When one talks about Latin America, one is talking about approximately 200 million people of a variable kind disproportionately divided among 20 republics comprising an area about 2.6 times the size of Continental United States, not including Alaska.

The method was based on the minimum dosage of 2,4–dichlorophenoxyacetic acid (2,4–D) that would produce strapping or cupping of cotton leaves. Dilutions of an unknown were applied to cotton cotyledons. The minimum dosage required to produce strapped or cupped leaves two weeks later was approximately 0.05 μg/plant. The results of this bioassay were comparable to tracer methods, but the latter can detect smaller quantities of 2,4–D.

Nutsedge tubers germinated readily in soil treated with EPTC. However, growth was suppressed and emergence delayed, the delay depending on the rate of application. EPTC at 12 and 16 pounds per acre with 8 and 12 weeks exposure was very effective in killing nutsedge tubers as indicated by tuber germination and condition of tubers that did not germinate.

The granular formulation of EPTC killed highly significantly more nutsedge tubers than the emulsifiable formulation. Repeat applications of EPTC were significantly better in terms of tubers killed than single applications of the same rate of the herbicide. Thorough incorporation of EPTC to a depth of 5 inches of mechanical means was significantly more effective than incorporation by leaching.

Inulin or a closely related analog was the major available carbohydrate component of western ironweed (Vernonia baldwinii Torr.) roots. Fructose, glucose, sucrose and other gluco-fructosans made up the remaining carbohydrate fraction. Reductions in ironweed vigor as a result of annual mowing were caused by a decrease in dry weight of the root system rather than a permanent decrease in carbohydrate percentage. Use of carbohydrate percentage in predicting a physiological condition of ironweed was regarded as questionable. Carbohydrate content of roots was not necessarily related to stage of growth. Treatment of ironweed with 2,4-D did not permanently affect carbohydrate levels in the roots. Changes in root carbohydrate content after 2,4-D treatment were not considered decisive in killing ironweed.

The effects of rainfall and temperature upon herbicidal activity of 2-chloro-N,N-diallylacetamide (CDAA), 2-chloro-4,6-bis-(ethylamino)-s-triazine (simazine), and 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), for the control of foxtail (Setaria spp.) were determined. CDAA spray was effective if applied to warm soil and if ½ inch of rain fell during the first week after application, unless a heavy rain fell immediately after application. The effectiveness of granules was not impaired by a heavy rain immediately after treatment or by a delay of 2 weeks before receiving ½ inch of rain. Simazine and atrazine sprays and granules were effective if 1 inch of rain fell within 15 days after application of simazine or if ½ to 1 inch fell within 15 to 20 days afterwards for atrazine. Mechanical incorporation aided in activation of simazine when rainfall was slightly below minimum required for activation.

Applications of 2,4–dichlorophenoxyethyl sulfate (sesone) were made to obtain a wide range of formative response in peanut seedlings. These reactions were rated (0 = no effect, 10 = complete kill) as the peanut seedlings emerged, and correlated with growth and development of the plants. It appears that plants from seedlings in the 0 to 3 range of response have an excellent chance to develop into healthy, productive plants. The seedlings in the 3 to 5 range have a questionable chance. The seedlings in the 6 to 10 range have little chance, because root rots were both frequent and severe at 8 to 9 weeks after seeding.

Effects of 2,4–dichlorophenoxyacetic acid (2,4–D), 2,4,5–trichlorophenoxyacetic acid (2,4,5–T), 2–methyl–4–chlorophenoxyacetic acid (MCPA) and 4–(2–methyl–4–chlorophenoxy)butyric acid [4–(MCPB)] on Oxalis latifolia H.B.K. were compared. 2,4,5–T killed leaves and up to 50% bulbs, 2,4–D was slightly less effective while MCPA and MCPB killed or distorted leaves but did not affect bulbs appreciably. Effectiveness of spray was increased by spraying in the evening rather than the morning and by applying nutrient solution for three weeks prior to spraying, but spray additives, sucrose, boric acid or urea gave no significant alteration. Studies with C14–labelled 2,4–D indicated accumulation in rapidly developing organs with less movement to organs of slower development.

During the first season, tubers of purple nutsedge, Cyperus rotundus L. planted in Piedmont Plateau soil at Experiment, Georgia at 1-ft intervals produced 3,090,000 plants and 4,420,-000 tubers and bulbs per acre. Tubers planted at 3-ft intervals produced 2,320,000 plants and 2,760,000 tubers and bulbs. The differences were not pronounced at the end of the second season. A single cultivation at the beginning of the second year did not appreciably affect the number of tubers and bulbs formed. Continuous heavy shade during the second year reduced tuber-bulb formation. No apparent interaction between shading and cultivation occurred.

The treatments in this 3-year study consisted of 54, 12, 6, 3, 1, ½, and no foxtail plants per foot of crop row. Yield reductions for the heaviest stand of foxtail averaged 25% for corn and 28% for soybeans. For both corn and soybeans, the increase in foxtail dry matter was proportional to the decrease in the dry matter from the crop; the combined yield did not vary significantly. As stand of foxtail increased, there was a decrease in yields of grain, cobs, stalks or straw, diameter of cornstalks, ear weight, light intensity beneath the crop, soil temperatures under corn, and number of soybean pods. There was little or no significant effect on moisture content of grain, height of crop, shelling percentage of corn, oil or protein content of beans, weight of 100 beans or number of beans per pod. Increased corn lodging was associated with increasing foxtail stand in one of three years.

The herbicide, N-(3-chloro-4-methylphenyl)-2-methylpentanamide was applied to the foliage of tomato, a tolerant species, and eggplant, a susceptible species. Both species increased in tolerance to the herbicide with age but tomato increased at a much faster rate. Selectivity did not appear to be a function of differential wetting of foliage. Photosynthesis was shown to be involved in the phytotoxic action of the herbicide and starvation is suggested as a possible mode of action. Carbohydrates increased the tolerance of tomato plants and the fixation of labeled carbon dioxide in eggplant leaves was prevented by the herbicide.

In the Peace River region, vegetative shoots of field horsetail, Equisetum arvense L., emerge from June 1 to July 1, and reach full growth about July 16. All herbicides studied were most effective applied July 16 to 30. Amitrole (3–amino–1,2,4–triazole) at 8 lb/A at this time gave 96% stand reduction the next year. For selective killing in barley, MCPA (2–methyl–4–chlorophenoxyacetic acid) at 4 to 8 oz/A killed 100% of the top growth in the year of application and gave 50 to 65% stand reduction the next year. Other herbicides tried were less effective.

Oats, sesbania (Sesbania macrocarpa Muhl.) and purple nutsedge (Cyperus rotundus L.) were grown as test plants in nine different soil types treated with 0, 0.5, 1, 2, 4, 8, and 16 ppm of ethyl N,N-di-n-propylthiolcarbamate (EPTC). Toxicity of EPTC was negatively correlated with the organic matter of the soil. A positive correlation was found between the sand and silt content of the soil and EPTC toxicity to oats and nutsedge. Toxicity of EPTC was not correlated with soil pH, cation exchange capacity, clay content, general reaction, or parent material. EPTC induced a dormancy of nutsedge tubers, of which the length was inversely related to the organic content of the soil.

Wild cucumber (Sicyos angulatus) and cultivated cucumber (Cucumis sativus) were treated with carboxyl-labeled C142,4–D (2,4–D*) and 2,4,5–T (2,4,5–T*) and autoradiographs developed. The distribution pattern of 2,4–D* was achieved in 24 hours and changed little by the end of 4 or 8 days. The pattern of 2,4,5–T* translocation continued to change during an 8-day period, indicating a highly mobile compound. Metabolic studies indicated that considerably more 2,4–D* than 2,4,5–T* was absorbed by these species but 75% of the absorbed 2,4–D* was converted into two major metabolites within 24 hours. The absorbed 2,4,5–T* formed only traces of these metabolites even after 8 days. Evolution of C14O2 was approximately 10 times greater from 2,4–D*-treated plants than from 2,4,5–T*-treated plants. The greater phytotoxicity of 2,4,5–T on these species seems to be related to the inability of the plants to detoxify this compound as rapidly as 2,4–D.

All herbicides were incorporated either as pretransplanting or posttransplanting treatments. Herbicides used were: ethyl N,N–di–n–propylthiolcarbamate (EPTC), propyl N,N–di–n–propylthiolcarbamate (1607), ethyl N,N–ethyl–n–butylthiolcarbamate (2060), propyl N,N–ethyl–n–butylthiolcarbamate (2061), O–(2,4–dichlorophenyl) O–methyl isopropylphosphoramidothioate (DMPA), 2–chloro–4–diethylamino–6–ethylamino–s–triazine (trietazine), and the dimethyl ester of 2,3,5,6–tetrachloroterephthalic acid (DCPA). EPTC, 1607, 2060, and 2061 at 3 lb/A (repeated 3 times), posttransplanting, and DMPA at 20 lb/A, pretransplanting, gave control of the annual weeds present with the exception of annual morningglory, and had no effects on tobacco yield or value. Nicotine, nornicotine, total alkaloids, and reducing sugar content of the cured leaf were not adversely affected by the thiolcarbamates, DMPA, amiben, or DCPA at rates used. Smoke and taste tests of tobacco treated with EPTC, DMPA, amiben, and DCPA revealed no undesirable flavors.

In field plantings, granular 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) were the most effective herbicides, but injured Spiraea media, S. trichocarpa, Syringa prestoniae and Physocarpus opulifolius. Diuron also injured newly planted evergreens. Granular 3-amino-2,5-dichlorobenzoic acid (amiben), isopropyl N-(3-chlorophenyl)carbamate (CIPC), 2-chloroallyl diethyldithiocarbamate (CDEC) and 4,6-dinitro-o-sec-butylphenol (DNBP) did not cause injury. Preplanting application of ethyl N,N-di-n-propylthiolcarbamate (EPTC) reduced the vigor of the deciduous shrubs. Chamaecyparis and Thuja species were tolerant to simazine under greenhouse conditions, while tolerance in Juniperus varied according to species.

Isopropyl N-phenylcarbamate (IPC) and isopropyl N-(3-chlorophenyl)carbamate (CIPC) were the most effective herbicides for controlling downy brome without serious injury to perennial grasses grown for seed production in eastern Washington. The disodium salt of 3,6-endoxohexahydrophthallic acid (endothal) gave good downy brome control at Spokane, but was not satisfactory for control at Hooper and Pomeroy, Washington.

The relative tolerance of cucumber and squash to amiben was established for germinating seeds, and for young plants with both foliage and root applications. In all cases, the dosage required for 50% inhibition of growth was 6 to 8 times greater for squash than for cucumber. Root applications of carbon-14 labeled amiben on reciprocal grafts of cucumber and squash plants indicated that the shoots were spared in these experiments by differential blocking of amiben transport from the roots. Shoots of either species appeared tolerant on squash roots and susceptible on cucumber roots. Radioactivity in the shoots of both species was much greater when grafted on cucumber than on squash. Foliage applications of carbon-14 labeled amiben showed more entry into cucumber than squash, but little movement to untreated plant parts in either species.

Excavation at biweekly intervals for 20 weeks of nutsedge clones grown from single tubers indicated that no dormant tubers formed until 6 weeks after foliar emergence. Tuber chains or fully mature rhizomes were not observed until the tenth week or long tuber chains until the eighteenth week. Rhizome length and tuber-basal bulb number increased throughout the season. Development of clones varied.

Dalapon–2–C14, applied as droplets, was employed in tracer studies by autoradiography and counting. That dalapon remained non-metabolized throughout the experiment was confirmed by chromatography. Surfactants greatly enhanced (cuticular) penetration. Small amounts of herbicide were sorbed almost instantaneously (15–30 seconds). Movement away from the treated area “showed” or “appeared as” first a diffusional pattern, but soon became channelized in veinlets and larger vascular bundles. Dalapon applied off the midvein did not enter the midvein in appreciable quantities during basipetal transport. Dalapon which entered the midrib originally remained highly concentrated in this channel. During transport, some dalapon was retained or retarded by tissues through which it passed. Retention was greatest in the basal sections (intercalary meristem regions) of young grass blades. A 10-fold build-up of dalapon was demonstrated following drop application off the main vein, but not after treatment on the midrib. Results are explicable on the basis of the known anatomy of Zea and the translocation of dalapon with assimilates.

Weed control has been a major problem in Hawaiian pineapple production. Hand-hoeing and mechanical cultivation gave way to activated oil emulsion sprays in the 1940's. The 1950's brought the use of preemergence herbicides especially 3–(p–chlorophenyl)–1,1–dimethylurea (monuron). Each method has brought a shift in species distribution. Today, large-seeded species and vegetatively-propagated species are less well-controlled than in the days of contact weeding with oil emulsion sprays. There is need for selective herbicides which will control the weeds which escape the present program.