Four concentrations of 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), 1-n-butyl-3-(3,4-dichlorophenyl)-1-methylurea (neburon) and 3-phenyl-1,1-dimethylurea (fenuron), adsorbed on photometrically uniform filter paper, were irradiated with ultraviolet light 253.7 millimicrons) or sunlight. Marked changes in the absorption spectra after irradiation indicated photodecomposition of the four herbicides was different with the two light sources.

Recrystallized 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), and 2-methylmercapto-4-ethylamino-6-isopropylamino-s-triazine (ametryne) were adsorbed on filter paper, and exposed to ultraviolet light (253.7 millimicrons) or sunlight. All underwent photodecomposition, which was different under ultraviolet light and sunlight.

Amitrole (3-amino-1,2,4-triazole) and 5-chlorobenzo-1,2,3-triazole were the only compounds tested that inhibited wheat root elongation and growth of carrot explants, produced chlorosis, and depressed catalase activity. Ten other heterocyclic compounds were more effective in inhibiting growth in wheat roots or carrot explants. Overall biological activity was reduced when substituents other than the amino group on the number three position were substituted on the triazole nucleus.

Seven different types of nozzles were compared as to uniformity of spray application, spray drift, and tendency to clog. The wide angle whirl chamber nozzles applied the spray more uniformly than other nozzles. Increasing nozzle height to 1.5 times the recommended height increased uniformity of spray application with most nozzles. Lowering the nozzle height to half the recommended height seriously reduced uniformity of spray application with almost all nozzles except the wide angle whirl chamber nozzles which provided a uniform spray at all 3 heights. The whirl chamber nozzles were least easily clogged of the nozzles studied. Wettable powders normally applied in 30 gallons or more per acre have been satisfactorily applied at rates of less than ¼ of this amount. Spray drift was reduced to a no crop hazard level, with effective coverage, at rates of application as low as 7 gallons per acre.

The rates of decarboxylation of 2,4-dichlorophenoxyacetic acid (2,4-D), 2-chloro-4-fluorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in excised leaves of blackjack oak (Quercus marilandica Muenchh,) were determined by collecting the C14O2 evolved from carboxyl-labeled herbicides. 2,4,5-T was decarboxylated only in trace amounts. 2,4-D was decarboxylated to a maximum of about 1 per cent and 2-chloro-4-fluorophenoxyacetic acid of about 7 per cent, of the amounts taken up by the leaf. Decarboxylation rates for 2,4-D in June were highest in persimmon (Diospryos virginiana L.) and blackjack oak, and were very low in winged elm (Ulmus alata Michx.), sweet gum (Liquidambar styraciflua L.), and green ash (Fraxinus pennsylvanica Marsh.). The rates of decarboxylation of 2,4-D apparently were not correlated with susceptibility to 2,4-D.

Collections of plants of medusahead, Elymus caput-medusae L., were made from natural infestations in Nez Perce County and Washington County in northern and southern Idaho, respectively. The ash and silica content (dry weight basis) decreased as the plant matured. The total ash of the entire plant contained from 72–89 per cent silica. Similar percentages of silica in ash were obtained in the culms, heads, and seeds of the plant. X-ray diffraction patterns and polarizing microscope examinations showed the mineral form of silica to be opal. Heavy deposition of silica was found in the barbs of awns, in the epidermis of the leaves, culms, glumes and seeds, and in strands beneath the epidermis.

Strains of hoary cress, particularly within the lens-podded species (Cardaria chalepensis (L.) Hand.-Maz.), varied greatly in leaf size and shape, spreading ability, stand density, and reaction to treatment with several herbicides. Without competition, heart-podded hoary cress (C. draba (L.) Desv.) spread farther and produced a denser stand than either lens-podded or globe-podded cress (C. pubescens (K. A. Meyer) Jarm.), and, in general, was more susceptible to 2,4-dichlorophenoxyacetic acid (2,4-D) and trichlorobenzoic acid (2,3,6-TBA) than lens-podded cress. Within 12 strains of lens-podded hoary cress no relationship was found between susceptibility to 2,4-D or 2,3,6-TBA and any other characteristic.

Bristly thistle (Cirsium horridulum Michx.) is an important perennial weed in Alabama pastures. It may remain vegetative many years before flowering and may regrow from the roots after flowering. A heavily infested pasture produced about 10,000 seedlings per acre per year of which 73% established from January through April. There was an average of 150 achenes per head but many did not contain fully developed seed. Essentially equal numbers of red and yellow flowered types were found. From two to as many as six successive cuttings below the soil surface were necessary to kill thistle plants. Thistles were effectively controlled by 2,4-dichlorophenoxyacetic acid (2,4-D), and 2-methyl-4-chlorophenoxyacetic acid (MCPA).

The use of insects in the biological control of weeds necessitates that these insects have very restricted host ranges. Specialized insects boring in stems or living in seed pods have adaptations which obligate them to their host plant. However, the leaf-feeding beetle, Chrysolina quadrigemina Suffrian, imported for the control of St. Johnswort (Klamath weed) (Hypericum perforatum L.) through its feeding habits, tropistic responses and synchronization of its life history to the growth phases of the plant has shown that it is restricted to its preferred host plant.

A single-gene homozygous recessive mutant in an S1 inbred line of corn resulted in an 8- to 10-fold reduction in 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one content. Aqueous suspensions of acetone extracts from low segregates formed little 2-hydroxy-4,6-bis(ethylamino)-s-triazine (hydroxysimazine) when incubated with 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine). Tolerance studies on 3:1 and 1:1 segregating ears indicated that the low segregates were somewhat less tolerant to 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) supplied in solution culture.

The amount of C14-labeled triazine herbicides absorbed by the upper and lower surfaces of peanut (Arachis hypogea) leaves was found to be significant with the exception of 2-methoxy-4,6-bis(isopropylamino)-s-triazine (prometone). Almost always a surface active agent increased the absorption of triazine herbicides by the leaves. The surface active agent did not play any role in diffusion of these herbicides. Among the four herbicides tested 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) and 2-methoxy-4,6-bis(isopropylamino)-s-triazine (prometone) were found to move both acropetally and basipetally, whereas 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) and 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine) moved only in the acropetal direction.

The toxicity of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) and 2-chloro-4-ethylamino-6-isoproylamino-s-triazine (atrazine) to eight crops was determined. The crops in order of increasing tolerance to these herbicides were Southern Giant Curled mustard (Brassica juncea (L.) Coss.), Missouri 0-205 oats, Straight Eight cucumbers (Cucurbita sativa L.), Knox wheat, Clark soybeans, RS610 grain sorghum, GT-112 inbred corn, and F-6 inbred corn. Inactivation of simazine and atrazine applied at 2 lb/A on field plots, as determined by soybean and oat bioassay, was most rapid when the soil environment was favorable for the growth of microorganisms. Very little inactivation occurred between September, 1960, and June, 1961, following a May, 1960 application. One year after application, 0.16 lb/A of atrazine and 0.31 lb/A of simazine were detected, but neither was detected after 16 months.

The alkanolamine salt of 2,4-dichlorophenoxyacetic acid (2,4-D), the dimethylamine salt of 2,3,6-trichlorobenzoic acid (2,3,6-TBA), and the sodium salt of 2,3,6-trichlorophenylacetic acid (fenac), were evaluated in controlling witchweed and toxicity to corn on germinating seed in petri dishes, as preplan ting, preemergence, and postemergence treatments in the greenhouse and as preplanting, soil-incorporated treatments in the field. Corn roots were affected more than the shoots by each herbicide. Fenac and 2,4-D inhibited root growth of corn seedlings in petri dishes more than 2,3,6-TBA. Fenac was the most effective herbicide for control of witchweed and weedy grasses when applied as a preplanting, soil-incorporated treatment and controlled witchweed at rates which significantly increased corn yields. Applied preplanting, 2,4-D did not control witchweed and 2,3,6-TBA at rates which gave witchweed control equivalent to that obtained with fenac was toxic to corn.

Flat pea (Lathyrus sylvestris L.), previously investigated as a forage plant in the United States, is a perennial legume with undesirable qualities of low palatability, difficulty of establishment, and a toxic principle. Characteristically aggressive and tolerant to a wide range of growth conditions, it is a potentially serious weed in its area of adaptation. A related species, everlasting pea (L. latifolius L.), has similar characteristics. A 2-lb/A rate of 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), 2-(2,4,5-trichlorophenoxy)propionic acid (silvex), or 2,3,6-trichlorobenzoic acid (2,3,6-TBA) followed by 2-lb/A of silvex a year later gave complete control of established plants and seedlings of flat pea.

2-chloro-4-isopropylamino-6-ethylamino-s-triazine (atrazine) applied at 3 lb/A to wheat stubble shortly after harvest in 1961 and 1962 controlled all vegetation for the remainder of the season. 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine) was nearly as effective as atrazine in 1962. Grain sorghum was planted in the spring of 1962. No preplanting tillage was used, and no weed control measures were needed in sorghum during the growing season on the treated plots, and crop stands, vigor, and grain yields were superior to those on the cultivated checks.

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.

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.

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.

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 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.