Field experiments were conducted to compare barnyardgrass control and rice grain yield following a single postemergence (POST) application of propanil plus clomazone with single or repeat POST applications of propanil alone or single POST applications of propanil plus pendimethalin, molinate, quinclorac, or thiobencarb. In four of 10 experiments, propanil plus clomazone controlled barnyardgrass better than single or repeat applications of propanil alone or single applications of propanil plus pendimethalin, molinate, quinclorac, or thiobencarb. The most consistent increase in rice yield over a single application of propanil occurred where clomazone was applied in mixture with propanil.

Field experiments were conducted to evaluate the effect of application time on common waterplantain control in wild rice with MCPA and 2,4-D. Common waterplantain control was greatest when MCPA or 2,4-D were applied at 1.1 or 1.7 kg ai/ha at the two-aerial leaf stage. The best late-season control was MCPA applied at the scape elongation growth stage. Common waterplantain was controlled adequately when 0.6 to 0.8 kg/ha of MCPA were applied at the scape elongation or early flowering stage. However, because of common water plantain interference and sensitivity of wild rice to late herbicide applications, the best treatment stage for wild rice yield was when MCPA was applied at 0.6 kg/ha to common waterplantain at the two-aerial leaf stage. Wild rice at this time is at the more tolerant one-aerial leaf growth stage.

Field experiments were initiated to determine the efficacy of fluazifop as influenced by growth stage for green, yellow, and giant foxtail, large crabgrass, and Japanese millet. Additionally, the influence of air temperature and simulated rainfall on fluazifop efficacy for green foxtail and Japanese millet was determined by greenhouse and growth-room experiments. In both 1983 and 1984, fluazifop activity was reduced as the growth stage increased from 3- to 5- to 7-leaf for all species. Significant differences among species in susceptibility to fluazifop were evident with the descending order of tolerance: green foxtail > large crabgrass > yellow foxtail > giant foxtail > Japanese millet. Increasing the air temperature from 18 to 30 C reduced fluazifop control of green foxtail at herbicide rates less than 0.14 kg ai/ha but did not affect Japanese millet. A 1- to 2-h rain-free interval was required for optimum control of green foxtail and Japanese millet at 0.07 kg/ha fluazifop; the interval was reduced to 45 and 15 min, respectively, when fluazifop rates were 0.14 kg/ha. The longer rain-free interval required for optimum control of green foxtail compared to Japanese millet may reflect a slower rate of herbicide absorption in green foxtail.

Field experiments were established in 1989 and 1990 to determine the effects of application rate and timing on sicklepod control and soybean tolerance to POST applications of AC 263,222 and chlorimuron. When applied to 3-, 6-, or 10-leaf sicklepod, 35 g ai ha-1 or more AC 263,222 controlled more than 85% of sicklepod early in the season, and season-long when applied to 3- or 6-leaf sicklepod. At all timings, 70 g ha-1 or more AC 263,222 resulted in better control than a PRE application of 420 g ai ha-1 metribuzin followed by 9 g ai ha-1 chlorimuron applied POST. At 35 g ha-1 or more AC 263,222, application timing did not affect sicklepod control. However, control was reduced with 18 g ha-1 when applications were delayed from 3- or 6-leaf to 10-leaf sicklepod. At the 10-leaf sicklepod growth stage, a PRE application of imazaquin increased both sicklepod control and soybean yield with 35 g ha-1 AC 263,222 as compared with AC 263,222 applied alone. Soybean injury and height reductions with AC 263,222 at 35 g ha-1 and above were greater than with chlorimuron; however, increased soybean injury or height reduction was not reflected in pod numbers or yield.

Glyphosate was evaluated as a preharvest treatment for enhancing corn kernel dry down and quackgrass control. Glyphosate at 0.4, 0.8, 1.3, and 1.7 kg ae/ha was applied to corn before physiological maturity (kernel moisture 44 to 47%) and at physiological maturity (kernel moisture 35 to 39%). Three weeks after treatment, grain moisture of plants treated at physiological maturity was 2.3 to 6.9% less than that of plants treated before physiological maturity which was 2.2 to 5.5% less than that of untreated plants. Glyphosate did not increase corn kernel drying effectively under high humidity conditions. Glyphosate applied to pre-physiologically-mature corn controlled quackgrass 49 to 64% in the fall of 1984 and 69 to 91% in the fall of 1985. None of the glyphosate treatments reduced corn yield. Glyphosate applied preharvest above the corn canopy may increase the rate of corn kernel drying and may control fall quackgrass in the northern corn belt.

Temporal changes in factors that contribute to the competitiveness of Florida beggarweed in peanuts were studied in 1986 and 1987. Florida beggarweed leaves were unifoliolate to the ninth node and trifoliolate thereafter. Peanuts grew taller than Florida beggarweed until the R-3 stage of peanuts, after which Florida beggarweed height increased logarithmically. Florida beggarweed branching was suppressed by the peanut canopy until the weed overtopped the peanuts. Florida beggarweed dry weight was reduced 80% by peanuts compared with Florida beggarweed grown alone. Peanuts reduced Florida beggarweed leaf area and canopy area. Percent light attenuation as a function of Florida beggarweed canopy area was described by the equation Y = lnX/25.5. Peanut yields in 60 cm of row on either side of a single Florida beggarweed plant were reduced 19%.

Field trials were conducted in New Jersey during 1991 and 1992 to evaluate the efficacy of nicosulfuron, primisulfuron, dicamba, and clopyralid on horsenettle control in field corn. Horsenettle biomass was reduced 74%, 68%, 64%, 61%, 48%, and 40% by primisulfuron + dicamba, primisulfuron, nicosulfuron + dicamba, dicamba, clopyralid, and nicosulfuron, respectively. No treatment was statistically more effective than dicamba. Corn yields were not influenced by the herbicide treatments. Horsenettle populations were not reduced by any treatment.

Fall-planted rapeseed and sudangrass were evaluated for weed control in potato during a two-year study. Rapeseed incorporated in the spring in a loamy sand soil reduced weed density 85 and 73% in 1992 and 1993, respectively, and reduced weed biomass 96 and 50% in 1992 and 1993, respectively, in following potato crops compared to potato after fallow. Potato following rapeseed yielded 25% and 17% more total tuber weight than potato following sudangrass in 1992 and fallow in 1993, respectively. In greenhouse trials, rapeseed tissue added to a loamy sand soil at 20 g fresh weight per 400 g dry soil reduced biomass of hairy nightshade and longspine sandbur by 90 and 83%, respectively. Similarly, white mustard tissue added at 20 g fresh weight per 400 g dry soil reduced biomass of hairy nightshade and green foxtail by 83 and 70%, respectively.

Weed Science Extension is in a period of change. Though there is decreased funding for extension in the United States and Europe, the number of programs including extension activities is increasing in developing countries as shown by World Bank funding. There is a perception problem with the name weed science; we need a strong, recognizable science name. Decreases in one-on-one contact method for teaching, fewer extension weed specialists, and the increased need for interdisciplinary projects to support Integrated Pest Management and Sustainable Agriculture will increase stresses on our positions. These factors also increase the challenge for weed specialists and extension advisors (agents) to become leaders in current programs, initiate new multidisciplinary programs, and choose those programs that will benefit our discipline. Our clientele and the method of communicating with them will change, presenting yet another challenge.

Field experiments evaluating 11 cereal cover crops were established at two locations in Ontario over a two-year period. Cover crops were interseeded into a ridge-tillage corn crop and evaluated in terms of biomass production and winter annual, biennial, and perennial weed species suppression. Seedling establishment and aboveground biomass production of cover crops were variable between locations and years. At both locations over two years, ‘Danko’ winter rye, ‘OAC Halton’ winter barley and ‘Rodeo’ spring barley were the most consistent cover crops in biomass production. However, cover crop residues had no significant effect on weed biomass or density due to a high degree of spatial variability present in the weed populations. Corn grain yields were not reduced by the presence of inter-seeded cover crops when compared with the bare ground control treatment.

Urea and ammonium nitrate are components of 28% nitrogen liquid fertilizer (UAN) that is often used as an adjuvant in addition to surfactants or oils with herbicides. Ammonium nitrate and/or UAN fertilizer enhancement of nicosulfuron phytotoxicity to large crabgrass or yellow foxtail depended upon the associated oil or surfactant adjuvant. Ammonium nitrate reduced the effectiveness of most block copolymers but not other surfactants with nicosulfuron for large crabgrass. Urea never enhanced and often reduced surfactant and oil adjuvant enhancement of nicosulfuron. Ammonium nitrate or UAN, but not urea, enhanced nicosulfuron phytotoxicity to yellow foxtail when the spray carrier contained sodium bicarbonate. These research results indicated that enhancement of nicosulfuron efficacy from UAN is mainly from the ammonium nitrate component. However, the benefit to nicosulfuron from UAN or ammonium nitrate depended upon the associated surfactant or oil adjuvants.

Observations of the effects of living organisms on weeds dates from 1795 when an insect, Dactylopius ceylonicus, was introduced for drooping pricklypear (Opuntia vulgaris Miller) control over a vast area. Since that time, biological control of weeds employed mainly the classical strategy of introducing natural enemies from areas of co-evolution. Self-perpetuation and dissemination of these introduced enemies was essential to suppress successfully the weed below economic levels. This classical tactic is suited particularly for weeds that are distributed widely in less intensively cropped or noncropped areas. Guidelines to introduce foreign organisms for biological control of weeds in the United States have been established.

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.

The isopropylamine salt of glyphosate at 420, 560, and 840 g ae/ha applied alone or mixed with the sodium salt of bentazon at 840 g ai/ha, chlorimuron at 9 g ai/ha, the sodium salt of fomesafen at 350 g ai/ha, or the ammonium salt of imazethapyr at 70 g ae/ha was evaluated for control of large crabgrass and broadleaf signalgrass. Neither grass was controlled by bentazon, fomesafen, or chlorimuron. Imazethapyr controlled large crabgrass and broadleaf signalgrass 30 and 72%, respectively, 3 weeks after treatment (WAT). Glyphosate at all rates controlled both grasses 100%. Control 3 WAT was unaffected by mixing bentazon, chlorimuron, fomesafen, or imazethapyr with glyphosate. Broadleaf signalgrass control 1 WAT was reduced 4 to 15% by mixing bentazon with glyphosate.

In full-season soybean experiments, adding glyphosate, paraquat, or HOE-0661 to chlorimuron, chlorimuron plus linuron, chlorimuron plus metribuzin, or imazaquin was required for effective weed control, especially eastern black nightshade. In double-crop soybean experiments, chlorimuron plus linuron provided similar weed control and yields with or without either glyphosate, paraquat, or HOE-0661. In both full-season and double-crop soybeans, metolachlor combined with chlorimuron mixtures did not enhance weed control or increase yield. These studies indicate a potential for reducing the use of nonselective herbicides or metolachlor when chlorimuron or imazaquin are components of tank mixes, particularly in double-crop no-till soybeans.

The spread of perennial weeds, such as foxtail barley, is a prime deterrent to adoption of no-till cereal production in the Northern Great Plains. In a 3-yr study, the isopropylamine salt of glyphosate at 0.56 kg ai/ha plus nonionic surfactant at 0.25% (v/v) did not control established perennial foxtail barley in early spring. However, adding ammonium sulfate at 2.8 kg/ha to glyphosate plus surfactant improved the effectiveness and year-to-year consistency of glyphosate for killing this weed. This spring treatment fits into no-till farm practice in the Northern Great Plains, providing no-till farmers with a defined strategy to manage this perennial bunch-grass weed.