Weed control was evaluated in no-till planted soybean in both burned and standing wheat stubble for 3 yr. High, intermediate, low, and no weed management following no-till planting of soybean were compared with a tilled treatment with high weed management. Herbicides for the high weed management were metribuzin plus metolachlor PRE followed by POST applications, as needed, of bentazon, acifluorfen, and fluazifop or quizalofop. Intermediate management included all of the above except metolachlor, plus the as-needed use of chlorimuron or lactofen POST. Low management had no PRE herbicide applications but included the above POST herbicides. Glyphosate was used as a preplant foliar applied desiccant in the stubble-planted soybean of all weed management levels. Yield of soybean was not affected by standing, burned, or tilled wheat stubble. Soil organic matter in the 0 to 2.5 cm of soil was not significantly affected at the end of the 3 yr. Yield of wheat was reduced by standing wheat stubble in the first year of the study. Total POST weed control was sufficient for maximum soybean yields in the second and third years of the study. The weed spectrum changed during the experiment for the no-weed-control treatment in soybean and in wheat. The major weeds present in soybean after 3 yr of no-till were southern crabgrass, nodding spurge, redvine, prickly sida, barnyardgrass, and johnsongrass; in wheat they were Italian ryegrass, little barley, mayweed chamomile, and hairy buttercup.

A synthetic data set was created by incorporating results from previously published papers on antagonistic and synergistic herbicide interactions between two herbicides applied as a tank mixture or sequentially, and then analyzed on the basis of various properties of the herbicides and target plants. Generally, interactions between herbicides were antagonistic more frequently than synergistic. This trend held no matter whether the interacting herbicides were absorbed by the same or different parts of the plant, had the same or different translocating abilities, had the same or different modes of action, and regardless of whether the target plants were annual or perennial plants, or crops or weeds. Antagonistic interactions occurred much more frequently when the target plants were monocot than dicot, and in the Compositae, Gramineae, or Leguminosae than in the Chenopodiaceae or Convolvulaceae families.

Information on the effects of multiple weed management tactics in corn is needed to develop integrated weed management systems. The effectiveness and compatibility of an in-row cultivator as compared to a standard interrow cultivator used with reduced rates of a soil-applied herbicide, rotary hoeing, and/or a bioeconomic model for POST herbicide selection was examined. Weed control with a single rotary hoeing at corn emergence controlled annual weeds similarly to two rotary hoeings. One-third recommended use rate of alachlor controlled weeds similarly to a two-thirds rate. Reduced rates of alachlor controlled more weeds than rotary hoeing over 2 yr. The in-row cultivator required early-season weed control (rotary hoeing or reduced alachlor rate) for optimum efficacy. The in-row cultivator provided better weed control than the standard cultivator while the cost of operating the two cultivators was similar. Thus, the in-row cultivator was more efficient than the standard cultivator. Furthermore, less intensive early-season weed control was required with the in-row cultivator for maximum weed control as compared to the standard cultivator. Rotary hoeing plus the in-row cultivator provided similar weed control to other weed management tactics that required both soil-applied and POST herbicides. Gross margin was influenced more by corn yield than cost of weed management tactics.

Field studies were conducted in 1991 and 1992 to evaluate the response of soybean and the subsequent rice crop to AC 263,222 applied alone and in tank mixtures with imazethapyr or imazaquin. In 1991, 18, 36, and 70 g ai/ha of AC 263,222 visibly stunted soybean 9, 19, and 35%, respectively. Adding imazethapyr at 36 g/ha or imazaquin at 70 g/ha to AC 263,222 in a tank mixture did not increase soybean response compared to AC 263,222 alone. Soybean yield was not reduced by any treatment. In 1992, 14 g/ha of AC 263,222 alone or in tank mixtures damaged soybean 38% or greater. In one study, rice was injured the year following application of AC 263,222 alone and in tank mixtures. Rice yield was reduced by 70 g/ha of AC 263,222 alone and by 36 g/ha of AC 263,222 when tank mixed with 36 g/ha of imazethapyr.

Soil cultivation (3 to 5 times/yr) and herbicide management (oxadiazon, 3.92 kg ai/ha), agricultural standards for reducing weed competition, were compared to three alternative nursery field management systems regarding weed suppression: ‘Norcen’ bird's-foot trefoil companion crop, ‘Wheeler’ winter rye cover crop/mulch, and grass sod (80% ‘Eton’ perennial ryegrass and 20% ‘Ruby’ red fescue). Field management treatment had a significant effect on observed weed populations. Weed densities were also subject to yearly variations caused by climate and endogenous weed life cycles. Herbicide management (oxadiazon) consistently provided the best control of undesired vegetation (0.3 weeds/m2) followed by the grass sod (0.7 weeds/m2), Wheeler rye cover crop/mulch (1.7 weeds/m2), Norcen bird's-foot trefoil companion crop (8.6 weeds/m2), and cultivated (55.7 weeds/m2) treatments, respectively. Although the grass sod treatment provided excellent control of undesired vegetation, as an alternative to cultivation and herbicide use, it proved to be excessively competitive with the nursery crop. The bird's-foot trefoil treatment quickly became infested with broadleaf weeds the eradication of which proved difficult. The Wheeler winter rye cover crop/mulch field management system provided acceptable weed control combined with other beneficial effects on the plant/soil environment. Results support the effectiveness of Wheeler winter rye and perhaps other allelopathic cover crop/mulch systems in controlling undesired vegetation in horticultural field production systems.

Field and greenhouse experiments were conducted to determine the effect of selected insecticides on cotton when applied in combination with pyrithiobac. In the field, acephate, azinphos-methyl, bifenthrin, chlorpyrifos, dicrotophos, esfenvalerate, malathion, methomyl, or oxamyl was applied foliarly with the sodium salt of pyrithiobac at 70 g ae/ha. Pyrithiobac plus malathion resulted in greatest injury when compared with other treatments. There were no differences observed in fruiting characteristics of cotton. Cotton yield was lower with oxamyl, methomyl, and chlorpyrifos when applied in combination with pyrithiobac in one of three experiments. In greenhouse experiments, injury due to pyrithiobac was greater in a cool (21 C day, 13 C night) temperature than in a warm temperature (30 C day, 21 C night), but differences were less than 15%. Pyrithiobac plus malathion in the cool environment injured cotton more severely 7 DAT than either pesticide alone. Adding insecticides to pyrithiobac did not influence injury in the warm environment.

Field experiments were conducted from 1986 to 1988 at Lacombe and Lethbridge, Alberta and Scott, Saskatchewan to determine growth and yield response of canola to mixtures of ethametsulfuron with specific grass herbicides. Ethametsulfuron did not usually cause canola injury when mixed with sethoxydim. However, ethametsulfuron mixtures with the following grass herbicides listed in decreasing order of injury potential, often caused canola injury and yield loss: haloxyfop > fluazifop > fluazifop-P > quizalofop > quizalofop-P. Canola yield losses were severe in some experiments, ranging from 59% with quizalofop mixtures to 97% with haloxyfop mixtures; in other experiments, the same mixtures did not cause significant yield losses. ‘Tobin,’ a Brassica rapa cultivar, tended to be more susceptible to injury than the B. napus cultivars ‘Pivot’ and ‘Westar.’ Canola injury symptoms were consistent with those expected from sulfonylurea herbicides. Therefore, we suggest that specific grass herbicides differentially impair the ability of canola to metabolize ethametsulfuron to inactive forms.

A rainfall simulator was used to deliver the equivalent of 1.3 cm of water in 0.25 h at 0, 3, 6, 12, 24, and 48 h after POST applications of asulam to johnsongrass in greenhouse and field studies. Johnsongrass control responses were similar when asulam was applied with either a crop oil concentrate or a commercially blended organosilicone/crop oil concentrate premix. Rainfall 24 h after asulam application reduced johnsongrass control in greenhouse studies. Maximum visual johnsongrass control of 80, 69, and 69% was obtained in field studies when rainfall occurred 20, 14, and 8 h after asulam application, respectively. Based on reductions in johnsongrass dry weight, rainfree periods needed to insure maximum performance with asulam in field studies ranged from 3 to 16 h. Variation in critical rainfree periods was related to plant growth stage when asulam was applied and environmental conditions and is indicative of the inconsistency in johnsongrass control commonly observed with asulam.

Field tests showed that the lawn spray-gun with a 4 gpm lawn tip reduced the percentage of application volume deposited 90 cm to 210 cm downwind from the spray swath edge when compared with XR8004 flat-fan or RA-6 wide angle hollow cone applications at wind speeds between 4.7 and 14.4 km/h. The percentage of applied volume collected at 210 cm downwind from the XR8004 flat-fan applications was 5 and 16 times greater than the percentage from the RA-6 Raindrop nozzle and lawn spray-gun applications, respectively. Visible injury alone with height increases and fresh weights from tomato plants located downwind from the applications concur with spray-drift data for all nozzle types. Triclopyr injury decreased as the distance from the swath edge increased. All tomato plants located downwind up to 210 cm from the XR8004 flat-fan applications were visibly injured (15 to 40%); whereas, only plants less than 150 cm downwind from the RA-6 Raindrop applications and less than 90 cm downwind from the lawn spray-gun applications were injured (2 to 8%).

Increased crop densities and postplant tillage were evaluated as nonchemical methods to supplement metribuzin for improved broadleaf weed control in dry pea and lentil. The effects of 50, 100, and 150% of recommended 220 kg/ha pea and 67 kg/ha lentil seeding rates and two dates of rotary hoeing and harrowing on pea, lentil, and broadleaf weeds were studied with and without metribuzin for two years. Under favorable growing conditions, crop competition gave 72 and 99% weed control in pea and 33 and 70% weed control in lentil with the 50 and 150% seeding rates. Under less favorable conditions, control was 21 to 39% with the low and high pea and lentil seeding rates. At recommended seeding rates, metribuzin gave greater than 90% control in either crop or year. Postplant tillage 12 to 27 d after planting slightly reduced crop densities in three tillage treatments in one year, but not the second. Postplant tillage did not affect crop yield or improve weed control. In all studies, pea was similar to or more competitive than lentil in suppressing broadleaf weeds. Because neither non-chemical practice significantly improves weed control, changes are not recommended for weed management in pea and lentil.

Studies were conducted to determine the effects of tillage level on weed control and yield of asparagus grown on a sandy loam soil under sprinkler irrigation. Without herbicides, horseweed and kochia populations increased in no-till asparagus production over a 3-yr period, compared to asparagus that was rototilled either once in the spring or once in the spring and again at layby. Without herbicides, hairy nightshade populations increased most when asparagus was rototilled both in the spring and at layby. Volunteer asparagus was controlled best when herbicides and tillage were combined in the spring and again at layby. Common groundsel was controlled without herbicides by rototilling both in the spring and at layby. Diuron at 1.4 kg ai/ha plus prodiamine at 1.4 kg/ha or metribuzin at 0.9 kg/ha plus norflurazon at 2 kg/ha controlled all weeds under all three tillage levels when split-applied in the spring and at layby. Tillage level had no effect on total asparagus spear number or weight if tillage was performed in mid March before asparagus emergence.

A large crabgrass population (PW2) that demonstrated resistance to fluazifop-P and sethoxydim was identified in Wisconsin during 1992. Dose-response experiments were conducted in the greenhouse to determine the level of resistance of a PW2 large crabgrass accession to aryloxyphenoxypropionate (APP), cyclohexanedione (CHD), and other herbicide chemistries relative to a large crabgrass accession (A310) which was susceptible to APP and CHD herbicides. Based on shoot dry biomass reduction, the PW2 accession was 337- and 59-fold resistant to sethoxydim and fluazifop-P, respectively, relative to the A310 accession. Resistance of the PW2 accession to fenoxaprop, haloxyfop, quizalofop, and diclofop ranged from 18- to 29-fold. The PW2 accession was only 7-fold resistant to clethodim. Both large crabgrass accessions were susceptible to imazethapyr and linuron. These results suggest that APP and CHD herbicides will be ineffective for the management of the PW2 accession. An integrated approach including cultural, mechanical, and alternative chemical methods, should be implemented for the management of the PW2 accession and to prevent additional resistance problems.

Greenhouse studies were conducted to investigate the effects of adjuvant and rainfall on bentazon spray retention, efficacy, and foliar washoff in hemp sesbania, sicklepod, smooth pigweed, and velvetleaf. Bentazon was applied at 0.28 to 2.24 kg ai/ha with Agri-Dex, a crop oil concentrate (COC) or Kinetic, an organiosilicone-nonionic surfactant blend (OSB) when weeds were at the three- to five-leaf stage. Plants were subjected to 2.5 cm simulated rainfall for 20 min at 1 and 24 h after application of bentazon. Shoot fresh weight reduction assessed 2 wk after treatment was similar with either adjuvant on velvetleaf and smooth pigweed. OSB enhanced bentazon efficacy in hemp sesbania and sicklepod as compared to COC. Rainfall at 1 h after application generally reduced bentazon activity in all weeds. OSB maintained bentazon activity in hemp sesbania when subjected to rainfall at 1 h after application as compared to COC. Overall, bentazon spray retention on plants was 9 to 550% higher with OSB as compared to COC among the species at 1 h after application. Amount of bentazon residue washed off from the foliage by rainfall within a weed species was relatively similar for both adjuvants except in smooth pigweed and ranged from 39 to 98% among the four weed species at 1 h after application. OSB exhibited specificity for certain weed species and the potential to minimize bentazon spray reaching the soil by increasing deposition.

Greenhouse and field experiments were conducted to evaluate the effectiveness of nicosulfuron and primisulfuron with different adjuvants on wirestem muhly control. The adjuvants evaluated with the two herbicides included a nonionic surfactant, crop-oil concentrate, crop-oil concentrate plus urea-ammonium nitrate, methylated vegetable-oil concentrate, and organosilicone methylated vegetable-oil concentrate. In the greenhouse, nicosulfuron and primisulfuron performance was similar, although small differences occurred between adjuvants and herbicides. In the field, changing adjuvant affected nicosulfuron performance more than primisulfuron and in general, greater control was achieved with nicosulfuron than with primisulfuron. Among adjuvants, methylated vegetable-oil concentrate provided greater wirestem muhly control with nicosulfuron and sometimes primisulfuron compared to the others, while the nonionic surfactant was the least effective with both herbicides. Regardless of adjuvant, none of the field-applied treatments controlled wirestem muhly much beyond the 12 wk-evaluation period.

The potential reduction in surface runoff loss of band-applied herbicides was studied in a rainfall simulation. Concentration and loss of atrazine, metribuzin, and metolachlor applied in a band 25, 50, or 75 cm wide on 1-m2 plots graded to < 0.5% slope were compared with that from a broadcast preemergence application. Herbicide concentration in runoff decreased with time after initiation of runoff and as application band width decreased. Band width reduced herbicide concentration in runoff to a greater extent than time after initiation of runoff. The 50-cm band treatment reduced atrazine and metribuzin loss 69 and 71%, respectively, from the broadcast treatment. Forty-nine percent less metolachlor was lost from the 50-cm band than from the broadcast treatment. Herbicide concentration or loss in surface runoff did not differ between the 50- and 25-cm band width treatments. Herbicide lost in runoff ranged from 4 to 7% of application with the smaller loss associated with narrower band widths. The greater reduction in atrazine and metribuzin loss in surface runoff than that associated with the reduction in input alone may be attributed to leaching or adsorption of herbicide by soil in the nonsprayed strip as runoff flowed from the treated to the nontreated areas. Band application of herbicides may provide an effective, consistent means to reduce herbicide loss in surface runoff.

Field studies were conducted from 1985 through 1987 to evaluate control of wild jujube, a deciduous, thorny shrub that causes complete wheat and other crop loss by preventing harvest operations. Initial herbicide or sweep tillage treatments were applied in late June or July, as plants approached maximum foliar development, to wild jujube regrowth from plants cut at ground level the previous fall. Nearly 1 yr after treatment, over 97% reduction of wild jujube regrowth was achieved with initial treatments of 7.2 and 10.7 g ae/L of the isopropylamine salt of glyphosate, 2.4 and 3.6 g ae/L of the potassium salt of picloram, and mixtures of glyphosate plus picloram at half those concentrations, followed 2 to 3 mo later with a repeat herbicide treatment or sweep tillage. About 60% reduction in wild jujube regrowth was achieved with two sweep tillage operations 25 cm deep. Mixtures of half rates of glyphosate plus picloram were less costly than full rates of glyphosate alone and had less carryover to wheat than full rates of picloram alone.

An integrated approach to weed management in pinto bean is needed since available herbicides seldom adequately control all weed species present in a field. A two-year study was conducted to assess weed control efficacy and pinto bean tolerance to mechanical weeding from a rotary hoe or flex-tine harrow at crook, unifoliolate, and trifoliolate stages of bean development. Weed control was similar for both implements and all timings in 1993. In 1994, mechanical weeding at trifoliolate and both crook and trifoliolate stages controlled more weeds than at other growth stages, regardless of type of implement. Using the flex-tine harrow reduced pinto bean stand, but results based on growth stage were not consistent each year. Damage to pinto bean hypocotyls and stems was observed with the flex-tine harrow used at both crook and trifoliolate stages in 1994. Rotary hoeing did not reduce pinto bean stand or cause injury. Yield and seed weight did not differ among treatments in either year.

Field experiments were conducted in 1992 and 1993 to evaluate wirestem muhly control in no-till corn with application of glyphosate, nicosulfuron, and primisulfuron. Glyphosate was applied preplant at 1.1 kg ai/ha. Nicosulfuron and primisulfuron were applied at 0.018, 0.036, and 0.072 kg ai/ha and 0.020, 0.040, and 0.080 kg ai/ha, respectively, at four postemergence timings that included a split application. Similar experiments were conducted with wirestem muhly grown from rhizomes and seed in the greenhouse. Glyphosate was the most effective herbicide in the greenhouse, providing at least 96% control. However, preplant application of glyphosate in the field was ineffective in controlling wirestem muhly. On average, nicosulfuron and primisulfuron never exceeded 72% control of wirestem muhly in the greenhouse or in the field. Nicosulfuron was generally more effective than primisulfuron. Control with split application timings was more uniform over a 12-wk period than single applications and late postemergence applications were often too slow acting to affect wirestem muhly growth. Although neither nicosulfuron nor primisulfuron controls wirestem muhly, both can provide suppression of this weed where other alternatives do not exist.

Field experiments were conducted from 1989 to 1992 to determine whether no-tillage corn grown in 38-cm rows and a 2× population could improve weed control relative to 76-cm rows and 1× population under reduced-herbicide options. A standard treatment including 1.12 kg ai/ha of atrazine plus 2.24 kg ai/ha of metolachlor was compared with a treatment including the same herbicides applied at 25% of the standard rates. Both treatments included 0.56 kg ai/ha of paraquat which controlled annual weeds established at the time of application. Weed control was less in the 25%-herbicide treatment than in the standard treatment in two of four years when corn was grown in 76-cm rows with a l× population. The 25%-herbicide treatment provided weed control and grain yields similar to the standard treatment in each year when corn was grown in 38-cm rows with a 2× population. Weed control was poor and yield was reduced when no herbicides were applied regardless of row spacing or population. The leaf canopy of corn in the 38-cm row/2×-population treatment reduced light transmittance 1 wk earlier than corn in the 76-cm row/1×-population treatment.

A small percentage (< 5%) of dent corn inbreds was sensitive to the herbicide nicosulfuron. Segregation within a backcross to inbred Ab18 demonstrated simple inheritance as a nuclear gene for corn sensitivity to this herbicide. Greenhouse tests indicated that cytoplasmic or maternal effects were not important in conditioning sensitivity. Tolerance in some crosses began to break down at application rates approaching twice that registered. Sensitivity was controlled by a single autosomal recessive gene in the inbred Ab18. Further testing will be required to determine whether this gene is common to other sensitive inbreds. Thorough screening continues to be necessary to identify sensitive elite inbreds in public and private breeding programs.