Brittleness and Other Responses of Corn to 2,4-Dichlorophenoxyacetic Acid

Abstract

Corn strains W22, WF9, W22xM14, and WF9xOs420 were sprayed at weekly intervals with 0.5 or 1 lb. (plus 0.25% Tide) per acre acid equivalent of triethylamine salt of 2,4-D at Ames, Iowa, on 8 dates beginning June 15, 1950, when plants were in the 3-leaf stage and ending at the early tassel stage. Stalk brittleness was progressively less pronounced in W22 and W22xM14 at 5, 11, 2, and 18 days after treatment during the 6- to 10-leaf stages. Fertilizer slightly increased brittleness in W22xM14. Histological studies suggest that a stimulation of meristematic activity in the brace root regions may interfere with normal development of the structurally important hypodermis and rind, and may be the major cause of stalk brittleness from 2,4-D. At harvest, stalk weakness was most severe after treatments which had caused greatest brittleness during the growing period, while shank weakness was pronounced only in W22xM14 plants treated at tassel emergence. Viability of seed produced by self-pollinated plants was reduced in W22 and W22xM14 only after treatment at tassel emergence. Vigor of subsequent seedlings was reduced in WF9 following most treatments, in WF9xOs420 following some midseason treatments, and slightly in W22 and W22xM14 after late-season applns. Yields of W22 and W22xM14 were greatly reduced by the 1-lb. treatment at tassel emergence and to a lesser extent in W22 at the 16-leaf stage. Yields of WF9 and WF9xOs420 were only slightly reduced by treatment at any time. Results of this investigation suggest that applns. of 2,4-D for weed control in corn should be made before the 6-leaf stage or between the 11- and 16-leaf stages to cause a min. amt. of injury to the corn crop.