Approximately 75% of the inhibitory effect of a foliar application of 4-chloro-2-butynyl N-(3-chlorophenyl)carbamate (barban) on wheat was eliminated by dusting the seed before planting with 4′-chloro-2-hydroxyiminoacetanilide at a rate of one ounce per bushel. Other highly effective antidotes were 2,4-dichloro-9-xanthenone and N-methyl-3,4-dichlorobenzene sulfonamide. Barban antidotes were found in those chemicals that produced formative effects on plants.

White mustard (Brassica hirta Moench) and foxtail millet (Setaria italica (L.) Beauv.), thinned to uniform stands, varied in a three-year study in their effects on peas depending on weed population, duration of competition, relative time of pea and weed emergence, and year to year variations in seasonal rainfall. Full-season competition from 3 mustard plants per square foot reduced pea stands 0 to 25%, pea vine weight 39 to 71%, and yields of shelled peas 0 to 64%, during the three years. In one direct comparison, 27 foxtail plants per square foot caused reductions in peas comparable to those caused by 3 mustard plants. When mustard emerged 3 days before peas, fresh weight of pea vines was reduced 54 percent; but when mustard emerged 4 days after peas, only 17 percent.

The relative growth rates of peas, Brassica hirta, B. Kaber, Amaranthus retroflexus, Polygonum Persicaria, Setaria italica, S. viridis, S. glauca, and Echinochloa crusgalli grown without intra- and inter-species competition suggest that the Brassica species would be the more severe competitors with peas and that weed competition usually would be more severe in late-seeded peas.

Winter wheat infested with four populations of coast fiddleneck (Amsinckia intermedia Fisch. & May) was treated with 2,4–dichlorophenoxyacetic acid (2,4–D). One weed per square foot reduced grain yield. Weeds competed strongly as early as the rosette stage. Treating the weed infested wheat with 2,4–D increased yield. A vigorous, early-established crop of wheat competed effectively with the weeds.

Species studied at Lincoln, Nebraska for 4 years were downy brome (Bromus tectorum L.), hairy chess (B. commutatus Schrad.), Japanese chess (B. japonicus Thunb.), and cheat (B. secalinus L.). These grasses were usually winter annuals, but also became spring annuals or biennials when sown in late March or early April.

In the greenhouse, an inductive period either of vernalization or short day lengths appeared necessary for panicle production by downy brome and hairy chess. For both species, long day lengths following the inductive period were necessary for flowering.

When a mixture of smooth bromegrass (Bromus inermis Leyss.) and 5.4 per cent of weed bromegrasses was sown in the fall, weed bromes made up 48 per cent of the total basal density and 87 per cent of the total seed yield the following summer. Panicles of weed bromes were absent or nearly so when this mixture was sown soon after April 1.

The best time for mowing hairy chess and downy brome for their control in pasture was approximately one week after the heads had emerged.

Practical control of weed bromegrasses has generally been obtained by prevention of seed production for two years. A practical program has included killing all emerged weed bromegrasses by tillage between April 1 and heading. A spring cereal or row crop, such as corn or sorghum, was then planted. The next season, timely tillage followed by the above crops, or summer fallow, has permitted return of fields to the usual alternate winter wheat and fallow sequence.

Effective control of weed bromegrasses also was accomplished by isopropyl N-phenylcarbamate (IPC), isopropyl N-(3-chlorophenyl) carbamate (CIPC), 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), sodium salt of trichloracetic acid (TCA), 3,6–endoxohexahydrophthalic acid (endothal), 4,6-dinitro-o-sec-amylphenol (DNAP), and mixtures of these herbicides.

Red alder (Alnus rubra Bong.) was readily killed by growing season treatments with a 1 to 1 mixture of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in diesel oil. Except for 1-inch-diameter trees, it was resistant to dormant season treatments. Treatments applied during moderate rain were less effective than during rain-free periods.

During a 48 hour period after spraying with 2,4–dichlorophenoxyacetic acid (2,4–D), the ribonucleic acid (RNA) in the subcellular particles of soybean hypocotyl tissue doubled with over half of the increase appearing in the microsomal fraction and one quarter in the soluble fraction. It is hoypothesized that the herbicidal action of 2,4–D lies in a renewal of nuclear activity in the tissue, leading to a synthesis of RNA and protein and to tissue proliferation, and that the cytochemical basis of auxin-herbicide action lies in a reversion to a meristematic metabolism.

The effect of 4,6-dinitro-o-sec-butylphenol(DNBP) and several phenylureas, s-triazines, chlorinated phenoxyacetic acids and chlorinated benzoic acids on the photolytic activity (Hill reaction) of chloroplasts isolated from turnip greens (Brassica spp.) was studied. Photochemical activity was measured potentiometrically with ferricyanide as the electron acceptor.

For the various members of each herbicidal group close agreements were obtained between inhibitions expressed against the Hill reaction and their relative phytotoxicities, except for the chlorinated benzoic acids. Of the five phenylureas tested, 1-n-butyl-3-(3,4-dichlorophenyl)-1-methyrurea (neburon) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) were most inhibitory and 3-phenyl-1,1-dimethylurea (fenuron) was least inhibitory to the Hill reaction. 2-Chloro-4,6-bis(isopropylamino)-s-triazine (propazine) and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) were the most inhibitory and 2-chloro-4,6-bis(diethylamino)-s-triazine (chlorazine) was the least inhibitory of seven s-triazines to the Hill reaction. DNBP inhibited the Hill reaction by 50 percent (I50) at 1.3 × 10-5 M. An I50 value of 5.1 × 10-4 M was obtained for 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) which was the most inhibitory of the chlorinated phenoxyacetic acids tested. 3,4,5-Trichlorobenzoic acid (3,4,5-TBA) was the most inhibitory chlorinated benzoic acid tested (I50 #x2A75; 2 × 10-3M).

I50 values were established and compared for chloroplasts isolated from turnip greens, corn and soybeans for diuron, simazine, DNBP, isopropyl N-(3,4-dichlorophenyl)carbamate (3,4-DCIPC), isopropyl N-(3-chlorophenyl)carbamate (CIPC), 2,4,5-T and 3,4,5-TBA. Chloroplasts from the three species were essentially equally sensitive to each of the seven herbicides. Hence, no evidence was obtained which would explain species tolerance or susceptibility.

When turnip-green chloroplasts were treated with inhibitory concentrations of diuron, simazine, DNBP, CIPC, 2,4,5-T and 3,4,5-TBA in the dark, the herbicides could be removed by washing without seriously impairing the photolytic activity of the chloroplasts. However, irreversible changes occurred when the chloroplasts were illuminated while in contact with the herbicides, i.e., photolytic activity was not completely restored when the chloroplasts were washed, except with simazine.

Among 15 different herbicides tested for eradication of Turkey oak (Quercus laevis Walt.) over a period of four years on Lakeland fine sand in Florida, only monuron, diuron, and fenuron at minimal rates of 10 lb/A were effective. One full growing season after application was required for complete kill. Phenoxy compounds gave variable top-kill but not satisfactory control. AMS, dalapon, and four formulations of benzoic acid were ineffective in these tests.

Out of 13 different grasses, Pensacola bahiagrass (Paspalum notatum Flugge) and weeping lovegrass (Eragrostis curvula Schrad.) were best adapted to these deep sandy soils. Seedbed preparation was essential to obtain a good stand of either. After establishment, the lovegrass vigorously persisted throughout the experiment; the bahia also persisted but the lack of fertilization was extremely evident. Both grasses could be established satisfactorily on soil treated two years earlier with monuron or diuron at 10 lb/A.

Fish used in these tests were the Israeli strain of the common carp, Cyprinus carpio; the Nile tilapia, Tilapia nilotica; the Java tilapia, T. mossambica; and the Congo tilapia, T. melanopleura. Israeli carp and either Nile or Java tilapia in ponds containing only these species virtually eliminated aquatic weeds, but when stocked into established populations of largemouth bass and bluegill results were less encouraging.

Medusahead (Elymus caput-medusae L.) matures later in the spring than most associated species, and has a seed head moisture content of above 30 per cent for approximately a month after leaves and stems begin to dry. High temperature is more injurious to seed viability when seed moisture content is high. Control burns of medusahead infested rangeland were most effective in late afternoon when burning slowly (into a mild wind) and at the soft dough stage of medusahead seed development.

Disking, relisting, cultivation and no repreparation were employed in repreparing for planting seedbeds that had received preemergence treatment with 3-(3,4-dichlorophenyl)1,1-dimethylurea (diuron). Only the relisting method of seedbed repreparation appeared hazardous with respect to crop injury from herbicidal residues. Retreatment with diuron tended to increase injury symptoms in replanted cotton but yields were not significantly reduced by retreatment. Early-season weed competition, preventable by preemergence treatment, appeared to be more hazardous to yields than slight to moderate herbicidal injury to the cotton. Cotton replanted on plots treated once or treated twice significantly outyielded that on untreated plots in one of the two years in which all plots were replanted.

Rhizomes were sampled from quackgrass sod weekly during two seasons. The activity of buds on one-bud sections from mature rhizomes was used to determine periods of growth and dormancy. The rhizome buds showed a steady decrease in activity from mid-April to June 1. During June, the buds were dormant. Recovery began in late June and continued the rest of the summer. Only one-third of all rhizome material in a three-year-old sod was viable. The amount of viable mature rhizomes decreased during the season while the viable new rhizomes increased, and the total viable level remained fairly constant. This suggested a definite cycle in rhizome production and decomposition from year to year and a short life-period in the soil. The term “late-spring dormancy” is suggested for quackgrass rhizomes, based on the prevailing cool and moist weather conditions and the late-spring time of occurrence during the year. This distinguishes the type of dormancy described from “summer dormancy”.

The propylene glycol butyl ether ester of 2,4-D or the dimethylamine salt of 2,3,6-TBA in 25 gallons water per acre effectively controlled Colorado rubberweed (Hymenoxys richardsonii (Hook.) Cockerell) at the prebud stage. From 2 to 4 pounds acid equivalent per acre of an ester of 2,4-D were satisfactory, depending on the relative importance of cost and speed of kill.

A procedure has been described for the partial purification of the simazine-resistance factor of Zea. The relative solubilities in various solvents and some of the chemical properties of this factor have been studied. Pyridine and hydroxylamine were also found to bring about the conversion of simazine-C14 to the 2–hydroxy analogue. Based on these substances as models, a mechanism has been proposed for the dechlorination of simazine in Zea.

Annual treatment with 1 lb/A of 2,4-D (2,4-dichlorophenoxyacetic acid) repeated for several years during mid- to late June gave excellent control of ironweed (Vernonia baldwinii). Later dates of treatment were not as effective. Mowing was not satisfactory as a weed control measure for ironweed. The populations in mowed plots in long-term experiments closely paralleled populations of untreated plots. Where numbers were reduced by spray treatment, recovery or reinfestation was comparatively slow. Quadrat counts were compared with visual estimation as methods of evaluating effects of treatments. The estimation method did not permit quantitative evaluation of year-to-year treatment or environmental effects.

In semi-arid areas, good control of field bindweed with 1 lb/A of 2,4–dichlorophenoxyacetic acid (2,4–D) will occur if there is at least 1.5 inches of available soil moisture when runners are 6 to 10 inches long. Under these conditions carbohydrates are high in the leaves and low in the roots. Analysis of rainfall records from Amarillo, Texas indicates that soil moisture conditions during May will be favorable for good bindweed control with 2,4–D 54% of the time.

Amiben (3–amino–2,5–dichlorobenzoic acid) was applied to the surface of various soil types in cylinders which were then leached with water. The leached soil was tested biologically for herbicide activity. Loss was most rapid from sand, followed by clay, with muck remaining phytotoxic much longer. There was only a slight increase in the toxicity of loam soil given repeated treatments with amiben. Incubation of treated soil for various periods of time indicated that microorganism breakdown is important in soils relatively high in organic matter.

A 7-foot V-plow was modified so herbicides could be sprayed beneath the soil surface in stubble mulch fallow operations. This permits the incorporation of volatile herbicides without destroying plant residues. Weed control is achieved by action of the 7-foot sweeps during the herbicide application and later by the incorporated herbicide.

Seedlings of barnyardgrass, green foxtail, and yellow foxtail emerged from seeds as deep as 5 inches in Sagemoor fine sandy loam. The number of emerged seedlings from depths of 4 to 5 inches decreased in the order of decreasing seed weights; yellow foxtail, barnyardgrass, green foxtail. Few seedlings developed in the field from seeds on the soil surface. Seedling emergence in spring or greenhouse seedings was greatest from the most shallow depths (½ or 1 inch) and decreased regularly as depth of planting increased. An autumn seeding gave maximum emergence at 1½ inches, possibly because some seeds sown shallower may have germinated in short warm periods but were killed by subsequent freezing.

Aqueous solutions of sodium and calcium polysulfides convert labeled simazine, 2-chloro-4,6-bis(ethylamino)-s-triazine-2,4,6-C14, to a chloroform insoluble, charcoal adsorbable derivative which is thought to be hydroxysimazine, 2-hydroxy-4,6-bis(ethylamino)-s-triazine-2,4,6-C14. In soil, calcium polysulfide accelerates the breakdown of simazine as shown by oat bioassay. These results suggest the possibility of using polysulfides to remove unwanted residues of chlorotriazine herbicides from crop lands.