compared to a nontreated check. However, little or no difference in yield was obtained when herbicide rate was increased.

A field study was conducted on tolerance of four seashore paspalum cultivars to postemergence (POST) herbicides in Georgia during 1995 and 1996. Quinclorac (0.8 kg/ha) and MON 12000 (0.07 kg/ha) at recommended rates were the only POST herbicides that did not affect the performance of any seashore paspalum cultivar (≥ 89%). When the rates were increased to three times recommended, the quality of ‘AP 10’ (≥ 96%) and ‘PI 28960’ (93%) cultivars was not affected, but the quality of ‘HI 25’ (≥ 84%) and ‘K-7’ (77%) was lower when compared with respective untreated plots. HI 25 recovered within 4 wk, but K-7 required 6 wk or longer. Dicamba at 1.7 kg/ha affected the quality of K-7 (69%) more at 2 wk than the other cultivars (85 to 92%). Diclofop, imazaquin, and 2,4-D plus mecoprop plus dicamba significantly reduced the quality of all cultivars 2 wk after treatment (WAT). The quality of all cultivars was similar at 2 WAT with diclofop at 1.1 kg/ha (79 to 84%). However, when treated with imazaquin at 0.4 kg/ha, the quality of K-7 (65%) was lower than AP 10 (85%), HI 25 (77%), and PI 28960 (81%), and when treated with 2,4-D plus mecoprop plus dicamba at 1.1 + 0.6 + 0.1 kg/ha, the quality of AP 10 (75%), PI 28960 (72%), and K-7 (57%) was lower than HI 25 (87%). POST applications of quinclorac, dicamba, and MON 12000 were safe to use for weed control in paspalum cultivars, whereas the safety of diclofop and imazaquin was marginal, and 2,4-D plus mecoprop plus dicamba was unacceptable.

Preemergence (PRE) and postemergence (POST) herbicides were sequentially applied to tall fescue over a 2-yr period to determine the lowest herbicide rates needed for acceptable large crabgrass control. Prodiamine was the only PRE herbicide that provided full-season large crabgrass control in tall fescue turf. The control was 85% in plots treated at one-third recommended rate (0.3 kg/ha) and 96% at the full rate (0.8 kg/ha). Sequential applications of oxadiazon at one-third recommended rate (1.1 kg/ha) in late February followed by fenoxaprop (0.2 kg/ha) in June controlled 85% large crabgrass in late August. Control was similar in mid-August when pendimethalin, dithiopyr, or oryzalin at one-third recommended rates was followed by fenoxaprop, but was not acceptable (≤ 74%) by late August. In most instances, large crabgrass control was higher when fenoxaprop followed the PRE herbicide application than with MSMA. Reduced herbicide rates may not provide full-season large crabgrass control in other areas with different soil and weather conditions. Tall fescue quality was not affected by prodiamine, dithiopyr, and oxadiazon. In 1996, pendimethalin at 3.3 kg/ha reduced turf quality 16% and oryzalin at 2.2 kg/ha reduced quality by 46%. In 1995, MSMA reduced the quality of tall fescue more (≤ 21%) than fenoxaprop (≤ 10%). When compared to the use of PRE and POST herbicides alone, sequential PRE plus POST herbicide programs did not affect turfgrass quality.

Broadleaf signalgrass control from preemergence (PRE) herbicides was usually lower in no-till than in tilled plots. Broadleaf signalgrass control was most nearly complete in tilled plots treated with metolachlor in 1995, a year that favored an herbicide with more soil persistence. Broadleaf signalgrass control was most nearly complete in tilled plots treated with acetochlor in 1996, a year in which rainfall to activate the herbicides did not occur until 9 d after planting. The 1996 data indicated that acetochlor was more stable on the soil surface under the drier conditions. There was no difference in broadleaf signalgrass control between the two acetochlor formulations. Alachlor, metolachlor, and dimethenamid controlled broadleaf signalgrass > 80% for about 4 wk, acetochlor provided control for about 4 wk under no-till conditions and about 8 wk in tilled plots, and pendimethalin provided about 2 wk broadleaf signalgrass control. Acetochlor provided consistent control regardless of the rainfall pattern after application.

Seed treatments with two acetolactate synthase (ALS)-inhibiting herbicides, the sulfonylurea herbicide nicosulfuron and the imidazolinone herbicide imazaquin, controlled the parasitic weed Striga hermonthica in corn. The XA-17 gene in ALS-modified P3180IR corn strongly reduced corn injury from herbicide seed treatments while another ALS modification was not effective. Combining seed treatment of ALS-inhibiting herbicides and ALS-modified corn with the XA-17 gene may offer a practical means for African growers to control Striga hermonthica.

Field studies were conducted from 1992 through 1994 to evaluate application timing of seven postemergence (POST) broadleaf herbicides alone and in mixtures for control of eclipta and pitted morningglory. Imazethapyr and 2,4-DB did not control eclipta while AC 263,222 applied early postemergence (EPOST) at 0.07 kg/ha provided greater than 90% control in 2 of 3 yr. EPOST applications of bentazon, acifluorfen + bentazon, and pyridate controlled eclipta at least 92% all 3 yr. Lactofen applied EPOST at 0.28 kg/ha provided similar levels of eclipta control in 2 of 3 yr. Imazethapyr controlled pitted morningglory > 70% when applied EPOST. AC 263,222 controlled pitted morningglory a minimum of 83% when applied EPOST at 0.04 or 0.07 kg/ha. Pitted morningglory control was at least 85% with 2,4-DB applied alone or in a mixture with AC 263,222, acifluorfen, imazethapyr, lactofen, or pyridate. Effective weed control increased peanut yields up to 98% over the untreated check.

Experiments were conducted from 1991 through 1993 to evaluate AC 263,222 and imazethapyr for yellow and purple nutsedge control in peanut. AC 263,222 at 0.05 to 0.07 kg/ha controlled purple nutsedge (88 to 99% late season) whether applied preplant incorporated (PPI), preemergence (PRE), early postemergence (EPOST) at peanut emergence, or postemergence (POST). Yellow nutsedge control with AC 263,222 was inconsistent at the 0.04 kg/ha rate; however, the 0.05 and 0.07 rate gave 88% early season yellow nutsedge control, but late season control was variable. Yellow nutsedge control with soil-applied treatments of AC 263,222 and imazethapyr were similar but AC 263,222 provided better postemergence control than did imazethapyr. Purple nutsedge control was similar for both herbicides across all application methods.

The efficacy of reduced rates of metolachlor plus cyanazine for weed control in sweet corn was evaluated over a 2-yr period. Early postemergence (POST) and POST herbicide applications at reduced rates gave control of broadleaf weeds comparable to control at the 1 × rate, except for the early POST application at the ¼ × rate in 1993. Preplant incorporated (PPI) and preemergence (PRE) herbicide applications at reduced rates gave poor broadleaf weed control, except for the PRE application at the ½ × rate in 1993. Early POST applications at the ¼ × rate resulted in significantly reduced grass control in 1994, while POST applications at the ¼ × rate gave significantly reduced grass control both years. Generally, POST applications controlled broadleaf weeds better than early POST applications, while grass control with early POST applications was superior to POST applications at reduced rates. Preemergence and PPI applications at reduced rates gave poor broadleaf weed control but satisfactory grass control. Preplant incorporated applications at reduced rates resulted in reduced yield both years, while PRE applications at reduced rates reduced yield only in 1994. Early POST and POST applications at reduced rates did not affect sweet corn yield. The addition of adjuvants to the ¼ × application rate had no effect on weed control or yield.

Field experiments were conducted in 1994 and 1995 to determine if the sodium salt of pyrithiobac or bromoxynil applied in a low-volume, air-assist spray system controlled entireleaf morningglory, pitted morningglory, and smallflower morningglory as well as treatments applied with a conventional hydraulic fan spraying system, and to determine if herbicide rates could be reduced when using the low-volume spraying system. Pyrithiobac at 0.035 and 0.071 kg ai/ha and bromoxynil at 0.56 and 1.12 kg ai/ha were applied alone and in combination with DSMA at 1.7 kg ai/ha or MSMA at 1.7 kg ai/ha. Spraying systems were calibrated to deliver 26 L/ha and 140 L/ha for the low-volume and conventional systems, respectively. No significant differences in control were noted between low-volume and conventional spray systems when herbicides were applied at the suggested use rates of 0.071 and 1.12 kg ai/ha for pyrithiobac and bromoxynil, respectively. Morningglory control was reduced when pyrithiobac and bromoxynil were applied at one-half the suggested use rate regardless of the spraying systems. Bromoxynil alone generally controlled pitted and entireleaf morningglory better than pyrithiobac alone regardless of rate and application method. However, pyrithiobac generally provided better control of smallflower morningglory than bromoxynil. Adding MSMA or DSMA to bromoxynil and pyrithiobac increased control of both weed species.

Releasing Tyta luctuosa on hedge bindweed in cornfields did not increase defoliation more than endemic herbivores. Larvae of T. luctuosa were rarely found after release, indicating they suffered high mortality or dispersed from test plants. Eleven species of endemic insects were found feeding on bindweed, all of which are known to be generalists feeding, in some cases, on economically important plants. Oidaematophorus monodactylus (L.) (Lepidoptera: Pterophoridae) was the most damaging species to the bindweed.

Angora goats have been suggested as biological control agents for leafy spurge, especially in environmentally sensitive or limited access areas. Dietary preferences and dietary nutritive content of herded Angora goats were evaluated over a two-year period in North Dakota. Relative preferences of forages were evaluated by comparing botanical composition of diets as determined by microhistological analysis of fecal samples to forage availability in the field. Leafy spurge and shrubs comprised the largest percentage of goat diets throughout each grazing season. Goats preferred leafy spurge and shrubs at all times and avoided most cool-season grass species. The nutritional requirements of Angora goats nursing kids were met throughout the grazing season. Use of Angora goats is another tool available to land managers to manage leafy spurge infestations in the Northern Plains.

Seven postemergence (POST) herbicides were evaluated alone and in various mixtures for Palmer amaranth control in peanut from 1992 through 1994. AC 263,222 at rates as low as 0.04 kg/ha controlled ≥ 95% Palmer amaranth. Imazethapyr at rates of 0.05 to 0.07 kg/ha controlled ≥ 90% Palmer amaranth in 2 of 3 yr. Acifluorfen alone or in combination with bentazon or 2,4-DB and lactofen alone controlled > 90% Palmer amaranth in 2 of 3 yr. Bentazon or pyridate failed to provide adequate control (≤ 60%), while 2,4-DB provided good control (80%) in only 1 of 3 yr.