Field studies were conducted to determine if varying the time N fertilizer was applied would affect downy brome interference in winter wheat. Five treatments were compared: four broadcast application times of NH4NO3 at 56 kg N ha-1 during the fallow-crop cycle: 1) during fallow; 2) at planting; 3) during crop dormancy; 4) before winter wheat jointing; and 5) a control where no N was applied. Downy brome was least responsive to N applied during fallow. All N applications during the growing season of winter wheat increased downy brome biomass and culms m-2. Downy brome interference prevented winter wheat from responding positively to N. For example, when crop season precipitation was only 70% of normal, applying N reduced grain yield of winter wheat infested with downy brome from 12 to 28%. This study indicates that N manipulation offers potential for reducing downy brome interference in winter wheat.

Experiments were conducted to monitor the dissipation of imazaquin and imazethapyr applied to the soil surface under conventional and no-tillage conditions. Imazaquin or imazethapyr dissipation rate was similar in no-tillage in 1985 and 1986. Dissipation of the herbicides under conventional tillage conditions varied. Imazaquin dissipation occurred 2.4 times faster in 1986 than in 1985. Imazethapyr dissipation was 3.5 times faster in 1986 than in 1985. Corn planted without tillage (no-till) was injured in 1986 where 210 or 280 g ha-1 of imazaquin or 105 g ha-1 of imazethapyr had been applied the previous year to conventionally tilled soybeans, but injury was not evident where these herbicides had been applied to no-tillage soybeans. Corn injury was evident 2 wk after planting in 1987 but yields were not reduced.

Black nightshade was selectively controlled along with other annual weeds in direct-seeded tomatoes by BAY SMY 1500 applied preemergence. BAY SMY 1500 was also found selective for transplanted tomatoes when applied prior to transplanting or soon after planting prior to black nightshade emergence. Black nightshade control and crop selectivity were obtained with BAY SMY 1500 at 0.75 and 1.25 kg ai ha-1 applied on sandy loam and clay loam soils, respectively.

Field studies were conducted in 1987, 1988, and 1989 to evaluate the effects of freshly applied residual levels (simulated residue carryover) of imazaquin and norflurazon on the growth and yield of corn, cotton, grain sorghum, rice, and wheat. Studies ware conducted on five soils, and concentrations of herbicides were determined at crop planting. Crop injury ratings were recorded 4 wk after emergence, and yields were measured at the end of each growing season. In simulated residue carryover studies, corn and grain sorghum injury occurred and yields were reduced when norflurazon concentrations were 450 ng g-1 soil or greater. Rice yields were reduced at norflurazon concentrations of 710 ng g-1. Corn, cotton, and wheat heights and yields were reduced when imazaquin concentrations were 13 ng g-1, 13 ng g-1, and 45 ng g-1 soil, respectively for crops. Comparisons between simulated carryover and actual carryover were made for corn and cotton grown in imazaquin treated fields as well as for corn grown in a norflurazon treated field.

Sequential applications of MSMA plus metribuzin with selected plant growth regulators interacted synergistically and increased injury of ‘Tifway’ bermudagrass 1 and 2 wk after treatment. However, the higher injury at 3 wk after treatment, from sequential MSMA plus metribuzin with flurprimidol plus mefluidide or paclobutrazol with mefluidide, was additive. The vegetative growth suppression of bermudagrass at 2 wk after treatment with 2,4-D plus mecoprop plus dicamba with flurprimidol was antagonistic. The higher growth suppression 2 wk after treatment for MSMA plus metribuzin and flurprimidol plus mefluidide was additive compared to flurprimidol with mefluidide alone.

Hoary cress germination decreased with lower osmotic potential. Knapweed germination was greatest at 0.0 and −0.5 MPa of osmotic potential. Salinity increases up to an electrical conductivity (EC) of 12 dS m-1 had no effect on germination of either species. Hoary cress and knapweed root growth were reduced by decreases in osmotic potential. Hoary cress root growth was not affected by increasing salinity up to an EC of 12 dS m-1. Knapweed root growth was reduced by the initial increase in salinity (4 dS m-1), but not by higher salt concentrations.

Field experiments were conducted in 1986 to 1990 to determine the effect of different rates and application times of BAS 514 and dithiopyr alone and in combination on control of large crabgrass and dandelion in Kentucky bluegrass, tall fescue, and perennial ryegrass. Herbicides evaluated were applied PRE, early POST, and late POST. Results indicated that both herbicides provided excellent PRE control in all years. BAS 514 rates ranged from 0.84 to 0.56 kg ai ha-1. Rates of dithiopyr ranged from 0.43 to 0.56 kg ai ha-1. In addition to crabgrass control, both herbicides controlled dandelion, BAS 514 exhibiting slightly better activity than dithiopyr. BAS 514 at 0.84 to 1.12 kg ai ha-1 and dithiopyr at 0.26 to 0.56 kg ai ha-1 resulted in excellent early POST crabgrass control when applied at the one- to three-leaf stage of crabgrass. BAS 514 and dithiopyr applied late POST (2 to 3 tillers of crabgrass) resulted in 63 to 85% control of crabgrass and 29 to 85% control of dandelion at 10 wk after application. No weed control enhancement was evident from tank mixing the two herbicides. Excellent turf safety was demonstrated by both herbicides on all three turf species.

Herbicides can persist in the soil and injure sensitive crops planted in the years following herbicide application. The response of sugarbeet to clomazone, imazaquin, imazethapyr, and chlorimuron residues in soil was examined. Clomazone at 1.1 or 2.2 kg ai ha-1 did not reduce yield of sugarbeet planted 1 or 2 yr after application. Imazaquin at 0.07 to 0.28 kg ai ha-1, and imazethapyr at 0.09 to 0.14 kg ai ha-1, can reduce yield of sugarbeet planted 1 yr after application. Imazaquin at 0.07 to 0.14 kg ha-1 caused 28 to 47% sugarbeet injury and imazethapyr at 0.09 kg ha-1 caused 54% injury 2 yr after application in soybean. A 25% yield loss occurred from the imazethapyr treatment. Sugarbeet injury 2 yr after application was greatest when sugarbeet also was planted the year following soybean. Chlorimuron at 0.02 to 0.08 kg ai ha-1 plus linuron at 0.4 to 0.9 kg ai ha-1 reduced yield of sugarbeet planted 1 yr after application when compared with linuron alone, regardless of soil pH. Visible sugarbeet injury of 38 to 66% was still evident from chlorimuron plus linuron treatments 2 yr after application. Sugarbeet should not be planted less than 25 mo following imazaquin, imazethapyr, or chlorimuron application.

In 1988, mowing C. thoermeri once at the bud stage, twice at the bud stage, or once at early bloom of the primary inflorescences, eliminated emergence of Rhinocyllus conicus, a weevil introduced as a biological control agent. Mowing at full bloom reduced weevil survival by 78.8%, whereas mowing at senescence had no effect. In 1989, mowing at full bloom or senescence did not affect weevil survival. Dicamba applied at the full bloom or senescence stage did not affect R. conicus survival, whereas hexazinone reduced R. conicus survival when applied at all growth stages.

EPTC applied at the time of ‘Saranac AR’ alfalfa establishment resulted in higher levels of crop injury from the octanoic acid ester of bromoxynil applied postemergence compared to alfalfa in areas not treated with EPTC. EPTC applied at 1.7 or 3.4 kg ai ha-1 did not injure alfalfa. At Rock Springs, PA, 0.54 kg ai ha-1 bromoxynil caused 28, 43, and 55% foliar injury in areas treated with 0, 1.7, and 3.4 kg ai ha-1 EPTC, respectively. A similar interaction was observed at Landisville, PA, although the level of injury due to bromoxynil was less severe. EPTC also predisposed ‘WL 316’ alfalfa to bromoxynil injury in greenhouse experiments.

Creeping wartcress was first identified in the Imperial Valley of southeastern California in 1982. From two limited invasions of approximately 2 ha each, by 1987 this weed had infested 1500 ha. Creeping wartcress can behave as an annual or biennial weed and is a member of the mustard family (Brassicaceae). Creeping wartcress seed germinates from September through March and flowers first appear in racemes in late February, continuing through May.

The adoption of herbicide use within Illinois has passed through four stages characterized by methods of application. These stages include an initial stage of POST applications, the PRE stage, the PPI stage, and the most recent stage marked by diversification of application methods. Data from 19 pesticide use surveys conducted in Illinois since 1957 were used to determine trends in pesticide use. Herbicide use has increased from 33% of the corn and 1% of the soybean hectarage treated in 1957 to applications on approximately 97% of all the corn and soybeans in 1990. Total herbicide use in Illinois peaked at 3.0 × 107 kg ai annually in 1982 and declined to 2.1 × 107 kg in 1990. Total herbicide use in Illinois between 1950 and 1990 is estimated at 5.0 × 108 kg ai.

Integrated weed management (IWM) is a component of integrated pest management (IPM), which is an interdisciplinary practice involving disciplines such as entomology, nematology, plant pathology, weed science, horticulture, agronomy, ecology, economics, and systems science. Most descriptions of IPM mention three elements: a) multiple tactics (for example, competitive varieties, cultural practices, herbicide usage) used in a compatible manner; b) pest populations maintained below levels that cause economic damage, and c) conservation of environmental quality. Integrated weed management was discussed in 1981 during a Weed Science Society of America (WSSA) Symposium entitled Integrated Weed Management Systems Technology for Crop Production and Protection. Topics presented included modeling weed biology, crop manipulation, biological control, herbicide technology, research needs, teaching approaches, and extension implementation. Our paper was presented as part of a symposium on IWM at the 1990 WSSA meeting. This paper describes some of the research that weed scientists have conducted during the past 40 yr. Topics examined include an introductory review of IPM, trends in several categories of weed research, goals and suggestions stated during the 1981 WSSA Symposium on IWM, IWM accomplishments since about 1981, and the future of IWM as a component of IPM.

A growing awareness of environmental issues in Canada has had a major influence on government policies. An initiative was launched by the government of Ontario to promote research toward the development of an integrated weed management (IWM) system. Research in IWM must take all aspects of the cropping system into consideration and evolve in a progressive manner. This approach must encompass the role of conservation tillage, knowledge of the critical period of weed interference, alternative methods of weed control, enhancement of crop competitiveness, modeling of crop-weed interference, influence of crop rotation and seed bank dynamics, and education and extension of the findings. The complexity involved in addressing these issues requires a multi-disciplinary approach.

The design and analysis of competition experiments should be based on an unambiguous objective. Recent criticisms of particular designs have been made without reference to objectives and may be misleading. Three common designs are discussed: additive, replacement series, and response surface. Additive designs are well suited to agronomic objectives; replacement series are useful for comparing pairs of species; response surface designs can be used for most objectives but may be unnecessarily complex. The published criticisms of additive and replacement series designs are argued to be acceptable limitations within the bounds of the objectives for which they are used. Concerns about these designs confounding density and proportion are irrelevant to the objectives for which they are most suited. The continued use of multiple comparison tests is argued to be illogical. Regression approaches to analysis are more relevant, many non-linear equations are now easy to fit to data and these can be used without the need for linearization. However, there are various pitfalls not adequately reported to date. In particular, error structures need to be checked carefully and over-elaborate equations should be avoided.

Soybean seed yield losses due to interference from common cocklebur, velvetleaf, and jimsonweed, with and without a PPI application of 0.42 kg ai ha-1 metribuzin, were determined in 1986, 1987, and 1988. Damage functions were calculated based on weed density, weed leaf density, and relative weed leaf area index, respectively. Functions relating crop yield losses to weed density varied significantly among treatments and years for each species. Weeds which escaped soil-applied metribuzin were shorter with fewer leaves at 3 wk after planting, and caused lower crop yield losses than control plants at equal densities. Yield loss estimates based upon relative weed leaf area at 3 wk after planting showed least variation between years and treatments.

Sub-Saharan Africa (SSA) has the world's largest human population growth rate, some of its poorest soils, and a high incidence of crop pests. Weeds are the major pest in virtually all of the agro-ecological zones of SSA. Parasitic and perennial weeds dominate the savanna vegetation zones whereas rapidly growing annual weeds overwhelm crops in the forest vegetation zones. High weed pressure coupled with inefficient weed control practices have tied up a disproportionate percentage of SSA's economically active population in the primary task of food production and also have kept crop yields down. In the absence of organized weed research and professional training in weed science to meet the needs of the region, improved cultivars of virtually all crops fall prey to weeds, and available arable land becomes limited to that area that can be kept free of weeds. A preponderance of annual weeds in humid parts of SSA together with hard-to-kill perennial grasses and parasitic weeds in the subhumid and arid agro-ecological zones hamper crop production and frustrate farmers throughout the region. Sustainable food production in the region can be achieved by introducing improved weed management technologies and by addressing other food production constraints of the region.