Factors influencing the effectiveness of sodium chlorate as a herbicide

does not appear. First page follows. Introduction 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.