The effect of glyphosate on growth and reproduction of two pathogenic fungi of green peas was evaluated in laboratory studies. Liquid and agar media containing 0 to 50 mM glyphosate were inoculated with two isolates each of Fusarium solani f. sp. pisi and Pythium ultimum. Mycelial growth and spore production of the fungi were inhibited or stimulated by glyphosate, depending on concentration. Glyphosate did not affect pathogenicity of F. solani f. sp. pisi. The effect of glyphosate on pathogenicity of P. ultimum was not determined. Under field conditions, glyphosate probably would not affect pathogenicity or survival of either fungus.

Horsenettle is a deep-rooted perennial weed that cannot be easily controlled by mechanical means or by a single chemical application. A study was conducted at two sites for two consecutive years to identify biological factors that might limit its growth. Insects, nematodes, and plant pathogens were collected from horsenettle growing in bermudagrass pastures. The insects most commonly found included the Colorado potato beetle and the eggplant flea beetle. An unidentified lepidopteron, family Gelechiidae, was found at very low frequency as pupae in hollow leaf chambers constructed at the apices of flowering meristems. Infested apices bore no fruit. Seven genera of nematodes were found in the soil at both sites, but only very low numbers of lesion nematodes were recovered from horsenettle roots, and these had caused little damage. Root rot was observed under wet soil conditions on plants damaged by trampling. A downy mildew was prevalent at both sites in both years in October.

The DNA sequence of a 196 base pair (bp) region of the acetolactate synthase (ALS) genes of three weed species, kochia, prickly lettuce, and Russian thistle, was determined. This region encompasses the coding sequence for Domain A, a region of the amino acid sequence previously demonstrated to play a pivotal role in conferring resistance to herbicides that inhibit ALS. The Domain A DNA sequence from a chlorsulfuron-resistant (R) prickly lettuce biotype from Idaho differed from that of a chlorsulfuron-susceptible (S) biotype by a single point mutation, which substituted a histidine for a proline. The Domain A DNA sequence from an R kochia biotype from Kansas also differed from that of an S biotype by a single point mutation in the same proline codon. This point mutation, however, conferred substitution of threonine for proline. Two different ALS-homologous sequences were isolated from an R biotype of Russian thistle. Neither sequence encoded amino acid substitutions in Domain A that differed from the consensus S sequence. The DNA sequence variation among the R and S kochia biotypes was used to characterize six Ada County, Idaho, kochia collections for correlation between phenotypic chlorsulfuron susceptibility and restriction digest patterns (RFLPs) of polymerase chain reaction amplification products. Most collections showed excellent correspondence between the RFLP patterns and the phenotypic response to chlorsulfuron application. However, one entirely R collection had the RFLP pattern of the S biotype, suggesting that resistance was not due to mutation in the proline codon.

The photolytic degradation of several imidazolinone herbicides in solution and on soil was investigated. Ultraviolet light caused 100% degradation of imazaquin, imazethapyr, and imazapyr, and 87 and 8% degradation of imazamethabenz and atrazine in aqueous solutions, respectively, after 48 h. The order of susceptibility to photolysis in decreasing order was imazaquin = imazethapyr > imazapyr > imazamethabenz > atrazine. In soil Studies, 45% of imazaquin and 52% of imazethapyr dissipated from moist sand after 48 h of exposure. Herbicide dissipation on air-dry sand and on field capacity and air-dry silty clay loam was less than 10% in most instances. Atrazine photolysis was not detected. This research indicates that photolysis of imidazolinone herbicides in solution is rapid. Photolysis on soil occurs readily on coarse-textured wet soils probably due to greater availability of the herbicide for photochemical alteration.

Metazachlor degradation in soil was studied in fields of spring barley, turnips, brussels sprouts, and leeks. Metazachlor in soil was transformed into 2-hydroxy-N-(2,6-dimethylphenyl)-N-(1H-pyrazol-1-yl methyl)-acetamide (compound 2), 2-chloro-N-(2,6-dimethylphenyl)-acetamide (compound 3), and 4,4′-methylenebis-(2,6-dimethylbenzenamine) (compound 4). Soil concentrations of compound 4 were always lower than 0.1 ppm. The half-life of metazachlor in the 0- to 10-cm soil layer was 1 to 3 mo. Metazachlor and compounds 2, 3, and 4 were not detected in the 10- to 20- and 20- to 30-cm soil layers. Metazachlor and metabolites (compounds) 2, 3, and 4 were not detected in barley grain or in the edible part of the vegetables. The sensitivity limit for these compounds was 0.02 ppm.

Efforts to screen and mass-rear insects and diseases for leafy spurge biocontrol agents have been hampered by low success in propagation and slow growth of leafy spurge in the greenhouse. The optimum greenhouse conditions for leafy spurge growth were determined. Leafy spurge was propagated from stem tip cuttings, with the basal end treated with 0.2% NAA, and the plants misted with water for 10 d. Optimum conditions for growth were 27 C air temperature, application of a complete fertilizer at 70 kg ha−1 weekly or 135 kg ha−1 biweekly 20 d after stem tip propagation, in a peat/perlite/vermiculite growth medium at pH 7 and a 16-h photoperiod. Regrowth from roots of parent plants was improved when cuttings were taken from plants at least 60 d old, and plants grew nearly twice as rapidly when the medium was maintained at 30 C compared to 22 C. Refrigeration of stem tip cuttings or roots before planting did not affect survival or growth vigor. Only gibberellic acid of nine plant growth regulators evaluated increased growth, but plants were etiolated. Biotypes from Nebraska and South Dakota were shorter than five others from the United States or Austria but had similar root and shoot dry weight. The time required to propagate vigorous leafy spurge was reduced to 2 mo compared to 6 mo required prior to the study.

Ducksalad, an annual broadleaf weed in rice, was infested by waterlily aphid which destroyed much of the above-water vegetation. Field experiments showed aphids reduced total weed biomass by 58 and 87% in 1985 and 1986, respectively. Biomass of seed pods was reduced by more than 82% in both years.

Adsorption and desorption of metribuzin and metolachlor were studied for 0- to 15- and 30- to 45-cm soil depths and at 5 and 28 C temperatures for two subarctic Alaskan agricultural soils. Surface soils had five to eight times the organic carbon content of deeper soils and had lower Freundlich isotherm slopes (1/n) for both herbicides. Surface soil Freundlich coefficients (Kf) were affected by both soil type and equilibration temperature, with soil type accounting for greater than 80% of the variation in Kf. Surface soil mean Kf values ranged from 1.5 to 2.4 for metribuzin and 4.4 to 9.2 for metolachlor. For soils from the 30- to 45-cm depth, neither soil type nor temperature affected Kf. Isotherm slopes for desorption were less than adsorption, indicating hysteresis. Regressions between desorption Kf and maximum herbicide adsorbed prior to desorption were highly significant with coefficients of determination (r2) between 0.50 and 0.99.

A system, including a specialized treatment vessel for pesticide uptake studies, was developed and experiments were carried out to determine the ability of Glomus intraradices (Schenck & Smith), G. vesiculiferium (Thaxter), and indigenous vesicular-arbuscular mycorrhizae (VAM) fungi to influence 14C-atrazine uptake and transfer to corn. Uptake by root systems with and without VAM infection was compared to uptake by VAM hyphal systems by controlling access to 14C-atrazine-treated soil. Hyphal systems of Glomus species were able to remove 14C-residue from soil and transfer these to corn. Amount of 14C-residue transferred to corn through hyphal systems was highly correlated to the level of VAM root infection which varied among VAM species. In root systems, variations in 14C-residue uptake resulting from mycorrhization were largely explained in terms of the negative correlation between level of infection and root mass located in 14C-atrazine-treated soil. Allocation of 14C-residue to shoot tissues of corn was greater when 14C-residues were taken up through root systems rather than through hyphal systems. There were significant effects of VAM species on 14C-residue compartmentalization between methanol extractable and nonextractable portions of corn tissues. Data from these experiments in a confined soil system were related to VAM cost-benefit relationships and indicate a significant role for VAM in determining atrazine fate in agricultural systems.

Manuscripts on the biology, physiology, or control of weeds, and on herbicides, growth regulators, or related topics will be considered for publication in Weed Science. Each manuscript must contain original material constituting a logical unit of related subject matter and must contribute to the advancement of knowledge. Acceptance is made with the understanding that the substance of the manuscript has not been and will not be published elsewhere other than as an abstract. Progress reports, unreplicated experiments, or simple observational information are not acceptable. Most experiments should be repeated in time or space and must provide confirming results. If repeated experiments do not provide confirming results, additional research may be required to determine why. Use objective measurements of responses; visual assessments are generally acceptable only as supportive evidence.

Harold Alley, Professor of Merit at the University of Wyoming, died in the summer 1991. He was an extension weed scientist, but he also conducted extensive research in range weed control, especially revegetation of range areas with herbicide and cultural management practices in grazing situations. He was very active in the Western Weed Science Society and was a fellow of WSSA. He also received the WSSA Outstanding Extension Specialists Award. He is survived by his wife Jean and three children.