Barnyardgrass and many broadleaf weeds were severely stunted by POST applications of isoxaben. Most grasses were only moderately affected by isoxaben at rates up to 1 kg/ha. POST activity was enhanced by soil interception, but evident with foliar interception alone. Cell swelling in stems and in interveinal leaf lamina was observed after foliar application. A radiotracer study in redroot pigweed showed that only a small amount (3.3% of applied) of isoxaben entered the leaf following foliar application, and that little (0.08% of applied) isoxaben migrated beyond the point of application. The potential of isoxaben as a POST herbicide may be limited, in part, by poor absorption and translocation.

Soil-water profiles of cotton, several weeds, and bare soil were compared in research conducted in 1989 and 1990 near Perkins, OK. Neutron probe access tubes were installed prior to plant establishment to facilitate nondestructive volumetric water content determinations at selected depths throughout the season. Planting was in a double-circle pattern concentric around each neutron probe access tube. Phenological and soil-water data were collected weekly. As plants began to senesce, aboveground biomass yield data were collected. In 1989, rainfall frequently replenished soil-water in the upper soil profile. The plants used the recharge water to varying degrees, particularly late in the season. Common cocklebur and johnsongrass extracted soil-water from greater depths than cotton and velvetleaf throughout the season. In 1990, the largest differences detected between bare soil and weeds early in the season were measured for common cocklebur, devil's-claw, and silverleaf nightshade. Later in the season, however, there was little difference in soil-water content in the upper soil profiles for all species. Johnsongrass emerged later than the other species in 1990 which affected its relative soil-water extraction.

Eight POST herbicides were evaluated alone or in various mixtures for spiny amaranth control in peanut in 1991 and 1992. Acifluorfen alone or in combination with bentazon, lactofen alone, or 2,4-DB alone applied late POST controlled spiny amaranth more than 80% at an early season rating. Lactofen applied early POST and 2,4-DB applied late POST controlled more than 90% late season. Imazethapyr and AC 263,222 controlled 72 to 90% of spiny amaranth, whereas bentazon and pyridate failed to provide adequate control.

Three corn root bioassays were evaluated for detecting imazaquin in soil. Two techniques, one which utilized a cone-shaped tube as the growth container and another, a petri dish, were compared to a method that utilized a thin layer of soil between two 20 by 20 cm glass plates. Corn root growth responded logarithmically to imazaquin regardless of bioassay method. Corn was most sensitive to low imazaquin concentrations when grown using the glass plate apparatus. At a low concentration (0.5 ng/g) of imazaquin, corn root length was reduced 6% using the cone-tube, 2% using the petri dish, and 24% using the glass plate method. In contrast, the cone-tube method provided a better measure of high imazaquin concentration (200 ng/g) than the other methods.

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.

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.

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.

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.

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.

Various mechanical plus chemical weed control systems for dry bean production were evaluated at Carrington, ND and Crookston and Staples, MN during 1991 and 1992. A dozen tillage plus herbicide weed control systems are available to growers that can provide selective and effective weed control in dry beans without reliance on chloramben—a standard herbicide on dry beans that has been lost. Dry bean yields were similar with low or high level tillage treatments because most of the herbicide treatments with one cultivation gave adequate weed control and any additional tillage did not improve weed control. Kidney bean yields and prices were greater than either pinto or navy beans so the net returns (bean market value minus production costs) were much greater for kidney bean production. Dry bean producers in the North Central part of the U.S. have at their disposal dependable mechanical plus chemical weed control systems, and their market value has been sufficient to make dry bean production very economical in this region.

This study characterized the emergence pattern of a weed community of 16 species between April 1 and August 31 over a 7-yr period. Weed seedlings were counted weekly in quadrats established in winter wheat stubble within no-till and conventional-till production systems. Weed emergence showed two peaks, the first between April 25 and May 9, and the second between May 30 and June 13. Tillage did not affect the weed community emergence pattern. Knowledge of weed community emergence pattern in conjunction with crop simulation models could be used to suggest cultural practices such as optimal planting dates that favor a crop over weeds, and possibly reduce herbicide use for within-crop weed control.

The sensitivities of tobacco, tomato, pepper, and cucumber seedlings to an aquatic herbicide, fluridone, were examined in growth chamber and greenhouse studies. New leaves of tobacco seedlings became chlorotic after 6-d exposure to fluridone concentrations of 5 μg/L or greater in hydroponic float culture, and dry weights were significantly reduced at 100 μg/L or greater. When treated only once at the beginning of a 2-wk evaluation period, all crops except cucumber exhibited injury symptoms at 100 μg/L. When grown in sand, pepper and tomato were injured at 25 μg/L; tobacco injury occurred at 10 μg/L. Dry weights of pepper, tobacco, and tomato seedlings decreased significantly at 250, 50, and 250 μg/L, respectively, on potting mix; effects on dry weights were not significant for plants on sand. Cucumber was injured by treatment at 100 μg/L or greater in sand, but there were no effects on dry weights in either sand or potting mix. When treated three times weekly for 2 wk with fluridone, pepper, tobacco, and tomato grown in potting mix were injured by 50, 25, and 100 μg/L; when grown in sand, injury occurred at 10, 5, and 10 μg/L, respectively. Dry weights of pepper, tobacco, and tomato were reduced by 50,50, and 100 μg/L, respectively, in potting mix; effects on dry weights were not significant for plants in sand. Cucumber seedlings were damaged by 250 μg/L or higher on potting mix and 100 μg/L or higher on sand, but there were no effects on dry weights regardless of substrate. Threshold injury levels for plants grown in potting mix to the second true leaf stage and then treated three times weekly were 25 μg/L for pepper and tobacco and 50 μg/L for tomato; dry weights were significantly reduced in pepper at 25 μg/L and in tobacco and tomato at 50 μg/L. Cucumber seedlings were not injured by any treatment in this test.

The repeated use of sulfonylurea (SU) herbicides to control broadleaf weeds in wheat fields and right-of-ways has selected for herbicide-resistant Russian thistle populations. A survey was conducted in 1991 and 1992 to ascertain the relative occurrence of SU-resistant Russian thistle in eastern Washington state. The 55 574 km2 survey area was divided into 149 equal sample areas. All sample areas were surveyed for Russian thistle and seed was collected from plants in 86 sample areas. No Russian thistle was found in the center of the remaining 63 sample areas. Seeds were collected, by plant, from 30 plants at each site. Site samples were tested in the greenhouse for resistance or susceptibility to chlorsulfuron. Populations that were either homogeneous or heterogeneous for chlorsulfuron-resistance were found in 70% of the sample areas and all of the plants were susceptible in 30% of the sample areas.

Redroot pigweed is a major weed worldwide. Increasing emphasis on modeling physiological processes of weeds for use in weed control decision support systems requires a knowledge of the response of weeds to resource levels and environmental conditions. The purpose of this study was to determine functional relationships for carbon exchange rate (CER) and transpiration based on photosynthetic photon flux density (PPFD) and temperature from measurements made on field-grown redroot pigweed. Measurements were made using a portable photosynthesis system on four dates. An equation that had the form of a power function on PPFD and a quadratic polynomial on temperature was fit to the data. The equation fit the measured CER data better than the measured transpiration data. The equations should be useful in modeling the physiological processes of pigweed within crop canopies.

Metham was applied in the dormant season to established cranberry for the control of false lily-of-the-valley. Rates of 108 to 214 kg ai/ha controlled false lily-of the-valley, but there were inconsistent results between years and fields. Soil temperature, organic matter content, and amount of water used for incorporation appeared to be important factors in determining results. The phytotoxicity of metham sodium to cranberry was sporadic, ranging from moderate at 214 kg ai/ha to severe at 108 kg ai/ha. The 142 kg ai/ha rate usually resulted in an acceptable level of crop injury. Sanding the bog after application reduced phytotoxicity and heat stress increased it.

Field research was conducted at Rosemount, MN in 1990 and 1991 to determine the effect of starch encapsulation on weed control in corn with alachlor, metolachlor, and atrazine under two weed densities. At low weed densities (122 total plants/m2), giant foxtail and Pennsylvania smartweed control were not different with full rates of herbicide applied in starch encapsulated or commercial formulations. Velvetleaf control was less with starch-encapsulated than commercial formulations regardless of velvetleaf density. At high giant foxtail densities (740 plants/m2), control was not affected by formulation with full rates of alachlor plus atrazine. However, giant foxtail control was less with starch-encapsulated formulations than commercial formulations with 75% rates of alachlor plus atrazine and both 75 and 100% rates of metolachlor plus atrazine. At low weed densities, corn yield was not different with any treatment, except starch-encapsulated metolachlor plus atrazine at 75% rates, compared to the weed-free control. Alachlor plus atrazine at full rates was the only starch-encapsulated treatment to result in corn yield not different from the weed-free control at high weed densities. Conversely, all commercial formulation treatments resulted in corn yields not different from the weed-free control at high weed densities.

The Spurgia esulae gall midge was introduced in North Dakota in 1986 as a biocontrol agent for leafy spurge. Spurgia esulae causes stem tip galls thereby decreasing seed production and it has been most successful near wooded areas. However, a second control method is needed to reduce the leafy spurge infestation and prevent spread from roots. Imazethapyr, 2,4-D, or picloram application did reduce the number of S. esulae galls but not the number of larvae per gall. Long-term S. esulae population was not affected by herbicide application. The integration of herbicides with S. esulae would prevent leaf spurge spread from a wooded area and would reduce seed production within an area where herbicides generally cannot be used.

Field experiments were conducted in Michigan, Minnesota, and Wisconsin to evaluate injurious interactions between nicosulfuron herbicide applied POST and nine insecticides applied at planting on ‘Pioneer 3751’ field corn in 1991. Insecticides were applied in-furrow, T-band, and surface band at planting. Corn injury from nicosulfuron and terbufos applications was more severe in Wisconsin than in Michigan. No corn injury was observed in Minnesota. Terbufos 15% ai granule (15G) or 20% ai controlled release granule (20CR) increased nicosulfuron injury to corn in Wisconsin. Nicosulfuron at 35 g ai/ha caused the greatest vigor reduction following terbufos 15G, intermediate vigor reduction following terbufos 20CR, phorate 20G, or phorate 20CR, and the least vigor reduction following fonofos, chlorpyrifos, chlorethoxyfos, tefluthrin, or carbofuran in Wisconsin.

Spent spearmint hay from mint that had been treated with clopyralid in the fall or spring injured ‘Russet Burbank’ potato planted into loamy sand soil amended with 50 g hay/kg soil. Lowering the ratio of mint hay to soil from 50 to 3.1 g/kg reduced, but did not eliminate, the injury to potato. Potato was inured by clopyralid at concentrations as low as 3 ppbw in soil.