Amitrole (3-amino-1,2,4-triazole) was applied to purple nutsedge (Cyperus rotundus L.) clones newly established in the field in the Piedmont Plateau. Applications were made one week after initial foliar emergence, then at biweekly intervals through the 20th week. The principal results were: (1) Nutsedge was most susceptible to amitrole applied 4 weeks after initial emergence. The next most susceptible stages were at 1 or 2 weeks; (2) Six weeks after emergence, nutsedge appeared resistant to amitrole; (3) All applications after 10 weeks were relatively ineffective; (4) Chemical analyses of tubers and bulbs indicated a high ash content early in the season, particularly at 6 weeks after emergence.

Twenty-nine s-triazines were evaluated as subsurface and surface preemergence sprays for the control of crabgrass in corn, grain sorghum, soybean, and cotton and as directed postemergence sprays in cotton. In preemergence experiments corn was tolerant to most chloro-alkylamino-s-triazines but was severely injured by most methoxy- and methylmercapto-alkylamino-s-triazines. 2-Chloro-4,6-bis(isopropylamino)-s-triazine [propazine], 2,4-bis(ethylamino)-6-trichloromethyl-5-triazine, and 2-chloro-4-isopropylamino-6-methylamino-s-triazine were about equally effective for selective preemeregnce weed control in grain sorghum. 2,4-Bis(ethylamino)-6-trichloromethyl-s-triazine and perhaps 2-methoxy-4,6-bis [(3-methoxy)propylamino]-s-triazine were sufficiently active and selective to suggest additional evaluation as preemergence herbicides for soybeans. Cotton exhibited tolerance to certain methylmercapto derivatives; 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine [prometryne] as a preemergence and as a directed postemergence spray appeared especially promising for control of weeds in cotton. Generally methoxy- and methyl-mercapto-alkylamino-s-triazines as preemergence and postemergence sprays were more effective for controlling crabgrass than corresponding chloro-alkylamino-s-triazines. The initial and residual toxicities of 14 of the more promising s-triazines were compared in four soils of the southern United States. Initial effective levels of the methoxy and methylmercapto derivatives varied more among soils than those of corresponding chloro derivatives. In most cases methoxy s-triazines were more toxic to the fifth oat crop than corresponding chloro s-triazines whereas chloro s-triazines exhibited the greatest initial toxicities. Certain methylmercapto derivatives appeared fairly persistent also.

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.

2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), ethyl N,N-di-n-propylthiolcarbamate (EPTC), and 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) were shown to aid in the establishment of rose clover (Trifolium hirtum All.) and harding-grass (Phalaris tuberosa L. var. stenoptera (Hack.) Hitch.) by reducing competition from resident annual plants, primarily medusahead (Elymus caput-medusae L.). The success of preemergence herbicides was shown to depend on fall precipitation in amounts great enough to permit seed germination and plant growth before winter temperatures become limiting. The degree of weed control necessary to aid in seedling establishment was low, sometimes lower than could be measured by estimates of ground cover.

Inclusion of any one of several ethoxylated nonionic surfactants in aqueous spray mixtures of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) greatly increased its toxicity to crabgrass (Digitaria sanguinalis (L.) Scop.). Phytotoxicity of sprays made up from commercially formulated diuron was greater than when technical diuron was used. The toxicity of diuron was also increased by the addition of any of several low-molecular-weight alcohols to the spray mixture.

The turbidity of diuron suspensions was greatly decreased by addition of any of several nonionic, anionic, or cationic surfactants which contained a fatty acid or fatty acid derivative as the hydrophobic portion of the molecule. Phytotoxicity of diuron applied with ethoxylated nonylphenol surfactants was associated with ethylene oxide (hydrophil) content. Surfactants containing nonylphenol, alkylthiol, or tridecylphenol as hydrophobes appeared essentially equal in their abilities to increase diuron toxicity, but dodecylphenol surfactants were slightly less effective.

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.

Barnyardgrass (Echinochloa crusgalli (L.) Beauv.) seeds which did not germinate because of low temperature, insufficient moisture, or seed dormancy were exposed to concentrations of ethyl N,N-di-n-propylthiolcarbamate (EPTC) lethal to emerging barnyardgrass seedlings. After different periods of exposure, seeds were removed from the EPTC-treated environments and germinated in untreated soil. Seed germination was not reduced by EPTC and there was no permanent injury to the seedlings. It was concluded that rates of EPTC used for selective weed control do not injure barnyardgrass seeds prior to germination.

Techniques were developed for evaluating herbicides on submersed, floating, and emersed aquatic weeds. Among 75 herbicides evaluated on three species of submersed weeds only 1:1′-ethylene-2:2′-dipyridylium (diquat); 1:1′-dimethyl-4:4′-dipyridylium (paraquat); di-N,N-dimethylcocoamine salt of 3,6-endoxohexahydrophthalic acid (endothal); and acrylaldehyde (acrolein) gave 85 percent or better control at 1 ppmw in still-water tests. Only acrolein and the di-N,N-dimethylcocoamine salt of endothal were effective on submersed weeds at 1 ppmw in the limited-exposure test. The evaluation of 17 herbicides on three species of floating aquatic weeds indicated that diquat was effective when applied at rates of 1 or 2 lb/A. The tertiary fatty acid amines of 2,4-dichlorophenoxyacetic acid (2,4-D) were more effective on floating weeds than an ester of 2,4-D. Many of the 78 herbicides evaluated on alligator-weed (Alternanthera philoxeroides (Mart.) Griseb.) killed the tops, but only two retarded the sprouting of underwater nodes longer than 6 weeks. Applications of 20 lb/A of 2-(2,4,5-trichlorophenoxy)-propionic acid (silvex) in two formulations retarded sprouting of underwater nodes for 8 weeks.

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.

Treatment of woollyleaf franseria, Franseria tomentosa Gray, with 2,4-dichlorophenoxyacetic acid (2,4-D) at three locations in Nebraska showed that June treatments were much more effective in reducing the stand than those made in July and August. The isopropyl ester and butoxyethanol ester of 2,4-D were somewhat more effective than the triethanolamine salt. Rates of 2 and 4 lb/A gave the most consistent results.

Spectrophotometric and chemical analyses indicated that photodecomposition of 3-amino-2,5-dichlorobenzoic acid [amiben] in water solution occurred rapidly during exposure to, sunlight or light from fluorescent sun lamps. Slow but definite photochemical alteration occurred when dry amiben on filter paper was exposed to light from the sun lamps. Several reaction products were separated by paper chromatography. Loss of herbicidal activity from 10-3 molar aqueous solutions of amiben approximated disappearance of amiben determined colorimetrically. Photochemical inactivation of the formulated triethylamine salt of amiben in aqueous solution was slower than that of chromatographically pure amiben. A method involving diazotization of amiben with nitrous acid and coupling the diazo form with chromotropic acid was suitable for quantitative determination of amiben.

Peach trees treated with the herbicide mixture of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) and 3-amino-1,2,4-triazole plus ammonium thiocyanate (amitrole-T) had higher leaf nitrogen and more growth than trees where the weeds were controlled by hand hoeing or a black plastic mulch. Apple trees had higher leaf nitrogen and more growth when treated with simazine and amitrole-T than with no weed control. In both peaches and apples more growth and higher leaf nitrogen resulted from the herbicide treatments than from supplemental nitrogen treatments, indicating that the herbicide influenced the nitrogen metabolism of these trees.

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.

Unshielded cultivation (during which soil is purposely moved into the drill row) and shielded cultivation (soil movement into drill row minimized) were compared in field plots of cotton [Gossypium hirsutum L. (var. DBES 8274)] which received no herbicide, a banded preemergence herbicide, one to three banded postemergence herbicide applications, or a combination of the banded pre- and postemergence herbicides. All plots were hoed and cultivated as needed to maintain reasonably good control of weeds. The study was a 3-year experiment replicated six times.

Unshielded cultivation was superior or equal to shielded cultivation as a weed control measure supplementary to hoeing or hoeing and herbicides as evaluated by effects on hoe-labor requirements, cotton yields, and weed infestations at harvest time. Replacing one or more postemergence herbicide applications with unshielded cultivation resulted in reduced control of weeds. Late season initiation of unshielded cultivation in plots previously shield cultivated had no detrimental effect on yield.

Significant increases in yield of cotton were obtained in plots treated with a preemergence herbicide as compared with plots receiving only hoeing and cultivation for weed control. Postemergence herbicide treatments (applied as a directed spray) did not result in significantly higher yields as compared with plots receiving hoeing and cultivation only. As measured by 3-year averages preemergence or postemergence treatments provided about 50 per cent control of weeds; combined they provided about 75 per cent control.

3-Amino-1,2,4-triazole (amitrole) sprayed on annual grassland infested with medusahead (Elymus caput-medusae L.) at 1/2 to 4 lb/A when medusahead was in the boot or soft dough stage reduced viable caryopses from 60 to 100 percent, and seed production the following year from 75 to almost 100 percent. 1,2-Dihydropyridazine-3-6-dione (maleic hydrazide) and 2,2-dichloropropionic acid (dalapon) reduced viability of medusahead seeds, but were less effective than amitrole. Viable caryopses of soft chess (Bromus mollis L.) were reduced and the year following treatment soft chess was decreased in the stands by early application (boot stage of medusahead) but not by late application of herbicides, when the soft chess heads were dry.

The toxic effects of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) to barley were avoided by feeding plants treated with 1.5 lb/A of simazine, sucrose, glucose, aspartate, and maltose. Shoots from plants fed glucose and maltose contained more soluble carbohydrate than the check. Plants fed glutamine and asparagine were higher in total nitrogen content than the check. Plants fed sucrose and maltose increased their nitrogen content over the check, but plants fed glucose did not. The harmful effects of simazine occurred primarily in barley shoots exposed to light. Plants grown in the dark showed a very small decrease in weight of shoots and soluble carbohydrate content as the level of simazine increased, while the weight of the shoots and soluble carbohydrate content of treated plants grown in the light decreased sharply. Simazine had little effect on root growth of plants grown in the light or dark. The data on root respiration showed that barley roots metabolized the added substances differently and that simazine differentially influenced their metabolism by the roots.

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.

Preplanting, soil-incorporated treatments of fenac (2,3,6-trichlorophenylacetic acid sodium salt) at 1, 2, 4, and 8 lb/A, 2,3,6-TBA (2,3,6-trichlorobenzoic acid dimethylamine salt) at 8, 12, and 16 lb/A, and 2,4-D 2,4-dichlorophenoxyacetic acid amine salt) at 12 lb/A applied in 1960 to six soil types infested with witchweed (Striga asiatica (L.) Kuntze) resulted in some control of witchweed as measured by visual observations and corn yield. Two or three additional postemergence applications of 2,4-D at 1 lb/A were required to prevent witchweed seed production for the growing season. Witchweed parasitism on corn was greatly reduced by a preplanting treatment of fenac at 2 lb/A plus 2,4-D as a postemergence treatment.

All rates of 2,3,6-TBA and fenac at 8 lb/A caused moderate to severe corn injury with the most severe injury occurring on soils with relatively high clay content in the subsoil. Soil residual studies and field observations indicated fenac and 2,3,6-TBA may be present in Coastal Plain soils for more than 18 months.

Dalapon (2,2-dichloropropionic acid) was applied as basally directed sprays to field grown cotton (Gossypium hirsutum L. var. Acala 4–42). Herbicidal rates of dalapon applied after heavy boll development (approximately 105 days after planting) were noninjurious; earlier applications appeared hazardous. Three or six pounds of dalapon per acre applied during early square or full flowering caused no noticeable injury symptoms but delayed maturity and reduced cotton yields in proportion to dosage. Analysis of eight seed and fiber properties showed no significant differences among treatments except for minor shifts attributable to dalapon-induced changes in maturity. Germination of seed from treated cotton was measurably retarded but final viability was not reduced. The retarding influence persisted for more than two years in storage. Accumulation of 8 to 21 ppm dalapon in the seeds was demonstrated by colorimetric and isotope dilution methods of analysis.

Rose clover (Trifolium hirtum All.), subterranean clover (T. subterraneum L.), and crimson clover (T. incarnatum L.), were sprayed at different growth stages with 2,2-dichloropropionic acid dalapon), and two formulations of 4-(2,4-dichlorophenoxy)-butyric acid [4-(2,4-DB)], in two growing seasons. Herbage yields, seed yields, and seed quality were for the most part unaffected by either formulation of 4-(2,4-DB) at the dates required for weed control. Only subterranean clover was tolerant of dalapon and then only at very low rates.