Between 1982 and 1986, spring treatments of haloxyfop, fluazifop, and sethoxydim all applied at 400 g ai/ha alone and combined with dalapon at 3400 g ai/ha were evaluated for quackgrass control and subsequent effect on established birdsfoot trefoil seed production. Haloxyfop alone and combined with dalapon were superior to fluazifop or sethoxydim alone or mixed with dalapon for controlling quackgrass and other grass weeds. Birdsfoot trefoil seed yield averages over 3 yr were 310, 160, 150, and 180 kg/ha after treatment with haloxyfop, fluazifop, sethoxydim, and dalapon, respectively, compared to a control yield of 80 kg/ha. Yields were lower, 220 kg/ha, with combinations involving haloxyfop plus dalapon compared to haloxyfop alone.

Foliar activity of the butyl ester of fluazifop on large crabgrass was determined by varying the concentration of a petroleum-based oil concentrate and the carrier volume. Increasing the concentration of petroleum oil or reducing the carrier volume improved large crabgrass control. Under greenhouse conditions, both visible injury and plant dry weight reflected greater control with adjuvant concentrations increasing from 0.62 to 5.0% v/v. Similarly, reducing carrier volumes from 374 to 47 L/ha increased grass control. No significant interaction between carrier volume and adjuvant concentration suggests the effects of these two variables are independent of one another. For both variables, effects were greater with sublethal rates of fluazifop.

Eight herbicides or herbicide combinations were evaluated for control of Wasatch milkvetch and other broadleaf plants. Triclopyr at 2.2 kg ae/ha controlled Wasatch milkvetch and associated mountain big sagebrush and mulesears 100%. A combination of triclopyr plus dicamba at 1.1 plus 1.1 kg ae/ha also controlled these species. When compared to untreated plots, grass production increased over 400% on plots treated with triclopyr at 1.7 and 2.2 kg/ha and more than 300% on plots treated with triclopyr plus dicamba at 1.1 plus 1.1 kg/ha.

Area-of-influence (AOI3) experiments measure the effect of a single weed on crop growth at intervals away from the weed plant. Effects of treatment variables, e.g., weed species or control measures, on the AOI of a single weed can be estimated. AOI experiments can be analyzed by regression of crop growth on distance from the weed plant, but this analysis violates an important regression assumption: independece of observations. Statistical dependence can occur among successive observations along the row because uncontrolled sources of variation are likely to act in similar ways on adjacent individuals. Multivariate analysis of variance (MANOVA) is a statistical technique that accounts for dependencies among crop growth measurements along the row. The technique tests three hypotheses: first, that different treatments cause weed AOI to differ in spatial distribution of competitive effects; second, that different treatments cause weed AOI to differ in size; and third, that the weed has an effect, i.e., crop growth near the weed differs from growth away from weed. MANOVA can be applied to most common experimental designs, e.g., randomized blocks or split plots, and can be implemented on various mainframe and microcomputer statistical packages.

A long-term study was established to determine the effects of rate, application method, and repeated applications of norflurazon on soil persistence and plant injury for sorghum, corn, and wheat. Preplant incorporated (PPI) and preemergence (PE) applications of norflurazon at 1.1 (1X) and 2.2 kg ai/ha (2X) initially were applied in 1981. Subplots were retreated in 1982 and 1983. Rotational crops were planted each year from 1982 to 1987. Evaluations taken in 1982 (14 months after initial treatment) showed slight injury to wheat, sorghum, and corn from 1X applications and significant injury from 2X applications. Evaluations 1 to 3 yr after final application indicated that repeated applications, even at the 1X rate, increased norflurazon residues and rotational crop injury. At both 1X and 2X rates, PPI treatments increased norflurazon persistence compared to PE applications.

A field experiment was conducted in 1986 and 1987 to determine the minimum effective rate (MER)3 of imazaquin and chlorimuron applied postemergence to common cocklebur. MER is defined as the quantity required to provide at least 90% control. Based on probit regression analyses, the mean calculated MERs of imazaquin and chlorimuron for 2-leaf common cocklebur were 27.5 and 4.5 g ai/ha, respectively. Under optimum growing conditions, the calculated MERs of imazaquin and chlorimuron for 6-leaf common cocklebur were 34 and 4.6 g/ha, respectively. When applied to 6-leaf plants under slight moisture stress, the calculated MERs for imazaquin and chlorimuron were 54 and 17.4 g/ha, respectively.

Barnyardgrass and bearded sprangletop are severe weed pests in rice in the southern United States. These weeds are controlled with standard herbicide programs of propanil alone or propanil combined with pendimethalin or thiobencarb. However, new herbicides, such as fenoxaprop, may be effective alternatives for grass weed control in rice. Fenoxaprop at 0.17 kg ai/ha applied postemergence in programs with propanil, thiobencarb, or pendimethalin controlled barnyardgrass and bearded sprangletop in rice and performed as well as or better than standard treatments of propanil with thiobencarb or pendimethalin. Rice yielded well, and grain was of high quality.

Field experiments were established to evaluate preemergence and postemergence herbicides for control of triazine-resistant smooth pigweed and common lambsquarters in no-till corn. When applied preemergence, alachlor in the microencapsulated formulation controlled smooth pigweed better than the emulsifiable concentrate formulation and better than either metolachlor or pendimethalin. These herbicides applied preemergence did not control common lambsquarters consistently. Pendimethalin controlled both triazine-resistant species when applied as a sequential treatment of a preemergence and an early postemergence application. Control of triazine-resistant smooth pigweed and common lambsquarters was excellent when dicamba was applied early postemergence in treatments containing alachlor, metolachlor, or pendimethalin applied preemergence and/or early postemergence. Thiameturon and CGA-131036 controlled triazine-resistant smooth pigweed with acceptable crop tolerance. Thiameturon also controlled common lambsquarters, but control was unacceptable with CGA-131036.

Velvetleaf, eastern black nightshade, wild mustard, common cocklebur, green foxtail, and yellow foxtail, grown for 4 weeks in nonaerated nutrient solution, developed satisfactorily compared to plants grown in soil. For experiments involving certain weed species grown in nutrient solution, aeration may be unnecessary.

Clomazone is effective as a chemical fallow herbicide; however, its soil residual properties in the Northern Great Plains are unknown. Clomazone was applied to soil at 0.6, 1.1, and 2.2 kg ai/ha at two locations in Montana in the spring of 1986. Soil samples were taken at each location at monthly intervals for 6 months. Residual levels of the herbicide were estimated by measuring the percent chlorosis by height in oat leaves. Clomazone at 2.2 kg ai/ha applied to a loam soil dissipated to levels below 0.1 mg/kg in 3 months and applied to a silty clay loam soil dissipated to 0.2 mg/kg 6 months after application. Half-lives (t½), determined from first-order rate plots, were 33 and 37 days in the Willow Creek loam and Bozeman silty clay loam, respectively. Thus, clomazone residue from labeled-use rates should not inhibit wheat in a wheat-fallow-wheat cropping system in Montana.

Alachlor plus linuron tank mixed with paraquat and applied preemergence (PRE) did not control giant foxtail all season in full-season no-till soybeans. Alachlor applied early preplant (EPP) plus PRE was necessary to control (>70%) giant foxtail acceptably all season. Metolachlor applied PRE or EPP plus PRE were equally effective in controlling giant foxtail (71 to 74%). Oryzalin at 1.7 or 2.2 kg ai/ha applied fall or spring EPP controlled giant foxtail better than 70% through July. Oryzalin applied PRE did not control giant foxtail acceptably.

Bioassays with soybeans and lentils were used to compare the persistence of 2,4,5-T, triclopyr, and picloram in soil after applying 0.038, 0.38, and 3.8 kg ae/ha under field conditions. Soil samples were collected from 1 to 269 days after spraying and were kept frozen until growth room bioassays were conducted. Triclopyr was slightly less persistent than 2,4,5-T, but neither herbicide was biologically active during the next season. At least 90% of picloram disappeared within 7 months, but its biological activity was more persistent than that of either triclopyr or 2,4,5-T. Nine months after treatment, neither lentils nor soybeans could be grown in soil treated with picloram at 3.8 kg/ka. Triclopyr and 2,4-D had smiilar soil thin layer chromatographic mobilities in four different scils. Picloram was significantly more mobile than either triclopyr or 2,4,5-T, primarily due to its lower adsorption in the soils examined.

The impact of three till-plant and two weed management systems on weed seed reserves of soil, yearly weed problems, and corn production was assessed under center-pivot irrigation for 3 consecutive years. Annual weeds were controlled in disced, bedded, and strip rotary till-plant systems with a moderate or intensive level of herbicides. Weed seed of seven annual weed species were identified, with common lambsquarters and stinkgrass, comprising 45 and 41%, respectively, of the initial 305 million seed/ha in the upper 25 cm of the soil profile. After the third cropping year, overall decline in total seed number in soil was 45% when averaged over till-plant and weed management systems. Grain yields did not differ between weed management systems, but the disced till-plant system produced 16% less grain than the bedded and strip rotary till-plant systems over 2 yr.

Seedling emergence and seed bank longevity were followed in field experiments with natural populations of common crupina for 4 yr. Emergence the first fall after dissemination was 90 to 98% of all seedlings eventually to emerge from the seedbank. Seedling emergence over time did not differ between plots which either were treated with the potassium salt of picloram or were hand weeded. No viable seed remained in the soil 25 to 26 months after seed production stopped. Five locations in a common crupina infestation undergoing eradication were sampled for seed in the soil. No viable seeds were found during the first year of the eradication, and no intact seeds were found after 4 yr.

Research conducted over 3 yr showed that volunteer Jerusalem artichoke was controlled effectively with clopyralid plus 2,4-D, dicamba plus 2,4-D, or 2,4-D alone applied postemergence at rates which did not injure spring barley. Glyphosate and paraquat applied preemergence to the crop did not reduce the number of Jerusalem artichoke shoots. Jerusalem artichoke which survived or escaped treatment was highly competitive with barley, as 4 to 6 surviving shoots/m2 could reduce seed yield 20%.

The loss of metribuzin and ethyl-metribuzin from soil and glass surfaces was studied to determine if volatilization and/or photodegradation could explain inconsistent weed control with these herbicides. In growth chamber experiments, phytotoxicity of ethyl-metribuzin decreased as the time between surface application and initial watering increased. Approximately 50% of the applied metribuzin and ethyl-metribuzin volatilized from soil within 24 h, with an additional 15 to 20% lost during the next 11 days, except about 5% additional ethyl-metribuzin was lost from Chehalis sandy loam. Both herbicides volatilized more rapidly from glass than from soil, with 75 to 90% of the loss occurring within 24 h and as great as 99% loss after 12 days. Loss by photodecomposition from soil or glass surfaces was minimal.

A common sunflower isolate of Alternaria helianthi collected near Stoneville, MS, was pathogenic to cultivated sunflower and common cocklebur. Soybean, cotton, rice, grain sorghum, corn, wheat, and 22 other weed and crop species/varieties in nine botanical families showed no response or only minor symptoms. Therefore, further research is warranted to determine the potential of A. helianthi as a biocontrol agent against common cocklebur in geographic areas where sunflower is not a crop.

Field experiments were established on a loamy fine sand to evaluate weed control in a conservation tillage system where cotton was planted into sorghum stubble. Preemergence herbicides for Palmer amaranth and volunteer sorghum control in cotton included methazole, dipropetryn, prometryn, metolachlor, and metolachlor plus dipropetryn or prometryn. Dipropetryn controlled both weeds without crop injury. Above 1.7 kg ai/ha, methazole provided effective control but injured the crop. Prometryn was less effective than dipropetryn or methazole against Palmer amaranth and controlled <40% volunteer sorghum. Metolachlor unacceptably injured cotton. Cotton yields were excellent when both weeds were controlled.

The methods used to teach weed identification at 20 U.S. universities were obtained for comparison through a telephone survey in December, 1986, and January, 1987. Weed identification is taught as a portion (30%) of the laboratory section in introductory weed science courses. Only five have a separate weed identification course. Field trips frequently are used to teach weed identification. Students must learn from 50 to 125 weed species with some seedling identification. Pressed plant collections of approximately 50 weed species normally are required. Most instructors strongly suggest using live plants and repetition for long-term learning.