Herbicidal applications to mesquite in Arizona (17), New Mexico (21), and Texas (5) indicate that the low-volatile esters of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) are usually more effective than amine salt formulations, but there have been instances where the reverse was true. This inconsistency has occurred only in isolated cases, but was of interest in that factors which affect differential susceptibility to the ester and the amine formulations are important and should be more fully understood. The purpose of this study was to determine whether mesquite has a different period of susceptibility to the ester than to the amine. Various biological and meteorological factors were also determined to test their relation to mesquite susceptibility.

The pre-emergence use of 3–(3,4–dichlorophenyl)–1,1–dimethylurea (diuron) offers a means of controlling weeds in cotton during the extremely critical period of stand establishment (1, 2, 6, 8, 9, 10, 11). The amount of diuron required to give effective weed control without injury to cotton has been observed to vary between locations. Factors such as temperature, moisture, light conditions, and physical and chemical properties of the soil may be involved in causing variation in the activity of this herbicide.

Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn) and wild buckwheat (Polygonum convolvulus L.) are annual weeds which are becoming increasingly prevalent on the Canadian prairie. Tartary buckwheat has become widespread in north central Alberta where over 2,500,000 acres are estimated to be infested, with over 500,000 acres heavily infested. The infested area is growing larger and in recent years has begun spreading into the neighboring province of Saskatchewan. Only one infestation, some 300 acres in size, has been reported in Manitoba. Because it is similar in size, the seed of tartary buckwheat is extremely difficult to remove from wheat, oats and barley and under the Canada Seeds Act, grains containing it may not be sold for seed. Commercial grain containing these seeds is severely degraded. As an impurity in wheat, the seed causes discolored flour. Consequently, the spread of this weed is being viewed with considerable alarm in western Canada.

The question of direction and rate of movement of herbicidal chemicals in aquatic plants often arises in considering effective methods of chemical control for plants of this type. Results obtained from studies of solute movement within terrestrial plants are not directly applicable to totally submersed aquatic species for two reasons: a) A liquid medium, in which dissolved substances may be distributed uniformly, surrounds all parts of the aquatic plant, and b) Vascularization is minimal in leaf and stem tissues of submersed aquatics. Reports of experiments yielding quantitative data on translocation patterns in submersed aquatic plants are rare or nonexistent. It is probable that mechanical difficulties encountered in separating root systems from leaf or stem tissues of submersed plants have been of greater hindrance to translocation experiments with aquatic species than any other factors.

The purpose of this study was to find more information on how and why certain herbicides act as they do on plants. The need for this kind of basic fact finding is often emphasized (1, 5, 6, 8). One approach to this problem is to study the effects of various environmental factors on herbicide behavior with plants. An effective way is to hold certain factors constant and alter the amounts or qualities of one or more other factors. Previous work with various colored fluorescent lights (4, 7) had shown marked differences in plant response to various portions of the visible light spectrum. Using essentially the same technique, this study was made of the influence of light quality in modifying the herbicidal effect of 2,4–dichlorophenoxyacetic acid (hereafter called 2,4–D) as various salts and esters. The combined herbicide–light effect was measured principally by dry weight variations from those of normal (control) plants.

Simazin, 2–chloro–4,6–bis(ethylamino)–s–triazine, is a relatively new herbicide that has shown much promise for pre-emergence weed control in corn (3,4,7). It is a white crystalline compound with a solubility of 5 ppm in water and 900 ppm in chloroform. This compound is non-flammable, non-corrosive, and has an acute oral toxicity greater than 5 g/kg for mice. Simazin is said to be highly toxic to cucumber, of intermediate toxicity to cotton, and non-toxic to corn. Schneider (6) reported it to be effective only when absorbed through the root system. This study was begun to determine whether the differences in susceptibility of these plants and the limitation of effectiveness of simazin to the root system could be correlated with its absorption and translocation.

Since the aerial brush control spraying operations in northern Minnesota have little research basis, the Lake States Forest Experiment Station has been carrying on some fundamental.studies aimed at improving the results of this increasingly important aid to forest management. These consist of analyzing two factors basic to all foliage spraying jobs whether they are done from the air or from the ground. These are:

1. The minimum amount of herbicide (in terms of acid equivalent) required to control a unit-area of brush of a given species and density, and

2. The minimum amount of solution needed to distribute the herbicide uniformly over the sprayed area.

The absorption and translocation of 2,4-D (2,4-dichlorophenoxyacetic acid) has been extensively studied by numerous investigators and a number of reviews have been written (3, 7, 8). The methods used in these studies have been critically evaluated (1, 5, 8) and the general conclusion is that in the study of the absorption and translocation of biologically unstable organic compounds, such compounds should be isolated and identified.

Recent investigations on the use of 2-chloro-N,N-diallylacetamide (CDAA), 2-chloroallyl diethyldithiocarbamate (CDEC), and ethyl N,N-di-n-propylthiolcarbamate (EPTC) for weed control have stressed soil incorporation rather than the more conventional application to the soil surface. By this treatment loss of the herbicides as vapors may be reduced, the risk of crop injury lessened, and weed control improved. Although both pre-planting and pre-emergence soil incorporation have been investigated, pre-planting treatments appear most promising. In many weed-crop situations the results obtained with EPTC have been especially promising.

The control of submersed aquatic weeds is a major problem in the management of Missouri fish ponds. Dense stands of aquatic vegetation in ponds cause serious crowding and stunting of fish populations. Recreational values are impaired by the physical interference of weeds with fishing and boating. Even more serious are the occasional partial or complete kills of fish caused by oxygen depletion as plants decay. These kills may occur either in summer or winter.

Along the lower Coastal Plain, from the western panhandle of Florida to the Carolinas, lie approximately ten million acres of deep sands. In northwest Florida the sandhills support chiefly scrub oaks and wiregrass (Aristida stricta). Oaks are mainly turkey oak (Quercus laevis) and bluejack oak (Q. incana). Once an understory to longleaf pine (Pinus palustris), the scrub oaks gained dominance as heavy, indiscriminate logging removed the pines. Today only scattered pines remain, and the oaks and wiregrass prevent seed from these pines from restocking the area.

A very useful technique in toxicological investigation is probit analysis. This method, which was developed by Bliss and other workers (notably Gaddum and Finney, but see reference 4, pp. 42–46) consists of plotting the log concentration of a toxicant against the percentage response on a probability scale, and fitting a weighted regression line to the data. Although the technique has found wide application in pharmacology, entomology, and plant pathology, it has been almost ignored by workers in herbicide research. It is the purpose of this paper to demonstrate that the concepts of probit analysis are applicable to herbicide research, and that the mere plotting of data on logarithmic probability paper may permit a very fruitful interpretation of experimental results. The technique is recommended at the screening level, for its results are very useful in the construction of field tests. It is in no sense a substitute for the carefully designed and executed field test, or for the analysis of test results by other statistical techniques.

It has been shown that with proper timing and the correct concentration, 2,4–D sprays can be used to control strawberry runner production (2). Other effects of this chemical upon the strawberry plants have been studied in a general way by Denisen (4) and Carlson (1). However, these effects have not been shown to be related to a specific influence of the chemicals on the morphological development of the strawberry plant. As the 2,4–D compounds used for weed control have exhibited growth regulating properties (3, 7, 10) it seemed likely that certain preparations might have a more unfavorable influence on plant growth than others. Also, since the molecular structure of the various preparations were different, it could be expected that the various preparations might differ in their influence on the developmental processes of the strawberry.

Early patent records show that a rotary-hoe type of implement has been in existence since 1839 (2). The rotary hoe was used on soybeans as early as 1915, and important considerations for weed control were discussed in “Soybeans in Indiana, 1928,” (1) but its use did not become widespread until about 1929.

In recent years the relationships of 3–(p–chlorophenyl)–1,1–dimethylurea (monuron) phytotoxicity and various factors in the soil have received considerable attention (1, 3, 5, 6). Similar information for 2–chloro–4,6–bis–(ethylamino)–s–triazine (simazin) is lacking because of its later development as a herbicide. The experiments reported here were initiated to compare (a) the toxicity of monuron and simazin in solution culture and in soil, (b) the inactivation of the two compounds in soil and, (c) their downward movement through soil columns.

Leguminous crops for hay, seed, pasture or soil improvement occupy a large portion of the total crop acreage. Plantings of legumes, particularly alfalfa, are often maintained long after production has dropped below an economic level. The reason may be reluctance of farmers to attempt establishment of new stands. In areas where fall seeding is possible but where mosture is often scant, spring seedings with the attendant hazard of annual weeds, must be relied upon for establishment of new stands.

Cotton is the major cash crop in Missouri's seven southeastern delta counties, and is second in cash value for the entire state, even though it comprises only about 6 per cent of the total acreage. Heavy infestations of weeds late in the season materially complicate the defoliation process, reduce the efficiency of both mechanical and hand pickers, lower the grade of the lint by contributing stains and trash, and account for greatly diminished net returns. Despite advances in this field, weed control still constitutes the principal remaining barrier to complete mechanization of cotton production.

The logarithmic, or variable-dosage, sprayer described by Pfeiffer, Brunskill, and Hartley (4) for use in experimental field plot studies appears to offer a means of materially reducing the time and space required to conduct field evaluations of herbicides in horticultural crops. The experiments described herein were conducted to determine the conditions necessary for the successful use of the sprayer in evaluations of this type.

Each year increasing numbers of garden chrysanthemums (Chrysanthemum morifolium Ram.) are grown in the field by commercial nurseries. The cost of labor for weeding and the scarcity of efficient seasonal labor presents a serious problem. This study was undertaken to determine if weeds in chrysanthemum plantings could be safely controlled chemically.

Systemic herbicides applied to leaves must move from the leaf surface into uninjured phloem in sufficient quantity to be translocated throughout the plant. Contact herbicides must at least enter the leaf. Leaves of terrestrial plants are adapted to exchange of gases —water vapor, CO2, O2—but are not adapted to absorb foreign solutes in applied solutions and to translocate them systemically; insectivorous species and some water plants may be exceptions. Failure of herbicidal effectiveness often may be due to lack of penetration. However, selectivity towards herbicides is not clearly related to differential absorption (5, 82, 172, 176).