The use of 2,4-dichlorophenoxyacetic acid (2,4-D) to control annual weeds such as pigweed (Amaranthus retroflexus L.) is common. Abundant evidence has been published to show that 2,4-D affects germination and subsequent seedling development. Allard et al. found that 2,4-D delayed germination and caused abnormalities in seedlings of 22 broadleaf and cereal species. Elongation of radicles was inhibited in mustard seedlings and in both non-dormant and embryo-dormant seeds as well as in seeds with impermeable seed coats. Germination can not only be delayed but can be inhibited, although at low concentrations of 2,4-D germination may be accelerated. Leachates produced by rainfall coming in contact with 2,4-D in soil were deleterious to seeds of flax and corn. To explore further the effects of 2,4-D on seeds, germination tests were made with scarified and nonscarified seeds of pigweed and on the effect on yield and germination of seeds harvested from pigweed plants that were sprayed with sublethal doses of 2,4-D in field plots.

Sodium 2,2-dichloropropionate (dalapon) has been one of the more successful herbicides in controlling grass type weeds that have an abundance of underground rhizomes such as Johnsongrass (Sorgum halepense) and quackgrass (Agropyron repens).

Because all agricultural chemicals applied to plants eventually reach the soil, and because many herbicides are applied directly to the soil for absorption through plant roots, it is desirable to test the persistence of these reagents in soils of varied types. Many such tests have already been conducted. Additional studies will be necessary as new phytotoxic chemicals are discovered. In this paper tests on some of the herbicides which have been studied during the past decade are described. Most of these herbicides are already in extensive use and much information has already been obtained relative to their reaction in soils. The data included here are submitted in an effort to round out the available information, particularly as related to long time effects of the herbicides in soils.

It has been recognized for some time that although short-chain alkyl esters of 2,4-D are very toxic, they do not translocate so well as the parent acid or the heavy esters. Two very plausible reasons for this are apparent: (1) These compounds, being highly lipoid soluble, dissolve readily in plant cuticle, and other lipoid phases, and tend to be held in this phase; (2) penetrating rapidly, these compounds are highly toxic to the treated leaves. This contact toxicity kills the mesophyll and fine vascular bundles of the leaf and stops translocation.

The great herbicidal developments of recent years give hope for chemical control of annual bluegrass, Poa annua, which is a major weed problem in bentgrass turf. Annual bluegrass produces an abundance of seed and quickly dominates bentgrass turf that is not growing at its optimum. Annual bluegrass might be controlled by prevention of seed set, pre-emergence control, and plant eradication. The original purpose of this study was to evaluate chemicals which offered promise of annual bluegrass control by checking seed set. However, necessity led to consideration of any promising chemical regardless of its method of control.

Amitrol (3-amino-1,2,4-triazole) has received considerable attention in recent years as a herbicide and defoliant. This material was noted to have growth-inhibiting and defoliating properties by Hall et al. in 1952. Hall et al. reported that amitrol caused chlorophyll destruction under certain conditions and that chlorophyll synthesis was impaired in tissues formed at the time of, or subsequent to, absorption of the chemical. These workers also reported that cotton treated with amitrol showed a loss approximately 50 percent of the original reducing sugars and sucrose. Herbert and Linck have reported an initial increase in the rate of respiration of Canada thistle following treatment with amitrol. This initial respiratory increase was followed by a decrease which was dependent upon time as well as the concentration of amitrol applied to the plants. Similar results were obtained by Miller and Hall using Avena sections and cotton leaf discs. Heim et al. found that amitrol caused decreases in catalase activity of certain plants. Reduction of chlorophyll content and catalase activity were obtained following application of amitrol to leaves of potato, barley, and sunflower. In experiments reported in a more recent paper by these workers, amitrol caused in vitro inhibition of catalase activity.

Since isopropyl N-(3-chlorophenyl)carbamate (CIPC) is being recommended for use on a limited acreage to control barnyardgrass (Echinochloa species) in drilled rice, it was of interest to the author to investigate the mechanism of selectivity involved. Although a difference in sensitivity among graminaceous plants to isopropyl N–phenylcarbamate (IPC) and CIPC has been recorded, the author was unable to find any explanation for this difference. Observations in the field indicated that Echinochloa seedlings were killed regardless of the depth at which the seed was located; whereas, most rice seedlings escaped injury if the seed was planted sufficiently deep. There appeared to be, however, a difference in response among varieties of rice. The following investigation was initiated to explain the differential response among varieties; however, the conclusions were expanded to explain the selective mechanism for controlling barnyardgrass in rice. The data presented in this paper are representative of results obtained in a series of experiments on this subject.

The physical adsorption of chemical substances onto surfaces in soils or inside plants has been of considerable interest with respect to the fate of herbicides in soils, the selectivity of growth regulator herbicides, and even with respect to the toxic activities of growth regulators in plants. Comparative measurements of the adsorption of various herbicides are limited in number and scope. Experiments are presented here which attempt to measure the relative adsorptive qualities of various chlorinated phenoxyacetic acids, and to provide some evidence concerning the bearing of adsorption on herbicidal action.

Canada thistle was named Carduus arvensis by Tabernaemontanus in 1687, Cirsium arvense by Tournefort in 1700, Serratula arvensis by Linné in 1753, Cirsium arvense by Scopoli in 1772, Carduus arvensis by Robson in 1777 and Cnicus arvensis by Hoffman in 1804. The name Cirsium arvense Tourn. was adopted, but more recently Canada thistle has been referred to as Cirsium arvense (L.) Scop. The cardinal number of chromosomes for the Cirsium genus is 17.

The chloro-substituted benzoic acids discussed in this paper have been evaluated experimentally as soil sterilizing herbicides for field bindweed (Convolvulus arvensis L.) control at the Ft. Hays Experiment Station since 1955. The value of soil sterilization in a perennial weed control program in the Great Plains region is evidenced by recommendations made by several state experiment stations. Prior to 1950, most semi-permanent soil sterilization was accomplished with such chemicals as sodium chlorate, boron compounds, and arsenicals. These compounds continue to be important even though the poisonous qualities of arsenic compounds and the hazards of handling sodium chlorate are well recognized.

Pensacola bahiagrass (Paspalum notatum F.) is a leading pasture grass in the Southeastern and Gulf Coast states where it produces high quality forage on relatively infertile soils low in available moisture. It is a major seed crop on which many farmers rely as a cash crop. Weeds compete strongly with this grass during its establishment and even after establishment of a sod, various annual or perennial weed species may encroach. Control of such weeds often is desirable.

The remarkable spread of a seed-bearing Spartina species (formerly incorrectly known as S. townsendii H. & J. Groves, now awaiting a new name) in mudflat areas on European coasts in the past 70 years is widely known. It was suspected from the sudden appearance of a new Spartina species in Southampton Water during the latter part of the 19th Century amongst accidentally introduced Spartina alterniflora Lois, and the British native Spartina maritima (Curt.) Fernald, that the plant was of hybrid origin. Some of the plants were found to be polyploid and this suggested an explanation for the extreme vigour and fertility of those plants which rapidly spread from Southampton Water, east and west along the south coast of England.

In using non-fortified oils for post-emergence weed control in cotton, it has been necessary to follow certain precautions because of differential plant response at different stages of cotton growth. Several workers emphasize that certain oils can be applied safely to young cotton hypocotyls three weeks after emergence, but as soon as small bark cracks begin to appear at the base of the stem, oil usually causes injury. Palmer and Ennis found that when an oil was applied to cotton stems 14 to 80 days old, it injured the stem, and reduced final yields when cotton was 27 to 59 days old at time of application. Plants less than 27 days old and more than 59 to 80 days old were not injured by the oil.

Bedstraw (Galium mollugo L.) is a deep-rooted perennial weed present throughout New York and many areas of the northeastern United States and Europe. It occurs in pasture, meadows, waste areas and along ditch banks and roadsides. This weed assumed importance comparatively recently and almost concurrently with the increasing popularity and widespread use of birdsfoot trefoil (Lotus corniculatus L.).

This paper reports on the synthesis and properties of 38 new herbicides, amino acid derivatives of 4–(2,4–dichlorophenoxy)– and 4–(2–methyl–4–chlorophenoxy)butyric acids. The biological evaluation of the compounds as selective herbicides is being conducted by other investigators and will be published later.

Leafy spurge is a perennial weed that is found in almost every state north of the fortieth parallel and in the southern portions of most Canadian provinces. Heaviest infestations are found in Minnesota, the Dakotas and the Prairie Provinces.

Typha angustifolia L. var. brownii (Kunth) Kronf., known as cumbungi in Australia and narrow leaved cattail in the U. S. A., is a deep rooted perennial widely distributed throughout the world. It occurs naturally in swamps and marshy areas and also in irrigation channels, where it may seriously impede the flow of water during the irrigation season. Various mechanical methods of control have beeen devised; the most successful consists of regular cutting and subsequent maintenance of 15 to 18 inches of water above the cut stalks. This method was successfully employed in the Murrumbidgee Irrigation Area of New South Wales for many years, but recently has been virtually discarded because of rising labour costs.