Herbicidal Properties of 2,4-Dichlorophenoxyacetic Acid Applied in Dusts Containing Hygroscopic Agents

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Abstract
2,4-Dichlorophenoxyacetic acid was applied in concs, of 0.5, 1, 2.5, 5, and 10% in dust carriers, at the rate of 4 lb. per 1000 sq. ft., to Kentucky bluegrass (Poa prat-ensis) and white clover (Trifolium repens) growing in a mixed stand in greenhouse flats. The 10% dusts were also tested on heal-all (Prunella vulgaris) and lawn pennywort (Hydrocotyle rotundifolia) in flats and on narrow-leaved plantain (Plantago lanceolata) growing in 3-in. clay plots in a greenhouse. Comparison of Pyrax, fuller''s earth, and Cherokee clay as diluents at each of the above conc, of 2,4-dichlorophenoxyacetic acid indicated that there was no marked difference between them. Complete eradication of clover from bluegrass turf was obtained by use of dusts containing either 10% or 5% of the acid but the bluegrass was severely injured by the 10% dusts and recovered slowly. A minimum conc, of 2.5% of acid was found necessary to kill an appreciable amt. (85%) of clover without injury to bluegrass. Heal-all, lawn pennywort, and plantain were likewise killed by application of dusts containing 10% of the acid. Addition of hygroscopic agents, such as Carbowax 1500 or glycerine, at the rate of 3% markedly increased the effects of the growth-regulating substance in dust mixtures in tests on morning-glory (Ipomea lacunosa), ragweed (Ambrosia bidentata), and lamb''s quarters (Chenopodium album). Caution should be exercised in applying 2,4-dichlorophenoxyacetic acid by the dust method, first to avoid accidental treatment of adjacent plants by drifting of the dust particles, and second to avoid breathing the dust mixtures during application until definite information is available on the non-toxicity of the acid to animals.

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