Field research from 1986 to 1988 evaluated control of alfalfa, dandelion, orchardgrass, and annual weeds in corn with sequential herbicide treatments. Glyphosate applied the previous fall controlled 95% or more of the dandelion and orchardgrass before postemergence treatments. Atrazine applied early preplant or with paraquat the day before planting only partially controlled the perennial species. Atrazine applied postemergence usually controlled vegetation escaping initial treatment except orchardgrass following the atrazine treatments. Adding tridiphane increased weed control with atrazine or cyanazine applied postemergence only when fall panicum was present. Herbicides applied postemergence increased corn yield compared to the initial treatments alone, and few differences among postemergence treatments were observed. Sequential treatments which included glyphosate applied in the fall controlled 82% or more of each perennial species before the next growing season. Orchardgrass control was 81% or less the following spring when the initial treatment was atrazine or atrazine plus paraquat.

Annual applications of three nitrogen (N) rates, two broadleaf herbicides, and six annual-grass herbicides in Kentucky bluegrass (Poa pratensis L.) turf were made from 1974 to 1981. With each increment increase in N (2, 4, and 6 kg N/200 m2), the percentage cover of crabgrass (Digitaria spp.) and number of common dandelion (Taraxacum officinale Weber # TAROF) plants were reduced when compared with the next lower rate. There was an interaction between crabgrass control by the annual-grass herbicides and fertilizer rates. When highly effective herbicides were used, there were no differences in crabgrass control related to N rate. When less effective herbicides or no annual-grass herbicides were used, there were great changes directly related to N rate. Each increment of increased N rate increased the turf quality rating. The broadleaf herbicides resulted in differential quality ratings, although differences were relatively small. Highest quality ratings were for plots treated with the three most effective annual-grass herbicides. Residues in the ppb range of some herbicides were detected in soils sampled about a year after the eighth annual herbicide treatments, but residues were below the phytotoxic level and therefore would have had no effect on control of weeds.

Sweet corn was grown with a living mulch of white clover, a dead mulch of rye, and without mulch, in both till and no-till conditions. Unplanted controls were also included in the experimental design. Corn yields were highest in clover treatments early in the experiment but lowest in later years. The declining yields in the clover living mulch were related to the strip application of glyphosate which allowed establishment of perennial and biennial weeds, notably dandelion and horseweed. These overwintering weeds apparently prevented effective control of summer annuals, especially redroot pigweed, common lambsquarters and large crabgrass, by atrazine and metolachlor. Presence of a rye mulch decreased weed biomass and had no detrimental effect on corn yield. In general, corn yield was not affected by tillage, although the number of marketable ears was reduced in the no-till treatments during the drought year of 1988. The much greater weed biomass in the unplanted control treatments showed the importance of crop competition for weed control in sweet corn cropping systems.

The efficacy of nine granular formulations of a bioherbicide containing the fungus Sclerotinia sclerotiorum (Lib.) de Bary was determined by assessing vegetative growth from tap roots of treated plants after incubation in a controlled environment. Plants treated with formulations 0788-03 or 0788-04 did not produce new petioles and leaves from tap roots after 96 h at 23 C and 100% relative humidity.

Spring-applied herbicides were evaluated in field studies conducted in 1985 through 1987 in western Nebraska for selective weed control in irrigated established alfalfa. Imazethapyr, norflurazon, pendimethalin, and prodiamine did not injure alfalfa but varied in their weed control spectrums. Overall weed densities were lowest in plots treated with norflurazon at 2.8 kg ai/ha and diuron at 1.8 kg/ha.

A method is presented to determine which of a set of sampling techniques is most nearly optimum for sampling weed abundance. To employ the method, one needs first to develop a set of sampling alternatives. A pilot survey is then conducted to determine time costs and sampling and measurement error variances associated with each technique. We used this method to determine which of three plot sizes (0.6 by 0.6 m, 0.6 by 1.5 m, 1.2 by 2.1 m) and two types of orchard scans is most nearly optimum for estimating weed abundance in apple [Malus domestica (Bork)] orchards. The results indicate that, for weed species that are fairly apparent, orchard scans are optimal when less than 8 h of sampling effort is expended, but when a high degree of precision is required, or when the weed species is more difficult to detect, plot samples may be the better choice. A size of plot ca. 0.6 by 1.5 m size was found to be most nearly optimum.

Large crabgrass [Digitaria sanguinalis (L.) Scop. ♯ DIGSA] control was higher when either DCPA (dimethyl tetrachloroterephthalate) or napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] was applied to bermudagrass [Cynodon dactylon (L.) Pers. ‘Common’] growing in soil with a pH of 5 than in soil with a pH of 6.4 in 2 of 3 yr. Soil pH did not influence the response of large crabgrass to oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] or benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine). Herbicides alone did not produce high-quality turf unless fertilizer was applied annually at 300 kg N/ha or more. Bermudagrass quality was higher after three yearly applications of 300 kg N/ha or more of fertilizer when soil pH was 5 than when soil pH was 5.6 or 6.4.

Field experiments were conducted to compare non-phenoxy herbicides with 2,4-D for broadleaf plantain, dandelion, and white clover control in cool-season turf. Herbicides tested were BAS 514, chlorflurenol, clopyralid, dicamba, triclopyr, and 2,4-D, alone and in combinations. Broadleaf plantain was controlled by 2,4-D and by clopyralid plus triclopyr at 0.21 plus 0.63 kg ae ha-1. Dandelion was controlled by 2,4-D, BAS 514 at 0.84 kg ha-1, and by the combination of clopyralid plus triclopyr at 0.16 plus 0.47 kg ha-1. Chlorflurenol, clopyralid, dicamba, or triclopyr did not control dandelion. White clover was controlled by all herbicides except 2,4-D. The combination of clopyralid plus triclopyr was the only non-phenoxy treatment which controlled broadleaf plantain, dandelion, and white clover.

Several plant growth regulators applied to established sod driveways in an apple orchard suppressed growth of the ground cover sufficiently to eliminate one to three mowings. MH at 4.5 or 6.7 kg ai/ha applied spring and fall reduced the growth of a single species sod cover crop, ‘Kentucky 31’ tall fescue, the year after treatment. MH at both rates also reduced the dandelion population growing in the mixed species orchard sod. Paclobutrazol or EPTC applied in the spring before or during initial grass growth reduced dry matter production in the fescue sod cover crop and the number of mowings compared to the mowed and non-mowed control plots.