In one study, twelve treatments consisting of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), 2-chloro-4,6-bis-(ethylamino)-6-isoproplyamino-s-triazine (simazine), 3-(p-chlorophenyl)-1,1-dimethylurea (monuron) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) applied alternately in a program pre- and postemergence to the weeds were evaluated on ten sugar cane plantations. Averaged data indicated that combinations including atrazine outperformed simazine in every instance and diuron was better than monuron on all plantations but one. Diuron was most effective on grasses, e.g., Digitaria spp. whereas atrazine was outstanding against Commelina diffusa Burm. In a second study on the same plantations, the initial treatment of 5 lb/A of atrazine followed by 3 lb/A of diuron gave outstanding weed control on five plantations. Using 3 lb/A of each material applied simultaneously had merit at times but some plantations required only a single application of either material. Net days of weed control obtained by diuron were inversely dependent on the amount of chemical adsorbed by the soil in both studies and total days control appeared to be dependent on ample rainfall in the second.

Seeds of largeseed dodder (Cuscuta indecora, Choisy), field dodder (Cuscuta campestris, Yuncker), and small-seeded dodder (Cuscuta approximata, Bab.) were studied on the basis of (1) germination at different temperatures, and (2) spring emergence of seedlings as related to soil temperature. Small-seeded dodder germinated at 35 to 45 F with maximum germination at 60 F. Largeseed dodder germinated very little and field dodder not at all below 50 F. They germinated best at 60 F and above. Dodder seeds were planted outside at different depths in a sandy loam soil during the autumns of two years. Daily counts on seedling emergence during the spring showed that small-seeded dodder was first to germinate, at a soil temperature of 39 F, largeseed dodder emerged from 7 to 10 days later at a soil temperature of 51 F, and field dodder emerged 2 to 4 days still later. Very few seedlings of the small-seeded dodder emerged after mid-May, but largeseed and field dodders continued to emerge throughout the summer.

Plants of Zebrina pendula L., Phaseolus vulgaris L., Sorghum halepense (L.) Pers., and Chenopodium album L. were sprayed with a solution containing herbicide (sodium 2,4-dichlorophenoxyacetic acid or sodium 2,2-dichloropropionic acid), surfactant (sodium dioctylsulfosuccinate), and fluorescent tracer (sodium pyrenetrisulfonate). In most instances plants having stomata relatively open absorbed more tracer (based on UV observation) and more herbicide (based on injury and growth responses) than those with stomata relatively closed. Differences, however, were less than those expected from studies using detached leaves, probably from poorer control of stomatal aperture in intact leaves. There was good agreement between degree of opening and tracer uptake.

Yield reductions from the heaviest stand of smooth pigweed (Amaranthus hybridus L.) averaged 39% for corn and 55% for soybeans. For corn the increase in pigweed dry matter about equalled the decrease in the dry matter from the crop; the total dry matter yield was relatively constant. Pigweed grew taller than soybeans, and the dry weight of crop plus pigweeds was 1⅓ times that of weed-free soybeans. As stand of pigweed was increased, there was a decrease in yield of grain, cobs and stalks or straw, diameter of cornstalks, height of crop, and soybean pods per plant. Yield reductions obtained emphasize the importance of both chemical and cultural measures for reducing competition between row crops and weeds.

Five strains of Johnsongrass [Sorghum halepense (L.) Pers.] in selected and random plantings received repeated foliar applications of 2,2-dichloropropionic acid (dalapon). For three characters studied, the residual variance was less with selected plantings than with random plantings. Johnsongrass strains differed in their response to dalapon.

Two lines of corn (Zea mays L.)—one, GT112 RfRf, resistant to 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), and the other, GT112, susceptible to both—were used. Both glucose and sucrose, supplied to the treated plant through a severed leaf tip, were found to protect GT112 from the toxic effect of atrazine and simazine. Glucose gave a slightly better protection. Oxygen uptake in excised roots of GT112 treated with atrazine gradually declined with age until death, while leaf discs of treated and untreated lines showed no distinct trend in oxygen uptake. Atrazine decreased root respiration in GT112 but had no effect on that of GT112 RfRf. Root respiration in untreated GT112 was higher than in untreated GT112 RfRf. Atrazine decreased leaf respiration when both lines were considered.

Results of studies with microorganisms suggest that 5-bromo-3-isopropyl-6-methyluracil (isocil) does not interfere appreciably with pyrimidine metabolism. Instead the uracil herbicides studied appear to act in higher plants as inhibitors of photosynthesis. Strong inhibition of the Hill reaction of isolated chloroplasts by substituted uracils was noted (I50 of 2.7 × 10−6 M for isocil). Exogenously supplied carbohydrates partially nullified toxicity symptoms in intact barley plants growing in the presence of inhibitory concentrations of isocil.

Monuron [3-(p-chlorophenyl)-1,1-dimethylurea] and neburon [1-n-butyl-3-(3,4-dichlorophenyl)-1-methylurea] were applied to a sandy loam soil which was planted to several crops in southern California. Monuron at 2, 4, and 8 lb/A and neburon at 2 lb/A were below phytotoxic levels by 12 months. Neburon at 4 lb/A persisted at phytotoxic levels for over 16 months, and at 8 lb/A for over 24 months.

Metabolism of C14-labeled and unlabeled atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) was studied in oats, soybeans, and beans (susceptible); cotton and peanuts (intermediate in susceptibility); and Johnsongrass, grain sorghum, and corn (resistant). Atrazine residues were found in all plants 11 days after a preemergence application of 1 lb atrazine/A. Methanol was found to be a better extraction solvent for atrazine and hydroxyatrazine than chloroform. Undegraded atrazine found in plants was roughly correlated with susceptibility, but atrazine absorption was not directly correlated with plant susceptibiliy. Radioactivity remaining in plant residue after methanol extraction likewise was not completely correlated with susceptibility. All plants converted some atrazine to hydroxyatrazine and the amount of hydroxyatrazine formed was somewhat correlated with resistance. The three resistant species converted at least twice as much atrazine to hydroxyatrazine as did the susceptible soybean and oats. Beans converted considerably larger amounts of atrazine than did other susceptible species.

When weeds were controlled in sorghum by hand-weeding or a herbicide there was no advantage or need for cultivation. Control of weeds in sorghum with preemergence herbicides was feasible, but the combination of cultivation and herbicides gave more dependable weed control than either method used alone. Preemergence applications of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) were the most effective for controlling weeds and increasing sorghum yields. In decreasing order of effectiveness were 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine), 2-chloro-N,N-diallylacetamide (CDAA) + trichlorobenzyl chloride (TCBC), and postemergence atrazine applications.

Band applications of residual preemergence herbicides were equal to timely shallow cultivations for the control of annual weeds in corn, and were superior when wet weather delayed or interfered with early shallow cultivations. The average corn yield reduction of 7.4 bushels per acre from weed competition observed over a 13 year period, suggested that under average conditions the net cost of herbicide treatment would be less than the value of corn lost through failure to control weeds.

When crop plants were competing with well-established quackgrass (Agropyron repens) for the same nutrient supply, chlorosis and stunting of crop plants occurred. Apparently this was due to the greater ability of quackgrass to withdraw available nutrients, especially nitrogen, and to a lesser extent phosphorus and potassium, from the nutrient solution. No evidence was obtained for a phytotoxic substance from living quackgrass roots or rhizomes that could inhibit germination or growth of alfalfa and oats. Quackgrass residues in large amounts caused chlorosis and stunting in alfalfa and oats when added to soil. The evidence obtained linked this behavior to the high C:N ratio with consequent temporary deficiency of available nitrogen. Water extracts of quackgrass leaves or rhizomes were not phytotoxic unless subjected to high temperatures during or subsequent to extraction. If soils contained decomposing quackgrass or crop plant residues, extremely phytotoxic extracts of such soils were obtained, but only when soils were saturated and decomposition was anaerobic.

This investigation studied simazine (2-chloro-4,6-bis(ethylamino)-s-triazine), atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), propazine (2-chloro-4,6-bis(isopropylamino)-s-triazine), and prometone (2-methoxy-4,6-bis(isopropylamino)-s-triazine). Preemergence applications of granular formulations of simazine on attaclay or calcium sulfate of simazine at 1 to 2 ppmw controlled Potamogeton, Najas, Ceratophyllum, Heteranthera and Zannichellia. Higher rates were required to control filamentous algae (Cladophora and Pithophora) and chara (Chara vulgaris). Early postemergence applications of wettable powder to submersed aquatics and filamentous algae were often effective. Atrazine gave similar results. Concentrations of 0.5 to 1.0 were effective in controlling Cladophora and Pithophora and three species of Potamogeton in pond applications. Spray applications, generally, were more effective than broadcasting granular atrazine. Propazine and prometone did not control submersed species in concentrations up to 3 ppmw.

Simazine had a relatively high margin of safety with respect to acute toxicity to fish. It was less toxic than propazine, prometone or atrazine. Granular forms were less toxic than wettable powder or emulsifiable concentrates. Laboratory tests on bottom organisms gave an acute LD50 toxic dosage of 28 ppmw. Field observations did not demonstrate a serious reduction in the production of bottom organisms. However, the control of aquatic vegetation brought about ecological changes affecting bottom dwelling and weed clinging organisms. These changes would affect certain fishes with special food habits.

The ribonucleic acid (RNA) content of corn roots and etiolated coleoptiles treated with amitrole (3-amino-1,2,4-triazole) was very similar to that in untreated tissues. Amitrole consistently decreased the acid-soluble nucleotide content of etiolated corn coleoptiles.

Bioassay methods are described for determining the concentration of 4-amino-3,5,6-trichloropicolinic acid in solutions and in soil. These methods are suitable for determining the concentration of the herbicide in the presence of other herbicides. These test methods can detect considerably less than one microgram of herbicide.

Marked differences in the response of field bindweed (Convolvulus arvensis L.) to 2,4-dichlorophenoxyacetic acid (2,4-D) were found among plants grown from seed obtained from 19 states in the U. S. and one province in Canada. These differences were not correlated with the origin nor with plant vigor. Inherent physiological differences seemed to be responsible.

A system involving resting cells of Euglena gracilis provides a rapid and convenient test system for screening potential herbicides which act as inhibitors of chlorophyll synthesis. The system appears to distinguish between inhibitors of chloroplast formation, such as 3-amino-1,2,4-triazole, and inhibitors of chlorophyll formation per se, such as ethionine.

The minimum red-light (> 590 mμ.) intensities from fluorescent tubes at which growth or maintenance of original fresh weight were obtained at 20 C in a growth chamber for 28 days were 11–20 foot-candles for waterstargrass (Heteranthera dubia [Jacq.] Mac M.) and 12–45 foot-candles for coontail (Ceratophyllum demersum L.). Duckweed (Lemna minor L.) frond number increased significantly at 45 foot-candles red light, and the fresh weight probably increased at 45 foot-candles. The intensites of 11–45 foot-candles constituted 1.0–3.8 percent of the red portion of full sunlight.

A grass seed attachment to a grain drill was modified to apply granular herbicides using positive metering mechanism. Uniformity of granule output was adjusted within ± 4% maximum error. Speed of travel did not appreciably affect the amount of granules applied per acre.

Alligator juniper (Juniperus deppeana Steud.) is a weed tree of Arizona and New Mexico. It sprouts from stems, roots, or especially from buds on the crown, whenever the top is destroyed. Adequate mechanical control requires that the root crown be removed from the soil. Treatment of stumps with pelleted 3-phenyl-1,1-dimethylurea (fenuron) on the soil or polychlorobenzoic acid (PBA) sprayed on the stumps are promising means of preventing sprouting.