Four forage grasses and five forage legumes were grown in greenhouse cultures containing 0.12, 0.25, 0.50, and 1.0 ppm of atrazine and of simazine in the soil. They were also planted April 2 and 9 in field plots which had been treated the previous spring with 0, 1, 2, and 4 lb/A of the same herbicides. In the greenhouse, atrazine produced more injury to the plants than simazine. In the field, residual simazine produced more marked injury. Tall fescue and alfalfa were the most tolerant crops. Timothy was the most susceptible. Red clover, Korean lespedeza, ladino clover, sweet-clover, orchardgrass, and bromegrass were intermediate.

Addition of surfactant (a polyoxyethylene thioether) to solutions of sodium 2,2-dichloropropionate (dalapon) increased the activity of both technical and formulated grades of dalapon on Johnsongrass (Sorghum halepense (L.) Pers.). The increase in activity was influenced by the rate and formulation of herbicide and in some instances by the volume of water in which treatments were applied. Varying the volume of diluent affected control with technical dalapon to a greater extent than that with formulated dalapon probably because of differences in surfactant concentrations. Plants arising from short rhizomes were more readily controlled by dalapon than those from longer rhizomes.

Triazines were applied to 1–0 stock (1-year-old, not transplanted) on sandy soils at ½, 1, and 2 lb/A and to 2–0 stock at 1, 2, and 4 lb/A. Simetone (2-methoxy-4,6-bis(ethylamino)-s-triazine) had no apparent effects on weeds or seedlings. All rates of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) and the higher rates of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) and 2-chloro-4-isopropylamino-6-methyl-amino-s-triazine (G–30026) controlled weeds but seriously injured 1–0 stock. All rates of 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine) controlled weeds without injuring seedlings. Atrazine and G–30026 at 4 lb/A injured 2–0 stock. Simazine at 2 and 4 lb/A and atrazine at 1 and 2 lb/A did not affect 2–1 transplants. CDAA (2-chloro-N,N-diallylacetamide) and CDEC (2-chloroallyl diethyldithiocarbamate) at 4 and 8 lb/A did not affect weeds or 1–0 and 2–0 stock. At 16 and 32 lb/A, CDAA was highly toxic to weeds and stock, while CDEC controlled weeds with only a temporary effect on seedlings at 32 lb/A. CDAA and CDEC at 4 and 8 lb/A did not affect weeds or 2–1 transplants. N-1-naphthylphthalamic acid (NPA) and sodium 2,4-dichlorophenoxyethyl sulfate (sesone) at 1.8 and 3.6 lb/A did not control weeds. Sesone injured 1–0 and 2–0, but not 2–1 red pine. Ethyl N,N-di-n-propylthiolcarbamate (EPTC) at 3 and 6 lb/A controlled weeds without injuring 1–0, 2–0, or 2–1 red pine. These experiments emphasized that many herbicides too toxic for nursery use may be useful in site preparation for planting or in plantation release.

An accurate method of determining loss of 2-chloro-N, N-diallylacetamide (CDAA) from soil surfaces was developed. It was found that under some circumstances the volatility response to temperature was reversed to give a decreasing loss with increasing temperature. The volatility-temperature relationship was found to be strongly influenced by the amount of water present on the soil colloid, with increasing amounts of water accelerating CDAA volatility loss. The mechanism for this reaction appears to involve competition between water and CDAA for adsorption sites; however, this factor cannot be differentiated from removal of CDAA from the soil by simple solubilization in water with subsequent steam distillation.

A direct correlation between organic matter content of the soil and resistance of CDAA to evaporation from that soil was shown.

Band applications of the best residual preemergence herbicides were equal to timely shallow cultivations for weed control in soybeans, and were superior when wet weather delayed the early shallow cultivations. The ten-year average soybean yield reduction of 3.8 bushels per acre from weed competition despite normal control methods suggests that, under normal conditions, the net cost of herbicide treatment would not exceed the value of the soybeans lost through failure to control weeds. Coarse broad-leaved annuals were a minor part of the weed populations and there was no giant foxtail, so the benefits of herbicides would probably be greater with these weeds present.

Early-spring, broadcast, disked-in applications of nitrogen fertilizers caused an increased germination of wild oat (Avena fatua L.) seed present in the soil. With adequate moisture, there was increased wild oat infestation in the seeded crop from early-spring application, whereas with dry weather the effects did not carry over into the crop period. The apparent breaking of seed dormancy by nitrates from fertilizer applications may offer another method for combating wild oats other than by herbicides. Fertilizer treatment might be used to deplete seed reserves in the fallow years and to reduce the amount of seed returned to the soil in the crop years by combining a fertilizer treatment with delayed crop seeding.

Chain- and ring-labeled 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) were supplied to corn by way of the nutrient solution. Autoradiographs of the paper chromatograms revealed that two identical C14-labeled metabolites were present in the extracts whether the plants were supplied with ring-or chain-labeled simazine. Corn, cotton, and soybeans all yielded appreciable amounts of C14O2 when grown in solutions containing chain-labeled simazine. One lb/A 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) (preemergence) caused a reduction in respiration as well as the activity of catalase, peroxidase, phenol oxidase, ascorbic acid oxidase, and glycolic acid oxidase in oats, soybeans, beans, cotton, peanuts, Johnsongrass, and corn, 7 and 11 days after treatment. Attempts to correlate enzyme activity with sensitivity to atrazine were unsuccessful, except that increasing phenol oxidase activity appeared to be roughly correlated with increasing resistance.

Stands of leafy spurge (Euphorbia esula L.) were reduced over 90 per cent by 20 combinations of crops, cultivation, and herbicides. Three of the best crop rotations in two 4-year trials were: (1) a short season of intensive cultivation, a mid-August seeding of alfalfa, a crop of alfalfa, spring wheat sprayed with ½ lb/A of 2,4-dichlorophenoxyacetic acid (2,4-D) (an ester formulation was always used) three postharvest cultivations, corn sprayed with $13 lb/A 2,4-D; (2) a short season of intensive cultivation, a mid-August seeding of bromegrass sprayed with 1 lb/A 2,4-D in early June and mid-August during the second and third years, and a crop of corn the fourth year; (3) spring oats sprayed with $13 lb of 2,4-D ester and three postharvest cultivations, three spring cultivations a close-drilled crop of sudangrass and fall cultivation, spring wheat sprayed with $12 lb/A of 2,4-D ester and three fall cultivations, a crop of corn sprayed. The best use of nonselective herbicides in four 2-year trials was spring application of 4 to 6 lb/A of 2,3,6-(trichlorobenzoic acid (2,3,6-TBA), plow 10 days later, followed by a corn crop and a spring oats crop, both treated with 2,4-D and 4 to 6 lb/A of 2,3,6-TBA applied after oats harvest, and the field plowed 10 days later. Reinfestation by seedlings was prevented by an annual spring application of $13 to $12 lb/A of 2,4-D per acre.

The observation that riboflavin overcomes the chlorosis response of higher plants to amitrole was confirmed. Amitrole was shown to be decomposed in the presence of riboflavin and light. It is suggested that this decomposition proceeds by a free radical mechanism, either in the culture medium or in the plant.

This paper extends previous observations on the interaction of 3-amino-1,2,4-triazole (amitrole) and riboflavin leading to the decomposition of amitrole to include the protective effect of amitrole on the photodestruction of flavins and flavoproteins. Photoactivation of radioactive amitrole in the presence of riboflavin causes the labeling of inert protein. Cupric ion, ascorbic acid, and oxygen can replace riboflavin and light in the destruction of amitrole and in the labeling of inert protein. The inhibition of fatty acid peroxidase previously reported by Castelfranco has been shown to be irreversible and to require the presence of a hydrogen peroxide generating system. The authors suggest a hypothesis for the mode of action of amitrole which depends upon the ability of this compound to interact with free radical generating systems, presumably by undergoing a one-electron oxidation.

Ninety-one herbicides and experimental compounds were evaluated for herbicidal activity on submersed aquatic weeds, Potamogeton pectinatus L. and P. nodosus Poir. Twenty-one of the compounds tested showed some phytotoxicity at 20 lb/A. The other compounds were completely inactive. 2,3,6-Trichlorophenylacetic acid (fenac) and 2,6-dichlorobenzonitrile (dichlobenil), showed outstanding activity with good persistence in water-saturated soil. Fenac and 2-(2,4,5-trichlorophenoxy)propionic acid (silvex), were tested in field trials in an irrigation canal in eastern Wyoming. The sodium salt and amide of fenac did not give adequate weed control at 5 lb/A. Spring applications of herbicides did not perform as well as fall ones. Mechanical incorporation of herbicides improved some results, but was of doubtful value.

Rates of evaporation of dalapon acid and four low-volatile esters of dalapon from open dishes at 38C. in pounds per acre per hour, determined gravimetrically, were dalapon acid, 180; propyleneglycol bis ester, 27; diethyleneglycol bis ester, 1.6; dipropyleneglycol bis ester, 0.83; and triethyleneglycol bis ester, 0.61. Foliar applications on an acid equivalent basis were phytotoxic to seedling oats in the increasing order of propyleneglycol bis ester, acid, dipropyleneglycol bis ester, diethyleneglycol bis ester, sodium salt, and tripropyleneglycol bis ester. Relative phytotoxicities were not altered by subjecting plants to rapid drying after spraying. These compounds did not differ significantly in phytotoxicity when added to the rooting medium of germinating oat plants. The triethyleneglycol bis ester, and possibly other esters of dalapon, may offer practical advantages as herbicides other than those related to volatility.

Foliar absorption of 2,4-D-C14 was rapid in both species. Cotton decarboxylated the side chain of 2,4-D several times faster than sorghum. Both species released C14O2 faster from the carboxyl than from the methylene position. Cotton slowly converted 2,4-D to a chromatographically different material in young leaves and bolls. Sorghum rapidly converted 2,4-D to a product different from 2,4-D and the 2,4-D-complex in cotton. After cotton recovered from 2,4-D-treatment, the regulator could not be detected in subsequent vegetative or reproductive growth.

Of the grasses studied over a 3-year period, Alta tall fescue (Festuca arundinacea) was most competitive and Troy bluegrass (Poa pratensis L.) least competitive with Canada thistle (Cirsium arvense). Ladino white clover was more competitive than birdsfoot trefoil (Lotus corniculatus) when present in full stands. Winter-killing of Ladino clover (Trifolium repens L.) resulted in an increase in Canada thistle, particularly at low irrigation levels. Irrigation favored an increase in Canada thistle numbers in the year the grass stands were established. In the next two years thistle numbers declined more rapidly on irrigated than on non-irrigated plots. High rates of nitrogen increased the competitive ability of the grasses.

Development was followed in Connecticut and Maryland. Germination of yellow foxtail (Setaria lutescens (Weigel) F. T. Hubb. occurred over a long time period. Tillering of the developing plants was affected by spacing between plants and location. The average number of tillers in Maryland was 75 for plants spaced 12 in. apart and 26 for plants spaced 2 in. apart. In the greenhouse under short day conditions seed heads were readily produced. Under continuous light no seed heads formed. Giant foxtail (S. Faberii Herrm.) followed a similar growth pattern but the plants were larger and formed fewer tillers. Growth of both species was severely affected by shading. Both species rooted from cuttings.

2-Methyl-4-chlorophenoxyacetic acid (MCPA) is widely used to control broad-leaved weeds in pea fields. Occasionally, peas are severely injured by MCPA. This study was conducted in 1959 and 1960 to determine the relationships, if any, of environmental factors and of chemical constituents of plants at the time of spraying to the tolerance of peas to MCPA. Plants were equally susceptible to MCPA at either the 5- or 10-node stages. The time of day at which plants were sprayed appeared to be the most important factor associated with the tolerance of pea to MCPA. Fresh weights of vines and yields of shelled peas from plants sprayed at noon and 4:00 pm were significantly lower than those from unsprayed plants or plants sprayed at other times of the day. The carbohydrate content of pea plants varied with the time of day (exposure to light). The carbohydrate content was associated with susceptibility to injury by MCPA. A high carbohydrate content at the time of spraying was associated with a high degree of susceptibility to MCPA. High temperature at the time of spraying tended to increase the rate of translocation of MCPA. However, in the absence of prolonged exposure to light prior to treatment, high temperature alone did not predispose peas to injury by MCPA.

The injurious effects of different rates of fenuron (3-peynyl-1,1-dimethylurea) on four species of brush were recorded for two years in two different types of southwestern brushlands, the Oak-chaparral and the Chihuahuan Desert Shrub. Fenuron was more injurious to fire sprouts than to mature plants of turbinella oak (Quercus turbinella Greene) in the Oak- chaparral type especially at 2 to 8 lb/A ai. The effects of fenuron on mature plants were reduced by burning, suggesting that much of the fenuron absorbed was residual in the stems, twigs, and leaves where it was destroyed by the fire. The effect of fenuron on the fire sprouts changed only slightly between six months and two years. Gibberellic acid was applied to sprouts and mature oak plants appeared to slightly reduce the injurious effects of some rates of fenuron during the first six months but no gibberellin induced differences were observed after two years. In the Chihuahuan Desert shrub type, tarbush (Flourencia cernua DC.) and whitethorn (Acacia constricta Benth.) were about equally susceptible to injury by fenuron with creosotebush (Larrea tridentata (DC.) Cov.) slightly more resistant. Summer applications just before the rainy season were most effective and 4 lb/A combined high shrub kill with greatest grass growth.

Although 8 and 16 lb/A ai killed and injured both grasses and shrubs on the oak plots, grass naturally reseeded into these plots within six months after treatment, but on the Chihuahuan Desert area grass had not recovered on the plots treated at 8 lb/A after two years. This difference in grass re-establishment was probably due to rainfall differences which would give differences in leaching of fenuron. Palatability of the grasses in the oak plots increased due to fenuron treatments, particularly on the heavily treated plots. These studies indicate that moderate rates of fenuron, applied just prior to favorable seasonal rains and repeated at several-year intervals, may be used to control turbinella oak sprouts and mature Chihuahuan Desert shrubs. However, treatments would only be economical where high forage and watershed values would result.

Ten herbicides were applied preemergence to proso millet (Panicum miliaceum), three Amaranthus species, and Chenopodium album L. The herbicides were either incorporated or left on the soil surface and plots were either sprinkler or furrow irrigated. The phytotoxicity of some herbicides was increased by soil incorporation and/or sprinkler irrigation. Some were unaffected by method of irrigation, and others were not affected by incorporation. Grass and broadleaf weed control were affected differently by incorporation and irrigation. When incorporated with furrow irrigation, five herbicides developed weed control patterns indicating a movement similar to salt movement. A more complex pattern occurred with non-incorporated herbicides.

Three-quarter inch seedlings of northern nutsedge (Cyperus esculentus L.) were transplanted into the field where numbers of plants, inflorescences and the rate of spread were recorded. Seed was collected from each plot and germination tests conducted. During one growing season, a single seedling developed into a stand of plants that produced a yield of 90,000 seeds with a germination of 51%.