Field experiments were conducted to evaluate pyridine herbicides for Virginia buttonweed control and turfgrass tolerance. Treatments included clopyralid and fluroxypyr applied at 35, 70, 140, 280, and 560 g ae/ha, compared to a three-way combination of 2,4-D plus dichlorprop plus dicamba (840 + 840 + 210 g ae/ha, respectively). Fluroxypyr applied at 140 g/ha or greater controlled Virginia buttonweed 80% or greater through 10 wk after treatment. A second experiment evaluated 280 g/ha clopyralid or 140 g/ha fluroxypyr alone or in combination with 0.25 or 0.50% (v/v) nonionic surfactant, compared to 280 g/ha dicamba or 1,120 g/ha 2,4-D alone or in combination with nonionic surfactant. The addition of nonionic surfactant to clopyralid or fluroxypyr did not increase Virginia buttonweed control. Fluroxypyr at 280 g/ha and higher produced 22 to 53% injury to bermudagrasses 2 wk after treatment. Common centipedegrass was injured through 3 wk after treatment with 4,470 g/ha fluroxypyr or greater. Zoysiagrass exhibited injury with 4,470 g/ha fluroxypyr at 2 wk after treatment; however, injury was less than 8% at 3 wk. Common St. Augustinegrass was severely injured with 2,235 g/ha or greater fluroxypyr through 7 wk after treatment. Clopyralid did not cause injury to any turfgrass species.

Understanding the effects of previous herbicide applications on cover crops is important if cover crops are to be successfully established during the same growing season. Greenhouse research was conducted to evaluate the sensitivity of annual ryegrass (Lolium multiflorum), oat (Avena sativa), crimson clover (Trifolium incarnatum), and medium red clover (Trifolium pratense) to EPTC plus R-29148, pendimethalin, and metolachlor plus CGA-154281 in a loam soil with 2.5% organic matter. Annual ryegrass density was reduced 96% by EPTC at 4.48 kg ai/ha and metolachlor at 2.24 kg ai/ha, whereas oat density was reduced 99% and 35%, respectively, from the two treatments. Pendimethalin at 1.68 kg ai/ha reduced annual ryegrass density 14%, but not oat density. Crimson clover biomass was reduced 33% by EPTC, 45% by metolachlor, and 15% by pendimethalin. All herbicides reduced the density of medium red clover > 25%, but biomass was reduced only by metolachlor. Field trials were conducted to determine whether persistence of these herbicides would affect the seeding time for annual ryegrass and crimson clover establishment. Annual ryegrass was successfully established following application of EPTC at 4.48 kg/ha when seeding was delayed 35 to 40 d after treatment (DAT). Pendimethalin at 1.68 kg/ha injured annual ryegrass > 15%, and annual ryegrass was severely injured by metolachlor at 1.68 kg/ha regardless of seeding time. Successful establishment of crimson clover following all herbicides was possible when seeding timings were delayed. Pendimethalin injured crimson clover less than 13% 15 to 17 DAT, and EPTC injured crimson clover less than 5% 28 to 35 DAT. Crimson clover injury from metolachlor was less than 16% 35 to 40 DAT. Herbicides with longer reported soil persistence generally require more time between herbicide application and cover crop seeding for safe establishment of the cover crop, particularly if the cover crop species is sensitive to the herbicide.

Producers in the semiarid Great Plains are seeking management strategies to delay development of herbicide resistance. The objective of this study was to determine if cultural systems could control weeds in proso millet (Panicum miliaceum), thus eliminating the need for herbicides and removing selection pressure. Initially, we evaluated individual cultural practices for improving competitiveness of proso millet. Increasing seeding rate, banding N fertilizer with the seeds, growing a taller cultivar, and eliminating tillage favored proso millet over redroot pigweed (Amaranthus retroflexus). Combining several cultural practices with delayed planting in a cultural system reduced biomass and seed production of two pigweed species 85% or more in both tilled and no-till systems, subsequently eliminating proso millet yield loss. Density of the two pigweed species was sevenfold greater in the tilled system, yet the cultural system approach was still effective. Cultural system impact on seed production suggests that pigweed densities will not increase over time. With cultural systems, producers can minimize selection pressure, thus delaying development of herbicide resistance.

Wild oat (Avena fatua) control often is an integral management practice in cropping systems that include cereal crops. Experiments were conducted at two locations in Saskatchewan (Saskatoon and Scott), Canada, from 1994 to 1997 to determine the influence of ICIA 0604 rate (50, 100, 150, and 200 g ai/ha), water volume (30, 50, and 100 L/ha), spray mixture pH (unbuffered, close to pH 7.0; reduced, pH 4.0), late morning and evening application times, and sodium bicarbonate concentration of water source (Saskatoon water, negligible; Scott water, 695 mg/L) on wild oat fresh weight and wheat (Triticum aestivum) grain yield. Reducing ICIA 0604 rate below the recommended label rate (200 g/ha) increased wild oat fresh weight by 22% and decreased wheat grain yield by 7% when applied with 50 or 100 L/ha of water. Applications with 30 L/ha of water resulted in more wild oat growth (19%) and less wheat yield (6%), regardless of the ICIA 0604 rates. Spray mixture pH or time of application did not modify the effects of ICIA 0604 rate and water volume on wild oat fresh weight and wheat yield at Saskatoon. At Scott, the negative effects of ICIA 0604 rates lower than 200 g/ha applied with 50 or 100 L/ha of water were most apparent when applications were made in the morning, especially with an unbuffered spray mixture. ICIA 0604 applications made in the evening with 50 or 100 L/ha of water resulted in the lowest wild oat fresh weights and greatest wheat yields, regardless of the ICIA 0604 rate or spray mixture pH. Antagonism between sodium bicarbonate in the unbuffered water from Scott, as indicated by the spray mixture pH effect, and the time of application effect were important factors controlling treatment responses at Scott. Lower than recommended ICIA 0604 rates often maintained net returns, even though wheat yield responded negatively to reduced ICIA 0604 rates. Understanding the effects of water quality on wild oat control will allow producers to make prudent decisions regarding the optimal application parameters for ICIA 0604.

Field research was conducted at three locations in Mississippi to evaluate CGA-277476 tank mixtures with four broadleaf herbicides for possible improvement of broadleaf weed control. Tank mixtures in this research were typically additive, although some instances of antagonism were noted. Control of morningglory (Ipomoea) species and hemp sesbania (Sesbania exaltata) was not consistently improved by the addition of acifluorfen, chlorimuron, fomesafen, or imazaquin to 59 or 79 g ai/ha CGA-277476. However, when a large population of weeds was present, the addition of acifluorfen, chlorimuron, or fomesafen to 59 or 79 g/ha CGA-277476 improved control over CGA-277476 alone. Prickly sida (Sida spinosa) was not controlled more than 68% with any treatment in this study; however, horse purslane (Trianthema portulacastrum) was controlled at least 90% with either 79 g/ha CGA-277476 alone or tank-mixed with acifluorfen, fomesafen, chlorimuron, or imazaquin. The addition of CGA-277476 to acifluorfen or fomesafen did not improve control over acifluorfen or fomesafen alone on any of the weeds evaluated; however, the addition of CGA-277476 to imazaquin improved hemp sesbania control over imazaquin alone. Tank mixtures did not result in yields greater than CGA-277476 alone in areas with moderate weed pressure, whereas in areas with severe weed pressure, tank mixtures improved soybean (Glycine max) yield over CGA-277476 alone.

Field experiments were conducted at Vegreville and Lacombe, AB, to determine the influence of barley (Hordeum vulgare) variety and seeding rate on interference of wild oat (Avena fatua) with barley. Barley variety and seeding rate affected barley density, height at maturity, and seed yield, as well as wild oat shoot dry weight and seed yield in most experiments, but there was no variety by seeding rate interaction. As expected, the semidwarf varieties Falcon and CDC Earl were the shortest. Barley seedling emergence and subsequent plant densities varied among varieties, locations, and years. The hull-less varieties Falcon and CDC Dawn had the poorest emergence in most cases, whereas AC Lacombe and Seebe had the highest emergence. Wild oat shoot dry matter and seed production was highest in the Falcon, CDC Dawn, and CDC Earl plots, suggesting that these were the least competitive with wild oat. Barley yield loss from wild oat interference also tended to be highest in these varieties. Poor emergence of Falcon and CDC Dawn and the shorter stature of Falcon and CDC Earl likely contributed to their relatively poor competitiveness with wild oat. Increasing the seeding rate improved the competitiveness of all varieties, as evidenced by reduced wild oat shoot dry matter and seed production and, in some cases, improved barley yields.

Producers in the semiarid Great Plains are including corn (Zea mays) in dryland rotations; however, weed management is difficult because the corn canopy is not competitive with weeds. My objective was to determine if cultural practices can enhance corn's competitiveness with weeds, thus supplementing current weed management strategies. Cultural systems, comprised of different row spacing, plant population, and nitrogen placement, were evaluated for effects on foxtail millet (Setaria italica) growth during three growing seasons. A cultural system comprised of 38-cm row spacing, 47,000 plants/ha, and N banded near the seeds reduced foxtail millet biomass 60% compared with the conventional system of 76-cm row spacing, 37,000 plants/ha, and N broadcast. Narrow rows had the greatest effect on foxtail millet growth. Corn's tolerance to foxtail millet interference also was improved, as yield loss in the system with narrow rows, high population, and banded fertilizer was reduced threefold compared with the conventional system. Integrating cultural systems with rotation design and residue management will further strengthen weed management in semiarid corn production.

This study assessed the tolerance of ‘Midlawn’ (Cynodon dactylon × C. transvaalensis) and ‘OKS 91-11’ (C. dactylon) bermudagrass to commonly used postemergence herbicides and compared visual assessment with vehicle-mounted optical sensing (V-MOS) for evaluating herbicide phytotoxicity. Two postemergence herbicides were applied to mature stands of Midlawn and OKS 91-11 at two and four times label rates, and seven postemergence herbicides were applied at standard and two times label rates. Visual evaluation and spectral assessments were made for turf color 2, 7, 14, and 21 d after treatment (DAT). Triclopyr and triclopyr plus clopyralid at 2× and 4× label rates caused significant damage on OKS 91-11 and Midlawn bermudagrass in both July and September experiments. MSMA at 2× rate and MSMA + metribuzin at 1× and 2× rate caused up to 73% color reductions that disappeared within 21 DAT in both cultivars. During July, 2,4-D plus mecoprop plus dicamba at the 2× rate caused at least 18% injury to Midlawn bermudagrass for 21 d. Metribuzin was safe at the 1× rate but caused significant injury for up to 7 d at the 2× rate. Imazaquin and halosulfuron-methyl each caused significant damage on one rating date. Pronamide caused no change in color regardless of rate or time of application. OKS 91-11 tolerated 2× rates of 2,4-D plus mecoprop plus dicamba better than Midlawn, but cultivar responses to other herbicide treatments were similar. V-MOS was effective for measuring green color reduction on bermudagrass turf. V-MOS and visual evaluation were linearly related (P < 0.01) at a strength of r = 0.58. Statistical results obtained using visual rating and V-MOS were the same in 86% of all cases.

Leafy spurge (Euphorbia esula) along long distances of railroad right-of-ways is often treated with the least expensive herbicides available that only control top growth. The objective of this research was to evaluate flea beetles, Aphthona nigriscutis and a mixed population of A. czwalinae and A. lacertosa, for establishment and potential to reduce leafy spurge infestations along railroad right-of-ways. In separate experiments, both Aphthona species established the first year following release, and the rate of spread was similar regardless of the initial number released. Aphthona nigriscutis reduced leafy spurge approximately 65% up to 16 m from the release point by 3 to 5 yr after release. The mixed population of A. czwalinae and A. lacertosa reduced leafy spurge density over 95% within 4 yr of release. Biological control is an alternative to chemical control for leafy spurge along railroad right-of-ways, and establishment at these sites could facilitate biological control agent movement into remote areas.

A Research Committee was established by the Weed Science Society of America to outline the direction of weed science research during the next decade. Weeds adversely affect humans in both agricultural and nonagricultural environments. It is the opinion of the research committee that weed science will be advantageously positioned for the future if research focuses on research decision processes, weed biology and ecology, weed control and management practices, herbicide resistance, issues related to transgenic plants, environmental issues, and potential benefits of weeds. These future weed science research directions endorse those of the commodity and grower input group Coalition for Research on Plant Systems (CROPS)'99, a U.S. Department of Agriculture (USDA)-supported initiative. The future of weed science is dependent on a joint effort from industry, government regulators, and the public sector consisting of grower groups, as well as USDA, Agriculture and Agri-Food Canada (AAFC), and university researchers. It is our opinion that efforts spent on these research areas will benefit not only growers, commodity groups, homeowners, and industry, but society at large, through the maintenance and improvement of the food and fiber production system, and the environment in North America.

Oxeye daisy (Chrysanthemum leucanthemum L.), a European perennial, was brought to North America as an ornamental. The plant is still grown in decorative gardens and it is one parent of ‘Shasta’ daisy (Holm et al. 1997). Tradition says that the oxeye daisy crept out of Massachusetts Governor Endicott's garden between Tuesdays, and claimed the whole nation in two centuries (Haughton 1978). It also arrived as a contaminant in imported hay and grain seeds (Haughton 1978). Oxeye daisy escaped cultivation and also spread quite readily from agricultural activities to become an aggressive competitor. It often forms thick patches, especially in cattle-grazed areas, reducing hay or forage production (Olson and Wallander 1999). Consequently, oxeye daisy has been declared a noxious weed in many areas (Holm et al. 1997). It is found throughout most of the United States and north into southern Canada from Labrador to British Columbia (USDA 1970).