Various species of barberry serve as alternate hosts of the destructive stem rust disease of wheat, oats, barley and rye. Eradication of susceptible barberry plants is one of the principal control measures.

Crop production on most lands of the western United States requires the use of supplemental water which is delivered through established irrigation canal distribution systems. These systems frequently support heavy growths of aquatic plants which prevent or impede the passage of water. Because a reduction in the carrying capacity of a canal makes it necessary to deprive potential productive land of the water required to grow a satisfactory crop, it is imperative to keep the waterways open.

The main factor determining the effectiveness of dinitro pre-emergence weed killers in the control of annual grasses and weeds is its distribution and concentration in the soil.

Most workers with herbicides agree that the effects brought about by many of these substances must be the results of altered enzymatic action within the plant. The actual mechanism is still a matter of conjecture in spite of some excellent research and well founded theorizing. A brief examination of enzymes and enzyme action in the light of results obtained with 2,4-D particularly, may suggest how this herbicide fits into the enzyme picture.

The following table of chemical and physical properties of some herbicides was compiled as an aid to agricultural research workers.

When wheat seedlings are injured by trichloroacetate (TCA) the leaves turn yellow in much the same manner as do those on plants growing in media where the nutrients are unbalanced. Accordingly, there is the possibility that TCA may have some effect on the intake of plant nutrients, and that injury was actually the result of nutrient starvation.

Before discussing the subject of “Trends in Teaching Weed Control”, let us consider the agricultural situation for a momentl According to agricultural statistics there is a trend towards larger farms. These can be operated most efficiently only by making economical use of equipment. It can also be said that farming is a business. Those operating farms are conscious of costs. Therefore, any weed control program that might be adopted would be favored principally because of its economic value. Farming is also becoming more scientific as we are now living in a scientific age. As farming becomes more scientific, those persons operating farms must have the ability to make use of new developments regardless of their own scientific tendencies.

In recent years, chemical control methods have been discovered for most common annual weeds with the notable exception of wild oats. Isopropyl N-phenyl carbamate (IPC) and isopropyl N-(3–chlorophenyl)-carbamate (CIPC) appeared promising in 1950 when they successfully controlled wild oats in barley at University Farm, Saint Paul, Minnesota. In the spring of 1951, investigations were started in an attempt to evaluate these two chemicals further for selective use in field crops.

Chemical control of brush in right-of-ways is now a generally accepted practice. Through the recent period of development and ultimate successful use of this practice, certain important aspects of chemical control have been noted by those in the field of research and commercial use. Many of these aspects are amply documented in the literature while numerous common observations have never been recorded. In this general discussion of chemical brush control, an attempt is being made to weave both types of observations together.

To most people, the word weeds signifies pest plants of the farm, roadside, or other upland areas. However, weeds also occur on, under, or near water. Fifteen million dollars have been spent on a single aquatic nuisance in the South—the prolific water-hyacinth which clogs navigable streams and lakes with its growth. Hundreds of thousands of dollars have also been expended on control of the waterchestnut or water caltrop in the Potomac River. In addition, smaller-scale local campaigns are continuing against cattails, reeds, giant cutgrass, maidencane, alligatorweed, needlerush, lotus, rose-mallows, willows, alders, buttonbush, and similar weeds that interfere with land use for recreation, irrigation, or other purposes. Since control of marsh and aquatic plants in wildlife habitat is an unfamiliar activity to most weed workers, broad aspects of its what, why, and how will be explained briefly.

The fate of herbicides in the soil is of great importance to both research workers developing chemical weed control methods and to growers employing these newer techniques. It is desirable to know whether herbicides applied to the soil will persist and be cumulative so that subsequent crops will be affected, if a short period of residual activity can be expected, or if the compounds are rapidly dissipated. In case of pre-emergence applications where timing is critical and results vary with such factors as soil type, moisture and temperature, the activity and persistence of a herbicide are of great importance. Thus it seemed pertinent to study the effects of soil type, exchange capacity, temperature and amount of rainfall on breakdown, leaching and retention of certain herbicides in the soil. The herbicides used were 2,4–dichlorophenoxyacetic acid (2,4–D), N–1 naphthyl phthalmic acid (NPA), trichloroacetic acid (TCA), 3–(p–chlorophenyl)–1, 1–dimethylurea (CMU) and isopropyl N–(3–chlorophenyl) carbamate (CIPC).

In the past 10 years, phenomenal advances have been made in the regulation of plant growth by organic compounds including some now used as herbicides. The introduction of new chemicals, new weed-control techniques, such as pre-emergence treatment, and low gallonage application are among the most important recent developments in the use of organic compounds for weed control. It is estimated that losses caused by weeds on farms have now reached 5 billion dollars annually, and at present well over 30 million pounds alone of the phenoxy compounds, 2,4–dichloro, 2,4,5–trichloro-, and 2–methyl–4—chlorophenoxyacetic acids (2,4–D, 2,4,5–T and MCP) are being used for herbicidal purposes to help combat these losses (9). The most recent of these three compounds to appear on the market in this country as an active ingredient in herbicidal formulations is 2–methyl–4–chlorophenoxyacetic acid. The chief claim made for its use as a herbicide is that it is less injurious to certain grasses, cereal crops and legumes and more effective on certain weeds than 2,4–D. Fertig (4) concludes that MCP is slower in action and definitely less injurious to legumes, and Crafts (3) cites a number of investigators who have shown that MCP is more selective than 2,4–D, particularly where clover, flax and other crops having leaves hard to wet are concerned. High specificity of the compound is indicated by numerous reports in the literature; Robinson's (8), on the effectiveness of MCP in selective weed control, is one example. However, from recent recommendations (1), there appears to be some disagreement on the use of MCP, indicating need for further testing and experimentation with the compound and its derivatives. MCP as sold may contain up to 40% of impurities by weight, some of which, according to Hansen (6), may have toxic properties.

Peas grown for canning purposes are subject to infestations of weeds even though recommended cropping practices are followed. If weeds are numerous they cause reduced yields of shelled peas and variable maturity. The quality of the pack of peas may also be affected for floral buds and fragments of the weeds are difficult to separate from the shelled peas. Excessive costs for seed peas may result from using high seeding rates in an attempt to control weeds by increasing the competitive ability of the peas.

The action of trichloroacetate, a herbicide of grass-type plants such as quack grass and Johnson grass, has been studied for several years by observing the morphological responses of treated plants. Its presence in such plants has been indicated by analyses for the trichloromethyl group with a colorimetric test using pyridine and sodium hydroxide (1, 10). A review by Barrons and Hummer (1) indicates that root absorption is a much more important avenue of entry than foliar absorption. They also report differences in TCA content in the expressed sap of several species of treated plants. At 20 lbs. per acre they found “very little” TCA in corn and beans (both TCA-susceptible). At 10 lbs. per acre, they found “not a trace of TCA” in corn, “very little” in beans, but “a relatively high concentration of TCA” in peas (a relatively TCA-tolerant plant). However, Tibbitts and Holm (10) found 100 to 500 μg. of TCA per g. of fresh snap bean tissue from plants whose culture solutions contained 15 mg. of commercial grade 80% TCA as sodium salt per 150 ml. of nutrient. In order to check these observations, and to see whether TCA itself is present in the plants, and if so to determine the pattern of its distribution within the plants, as well as to look for possible metabolic products, C14-labeled TCA was synthesized and used in tracer experiments with corn and pea plants.

Brush species treated under field conditions have exhibited a variable response to growth-regulator type herbicides which cannot be explained by previous research findings. Light and temperature are known to influence the response of plants to these materials. Field observations have indicated that environmental factors such as relative humidity and soil moisture may also control to some degree the reaction of plants to herbicides. This chamber is being used to subject seedlings and small plants to controlled conditions of environment for evaluating the hypotheses suggested by field observations.

Research, education and regulatory work in the weed control field had much in common fifteen or twenty years ago. Few materials were then available for chemical weed control and a great deal of emphasis was placed on cultural methods. The regulatory man was doing extension work and the extension man in some states was doing regulatory work, assisting with or actually setting up weed districts, the overall objective, however, being control.

The basis for a sound weed control program is the ability of the majority of the people to identify weed plants and seeds. Too often a patch of weeds becomes a menace to the community before the seriousness of it is realized. Lack of interest in identification led to the investigation of methods, aids and techniques that could be employed to reach and teach people, both adults and youth, to identify weed plants and seeds. The approach was through weed plant identification mounts, weed seed identification boards and through the use of slides. Also utilized were tours, field trips, botany schools, etc. Emphasis will be placed on aids that have been constructed for general use for indoor meetings. It should be stressed at the outset that there is no best way, one needs to utilize every method at his command.