In 1987 and 1988, effects of full-season interference of individual weeds on cotton yield were measured with area of influence procedures. In 1987, one spurred anoda, common cocklebur, large crabgrass, jimsonweed, common lambsquarters, redroot pigweed, common ragweed, or prickly sida plant per 3 m of row reduced cotton yield between 1% and 7%. Sicklepod did not cause a detectable yield loss. Redroot pigweed, common cocklebur and common ragweed caused 7%, 6% and 5% yield loss, respectively, in 1987. In row weed influence varied from 17 cm (large crabgrass interference) to 86 cm (common cocklebur interference). In 1988, yield losses by individual weeds ranged from 3% to 27%. Common cocklebur, jimsonweed, and common ragweed reduced cotton yields 28%, 15% and 12%, respectively. Spurred anoda and common cocklebur influenced 160 cm and 136 cm of cotton row, respectively. Sicklepod influenced only 47 cm of cotton row.

An area of influence method with biweekly destructive harvests 5 through 19 wk after planting (WAP) was used to monitor the reciprocal interference of common cocklebur and cotton in 1987 and 1988. Plant heights, leaf area, and leaf, stem, boll, fiber, and total plant biomass dry weights were measured in 15-cm increments away from common cocklebur or from a randomly selected cotton plant out to 105 cm. Data indicated that cotton less than 60 cm from common cocklebur was shorter, had less leaf area and lower leaf, stem, boll, and biomass dry weights than cotton beyond 60 cm from common cocklebur or cotton grown without common cocklebur interference. Differences in leaf area and biomass between cotton grown with and without common cocklebur interference were greater at and beyond 13 WAP sample dates than before 13 WAP. By 15 WAP, cotton leaf area and biomass were reduced an estimated 11% and 15%, respectively, averaged over the entire 105 cm of row. Cotton yield, harvested 27 WAP, was reduced an estimated 31% on plants grown with one common cocklebur plant per 2.1 m. Cotton yield was reduced on plants out to 99 cm from common cocklebur. Common cocklebur and cotton plants grown alone were taller, had greater leaf area, and greater leaf, stem, and biomass dry weight than those respective plants grown adjacent to cotton. Common cocklebur grown alone produced 67% more biomass than did cotton grown alone. Cotton plants grown adjacent to other cotton plants produced 89% and 96% less boll and fiber weight, respectively, than plants grown alone.

The objective of this research was to modify the senior author's previously developed method for predicting yield losses in maize crops attributable to johnsongrass. The new method is based on the following assumptions: a) relative leaf frequency determines relative biomass; b) total biomass is constant despite the crop/weed ratio; and c) biomass, and therefore leaf frequency, are related to grain yield. Experiments in Argentina from 1986 to 1989 supported the above hypotheses, and the new method was more accurate than the old for predicting relative species biomass in johnsongrass/maize mixtures. Maize grain yield reductions associated with weed interference were also more accurately predicted.

Sicklepod control with seven chemical treatments was evaluated in 25-cm and 97-cm soybean row widths. Metribuzin applied preplant incorporated followed by metribuzin applied preemergence, and metribuzin applied preplant incorporated followed by either imazaquin or chlorimuron applied postemergence controlled sicklepod over 90% early in the season, and row spacing did not influence control at that evaluation. In late season ratings, all herbicide treatments controlled sicklepod better in 25-cm rows than in 97-cm rows. However, only imazaquin applied sequentially or metribuzin followed by chlorimuron in 25-cm rows controlled sicklepod greater than 80% late in the season. Sicklepod control in 25-cm row soybean with either imazaquin or metribuzin plus chlorimuron applied preplant incorporated was equivalent to or better than sequential preemergence and postemergence treatments of these three herbicides in 97-cm rows. All treatments resulted in lower yields than the weed-free check in the 97-cm rows, whereas all herbicide treatments except the sequential application of metribuzin gave yields equivalent to the weed free check in 25-cm rows.

Glyphosate plus 2,4-D at 0.3 + 0.5 or 0.4 + 0.7 kg ae ha-1 applied 31 to 1 d before seeding did not affect wheat yields or grain test weights, in field experiments in conventionally tilled and no-till winter wheat. In the conventionally-tilled system in each of two years and in the no-till system in a year with 48 mm rain within 7 d before wheat was seeded, picloram applied at 0.14 kg ai ha-1 from 31 to 1 d before seeding reduced crop yields by 7 to 8%. In the conventionally-tilled system in a year with only 2 mm rain within 7 d before wheat was seeded, 2,4-D at 3.4 kg ae ha-1 and dicamba at 0.14 kg ae ha-1 applied 30 to 1 d before seeding, reduced wheat yields by 7 and 4%, respectively. Grain test weights in both tillage systems were increased slightly by picloram at 0.14 kg ha-1, but were decreased slightly by dicamba at 0.14 kg ha-1, in the year with little rain before sowing. Test weights did not differ among herbicides or tillage systems in the year with significant rain a few days before seeding.

Greenhouse and field herbicide evaluation, flooding, and soil saturation studies were conducted to investigate the control of oldfield cinquefoil in cranberry. Chlorimuron ethyl and dichlobenil were found to be promising herbicides for control of this weed in both greenhouse and field studies. The number of leaves, leaf area, shoot, root, and total dry weight of oldfield cinquefoil were reduced by dichlobenil at 1.1 to 4.5 kg ha-1 and chlorimuron ethyl at 17.5 to 35 g ha-1, at 12 wk after treatment. The higher rate of dichlobenil, however, caused reduction in cranberry height and total dry weight. Field treatment at time of cinquefoil emergence did not provide adequate weed control. Postemergence application to cinquefoil of 4.5 kg ha-1 dichlobenil, 35 g ha-1 chlorimuron ethyl, and 2.2 to 4.5 kg-1 ha terbacil reduced the number of leaves and shoot dry weight. Only terbacil at 4.5 kg ha-1 reduced cranberry shoot and fruit fresh and dry weight. Flooding for up to 72 h did not affect oldfield cinquefoil growth. At 22/18 C, 4 wk of soil saturation reduced runner development and fresh and dry weight of oldfield cinquefoil. At 13/9 C, no runners developed in either saturated or control soils, and there was no effect of soil saturation on fresh and dry weights. This suggests that oldfield cinquefoil grows better in an unsaturated soil condition, but needs a relatively warm climate to develop.

Preemergence herbicides were applied on February 28 at the recommended and three times the normal rate to determine the tolerance of tall fescue that was seeded in September, October and November of the preceding year. Fall seeding date of tall fescue significantly affected its tolerance to spring-applied preemergence herbicides. Generally, preemergence herbicides at normal rates were safe to apply to September- or October-seeded tall fescue. No herbicide was completely safe to apply to November-seeded tall fescue. The density of November-seeded tall fescue was generally reduced less with benefin, bensulide, dithiopyr, oxadiazon G and WP than with benefin plus oryzalin, oryzalin, or pendimethalin.

Greenhouse and field experiments were conducted at the Lacombe Research Station to evaluate mixtures of sethoxydim and fluazifop on green foxtail, wild oat, wheat, and barley in canola. In both environments the two herbicides interacted on the grass species in a synergistic manner. Many of the observed responses to mixtures of sethoxydim and fluazifop were 100% greater than those expected assuming an additive interaction between the herbicides. Mixtures with at least 80 g ha-1 of sethoxydim and 80 g ha-1 of fluazifop controlled more than 90% of green foxtail, wild oat, wheat, and barley under field conditions. These experiments indicate that the sethoxydim/fluazifop mixture is both complementary and synergistic. The mixture may allow reduced herbicide application rates and therefore reduced herbicide costs and less potential for negative environmental impact.

Postemergence spring applications of picloram and picloram plus 2,4-D frequently reduced mature height and peduncle length of hard red winter wheat in field experiments. Yield reductions were more severe from picloram applied alone to the first joint growth stage than late tillering stage wheat. In two of six experiments picloram plus 2,4-D reduced yield more than picloram alone. Yields of four wheat cultivars were reduced by picloram and picloram plus 2,4-D at one of two locations. At the second location only the yield of ‘Chisholm’ and ‘Rohm and Haas Seed 7837’ were reduced by those herbicides.

Control of Texas panicum and southern crabgrass with sethoxydim was reduced under field conditions when bentazon, acifluorfen, bentazon + acifluorfen, pyridate, or naptalam plus 2,4-DB was added. The addition of lactofen to sethoxydim did not result in antagonism. Complete control of annual grasses did not appear to be a necessity in order to improve peanut yields. Peanut yields in plots with 70 to 80% control of annual grasses were comparable to those where annual grass control was 99%.

Three seed lots each of two varieties of field corn were compared in greenhouse and field studies. Cold test germination percentages of the seed lots were as follows: 79, 85, and 93% for ‘DK656’; 77, 84, and 91% for ‘T1100’. Tank mixes of metolachlor or metolachlor with safener CGA-154281 plus atrazine or formulated metolachlor/atrazine with and without the safener were applied preemergence. Crop stand of either variety or among seed lots within a variety was not affected by herbicide treatments. In the greenhouse, fewer corn plants were injured and growth of plants was greater with herbicides with safener than herbicides without safener. Plant heights and weights at harvest from the most vigorous seed lot of DK656 were higher than those of the other two seed lots. Herbicide treatments with the safener did not cause significant injury to corn in the field. Yields of both varieties increased with herbicide treatments in one conventional planting. No significant differences in injury or yields occurred among seed lots within varieties.

Field experiments were conducted to compare herbicides applied preplant incorporated (PPI), preplant incorporated/preemergence (PPI/PRE), and preplant incorporated/early postemergence (PPI/early POST) to control woolly cupgrass in corn. Although good early-season control of woolly cupgrass from PPI cycloate plus cyanazine, EPTC plus dietholate or SC-0058, and butylate plus cyanazine sometimes was observed, middle- and/or late-season control was often limited. Generally, better woolly cupgrass control and higher corn yields were obtained from split PPI/PRE applications rather than from single PPI applications of alachlor, metolachlor, and acetochlor. The highest and most consistent full-season woolly cupgrass control resulted when cycloate or EPTC plus dietholate applied PPI was followed by cyanazine plus either pendimethalin, alachlor, metolachlor, or acetochlor applied early POST. However, in 1989 adverse weather conditions near the early POST application timing injured corn and reduced yields.

Field experiments were conducted to compare efficacy of BAS 514, bromoxynil, fenoxaprop, sethoxydim, and triclopyr with standard herbicides for barnyardgrass and bearded sprangletop control in rice at four locations. Sequential applications of BAS 514 and fenoxaprop, or propanil and sethoxydim consistently controlled barnyardgrass and bearded sprangletop as well as or better than standard treatments of propanil, thiobencarb, or pendimethalin alone or combined; and rice so treated produced high yields. BAS 514 applied postemergence alone, BAS 514 applied sequentially with sethoxydim, or BAS 514 tank mixed with propanil controlled barnyardgrass but not bearded sprangletop. Bromoxynil or triclopyr tank mixed with fenoxaprop or sethoxydim antagonized activity on barnyardgrass and bearded sprangletop. Combinations of fenoxaprop with BAS 514 or propanil consistently provided barnyardgrass and bearded sprangletop control and high yields.

Selected sweet potato clones were evaluated in greenhouse and field trials to identify clones with superior tolerance to bentazon. ‘Julian’ and NC 1519 were the most tolerant in the greenhouse. ‘Sweet Red’ exhibited foliar injury in the field, but yields were not reduced. The clone 79-BM-17 was equally tolerant in the field as Sweet Red, but in the greenhouse exhibited only intermediate tolerance. ‘Jewel,’ a widely grown commercial cultivar, was sensitive to bentazon in both the greenhouse and field. When averaged over all clones sweet potato injury increased as bentazon rate was increased from 1.1 to 2.2 kg ai ha-1, but it decreased as the season progressed. Bentazon did not reduce marketable yields at Clayton, NC. Bentazon as a split or late application at the 2.2 kg ha-1 rate, reduced yields at Clinton, NC. Percent culls among bentazon treatments did not differ at either location.

The U.S. Plant Introduction Collection for six pepper species (2694 accessions) was evaluated for tolerance to bentazon in a field study. Based on injury ratings, Capsicum annuum, C. chinense, and C. frutescens accessions were mostly intermediate in response to bentazon with relatively few highly tolerant or susceptible. Most of C. bacatum, C. chacoense, and C. pubescens and the unspeciated accessions were susceptible. Greenhouse experiments indicated that although most of the tolerant selections were highly tolerant, none was more tolerant than the C. annuum cultivars ‘Santaka’ or ‘Bohemian Chili’. None of the susceptible selections were more susceptible to bentazon than the C. annuum cultivar ‘Sweet Banana’. Individual plants that were highly tolerant were self-pollinated to produce progeny that were all highly bentazon tolerant, but none was more tolerant than Santaka or Bohemian Chili.

The influence of ammonium sulfate on the activity of sethoxydim on wild oats and barley was examined under field conditions in 1989 and 1990. A chlorophyll assay, together with plant height and dry weight determinations, was used to quantify the visual ratings for sethoxydim activity. Ammonium sulfate enhanced the activity of 75 and 150 g ai ha-1 sethoxydim in 1989. In 1990, ammonium sulfate increased the activity of the lower rate of sethoxydim only. Of the three quantitative assays, chlorophyll concentration alone differentiated the more rapid development of injury symptoms with added ammonium sulfate that was observed in the visual ratings. The chlorophyll assay was not better than the visual rating assessment, however, and appears to offer no advantages that would justify the time required.

Field studies were conducted in second-ratoon crops of sugarcane infested with rhizome johnsongrass to determine the effects of aqueous diluent volumes ranging from 47 to 561 L ha-1 on the performance of asulam. Trend analyses of johnsongrass recovery, based on panicle numbers late in the growing season, indicated a quadratic response with panicle numbers being lowest when asulam at 2.8 kg ai ha-1 was applied in a diluent volume approaching 187 L ha-1. The response was similar regardless of whether droplet size or number was altered to obtain these diluent volumes. Differences in late-season johnsongrass control were reflected in harvested sugarcane stalk populations and net cane yields. In greenhouse studies, johnsongrass plants were thoroughly washed with water 24 h after treatment with asulam at 2.8 kg ha-1 at water volumes ranging from 47 to 374 L ha-1. Asulam absorption, as evidenced by reduction in the growth of johnsongrass, was higher when surfactant was included, but was not affected by diluent volumes in the range evaluated.

We conducted research to determine if soybeans can be grown successfully in a no-till environment, in the semi-arid areas of the central Great Plains near North Platte, NE. Soybeans planted no-till into winter wheat stubble that was sprayed with glyphosate yielded more than when planted into soil that was rototilled in a winter wheat-soybean-fallow rotation. However, grain yield averaged only 420 kg ha-1 during 1975, 1976, and 1977. No-till soybean grown in a winter wheat-grain sorghum-soybean rotation during 1982 through 1985 yielded an average of 1370 kg ha-1. Low yields were associated with lack of precipitation during the fallow period after winter wheat harvest or grain sorghum harvest and during the soybean pod elongation and filling period. Several herbicides gave excellent weed control in soybeans when applied either after wheat harvest, early preplant, or at planting time. None of the herbicides persisted long enough to reduce grain yields of winter wheat planted into the soybean residue. With present production costs these nonirrigated rotations are not economical in the semi-arid region of the central Great Plains of the United States.

Two experiments were conducted. The first experiment compared sweet corn tolerance to clopyralid at 0.2 to 1.1 kg ha-1, EF-689 at 0.07 to 0.6 kg ha-1 and 2,4-D at either 0.3 or 0.6 kg ha-1. Sweet corn tolerated all rates of clopyralid. EF-689 at 0.2 kg ha-1 or greater caused stalk curvature, stunting, and yield reductions. Stalk curvature also resulted from 2,4-D, but not stunting or yield reductions. The second experiment determined the effect of sweet corn genotype and growth stage at application on injury from EF-689. Injury was genotype and growth stage dependent. Stalk curvature was most severe from treatments 6 wk after emergence, whereas the greatest stunting was from treatments at 4 wk. ‘Supreme’ had the least and ‘Maple Sweet’ the most stalk curvature.