Dinitroaniline herbicides have been used on the Texas Southern High Plains since the mid-1960s. Over this same period, cotton yields in this region have declined in spite of improved varieties and technology. Repeated applications of trifluralin and pendimethalin, each applied at 1x and 2x rates, were incorporated in 1983 through 1988. Variations in cotton stands, yields, and fiber quality were high due to environmental conditions. After six repeated applications, no reductions in cotton growth or yield were observed, even at the highest rates.

Quizalofop controlled 2- to 3-leaf and 5- to 6-leaf red rice better than fluazifop-P, haloxyfop, or sethoxydim applied alone. Red rice control increased when acifluorfen was tank mixed with haloxyfop, fluazifop-P, or sethoxydim. Antagonism was most severe when imazaquin was tank mixed with any of the grass herbicides. The efficacy of sethoxydim, fluazifop-P, and haloxyfop was reduced when applied with chlorimuron or bentazon. In greenhouse experiments, all of the grass herbicides, except for fenoxaprop, reduced fresh weight of red rice 71% or more. Based on fresh weight reduction, acifluorfen, fomesafen, and lactofen only reduced the activity of fluazifop-P, while imazaquin decreased the activity of all grass herbicides.

Research was conducted to determine the influence of water carrier quality on grass control from sethoxydim. Water from a well near Halliday, ND, where sethoxydim failed to control grasses, contained 650 mg/L sodium and 1650 mg/L bicarbonate. Both sodium bicarbonate and sodium carbonate when included in the sethoxydim spray reduced grass species control in the greenhouse and field. Sodium carbonate in the spray generally was more antagonistic than sodium bicarbonate to sethoxydim toxicity to grasses. The antagonism from sodium bicarbonate at 6000 mg/L was overcome by diammonium sulfate or ammonium nitrate at 2.8 kg/ha or a 28% nitrogen liquid fertilizer at 9.4 L/ha in the sethoxydim spray. These compounds also overcame sodium carbonate and partly overcame the antagonism of sethoxydim by bentazon. Three commercial adjuvants for use with sethoxydim differed in their effect on wheat and oats control with sethoxydim alone or with bentazon.

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.

Duncecap larkspur was not killed by triclopyr, picloram, or clopyralid applied once at recommended rates. Triclopyr at 1.1, 1.7, 2.2, and 4.6 kg ae/ha applied twice to the same plots in two consecutive years reduced duncecap larkspur density from 29 to 64%. However, the higher rates of triclopyr left 2 plants/m2, an unacceptable level for preventing cattle poisoning.

Weed control research includes comparisons of herbicides, spray volumes, carriers, and application times in tall crops such as grain sorghum and corn. To accomplish this, a plot sprayer was constructed on a 15-kW tractor with 1.5-m clearance. Ten spray cans held spray mixes that were propelled by compressed air supplied by a two-cylinder single-stage compressor. Using this sprayer, two people could spray up to 66 plots per h to evaluate herbicides, growth regulators, and insecticides in tall weeds and crops using different speeds, controlled droplet applicators, rope wicks, or air-assist nozzles at low- and high-spray volumes.

From ancient times to the present, common dandelion (Taraxacum officinale Weber in Wiggers ♯3TAROF) has been considered one of the most delectable of garden vegetables. People have carried the seeds from place to place for cultivation since before written history (9). According to legend, Theseus ate a dandelion salad after killing the Minotaur. Romans ate the plant as did the Gauls and Celts when the Romans invaded the North (9). The Anglo-Saxon tribes of Britain and the Normans of France continued to use the plant as food and as medicine to control scurvy and as a diuretic; it was planted in the medicinal gardens of monasteries (9).

Four experiments were conducted in 1985 and 1986 at three locations to assess weed control efficacy and phytotoxicity of several preemergence herbicides applied between beds (row middles) of polyethylene-mulched cauliflower grown on raised beds. Efficacy of most herbicide treatments varied among the four experiments; however, 4.5 kg ai/ha diethatyl and tank mixes of oxyfluorfen with cinmethylin consistently controlled weeds best. Plant stand, yield, and cauliflower curd size were not affected by treatment for any of the varieties used at any of the locations.

The tolerance of 41- and 76-cm tall corn to sethoxydim applied with a precision postemergence-directed sprayer was evaluated in field studies in 1987 and 1988. Corn 41 cm tall at application tolerated directed sethoxydim more than corn 76 cm tall. Sethoxydim plus crop oil concentrate at 110 to 220 g/ha plus 1.3% (v/v) applied to 41-cm corn resulted in little or no injury and no corn grain yield reductions. When sethoxydim at rates exceeding 110 g/ha plus crop oil concentrate was applied to corn 76 cm tall, injury occurred which reduced corn grain yield. Good tolerance of 41-cm tall corn validates the safety and effectiveness of postemergence-directed sethoxydim when applied with precision sprayer equipment.

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.

Picloram was applied broadcast on kleingrass pastures in the spring either as sprays or as pellets containing 2, 5, or 10% ae. The carrier in 5 and 10% pellets was inert clay, but 2% pellets were formulated with sufficient ammonium sulfate to contain 14.4% N. Dry formulations of picloram (10% ae), dicamba (5% ae), and tebuthiuron (20% ai) were compared to sprays at equal rates in a coastal bermudagrass pasture. Picloram was more effective as a spray than as pellets in two of five experiments. Few differences in weed control were observed with 2, 5, and 10% picloram pellets. Picloram applied up to 3 kg ae/ha as 2% pellets did not reduce kleingrass standing crop and up to 29 kg/ha of N as ammonium sulfate applied with or without picloram did not increase kleingrass production. None of the herbicides controlled weeds during the year following application.

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.

Two 5-yr experiments in a winter wheat-grain sorghum rotation were conducted near Hesston, KS, to evaluate selected foliage-applied herbicides to control honeyvine milkweed in the fall after wheat harvest. Herbicides that suppressed honeyvine milkweed stem populations 9 months after treatment included glyphosate, glyphosate plus dicamba, glyphosate plus 2,4-D, picloram, and four combinations of picloram plus 2,4-D. Honeyvine milkweed had regrown sufficiently by 24 months after herbicide application to require retreatment. Stem populations were suppressed following repeat treatments. Herbicide treatments increased yields of grain sorghum planted 9 months later but did not increase yields of winter wheat planted 13 months or longer after herbicide application.

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.

Six, 9, and 12-mm diam dicalcium phosphate tablets were evaluated for their release of acetochlor, metolachlor, and metribuzin. Greenhouse bioassays with Italian ryegrass demonstrated that herbicides from the smaller tablets did not control grass as long as from the larger tablets. Italian ryegrass was controlled within a 5- to 7-cm diam circle around the 12-mm diam tablet and a 5-cm diam circle around the 6-mm diam tablet. All tested herbicides responded in a similar fashion. Six-mm diam tablets released metolachlor for 11 weeks, while the 12-mm tablet was active for 28 weeks.

The effect of ammonium sulfate on absorption of 14C-sethoxydim applied alone and with bentazon was studied in large crabgrass. Adding ammonium sulfate to 14C-sethoxydim increased 14C absorption 6-fold at 0.5 h after application but did not affect the amount of 14C absorbed 1 or 4 h after application. Applying bentazon with 14C-sethoxydim reduced 14C absorption 26%. When 14C-sethoxydim was applied with bentazon and ammonium sulfate, 14C absorption and translocation were similar to those with 14C-sethoxydim alone.