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.

Experiments were conducted in 1988 and 1989 at four sites in Virginia to test weed control efficacy in double-crop, no-till soybean production systems with reduced rates of nonselective herbicides. Chlorimuron plus linuron at 0.04 plus 0.46 kg ha-1 gave more than 94% control of five weed species, but only 81 to 86% control of three weed species. Tank mix additions of reduced rates of either glyphosate, HOE-0661 or paraquat to the chlorimuron plus linuron treatment increased large crabgrass and common ragweed control.

The herbicide 2,4-D has been in commerce and a subject for research since 1944. It is undoubtedly among the most thoroughly researched pesticides in the world. In our society, 2,4-D has played an indispensable role. It is most important in the production of our food and fiber; in the control of noxious weeds causing public health problems such as common ragweed (Ambrosia artemisiifolia L.) and poison-ivy [Toxicodendron radicans (L.) Ktze.] in the maintenance of our utility supply lines and highway and railroad systems; and as a useful tool for creating desirable wildlife habitats and beautifying our parks, golf courses, and the grounds about our homes.

Recently completed toxicological studies support the conclusions of earlier studies that 2,4-D may be used without undue risk to man, wildlife, or the environment. This does not mean, of course, that we should lessen our precautions to avoid exposure to applicators, prevent spray drift from getting on bystanders, or on pets such as dogs and cats, and following general good sanitation practices in its use.

There have been some reports of an association between the use of 2,4-D and NHL. However, in our opinion after considering all the toxicological and epidemiological evidence, it has not been established that the use of 2,4-D causes NHL or any other type of cancer including soft tissue sarcomas and Hodgkin's disease. As cited in this review, most scientific experts who have carefully examined all the data share this opinion.

The first weed contest was held at the Eli Lilly Research Farm at Albany, GA, in late May 1980. From the original idea of David Teem of FL, a contest evolved that was sanctioned by the Southern Weed Science Society in 1981. In August 1981, the first North Central Collegiate Weed Science Contest was held at the Agri-Growth Research Farm, Hollandale, MN. An undergraduate division was established in 1982. The Northeast Collegiate Weed Science Contest began in 1983 at the Wye Research Center in Queenstown, MD, with both graduate and undergraduate formats. The North Central contest annually has the most participants followed by the Southern and Northeast contests. Representatives from 39 universities have competed in at least one contest. The three contests follow a similar format that includes four events: plant and seed identification of weed species, identification of herbicides from plant symptoms, calibration of herbicide application equipment, and crop/weed problems and recommendations. Preparation by universities has varied from minimal to establishing a class to prepare students for the contest. Regardless of the level of preparation, the weed contests have developed into one of the most anticipated and worthwhile experiences for students and university and industry personnel.

The effects of 1.24 kg ha-1 ammonium sulfate, 5 g ae ha-1 of the isopropylamine salt of imazapyr, and air temperature of 18, 27, and 35 C at 40 and 100% relative humidity on the phytotoxicity of 35 g ae ha-1 of the ammonium salt of imazethapyr applied postemergence to pitted morningglory were evaluated. Both ammonium sulfate and imazapyr increased imazethapyr phytotoxicity to pitted morningglory. Ammonium sulfate enhanced imazethapyr phytotoxicity the most at 40% whereas imazapyr was most effective at 100% relative humidity. Imazethapyr phytotoxicity was enhanced more by the combination of ammonium sulfate and imazapyr than with either alone regardless of relative humidity. Variations in temperature had little effect on phytotoxicity.

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.

A random mail survey of Ohio growers was conducted to determine the geographic distribution of weeds across Ohio and the influence of production practices on the severity of agronomic weed problems. Statewide, the ten most severe weed problems, in descending order, were Canada thistle > foxtail spp. > velvetleaf = common ragweed > common cocklebur > giant ragweed = annual morningglory spp. > quackgrass = common lambsquarters = Pennsylvania smartweed. Distribution of most weeds varied geographically. Infestations of common and honeyvine milkweeds, hemp dogbane, and tree seedlings increased as tillage was reduced. Infestations of common cocklebur and common ragweed decreased as tillage was reduced. As crop rotation became more diverse, infestations of velvetleaf, common cocklebur, giant ragweed, Pennsylvania smartweed, and jimsonweed decreased. Where rotations included forage or hay crops, infestations of large crabgrass, common chickweed, wild carrot, and common dandelion increased.

Three experiments evaluated sicklepod interference with soybean with and without preplant incorporated applications of chlorimuron plus metribuzin or imazaquin. Sicklepod density, weed-free period, and weedy period were examined. In the absence of herbicides, soybean seed yield was reduced with 2 sicklepod plants row m-1, whereas 8 plants row m-1 were necessary to reduce yield when herbicides were used. Herbicide use also increased soybean yield at higher sicklepod densities. Chlorimuron plus metribuzin reduced sicklepod dry matter at 8 plants row m-1. To maintain soybean yield, a weed-free period of 4 wk after emergence was required, regardless of treatment. Both herbicide treatments resulted in increased soybean yield at the zero and two wk weed-free periods; however, they did not affect soybean yield when the weed-free period was 4 wk or more. Imazaquin reduced sicklepod density when plots were left weedy full-season, and further reductions were noted with chlorimuron plus metribuzin. A sicklepod weedy interval of 8 wk reduced soybean yield when untreated, but either herbicide treatment extended that interval to 16 wk.

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.

Believed native to the Mediterranean region, dwarf snapdragon [Chaenorrhinum minus (L.) Lange ♯ CHNMI] was introduced into North America in the late 19th century. Since its introduction, it has spread, mainly along railroad lines, to at least 30 states as far west as Kansas and Nebraska. Increased use of herbicides by railroad companies has resulted in a marked decrease in its abundance in recent years.

Suspected triazine resistant Pennsylvania smartweed plants were discovered near Holy Cross, Dubuque County, IA. Subsequent variable chlorophyll a fluorescence assays confirmed these selections to be triazine resistant. This is the first reported evidence of s-triazine resistance in Pennsylvania smartweed.

Eleven herbicides applied in May, were evaluated for yankeeweed control in East-Central Texas. Yankeeweed cover 1 yr later was reduced to 5% or less by 0.28 kg ha-1 of picloram; 0.56 kg ha-1 of clopyralid, glyphosate, or dicamba; 0.28 + 0.84 kg ha-1 of dicamba + 2,4-D, and 1.1 kg ha-1 triclopyr compared with 30% cover in the untreated area. Chlorsulfuron and metsulfuron at 0.07 kg ha-1 reduced yankeeweed cover to 12 and 7%, respectively. Dalapon, 2,4-D, and tebuthiuron were relatively ineffective. Most herbicides, reduced woolly croton cover within 1 mo after treatment compared to the untreated areas, but 2,4-D at 0.28 kg ha-1 and chlorsulfuron at 0.02 kg ha-1 and 0.07 kg ha-1 were most effective after 4 mo. All herbicides, except dalapon at 1.1 kg ha-1 or less and most rates of 2,4-D and tebuthiuron, reduced partridgepea cover during the year of application. Total grass cover was increased 4 and 12 mo following treatment with clopyralid, picloram, dicamba, and triclopyr. On separate sites, bahiagrass and coastal bermudagrass accounted for most of the increased grass cover.