Air-assist nozzles that use pneumatic energy to help atomize the spray liquid were reviewed. These nozzles use larger orifices than conventional hydraulic nozzles for low-volume applications. By changing the air pressure, various droplet sizes can be produced without changing nozzle tips. Several systems use air to transport the atomized spray to specific target sites. Various air volumes and velocities have been evaluated in these systems. Preliminary research indicated that air can improve canopy penetration and can cover the entire plant more uniformly. Undersides of leaves can be treated easier with air-assist systems compared to conventional applications with hydraulic nozzles.

Wells and streams in 10 North Dakota counties were surveyed for picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), the major herbicide used to control leafy spurge (Euphorbia esula L. # EPHES). Three rivers and 144 wells were sampled in 1985. Picloram concentration ranged from <0.1 to 12.4 ppb in the water from five wells in five counties and from <0.1 to 6 ppb in two rivers. An additional 44 wells were sampled in 1986; they were located within 2 km of the five wells where picloram was detected in 1985. Picloram concentrations in 1986 ranged from non-detectable to 6.7 ppb in the original contaminated wells and was 0.97 ppb in water from one of the additional 44 wells. Picloram concentration in the river water was lower in 1986 than in 1985 but was detected farther downstream. All contaminated wells were within 1.5 km of an area treated for leafy spurge, but picloram had been spilled accidentally or misapplied near all but one of the wells. The concentrations detected were at least 100 times below suggested tolerance levels for water.

Herbicides were evaluated alone, in combinations, or as sequential treatments on direct-seeded tomato each year from 1982 through 1984. Diphenamid at 4.5 kg ai/ha or napropamide at 1.1 to 2.2 kg ai/ha alone are registered but frequently do not control weeds adequately, particularly when yellow nutsedge and/or Florida pusley is common. Combinations or sequential treatments are necessary to overcome these weed problems in cropping systems. Metolachlor at 0.8 to 3.4 kg ai/ha injured direct-seeded tomato in proportion to the rate applied. Pendimethalin at 0.6 kg ai/ha also injured tomatoes. Fluazifop at 0.3 to 0.6 kg ae/ha and sethoxydim at 0.2 to 0.5 kg ai/ha effectively controlled annual grasses without injuring tomato seedlings. These herbicides would reduce competition and would increase harvesting efficiency where grass weeds are a problem.

Seed of three weed species collected from the grain bins of combines while standing hard red winter wheat was harvested germinated better than hand-harvested seed. Combine-harvested curly dock seed germinated from 4 to 24% more than hand-harvested seed. Curly dock seed harvested with a commercial-type combine germinated better than those harvested with a small-plot combine. Harvesting slimleaf lambsquarters and Venice mallow seed with a commercial-type combine also enhanced germination compared to hand-harvested seed.

Contact, induction, and corona electrostatic charging systems for pesticide spraying are reviewed and are compared with uncharged spraying systems. When uncharged sprays are poorly intercepted by plants, charging significantly increases deposition, drawing from the reservoir normally deposited on the soil. Post-emergent herbicide spraying is the one area where the benefits of electrostatic charging are identified least easily. For insecticides and fungicides where the young crop is the ‘general’ target, increased capture of charged spray may permit reducing doses with economic and environmental benefits. While charging may not increase total capture where uncharged spray interception is good, it does alter spray distribution throughout the crop canopy. The biological consequences of modifying spray distribution depend upon the ‘real’ pesticide target. In situations where the crop acts as an electrical shield limiting spray penetraton, air assistance is necessary to augment charged spray deposition within the crop canopy. Drift of charged spray clouds should be related to drop spectra, velocities and trajectories and requires further study as do protocols for spray charge measurement and definition. In addition to biological performance, the transfer of electrostatic technology to farms is limited because of financial, legal, and practical factors. Identifying specific major crop/pest problems will help to introduce electrostatic spraying, which will complement, rather than replace, traditional spray systems.

Field studies were conducted in 1982 to 1984 to determine the effects of common lambsquarters on growth, yield, and nutrient concentration of transplanted tomato. Common lambsquarters densities ranged from 16 to 64 plants/m tomato row and fresh weight ranged from 26 360 kg/ha at 16 plants/m to 46 000 kg/ha at 64 plants/m row. Common lambsquarters did not affect tomato shoot dry weight at the vegetative stage but decreased the weight at the early fruit stage. Season-long interference of common lambsquarters reduced marketable tomato fruit number and also, marketable fruit weight ranging from 17% at 16 plants/m to 36% to 64 plants/m row. Concentrations of N in tomato leaves were unaltered at vegetative and flowering stages but decreased regardless of common lambsquarters density at early fruit and harvest stages. Weed density did not alter concentrations of P, K, and Ca in tomato leaves.

Strategies to prevent chemical contamination of groundwater will be more effective and cost less than cleaning up groundwater. Advances in weed control technologies have improved timing of herbicide applications, have reduced application rates from kg/ha to g/ha, and have distributed herbicides better within the weed-crop complex. These technologies include microbial pesticides, controlled-release formulations, herbicide chemistry, improved integrated weed management systems, and bioeconomic weed-crop models that reduce herbicide use. These new technologies should reduce the quantity of herbicides used by farmers and lessen the chances of groundwater contamination.

A seed remover using a modified water-spray system was constructed to separate weed seeds rapidly and effectively from a silt loam soil A 1-kg soil sample can be washed through the seed remover in 6 min. Using a 500-μ mesh sieve, only 70% of small shepherdspurse seeds were recovered, while 100% of larger seeds of henbit, curly dock, wild oats, and downy brome were recovered. The modified seed remover system reduced the required man-hours by more than 50% compared to previous systems.

In the late 1930s, European engineers discovered that, for very low flow rates, rotary disk atomizers produced a more definable range of droplet sizes than hydraulic atomizers. In the late 1970s, a cup-like spinning atomizer was developed to apply herbicides at low and ultra-low volumes. Rotary atomizers distribute droplets in a pattern similar to hollow cone nozzles. The droplet trajectory could affect deposits adversely since droplets released horizontally are exposed to wind and other environmental effects longer than hydraulic spray nozzles. Propellers and fans were used to enhance downward movement of droplets without considering that droplet impingement velocity was critical for efficient deposition. In the early 1980s, rotary atomizers were promoted to reduce herbicide rates, but the claims were products of unconfirmed testing. Herbicide efficacy in confirmed research was not influenced by application with the rotary atomizer, but lower carrier rates reduced the amount of water handled during the spraying operation. The cost of the atomizer, more maintenance, and greater care during operation with no decrease in herbicide rates discourage continued use.

When Scotland was under an imminent Viking invasion, the Scots piled the beaches with thistles and waited. During the night of the invasion, the sandal-clad Norsemen leaped onto the thistle-strewn beach and let out cries of pain and curses. Warned of their approach, the Scots drove the Norsemen back to their ships. Small wonder that the thistle became Scotland's heraldic emblem and the source of her motto, “Touch Me Who Dares”. Since 1687, induction into Scotland's Order of the Thistle has been a great honor. Linnaeus named Scotch thistle, Onopordum acanthium L. # ONRAC, from the Greek onos, or donkey, and perdo, to consume; the species name is from the Latin acanthus, meaning spiny. Thus it is a spiny plant eaten by donkeys.

The growth of two mallow family weeds, velvetleaf and prickly sida, was inhibited 50% when seedlings were treated with less than 200 g ai/ha of thidiazuron. Spurred anoda was unaffected by treatment with up to 1120 g/ha of thidiazuron. Cotton, okra, and hibiscus, all in the mallow family, also were susceptible to thidiazuron treatment. Leaf development in 2-week-old cotton seedlings was inhibited 20% by less than 35 g/ha thidiazuron as were seedling okra and hibiscus. Plants of all these susceptible species were more resistant when grown for 2 months before treatment. Seedlings of soybean displayed localized injury after treatment, but plant height, biomass, and seed production were not significantly affected 10 weeks after treatment with up to 1120 g/ha thidiazuron. Seedlings of corn appeared unaffected by treatment with up to 1120 g/ha thidiazuron.

Field studies were conducted from 1984 to 1986 to assess cabbage injury and yield response to several acetanilide herbicides. When incorporated, metolachlor significantly injured cabbage and reduced yields while post-transplant applications caused foliar flecking but did not reduce yields. Crop injury from pretransplant applications of 4.4 kg ai/ha was significant for all herbicides in both 1985 and 1986. Although total yields in 1985 and 1986 were comparable, maturity was delayed in 1986. With few exceptions, the acetanilides did not differ in either injury or yield-reducing potential. However, compared to trifluralin, metolachlor reduced yields in both years and at both rates.

Crabgrasses (Digitaria spp.), the first cultivated grains, were grown for food thousands of years before they were considered weeds. Digitaria, a genus of about 60 species, grows in the world's temperate and tropical regions. Many of the species are good forage grasses. Thirteen weedy Digitaria species infest the United States, but large crabgrass (D. sanguinalis # DIGSA) and smooth crabgrass (D. ischaemum # DIGIS) are the most common.

Allelochemicals representing numerous chemical groups have been isolated from over 30 families of terrestrial and aquatic plants. Some of the compounds also have been isolated from soil in quantities sufficient to reduce plant growth. Although selected allelochemicals are believed to influence plant densities and distributions, none isolated from higher plants have been considered active enough for development as commercial herbicidal products. Almost all herbicidal allelochemicals exist in plants in nontoxic, conjugated forms. The toxic moiety may be released upon exposure to stress or upon death of the tissue. The most successful use of allelochemicals in weed control has been management of selectively toxic plant residues. For example, rye residues have controlled weeds effectively in a variety of cropping systems. Several weed species may interfere with crop growth through chemicals released from their residues. A number of noxious perennial species appear to exploit allelochemicals in their interference processes. This review focuses on the more recent chemical discoveries and how they might be exploited for weed control.

A rationale for the study of phytotoxins from fungal pathogens of plants is presented. Structural chemistries and biological data are given for numerous, recently discovered phytotoxins in such diverse chemical classes as polyketides, terpenoids, diketopiperazines, and isocoumarins. The biological activities of these compounds range from broadly toxic (curvulin) to host specific (maculosin-1). Phytotoxicology offers a viable supplement to organic synthesis as a means of developing and implementing new, biorational, and economical herbicides.

Metribuzin and the ethyl ester of chlorimuron were evaluated alone and in combination for preemergence broadleaf weed control in soybeans. Neither herbicide alone controlled all broadleaf weeds tested, but combinations showed both complementary and additive action. Two field studies quantified these interactions on broadleaf weeds and showed that low rates of either herbicide alone controlled Pennsylvania smartweed and redroot pigweed. Metribuzin was more effective than chlorimuron in controlling prickly sida and hemp sesbania, while chlorimuron was more effective on common cocklebur, sicklepod, and ivyleaf and pitted morningglories. Additive action was most important on velvetleaf, sicklepod, annual morningglories, and hemp sesbania. Because the components were both additive and complementary, a range of mixture rates and ratios were more effective for weed control than either herbicide alone.