The potential of imazethapyr as a selective herbicide in four pulse crops was investigated at Melfort, Saskatchewan in 1988 and 1989. Lentil, field pea, faba bean and annual vetch were tolerant to imazethapyr applied preemergence to a silty clay loam soil at 0.05, 0.10, 0.15, and 0.20 kg ai ha-1. Postemergence treatments above 0.05 kg ha-1, however, stunted lentil and vetch in both years. Environmental factors, the dominant weed in the experimental site, as well as timing of application strongly influenced the performance of imazethapyr. Seed yield increases observed with imazethapyr treatments, compared to metribuzin or untreated check, were greater in 1989 when wild oat was the dominant weed and moisture was not a limiting factor in the early stages of crop development, than in 1988 when field pennycress was the dominant weed. Mean seed yield for all imazethapyr treatments, compared to the check, increased 0 and 930%, 24 and 89%, 21 and 600%, and 47 and 44% in 1988 and 1989, for lentil, field pea, faba bean and vetch, respectively. Significant increases in lentil seed density, seed size, and germination were also obtained though protein content decreased 2%.

Combinations of thifensulfuron with carbaryl, chlorpyrifos, malathion, and methomyl caused soybean injury that exceeded the expected injury based on effects of herbicide and synergists applied alone. Thifensulfuron-induced injury and growth reductions generally increased as insecticide rates increased from 140 to 560 g ai ha-1. TBPT and fenarimol also synergistically enhanced thifensulfuron injury in soybeans. Yellow foxtail control by thifensulfuron was enhanced slightly by all insecticides except carbaryl. Insecticides did not enhance kochia control by thifensulfuron.

Chlorimuron applied postemergence at 2.2, 4.4, 8.8, 18, and 35 g ai/ha to cotton at either the 4-leaf, pinhead-square, first-bloom, or full-bloom growth stage was evaluated for potential as a plant growth regulator. Chlorimuron did not reduce bolls per plant at any rate or time of application, but the proportion of open to closed bolls decreased as rate increased. Seed cotton yields decreased with increasing chlorimuron rate and cotton age. The use of chlorimuron as a plant growth regulator for cotton appears limited.

Field experiments were conducted to determine effects of adding 2.8 kg/ha (NH4)2SO4 and/or substituting BCH 81508 S for crop oil with sethoxydim applied to large crabgrass, corn, johnsongrass, and common bermudagrass. Adding (NH4)2SO4 did not affect control of johnsongrass or common bermudagrass but did increase control of large crabgrass and corn by 6 and 15%, respectively. Cora control was enhanced more by (NH4)2SO4 at lower sethoxydim rates. Substituting BCH 81508 S for crop oil increased seedling johnsongrass, large crabgrass, common bermudagrass, rhizome johnsongrass, and corn control by 7, 9, 9, 10, and 15%, respectively. A sethoxydim rate by spray adjuvant interaction was observed with seedling johnsongrass, common bermudagrass, and corn where response to BCH 81508 S decreased as sethoxydim rates increased. The effects of substituting BCH 81508 S for crop oil and adding (NH4)2SO4 were independent.

The effect of the isopropylamine salt of glyphosate and the ethyl ester of quizalofop on the rhizome bud viability of five quackgrass biotypes was tested. Two bioassays used were: direct measure of the growth of the bud on an agar medium and determination of the respiratory activity with tetrazolium chloride. The response to herbicide treatments differed among biotypes. The growth bioassay showed lower viability than the tetrazolium bioassay. Quizalofop reduced viability more than glyphosate. Viability of untreated buds increased with increasing distance from the base of the rhizome. The viability of herbicide-treated buds was more or less equal regardless of the position. It appeared that both herbicides were translocated to all the rhizome buds.

Primary tillage is an inexpensive method to control foxtail barley, a perennial bunchgrass which is an increasing concern to no-till cereal farmers in the Northern Great Plains. Moldboard plowing or chisel plowing in fall followed by field cultivation-harrowing in spring effectively controlled established foxtail barley on previously untilled sites before planting spring wheat. In contrast, chisel plowing in spring followed by field cultivation-harrowing did not control this weed completely.

Field experiments were conducted to evaluate the critical period for velvetleaf interference with cotton and to assess the reliability of using weed growth variables as predictors of cotton lint yield losses. An inverse linear relationship existed between velvetleaf dry weight and cotton lint yield. The relationship between the number of velvetleaf main-stem nodes or velvetleaf height with cotton lint yield was best described by quadratic regression equations. Weed dry weight appeared to be the most accurate predictor followed by weed height and by number of velvetleaf main-stem nodes. A nonlinear equation best described percent lint yield loss as a function of critical-period interference intervals.

Full-season johnsongrass competition reduced sugar yields by 53 and 44% in ‘CP 70–321’ and ‘CP 72–370’ sugarcane, respectively, primarily by reducing sugarcane stalk populations. Stalk population and height and sugar yields of both cultivars were optimized when asulam was applied at 3.7 kg ai/ha during April and early May. Asulam at 3.4 kg/ha, applied a second time 8 weeks later, generally increased johnsongrass control but did not increase sugar yields over one early application. By delaying the application, the potential for sugarcane injury from asulam applied once or twice increased in both cultivars. Injury appeared to be related to the stage of sugarcane growth and temperature and moisture stress at application time with asulam phytotoxicity being more pronounced in CP 72–370. Populations of johnsongrass stems in the year after treatment reflected the degree of johnsongrass control by asulam and the competitiveness of the crop in the previous year.

Pronamide was applied to a ‘Tifway’ bermudagrass golf green overseeded with perennial ryegrass during 1988 and 1989 to determine how herbicide rate and date affected ryegrass injury on transition back to a bermudagrass monostand. In most instances, perennial ryegrass was injured less when pronamide was applied at 0.28 or 0.56 kg ai/ha March 30 or April 13 than when application was delayed until April 28 or May 14. Perennial ryegrass injury lasted longer when 0.28 kg/ha was applied twice (March and/or April) than when applied singly at 0.28 kg/ha March 30 or April 13. The optimum time and rate of pronamide for effective transition was April 13 and 0.56 kg/ha, respectively.

A soilless unit was devised in which host plant (carrot, tomato) roots can be readily infected with broomrape. The simple, inexpensive and reusable unit consists of two glass plates, synthetic cloth, and foam rubber. The host plants are placed (or grown) between the glass plates, being held against one of the plates by foam rubber. The unit provides proper growing conditions, convenient visibility of host roots and parasite from an early stage of infection, and nondestructive access to the roots and parasite. Exposure of the broomrape seeds to a synthetic germination stimulant (GR 24) prior to their application to the host roots, generally, but not always, caused some increase in the number of parasitic infections and/or the rate of broomrape growth.

Subterranean clover as a living mulch was evaluated for weed control and its effect on field corn silage and grain yield in 1986 to 1988. Treatments included combinations of subterranean clover living mulch, rye dead mulch, and no mulch with three superimposed tillage practices (conventional, minimum, and no-tillage). Results indicated that subterranean clover living mulch effectively controlled ivyleaf morningglory. Little control of fall panicum was obtained in 1986; however, living mulch combinations effectively controlled fall panicum in 1987 and 1988. Weed biomass was reduced significantly by all living mulch combinations, but all other combinations resulted in higher weed biomass than living mulch. Corn silage and grain yields from the no-tillage plus living mulch treatment were comparable to or higher than those obtained with the conventional tillage plus no mulch treatment.

The distance-of-influence of an individual devil's-claw plant to cotton leaf, stem, boll (reproductive parts), and combined aboveground plant parts was determined in two field experiments. The distance-of-influence could not be detected for the first 6 weeks after emergence; by 9 to 12 weeks, it extended up to 25 cm or more; and by the end of the season, up to 50 cm on each side of the weed. Cotton leaf and stem weights were less sensitive than cotton boll weights for measuring distance-of-influence from devil's-claw. At maturity, cotton boll weight was reduced 62 and 51% in 1983 and 45 and 29% in 1984 for sampling intervals of 0 to 25 and 25 to 50 cm, respectively. Interference from cotton reduced devil's-claw stem weight, seed capsule weight, and whole plant biomass by 6 weeks after emergence and reduced leaf biomass by 9 weeks in 1983. All except stem biomass were affected in 1984. Distance-of-influence and weed-density interference studies predicted lint yield loss similarly.

The effects of different periods of green foxtail competition on the components of potato yield were investigated. Delaying the removal of green foxtail for 2 wk following crop emergence reduced total and marketable tuber yield by 19 and 29%, respectively, when averaged over 2 yr. Similarly, the number and average weight of marketable tubers were reduced by 24 and 6%, respectively. The proportion of unmarketable tubers comprising the total yield increased as the duration of weed competition was increased. Successively longer periods of green foxtail competition further decreased the measured parameters.

Field studies with flatfan, twinjet, flood and rotary atomizers were conducted in 1987 and 1988. The results indicated that tridiphane at 0.6 kg ai/ha plus atrazine at 1.7 kg ai/ha with 2.0 L/ha of soybean oil adjuvant was more effective in controlling giant foxtail and common lambsquarters when applied by the flatfan, twinjet, and rotary atomizers. Image analysis indicated that weed control by a postemergence herbicide was generally enhanced by better application coverage. Droplet size measurement by phase droplet particle/droplet analyzer demonstrated that the rotary atomizer produced a narrower range of droplet diameters between the Dv.1 and Dv.9 volumes than any of the other atomizers.

Freshly collected redroot pigweed seeds were buried 5 cm deep in the field in November of 3 yr in succession. Treatments applied to the soil surface included KNO3 (400 kg ha-1) in midwinter, ethephon (11 kg ha-1) in late spring, and a soil cover (polyethylene sheet for 2 wk) in late spring. Seeds were recovered within 1 yr after treatment, examined for in situ germination, and tested for viability. The 3-yr averages for viable seeds remaining by October in the year after treatment with KNO3 or soil cover, either alone or in combination, did not differ from nontreated checks and averaged 47% of the original population. Viable seeds remaining in soil treated with ethephon either alone or combined with KNO3 were reduced to 21% of the beginning population. The most effective treatments were ethephon either combined with a soil cover or with a soil cover plus KNO3 which reduced the viable seeds to an average of 8% of the original. Ethephon plus a soil cover has the potential to reduce greatly redroot pigweed seed populations in the field.

The weed sicklepod, a problem in the cultivation of soybean, cotton, and peanut, can be controlled by the mycoherbicide, Alternaria cassiae. However, the presence of water (dew) for an extended period is required by the fungal spores to germinate and infect the target weed. Preliminary tests with invert (water-in-oil) emulsions containing paraffin wax, paraffin oil, lecithin, and water indicated that about 10% (w/w) water, maintained over an 18-h period, was necessary under laboratory conditions for significant germination of the fungus. The ability to maintain that amount of water in the invert emulsion depended upon spray deposit size, adjuvants, and oil phase: water ratio. Paraffin wax was an effective adjuvant for reducing water evaporation and increasing sicklepod mortality in the greenhouse.

Field studies were conducted to compare preplant-postemergence-applied paraquat, glyphosate, SC-0224, and HOE-39866 on subterranean clover, crimson clover, and hairy vetch cover crops. Subterranean clover control with paraquat at 1.1 kg ai/ha was about 80 and 100% when applied in early April and early May, respectively, regardless of spray volume (190 vs. 370 L/ha). Glyphosate and SC-0224 at 1.7 and 2.8 kg ai/ha applied in April controlled about 53% of subterranean clover. Subterranean clover control with HOE-39866 at 0.8 kg ai/ha applied in April was excellent. Paraquat at 0.6 kg ai/ha and HOE-39866 at 0.8 kg/ha regardless of application time controlled both crimson clover and hairy vetch. Grain sorghum and soybean yields following the legume cover crops generally were similar for the herbicide treatments.

Chlorsulfuron was applied to wheat at rates of 0, 10, 20, and 40 g ai ha-1 in three locations at Lethbridge and Brooks between 1980 and 1984. The soil pH and organic matter contents at Lethbridge and Brooks were 8.0 and 2.1% and 7.4 and 3.0%, respectively. Rotational crops were seeded for up to 7 yr after chlorsulfuron application. The criteria used to indicate when susceptible crops will grow safely were no significant yield loss at the 40 g ha-1 rate and the magnitude of the upper confidence limit for this difference. The following times after application before crop yields were not affected were required at Lethbridge: barley, 2 yr; canola, 3 yr; peas, beans, 4 yr; flax and potatoes, 5 yr; alfalfa and sugarbeets, 6 yr; and lentils at least 7 yr. The effect of chlorsulfuron residues in the soil on rotational crops appeared to be similar at Brooks and at Lethbridge. Estimated chlorsulfuron concentrations were related to the tolerance of rotational crops.

Cyanazine and 2,4-D were the most effective herbicides for horseweed control before establishing full-season no-till soybeans. Paraquat plus 2,4-D was less effective than 2,4-D alone but superior to paraquat alone. Chlorimuron plus metribuzin or chlorimuron plus linuron was less effective than cyanazine but controlled horseweed better than metribuzin, linuron, or imazaquin. Herbicides were generally more effective when applied early. These studies indicate paraquat was antagonistic to 2,4-D for horseweed control when these herbicides were combined.

Greenhouse and field studies were conducted to examine the interaction of sethoxydim or fluazifop-P tank mixed with chlorsulfuron or thiameturon for selective weed control in safflower. Under greenhouse conditions, the addition of chlorsulfuron to sethoxydim or fluazifop-P slightly improved the control of green foxtail above that achieved with either herbicide alone. Control of wild oat and wild mustard was similar with the tank mixes and each herbicide alone. In the field, control of wild oat with sethoxydim or fluazifop-P was not altered by adding chlorsulfuron or thiameturon in tank mixes. Similarly, control of common lambsquarters and wild mustard with chlorsulfuron or thiameturon was not affected by adding either sethoxydim or fluazifop-P in tank mixes. Plant height, date of flowering, seed yield, and quality data indicated that safflower tolerated these herbicides applied alone or in combination. Sethoxydim or fluazifop-P tank mixed with chlorsulfuron or thiameturon provide a postemergent alternative for selective control of grass and broadleaf weeds in safflower.