Experiments were conducted in 1990 and 1991 to determine bioavailability of PRE herbicides at three soil profile depths and two soil types in established common bermudagrass sods. Prodiamine and oryzalin reduced ‘Tifgreen’ bermudagrass root growth in the 5- to 7.5-cm layer of a Bosket very fine sandy loam soil at 2 and 4 wk after treatment in 1991. These herbicides decreased bermudagrass root weight in both the Bosket and Marietta sandy clay loam both years in samples taken from the 2.5- to 5-cm depth layer. In the 0- to 2.5-cm soil layer, all herbicides reduced root weight in 1990. In a bioassay, prodiamine caused decreased Tifgreen bermudagrass root growth at concentrations as low as 4 ppb by wt in the very fine sandy loam soil, while 8 ppb was necessary in the sandy clay loam soil. Prodiamine was detected in the very fine sandy loam at 4 wk after treatment at all depths in 1991 (65, 45, and 39 ppb in the 0- to 2.5-, 2.5- to 5-, and 5- to 7.5-cm soil layers, respectively). Oryzalin was also detected at all depths in 1991 when sampled at 2 and 4 wk after treatment in the very fine sandy loam. Pendimethalin was present in concentrations of 38, 39, and 37 ppb in the sandy clay loam at 2 wk after treatment in the 0- to 2.5-, 2.5- to 5-, and the 5- to 7.5-cm soil layers, respectively. Pendimethalin was also detected in the very fine sandy loam at 2 wk after treatment at concentrations of 55, 69, and 36 ppb in the 0- to 2.5-, 2.5- to 5-, and 5- to 7.5-cm soil layers, respectively.

Irrigated sandy soils have a high potential for leaching of agricultural chemicals to ground water. Objectives of this study were to determine the movement and persistence of metolachlor applied annually to a Hubbard loamy sand soil (Udorthentic Haploboroll) under irrigated potato production. Metolachlor was applied to the plots at rates of 1.7 and 3.4 kg ai ha-1. A KBr tracer was applied to the same plots at the rate of 130 kg ha-1. Intact soil cores were collected before and after herbicide application during the cropping season. Water samples were collected weekly from suction samplers, 90 and 150 cm deep in each plot, during the growing season. Potato yields of 60 and 59 Mg ha-1 in 1989 and 1990, respectively, were above Minnesota state averages. Bromide tracer data confirmed the movement of water through the soil profile to at least a 150-cm depth. No detectable quantities of metolachlor were found below 30 cm in soil during either year. Time for dissipation of 50% of metolachlor ranged from 85 to > 106 d. Dissipation in 1990 appeared slower than in 1989 and residues remaining at the end of the season, averaged across application rates, were 44 and 64% in 1989 and 1990, respectively. No water samples contained metolachlor in 1989. Metolachlor was detected in 18 of 409 water samples collected during and after the growing season in 1990. Median detectable concentration of metolachlor was 0.4 μg L-1 in water samples from suction samplers at 90- and 150-cm depths in eight of 16 plots. Metolachlor Kd and Koc values, 3 and 220, respectively, were similar to reported values. Metolachlor sorption in the soil profile was correlated, in order of contribution, to organic carbon content, cation exchange capacity, percent sand, and percent clay.

This study was conducted to determine if field evaluations could be used to select insects for biological control of musk thistle. Host specificity and larval development of a weevil, Hadroplonthus trimaculatus, and a fleabeetle, Psylliodes chalcomera, were studied in field trials near Rome, Italy, in which insects were allowed free choice of several hosts. Natural populations of these two insects, which do not occur in North America, were exposed to North American species of Cirsium, Carduus, and selected crops. Adult insects and larvae on host plants were identified and counted on test plants from North America and native attraction plants. In addition to infesting musk thistle, weevil adults and larvae were recorded on flodman thistle, wavyleaf thistle, and spinosissimum thistle. Consequently, this insect was not suitable for introduction into North America. The fleabeetle would be satisfactory for biological control since no adults or larvae were recorded on Cirsium spp. or economic plants. These studies show that field trials are a valid method for identifying specific and nonspecific candidate insects for biological control of weeds.

Terbufos and primisulfuron interactions were evaluated under growth chamber conditions using a sand culture system. Terbufos was applied to transplanted corn seedlings, followed in 5 d by foliar applications of primisulfuron plus nonionic surfactant. Primisulfuron and terbufos alone did not cause corn injury; however, shoot dry weight and shoot length were reduced 28 and 36% in terbufos treatments 96 h after primisulfuron application. Primisulfuron absorption and translocation were not affected by terbufos, but the half-life of primisulfuron increased from 2 to 3.5 h in terbufos treatments. Terbufos did not affect primisulfuron metabolite profiles. The basis for increased primisulfuron phytotoxicity in terbufos treatments appeared to result from reduced primisulfuron metabolism.

A survey was conducted in Mississippi from 1976 and in Arkansas and Louisiana from 1977 through 1991 to determine annual variation of johnsongrass infestation in cotton and soybean fields. The survey route was 1534 km long. Levels of johnsongrass infestation were estimated in 752 ± 296 cotton fields and 884 ± 407 soybean fields in each year of the survey. The area of fields surveyed annually was 47 000 ± 21 000 ha of cotton and 52 000 ± 19 000 ha of soybeans. Johnsongrass was present in 55 to 90% of the cotton fields. The percent of cotton fields with johnsongrass was about the same in 1991 as in 1976–77. About 90% of the soybean fields in Mississippi and Louisiana had johnsongrass, but only 70 to 80% of soybeans fields in Arkansas had johnsongrass. Soybean fields with 1 to 5% levels of infestation increased slightly in Mississippi but remained about the same in Arkansas and Louisiana. Soybean fields with infestations of 6% or more slightly decreased in Arkansas and Louisiana but not in Mississippi. It was estimated that johnsongrass reduces the average annual value of harvested cotton $5.8 ± 1.9 million and soybeans $23.7 ± 0.6 million in the three states.

A strain of Fusarium oxysporum was isolated from infected sicklepod stems in Stoneville, MS, in 1989. When formulated as granules either in a fungus-infested rice preparation or encapsulated in a wheat-gluten matrix called ‘Pesta’, biocontrol of sicklepod, coffee senna, and hemp sesbania was achieved with preemergence or preplant-incorporated treatments. Liquid conidial applications were less effective. Plants were killed by a preemergence damping-off. Applications made postemergence were significantly less effective. Results of these tests suggest that this fungus has potential as a mycoherbicide for controlling sicklepod, coffee senna, and hemp sesbania.

Leaf washing was used to determine relative rates of uptake of 2,4-D and dicamba dimethylamine salts by wheat following field application of a postemergence tank mixture (3:1) of 476 g ae ha-1 at the 4- to 5-leaf growth stage. Foliar herbicide deposits and total acid residues in the crop were determined the day of spraying as well as 2 and 7 d after spraying. Leaf washing of foliage samples collected on the day of spraying indicated that the crop/weed canopy intercepted 51% of the application, and that dicamba was taken up more quickly than 2,4-D. Within a few hours of spraying, approximately 80% of the deposited dicamba and 65% of 2,4-D were taken up by the crop. A 35-mm rain during the first 48 h after application reduced plant surface deposits of both herbicides by more than 98%. During this 2-d period, dicamba residues within the crop were metabolized more quickly than those of 2,4-D. There was little difference in effectiveness among water, 10% methanol, 25% methanol, or 90% methanol in removing plant surface deposits of 2,4-D and dicamba from wheat.