Optimum temperature for bud activity and shoot growth of quackgrass (Agropyron repens (L.) Beauv.) occurred between 20 and 27 C. CO2 and O2 gas concentrations normally occurring in soil air were not found to affect bud activity and shoot growth appreciably.

The temperature at which seeds of witchweed (Striga asiatica (L.) Kuntze), an obligate parasite, were stored markedly influenced the length of time that the seeds remained dormant. Dormancy was broken completely by storing seeds collected in August, 1960, at 88 F for 6 weeks, at 75 for 24 weeks, at 40 for 32 weeks and at 0 F for 40 weeks. Seed viability was lost rapidly when the storage of seeds was continued at 88 or 100 F plus 100% relative humidity after seed dormancy had been broken. All of the seeds stored under those conditions were non-viable within 20 weeks after storage began. The viability of seeds stored at 75, 40 or 0 F had not decreased after 26 months for 1960 seeds. Seeds collected in 1961 and stored at those three temperatures or at 88 F plus 20% relative humidity for 14 months did not decrease in per cent viability. A hypothesis on the physiology of the dormancy, viability, and germination of witchweed seeds is presented.

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.

Autoradiographs following treatment of Cyperus esculentus L. with C14-labeled amitrole indicated that it was readily translocated from the point of application to the seed. Seed germination was significantly reduced following amitrole applications.

In agar cultures 1-naphthaleneacetic acid (NAA) reduced bud activity of quackgrass (Agropyron repens (L.) Beauv.) rhizomes, while indole-3-acetic acid (IAA) had little effect. Gibberellic acid (GA) acted antagonistically with NAA. Maleic hydrazide (MH) had less effect on bud activity than isopropyl N-phenylcarbamate (IPC), 2,3,6-trichlorophenylacetic acid (fenac), or phenoxy compounds at high rates. GA or its active metabolite was translocated throughout the plant. 2,3,5-Triiodobenzoic acid stimulated bud activity on intact rhizomes.

The response of purple nutsedge (Cyperus rotundus L.) clones grown from single tubers to 3-amino-1,2,4-triazole (amitrole), butoxyethanol ester of 2,4-dichlorophenoxyacetic acid (2,4-D), and ethyl N,N-di-n-propylthiolcarbamate (EPTC), and the response of established nutsedge to amitrole were studied under field conditions of the Georgia Piedmont Plateau. Clones were essentially eradicated by two applications of amitrole initiated up to 4 weeks after shoot emergence and by EPTC incorporated at 1 or 2 weeks after emergence. Excellent control resulted from 9 applications of 2,4-D initiated 1 or 2 weeks after shoot emergence. Timely applications of amitrole to an established stand controlled but did not eradicate nutsedege. This decreased response in an established stand seemed due, in part, to irregular emergence of plants in the established stand.

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.

Amitrole-5-C14 was rapidly degraded in unsterile soil but underwent only minor modification in sterile soil. An unidentified chemical product of amitrole was formed in both sterile and unsterile soil. The principle metabolic product of amitrole was carbon dioxide; however, at least 13 additional compounds were formed. One or more metabolic compounds formed from amitrole are tenaciously bound to the soil and appear to be resistant to degradation.

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.

Polychlorobenzoic acids (PBA), 2,3,6-trichlorobenzoic acid (2,3,6-TBA), and 2,3,6-trichlorophenylacetic acid (fenac) sprays were applied safely for the eradication of perennial weeds at not over 20 pounds per square inch in winds less than 11 miles per hour in and near cotton. Use of these herbicides near soybeans was hazardous because very small quantities of them caused leaf deformities and some loss in seed yield.

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) applied in nutrient solution to corn, cotton, and soybeans reduced transpiration both in intact plants and excised shoots. This effect occurred only in the light. Microscopic examination revealed that atrazine caused closure of the stomates. Atrazine treated plants had higher moisture levels than the checks 12–24 hours after treatment, but later percentages were lower than the checks.

In a “closed system” nutrient solution experiment, shoot growth of downy brome (Bromus tectorum L.) was: (1) more rapid during early growth, (2) accelerated earlier by nitrogen, and (3) increased more by low to intermediate levels of nitrogen than that of crested wheatgrass (Agropyron desertorum Fisch. ex Link). Shoot growth of crested wheatgrass was increased more by high levels of nitrogen and at a more mature stage of growth than that of downy brome. Root growth of crested wheatgrass was greater at all nitrogen levels than that of downy brome and was increased by the high nitrogen levels. Downy brome removed more nitrogen from solution at the intermediate nitrogen level than did crested wheatgrass and more phosphorus at both the low and intermediate nitrogen levels. At the highest nitrogen level, crested wheatgrass removed more nitrogen from solution than did downy brome.

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.

Herbicidal control of tall larkspur, Delphinium occidentale Wats. was investigated in the Sawtooth National Forest near Oakley, Idaho. When larkspur was in a prebud stage, 4 and 8 lb/A of the propylene glycol butyl ether esters of 2-(2,4,5-trichlorophenoxy)propionic acid (silvex) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) gave good control, with significant increases in yield of native grasses. At the bud and flower stages neither herbicide gave satisfactory control at 12 lb/A. Granular silvex at 400 lb/A total product (80 lb/A ae) killed all larkspur with only slight injury to rabbitbrush, sagebrush, and native grasses. A chlorate-borate (25%–75%) mixture gave a complete larkspur kill at 1740 lb/A.

A laboratory sprayer for precision application of herbicides to pot cultures consists of a miniature compressed-air sprayer mounted as a pendulum and equipped to automatically spray a pot placed beneath the center of its arc of swing.

Disodium endothal (3,6 endoxohexahydrophthalic acid) was applied to a number of emergent and submerged aquatic species and was found to be particularly effective in controlling pondweeds, Potamogeton spp. On P. foliosus, P. crispus, and P. pectinatus, liquid and granular preparations appeared to be equally effective. Endothal was not very effective on some species, such as waterwillow, Justicia americana, and creeping waterprimrose, Jussiaea repens L. var. glabrescens, although defoliation did occur.

The herbicides n-propyl ethyl-n-butylthiolcarbamate (PEBC), PEBC + 2,3-dichloroallyl diisopropylthiol-carbamate (DATC), PEBC + ethyl N,N-di-n-propylthiolcarbamate (EPTC), and PEBC + 2,3,3-trichloroallyl diisopropyldithiolcarbamate (CP-22819) among others produced effective control of lambsquarters (Chenopodium album), pigweed (Amaranthus retroflexus), Setaria spp. and other weed species without undue injury to sugar beet seedlings. PEBC + DATC also gave control of wild oat (Avena fatua), and increased the control of lambsquarters; however, this latter effect was inversely related to the control of other broad-leaved weeds. Control equal to PEBC was produced by PEBC + EPTC with 2.5 lb. less total active ingredient per acre. The herbicide 3,6-endoxohexahydrophthalic acid (endothal) gave inferior control of weeds. None of the herbicides tested effectively controlled kochia (Kochia scoparia).

During a 12-hr incubation low concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) enhance the metabolic breakdown of ribonucleic acid (RNA) whereas high concentrations of the auxin almost completely inhibit RNA breakdown after 4 hr of treatment. The data, from experiments where the incorporation of adenosine-8-C14 into RNA was followed, clearly show that the role of auxin in this system is not to appreciably alter net synthesis of RNA, but rather to alter some process(s) related to the degradative metabolism of RNA.

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.

Smooth bromegrass, Bromus inermis, and red fescue, Festuca rubra, were sown in 1952 on a fertile soil severely infested with yellow toadflax, Linaria vulgaris Mill., in the Peace River section of Alberta. Annual applications of 2,4-dichlorophenoxyacetic acid (2,4-D) were made at late flower-bud stage at nil, 1, 2, 3, and 4 lb/A acid equiv. In 1958, the average per cent of toadflax in the brome was 1, 0.5, 0.5, 0, and 0, respectively. Red fescue had 6 to 0.1% of toadflax. All rates of 2,4-D prevented seed production. The sods were broken in 1959, and toadflax re-established strongly on all plots from dormant seed and residual plants. In 1961, the brome, rejuvenated by breaking, strongly suppressed toadflax, while fescue failed to compete with it.