A mixture of activated carbon and vermiculite was used to increase the tolerance to 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) of direct-seeded cucumbers (Cucumis sativus L., var. Wisconsin SMR-15) in greenhouse tests and direct-seeded tomatoes (Lycopersicum esculentum Mill, var. Bouncer) in greenhouse and field (var. Heinz 1370) tests. The tolerance of cucumbers to dimethyl tetrachloroterephthalate (DCPA) and 4-(methylsulfonyl)-2,6-dini tro-N,N-dipropylaniline (nitralin) also was increased in field trials. When the mixture was placed in a hole (0.75 inch deep by 1 inch diam) over the crop seed to the level of the soil surface, preemergence herbicides were detoxified in the small area; and the crop plant was not injured. The herbicide remained active outside the small protected area. Also, a wafer consisting of an activated carbon-vermiculite mixture, fertilizer, and seed provided protection to direct-seeded crops.

Downy brome (Bromus tectorum L.) seedling emergence was greatest from soil depths of 1 inch or less, but occasionally seedlings emerged from depths of 4 inches. Downy brome seed covered by soil germinated more rapidly than those seed on the soil surface. More downy brome seedlings emerged, and from greater depths, from coarse-textured soils than fine-textured soils when moisture was not limiting. Soil type did not influence longevity of downy brome seed buried in the soil. Most (98%) 8-month-old downy brome seed buried 8 inches in the soil germinated but did not emerge in 1 year; and none remained viable in the soil after 5 years. The moldboard plow was more effective in reducing downy brome populations than a sweep plow or one-way disk in a continuous winter wheat (Triticum aestivum L.) cropping system.

MH (1,2-dihydro-3,6-pyridazinedione) was applied at 4 to 6 lb/A, in spring and fall, with and without (2,4-dichlorophenoxy)acetic acid (2,4-D), on roadsides normally mowed from 2 to 12 times a year. MH at 6 lb/A applied in spring generally reduced grass height. Lower rates and fall applications were generally ineffective. Depending on area, rural or urban, and retardant effectiveness, between zero and five mowings per year were saved. When the MH was effective and the turf was not strong and vigorous, annual weeds such as crabgrass (Digitaria spp. Heist.), foxtail (Setaria spp. Beauv.), and ragweed (Ambrosia spp. L.) often increased and gave the roadside an undesirable appearance. When MH was used without 2,4-D, the roadside generally had a poorer appearance than when not treated. When MH was applied with 2,4-D and no application ‘'skips” or annual weed infestation occurred, the roadside sometimes had a satisfactory appearance. The time when MH can be effectively applied is short (about 2 weeks). Rains, winds, and springtime roadway work make proper timing of applications difficult under Minnesota conditions. Applications of 2,4-D alone or with MH were effective in reducing roadside weeds.

Postemergence directed application of 0.56 kg/ha of 2,3,5-trichloro-4-pyridinol (pyriclor) gave control of witchweed (Striga lutea Lour.) equivalent to 2.24 kg/ha of (2,4-dichlorophenoxy)acetic acid (2,4-D) without injuring corn (Zea mays L.). Pyriclor applied to the soil surface or incorporated did not significantly injure tobacco (Nicotiana tabacum L.) at rates of 2.24 kg/ha and less. Peanut (Arachis hypogaea L.) was not injured by pyriclor incorporated in soil at 0.56 kg/ha; Irish potato (Solanum tuberosum L.) was slightly injured. Treatment with 0.56 kg/ha of pyriclor applied in the same manner killed six crop species and four weed species also included in the experiment. In 2 years of field experiments, application of pyriclor at 0.21 and 0.63 kg/ha to soil before transplanting, or these rates applied over the top of tobacco after transplanting, controlled large crabgrass (Digitaria sanguinalis L. Scop.) until maturity of the tobacco, and did not significantly reduce yield or cause permanent injury to the crop.

The uptake of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) was studied in sudangrass [Sorghum sudanense (Piper) Stapf, var. Piper], grain sorghum [Sorghum bicolor (L.) Moench], and corn (Zea mays L.) to find whether differences in atrazine uptake exist among these species. The uptake of atrazine followed closely the growth patterns of corn, sorghum, and sudangrass during the first 5 weeks of growth. Concentration of 14C from ring-labeled 14C-atrazine in the soil reached a peak in corn, sorghum, and sudangrass plants after 2 weeks of growth and then declined. The 14C concentrations were two to three times greater in sorghum and sudangrass than in corn throughout the 5-week period. Atrazine uptake per gram of plant growth by these crops was directly proportional to the concentration of atrazine in the soil and the proportionality factors were in the order: sudangrass < sorghum ≫ corn. Total uptake and the total growth were in order: corn ≫ sorghum = sudangrass. In a study where relative humidity was a variable, the amount of atrazine absorbed per ml of water was inversely related to total water usage.

Root and shoot extracts of 3-week-old sudangrass [Sorghum sudanense (Piper) Stapf, var. Piper], grain sorghum [Sorghum bicolor (L.) Moench], and corn (Zea mays L.) plants degraded 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) in order: shoot > root and corn ≫ sorghum = sudangrass. In 3-week-old detopped plants, the rate of atrazine exudation was 14 times greater in sudangrass and sorghum than in corn when grown in Keith sandy loam containing 0.5 ppmw 14C-atrazine. Extraction and analysis of plant shoots revealed that 7 to 8% of the 14C was present as atrazine in sudangrass and sorghum whereas no atrazine was found in corn. In 14C tracer studies, thin-layer chromatography showed that sudangrass and sorghum metabolized atrazine by a pathway which differed from the pathway in corn. Sudangrass and sorghum metabolized atrazine primarily to 2-chloro-4-amino-6-(isopropylamino)-s-triazine and 2-chloro-4-amino-6-(ethylamino)-s-triazine which are only partially detoxified compounds. Corn metabolized atrazine to 2-hydroxy-4-(ethylamino)-6-(isopropylamino)-s-triazine (hydroxyatrazine) which is non-phytotoxic.

A mixture of dimethyl sulfoxide (DMSO), glycerol, phytobland oil, and water (50:25:15:10, v/v) proved to be outstandingly effective as a carrier for water-soluble formulations of 4-amino-3,5,6-trichloropicolinic acid (picloram), (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), and mixtures thereof. The carrier was selected after numerous experiments in which these and other adjuvants, used individually, gave at least some degree of herbicidal enhancement on velvet mesquite seedlings [Prosopis juliflora var. velutina (Woot.) Sarg.]. Maximum synergism between the carrier complex and herbicide occurred with the triethylamine salt of 2,4,5-T; relatively little influence on the butoxyethanol ester was observed. Picloram and 3,6-dichloro-o-anisic acid (dicamba) were intermediate in activity between the two phenoxy formulations.

The herbicide 3,6-dichloro-o-anisic acid (dicamba) is very mobile in Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.), a susceptible weedy species. After foliar or root application, the compound was translocated rapidly to meristematic tissues at the shoot apex and in leaf axils. Redistribution of dicamba in the shoot, to young tissues, continued for at least 20 days. Metabolism of dicamba occurred very slowly, both in intact plants and in detached leaves, and the only metabolite detected was conjugated with sugars. The nonphytotoxic metabolite was identified by paper and thin-layer chromatography as 5-hydroxy-3,6-dichloro-o-anisic acid. Decarboxylation of dicamba also occurred in the plants but extremely slowly. The rapid entry and translocation of dicamba, its continued mobility in treated plants, and its very low rate of detoxification are major contributing factors to the effectiveness of dicamba for controlling Tartary buckwheat.

Greenhouse studies indicated that 3,6-dichloro-o-anisic acid (dicamba) or its metabolic derivative was strongly accumulated in meristematic tissues of Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.) and wild mustard (Sinapis arvensis L.) following both foliar and root uptake. In barley (Hordeum vulgare L.) and wheat (Triticum vulgare L.), it was distributed throughout the plants. Detoxification of dicamba occurred in all four species though not at equal rates, and a common major metabolite was identified chromatographically as 5-hydroxy-3,6-dichloro-o-anisic acid. A minor metabolite, 3,6-dichlorosalicylic acid, was found in barley and wheat but not in Tartary buckwheat or wild mustard. The four species tolerated dicamba treatment in the order of wheat, barley, wild mustard, and Tartary buckwheat. This ranking corresponds with the ability of the plants to detoxify dicamba and is inversely related to the extent of dicamba absorption and translocation in them.