University of California

Factors influencing the effectiveness of sodium chlorate as a herbicide


A. S. Crafts

Author Affiliations

A. S. Crafts was Assistant Botanist in the Experiment Station.

Publication Information

Hilgardia 9(9):437-457. DOI:10.3733/hilg.v09n09p437. July 1935.

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With the recognition that the principal action of sodium chlorate on deep-rooted perennial weeds takes place through the soil(1), (9), (10), (11) comes a clearer understanding of the importance of those factors that influence the absorption of this material from the soil. The newer concepts of chlorate action(9), (10), (11) promise a distinct advance in the technical use of this chemical, especially in those regions where summer rains do not occur.

In regions of frequent summer rains, freezing winters, and relatively shallow soils, the chlorates have been notably effective as herbicides. In the western states, however, chlorates have given erratic results and in many instances have been practically worthless when applied in early summer as recommended in the more humid states.

Most of the deep-rooted perennials of the West blossom in April, May, or June, and chlorate sprays applied during these months lie in contact with organic matter, exposed to the decomposing action of the ultraviolet rays of the sun, from four to eight months before being leached into the soil. Though killing of the tops may be rapid and complete when the applications are made according to recommended methods, root killing is usually slight or absent; and by autumn, decomposition of the chlorate has greatly reduced its concentration. Winter rains are so variable in amount and distribution that the depth of leaching is uncertain. Root systems of the weeds may extend to depths of 10 to 20 feet or more and are seldom injured by freezing temperatures except in the extreme Northwest or at high elevations.

Literature Cited

[1] Åslander Alfred. Experiments on the eradication of Canada thistle, Cirsium arvense with chlorates and other herbicides. Jour. Agr. Research. 1928. 36:915-934. Illus

[2] Crafts A. S. The use of arsenical compounds in the control of deep-rooted perennial weeds. Hilgardia. 1933. 7(9):361-372.

[3] Crafts A. S. The toxicity of sodium arsenite and sodium chlorate in four California soils. Hilgardia. 1935. 9(9):459-498. DOI: 10.3733/hilg.v09n09p437 [CrossRef]

[4] Crafts A. S., Kennedy P. B. The physiology of Convolvulus arvensis(morning-glory or bindweed) in relation to its control by chemical sprays. Plant Physiol. 1930. 3:329-344.

[5] Fron M., Bertrand R. Contribution à l’études de l’influence des chlorates sur la vegetation. Ann. Agron. [Paris]. 1934. 4:1-25.

[6] Hulbert H. W., Bristol R. S., Benjamin L. V. Methods affecting the efficiency of chlorate weed killers. Idaho Agr. Exp. Sta. Bul. 1931. 189:1-12.

[7] Kennedy P. B., Crafts A. S. The application of physiological methods to weed control. Plant Physiol. 1927. 2:503-506.

[8] Latshaw W. L., Zahnley J. W. Experiments with sodium chlorate and other chemicals as herbicides for field bindweed. Jour. Agr. Research. 1927. 35:757-767.

[9] Loomis W. E., Bissey Russell, Smith E. V. Chlorates as herbicides. Science. 1931. 74(1924):485

[10] Loomis W. E., Smith E. V., Bissey Russell, Arnold L. E. The absorption and movement of sodium chlorate when used as an herbicide. Jour. Amer. Soc. Agron. 1933. 25:724-739.

[11] Muenscher W. C. Killing perennial weeds with chlorates during winter. New York (Cornell) Agr. Exp. Sta. Bul. 1932. 542:1-8.

[12] Yamasaki M. On the variation of rice varieties in the resistance to the toxic action of potassium chlorate, and its practical significance. Jour. Imp. Agr. Exp. Sta. Tokyo. 1929. 1(1):1-24. (Summary in English.) Illus

[13] Yamasaki M. The variation and correlation among varieties of wheat and barley in regard to the resistance to the toxic action of potassium chlorate. Jour. Imp. Agr. Exp. Sta. Tokyo. 1929. 1(2):139-162. (Summary in English.) Illus

Crafts A. 1935. Factors influencing the effectiveness of sodium chlorate as a herbicide. Hilgardia 9(9):437-457. DOI:10.3733/hilg.v09n09p437

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