Diclofop and dithiopyr were applied in April and early May during 1992 and 1993, to a ‘Tifway’ bermudagrass golf green overseeded with perennial ryegrass, to determine the effects of rates and dates on perennial ryegrass injury and on transition from a mixed cool- and warm-season grass to bermudagrass turf. Diclofop applied as a single application at 0.6 kg/ha or two applications at 0.3 kg/ha during April and/or early May gradually reduced perennial ryegrass during June and July when compared with untreated turf. During this period, both grasses treated with diclofop maintained 94% or greater cover. However, perennial ryegrass was moderately to severely injured from the treatments. Maximum injury from the 0.6 kg/ha rate ranged from 40 to 55% during 1992 and 29 to 33% during 1993. The injury was pronounced over a period of one to three weeks. Maximum injury from 0.3 kg/ha applied on April 3 and repeated at the same rate on April 17 was 28% in 1992 and 37% in 1993. Perennial ryegrass injury from split applications was lower than from the single 0.6 kg/ha rate in 1992. The optimum time and rate for effective spring transition with least amount of perennial ryegrass injury was 0.3 kg/ha applied on April 5 and repeated at the same rate on April 17. Dithiopyr did not affect the spring transition of overseeded perennial ryegrass to bermudagrass, regardless of rate and application date.

The absorption and translocation of the isopropylamine salts of 14C-glyphosate and 14C-imazapyr were compared in established terrestrial alligatorweed. Results indicated that more than twice as much imazapyr as glyphosate was absorbed by treated leaves of alligatorweed. In addition, more imazapyr was translocated to the underground storage tissues in alligatorweed than was glyphosate. This difference in translocation to roots and subterranean storage tissues is proposed as a mechanism for tolerance of alligatorweed to glyphosate and susceptibility to imazapyr.

Field studies were conducted during two soybean-corn rotations to evaluate the effect of tillage systems on quackgrass growth and control with and without glyphosate. In the final year of the study, tillage alone (compared to no-till) resulted in 88%, 78%, 64%, and 31% control of quackgrass with fall moldboard plow, spring moldboard plow, fall soil-saver, and spring soil-saver tillage, respectively. When glyphosate was used to control quackgrass, crop yields increased as tillage was reduced and excellent control of quackgrass in no-till was achieved. Increased shoot growth (in moldboard plowed and fall soil-saver tillage plots), exposure of rhizomes in winter (in fall tilled plots), and increased depth of rhizome burial (in spring tilled plots) increased quackgrass control. In general, the total biomass of quackgrass was reduced in drier years. Nonetheless, drought increased crop yield losses caused by quackgrass interference.

Herbicides and interim summer crop treatments were studied in 1984 to 1987 to replace fungal endophyte-infected with endophyte-free tall fescue or red clover to improve forage quality. Foliar glyphosate or paraquat were applied in spring across interim crops with PRE herbicides. The interim crops, grain sorghum with atrazine, sorghum-sudangrass hybrid with metribuzin, or soybean with imazaquin, were each applied as confounded treatments across glyphosate or paraquat. Within an interim crop system, a follow-up glyphosate treatment was serially applied the next fall or spring. Then either red clover or endophyte-free tall fescue was spring drilled within the fall or spring glyphosate follow-up treatments. Glyphosate controlled old tall fescue better than paraquat, and improved the stand of the endophyte-free tall fescue. Control of tall fescue was 97% from 1.7 kg ai/ha glyphosate. Glyphosate reduced the endophyte from a 77% original infection level to 20% over all interim crops after drilling the endophyte-free tall fescue. Among interim crops, grain sorghum or the sorghum-sudangrass hybrid was more competitive than soybean with the uncontrolled tall fescue. Replacement with endophyte-free tall fescue was best in grain sorghum or sorghum-sudangrass hybrid stubble the next spring. Grain sorghum or sorghum-sudangrass hybrid following foliar glyphosate or paraquat treatment of endophyte-infected tall fescue reduced endophyte infection level in tall fescue to 28%. A follow-up fall treatment with glyphosate controlled tall fescue better than the spring retreatment and red clover and endophyte-free tall fescue were established better from fall retreated glyphosate. Red clover was easily established by drilling into the sod after treating endophyte-infected tall fescue with either glyphosate or paraquat.

Field studies were conducted in 1988 and 1989 under dryland and irrigated conditions to determine effects of various herbicides for use in peanuts on weed control and peanut yield under a reduced tillage system. Under dryland and irrigated conditions, sethoxydim + acifluorfen consistently controlled Texas panicum. Paraquat + bentazon controlled Texas panicum poorly under dryland conditions. Pendimethalin + metolachlor provided ≥ 80% Texas panicum control under irrigated conditions.

The availability of postemergence grass control herbicides can prevent dependence on potentially unnecessary preemergence herbicides. No postemergence grass control herbicides have federal registration for kenaf in the United States. This research was conducted to collect data to support such registration. Clethodim, fluazifop, quizalofop, and sethoxydim applied at three rates did not injure established kenaf, reduce plant populations, reduce plant heights, or reduce stalk yields.

Field experiments were conducted in 1988 and 1989 to (i) evaluate annual weed control with nicosulfuron applied at rates of 17 to 70 g ai/ha with several additives and (ii) evaluate annual weed control with nicosulfuron applied at rates of 17 to 105 g/ha at three corn growth stages. In 1988, in the adjuvant study, giant foxtail control increased linearly with no additive or with urea ammonium nitrate as the rate of nicosulfuron increased. Petroleum oil concentrate, nonionic surfactant, and a combination of either petroleum oil concentrate or nonionic surfactant with urea ammonium nitrate applied with nicosulfuron increased giant foxtail control to 90% or greater regardless of rate both years. Nicosulfuron at all rates with no additive and in combination with all additives controlled 93% or more of redroot pigweed and Pennsylvania smartweed both years. Corn grain yield was related to the level of giant foxtail control. In the rate by corn growth stage study, giant foxtail, redroot pigweed, and Pennsylvania smartweed control was 90% or greater regardless of nicosulfuron rate or application stage both years. Corn grain yield was related more to the duration of weed competition than the level of weed control with grain yield 8 to 12% lower with nicosulfuron applied at the V7 growth stage compared with the V3 or V5 growth stage.

Laboratory and field experiments were conducted to determine whether manipulation of radiation environment during the period of winter wheat establishment can be used to improve wheat yields in Italian ryegrass-infested fields. Percentage of total irradiation and ratio of red (R) light (around 660 ηm) to far-red (FR) light (around 730 ηm) reaching the soil surface were important factors in regulating Italian ryegrass germination, growth, and competitive interactions with wheat. Reducing total irradiation to about 10% of full sunlight while maintaining the normal R/FR ratio of about 1.0 reduced wheat grain production in the presence of Italian ryegrass by about 40% compared with weed-free wheat in full sunlight. Further, reducing total irradiation to 3% of full sunlight plus reducing the R/FR ratio to about 0.2 reduced wheat grain production competing with Italian ryegrass by about 35% compared with production in the control conditions. Wheat production of dry matter, spikes, and seeds in the presence of Italian ryegrass increased more than threefold under both shading treatments compared with production in full sunlight.

In controlled-environment chambers, serrated tussock achieved maximum growth in temperature regimes of 18/11, 18/23, 24/23, or 24/17 C day/night. Growth was significantly reduced at 30/11 C, and no plants survived at 36/29 C. Serrated tussock seedlings grew slowly at first but eventually produced vigorous tussocks with as many as 2800 tillers after 140 d in the 24/17 C regime. Comparisons of climatic conditions in New South Wales, Victoria, New Zealand, South Africa, and the United States revealed that similar temperature conditions occur during the warmest eight mo of the year in areas as diverse as Oregon, Washington, the Sierran Nevada foothills of California, upper elevation rangelands in Arizona, and the southern Appalachian highlands. None of these areas has a precipitation pattern similar to those of the sites of serrated tussock weed infestation in the Southern Hemisphere. However, poorly managed pastures and unimproved rangelands in these diverse areas may be vulnerable to invasion by serrated tussock, should the weed become established in the United States.

The influence of PRE herbicides on rooting characteristics of bermudagrass turfgrass was studied using sod plugs removed from the field. Greenhouse root fresh weight was reduced the greatest with dithiopyr or prodiamine. Pendimethalin caused fewer fresh weight reductions compared to dithiopyr or prodiamine and these reductions were usually for a short period. Root weight loss was due to lower root density and root malformation. Significant numbers of malformed roots were also observed for greater periods of time where dithiopyr or prodiamine had been applied.

Experiments conducted over three years compared weed cover and grain yields in corn which received cultivation alone, herbicide alone, and treatments combining mechanical and chemical weed control. Weed cover averaged 30% with cultivation alone compared to 9% for the other treatments. Grain yields were 7% lower in one year. In the cultivation-alone treatments the rolling cultivator was less effective in controlling weeds than the shovel/sweep cultivator. In-row weed cover was greater than between-row weed cover with cultivation alone. With banded herbicide plus cultivation, in and between-row weed cover was the same. Weed cover and grain yields following banded herbicide plus cultivation were equivalent to broadcast herbicide with or without cultivation.

The effects of metribuzin herbicide and phorate insecticide were studied on summer harvest chipping-potatoes at Muscatine, IA, from 1989 to 1991. Phorate at 1.5 kg/ha increased total and ‘A’-size tuber yield and tuber specific gravity. Metribuzin applied at 0.56 kg/ha postemergence decreased total and ‘A’-size tuber yield. Metribuzin applied at 0.56 kg/ha preemergence and 0.28 kg/ha postemergence did not reduce Atlantic cultivar yield. Metribuzin did not affect ‘B’-size tuber yield or specific gravity. Phorate in combination with metribuzin did not increase plant injury or reduce tuber yield.

The influence of temperature, soil moisture, and light intensity on the tolerance of spring wheat, durum wheat, and spring barley to imazamethabenz and safened fenoxaprop-p-ethyl was determined in growth chamber experiments. Imazamethabenz at 500 g/ha reduced plant height and shoot fresh weight of durum and spring wheats grown under prolonged 70% shade. The height of durum and spring wheats was reduced by imazamethabenz under a low temperature regime. Compared to the plants grown under standard conditions, the shoot weight of spring and durum wheat plants was not reduced by imazamethabenz under drought, or high and low temperature conditions. Barley tolerance to imazamethabenz was not affected by environment. All three spring cereals were tolerant to fenoxaprop-p-ethyl plus a safener at 92 g/ha; and such tolerance was not greatly affected by various environments examined.

Field studies were conducted from 1989 to 1992 to evaluate soybean and rotational crop tolerance to PPI applications of chlorimuron (23 to 140 g ai/ha), clomazone (560 to 3360 g/ha), imazaquin (70 to 420 g/ha), and imazethapyr (53 to 310 g/ha). Soybean injury was evident only in 1989. Soybean height reduction 45 d after application increased linearly with increasing rates of chlorimuron, imazaquin, and imazethapyr. Chlorimuron at 140 g/ha and imazaquin at 420 g/ha reduced soybean height 120 d after planting. None of the herbicides influenced soybean density. Chlorimuron and imazaquin reduced soybean seed yield linearly as rates increased. None of the herbicides reduced subsequent wheat yield. Corn height reduction increased as the rate of imazaquin and imazethapyr increased. Imazethapyr and imazaquin caused 2 to 40% and 1 to 12% height reduction at 30 d after planting, respectively. Imazethapyr at 310 g/ha applied the previous year reduced corn height at 120 d after planting. There were no differences in corn density. Imazaquin and imazethapyr at 420 and 310 g/ha, respectively, applied the previous year reduced corn yield.

Understanding the biology of tropical soda apple (TSA) is necessary to develop effective control strategies. Tropical soda apple seedling emergence, growth, and regeneration from roots were evaluated. Plant growth (height, leaf number, flowering) was monitored over 110 d in a greenhouse experiment. Emerged seedlings required 83 d to reach a height of 40 cm and 108 d to flower. Total nonstructural carbohydrate concentrations in TSA root and stem fractions, monitored monthly for 1 yr, were highest in December (35%-root, 18%-stem). Seedling emergence as affected by planting depth (0, 1, 2, 4, 8 cm) and regeneration from root segments (7.5, 15 cm long) placed on the soil surface and 5 and 10 cm deep were studied in separate greenhouse experiments. Seedling emergence was lowest (P < 0.05) for seed placed on the soil surface (6.9%) and at a depth of 8 cm (19.4%) with the highest level of TSA emergence predicted at 63% for seed planted 3.6 cm deep. Regeneration from roots was higher (P < 0.05) for the 15-cm root segments than for the 7.5-cm segments while depth of root segment placement did not affect regeneration. Weed control strategies should involve cultural and chemical practices that affect both roots and seeds.

Detectspray™ weed-activated sprayer (WAS) technology enables individual nozzles on a sprayer to turn on and off in response to the presence of green vegetation. WAS operated full season at two fallow sites in North Dakota reduced POST herbicide requirement 47 to 88%. Full-season WAS applied as needed at West Fargo reduced cost to the farmer by only 13% compared with broadcast application with a farmer-owned sprayer and assuming free labor. Winds of 8 to 16 km/h apparently moved spray off target, thereby necessitating retreatment and increasing the relative costs of WAS at Fargo. The percentage of sample quadrats having greater than 3% vegetative cover correlated positively (r = 0.78 to 0.80) with percentage reduction in spray volume achieved by WAS.

Imazapyr, imazaquin, and imazethapyr were evaluated for control of leafy spurge. Herbicides were applied at 70, 140, and 280 g ae/ha in Fall 1989, 1990, or 1991 on a sub-irrigated meadow near Ainsworth, NE and a tallgrass prairie near Columbus, NE. Imazapyr, imazaquin, imazethapyr at 280 g/ha controlled leafy spurge 58, 82 and 73%, respectively, 9 mo after treatment (MAT) at Ainsworth. Leafy spurge control averaged 49% 9 MAT at Columbus where 280 g/ha of the imidazolinone herbicides were applied. Leafy spurge yields were reduced at Ainsworth by 29 and 78% where the imidazolinones were applied at 140 and 280 g/ha. By 11 MAT, leafy spurge control on areas treated with 280 g/ha declined to less than 60% at Ainsworth and 10% at Columbus. Perennial forage grass yields at both sites were generally unaffected by imazaquin or imazethapyr, but imazapyr at 280 g/ha reduced yields by 69 and 44% at Ainsworth and Columbus, respectively. Imidazolinone herbicides applied in the fall partially controlled leafy spurge, but did not increase perennial forage grass yields.

A long-term study was conducted at Lethbridge, Alberta, to determine the response of weed populations to various crop rotations and tillage treatments. Weed density and species composition differed with rotation, tillage, and date of sampling within years. Fewer weeds were found in winter wheat-fallow than continuous winter wheat, winter wheat-lentil, or winter wheat-canola rotations. A dense infestation of downy brome developed in the continuous winter wheat rotation. In all rotations, more weeds were present in zero tillage plots than in either minimum or conventional tillage plots. Dandelion and perennial sowthistle densities increased slightly over years in the minimum and zero tillage treatments. Flixweed, field pennycress, wild buckwheat, and common lambsquarters densities decreased in zero till but densities of downy brome, redroot pigweed, and Russian thistle increased. Russian thistle was not well controlled with trifluralin and its density increased in the winter wheat-canola rotation.

Kansas and North Dakota kochia populations identified as chlorsulfuron resistant (R) contained 20 and 30% susceptible (S) plants, respectively. Biotypes that were chlorsulfuron R or S were selected from each field R or S collection and selfed through three generations in the greenhouse. Chlorsulfuron at 7.6 and 17.8 g ai/ha suppressed shoot biomass of the Kansas and North Dakota R biotypes by 50%, respectively, which was a 30- and 105-fold greater dose than that required to reduce the respective S biotypes growth 50%. The R and S kochia biotypes are diploid with 2N = 18 chromosomes. Chlorsulfuron resistance is inherited in kochia as a dominant trait controlled by a single nuclear gene. Thus, the resistance trait can be spread by seed and pollen.

Pecan trees subjected to different weed control and irrigation regimes from planting in 1986 through 1993 produced similar yields when irrigated (400 kg/ha, 3-yr avg) and not irrigated (320 kg/ha, 3-yr avg). Trees receiving total chemical weed control produced over five times more pecans (735 kg/ha, 3-yr avg) than weedy trees (131 kg/ha, 3-yr avg). Trees receiving disking produced more pecans when irrigated (677 kg/ha, 3-yr avg) than when not irrigated (339 kg/ha, 3-yr avg). Growth rate, expressed as increase in tree stem diameter, decreased for trees in all treatments once trees began bearing.