Canada thistle has been considered a serious weed to agriculture in the northern parts of this country since its introduction. The plant characteristics and growth habits are described by Detmers (3) and Rogers (5) who also point out the seriousness of this weed to agriculture.

Foliage applications of 2,4–dichlorophenoxyacetic acid (2,4–D) to marabú (Dichrostachys nutans), a woody weed found in Cuba (3), generally give complete defoliation with varying amounts of stem kill. The older, more basal areas are not killed and the roots are rarely damaged by single applications of 2,4–D. Presumably therefore, little if any of the herbicide moves downward after these applications.

Most farmers are not taking full advantage of the information available on herbicides and weed control methods. With few exceptions there is too long a delay between the development of a new weed control practice and its use on the average farm. This lag may be attributed to the following factors:

1. Failure of public and commercial extension workers to inform individual farmers.

2. Unsatisfactory experiences by farmers due to improper use of herbicides.

3. Grower unwillingness to try something new without visual proof.

4. General complexity of herbicide usage.

5. Unwillingness of a large number of farmers to be the first to accept a new practice.

Extracts of many plants have been shown to contain germination and growth inhibitors (1, 2, 3, 4, 5). In some instances these inhibitors play a role in the distribution of species. Thus dried Encelia leaves contain a material which leaches slowly into the ground and inhibits the growth of species susceptible to it (2). This suggests that certain weeds may be aided in their competition with crop plants by similar inhibitors. Helgeson and Konzak (4), for example, found that aqueous extracts of field bindweed (Convolvulus arvensis) and Canada thistle (Cirsium arvense) inhibited the germination of seeds and growth of seedlings of certain crop species.

Weeds in pastures are eaten in varying amounts and when consumed probably contribute to the diet of grazing livestock. However, many are not taken by the grazing animals and thus are largely useless plants that are using nutrients, water and light that would grow plants of higher value. In addition to the low palatability of some weeds, many are annual plants that fluctuate more widely in production with adverse weather than the more desirable perennial plants.

Big sagebrush (Artemisia tridentata, Nutt.) is such an aggressive increaser that most of the formerly grassy ranges of the inter-mountain and northwest regions have long since acquired a sagebrush aspect. A suggestion as to the impact of this change upon grazing capacity is apparent from a three-year study in northern Nevada. An average reduction in yield by 20 native and exotic grasses and weeds of about 70 per cent was shown under limited competition with big sagebrush (12).

Investigations during the past 3 years have established sodium 2,4,5–trichlorophenoxyethyl sulfate, hereafter referred to as 2,4,5–TES, as a potential herbicide for control of weeds in tomatoes. The chemical has been succesfully applied just after the last cultivation. The material may be applied either as a basal-directed spray or an overall spray in tomatoes since it becomes phytotoxic only after contact with the soil. Its promise as a herbicide suggests the need for a critical evaluation of possible effects on quality of the fruit. Three measures of quality which may be affected include taste, chemical composition, and malformations such as cracking, blossom-end rot and seedlessness.

A number of investigators have tested 2,4–D (2,4–dichlorophenoxyacetic acid) for the control of weeds in asparagus. Several workers (1, 3, 4, 6) have suggested the use of 2,4–D at rates varying from one to three pounds acid equivalent per acre as a pre-emergence treatment after disking in the spring and again after disking at the end of the cutting season. Warren and Hernandez (5) applied 2,4–D at the rate of four pounds per acre on April 28 just after the asparagus bed was disked. The yield and appearance of the asparagus spears was not affected by the treatment. According to Ahlgren et al. (1), pre-emergence application of 2,4–D caused injury to the first emerging spears in some cases, but caused little permanent damage. These and other investigators found asparagus plants susceptible to foliage applications of 2,4–D and warned against spraying the fern.

The herbicide, 3–(p–chlorophenyl)–1,1–dimethylurea (CMU), first reported by Bucha and Todd (1), is finding increasing uses in the field of weed control. The mechanism of action of this compound, however, is as yet unknown. One of the early symptoms of CMU toxicity is a chlorosis (2) which develops in both monocotyledonous and dicotyledonous species. Muzik et al. (5) have shown that while CMU will inhibit root growth, the primary toxic action of this compound is on the aerial portion of the plant. Cooke (3) showed that CMU brought about a large decrease in the sugar content of plants and suggested that the mode of action was through an interference with photosynthesis.

In studies on the growth of weeds, especially in the seedling stage and also in plant taxonomy in general, the problem frequently arises of finding a precise and simple means of describing a leaf or a cotyledon. To overcome this problem, we are using a system which, for want of a better name, we call the Budd-Best system. Briefly it is a system of using three numbers and a descriptive term (Figure 1).