Control of Weeds in Legume Seedings with 4-(2,4-DB), Dalapon, and TCA

Abstract

rHE small size and slow growth of legume seedlings make them I susceptible to damage or elimination by weed competition. Various methods of establishment such as sowing in late summer, sowing with a small grain companion crop, or mowing have not been entirely successful. The increased use of weed-controlling chemicals has awakened considerable interest in the establishment of legumes with the aid of herbicides. Research workers are in agreement that 4(2,4-DB) [4-(2,4-dichlorophenoxy)butyric acid] can be safely used to control broad-leaved weeds in legumes (2, 5, 6, 7, 9, 13, 14). However, there is some difference of opinion as to the rates of various formulations that can be safely used (2, 9, 13). Weed grasses are not controlled by 4-(2-DB) and often the removal of the broad-leaved canopy encourages the growth of weed grasses. Kerr3 showed that weed grasses are more injurious to birdsfoot trefoil than broad-leaved weeds. A number of workers have found that weed grasses can be controlled without injury to alfalfa and birdsfoot trefoil by rates of TCA (trichloroacetic acid) ranging from 4 to 9 lb/A and by rates of dalapon (2,2-dichloropropionic acid) ranging from 2 to 6 lb/A (1, 3, 4, 8, 10, 11, 12, 17). However, some workers (15, 16) report moderate to severe injury from both TCA and dalapon. To obtain control of both broad-leaved weeds and weed grasses, combinations of herbicides appear to be necessary. Several workers report good results from using mixtures of 4-(2,4-DB) and dalapon to control both types of weeds (9, 15). The first part of the work reported in this paper was designed to compare an amine with an ester of 4-(2,4-DB) at several rates to determine which rates of each herbicide give practical weed control with minimum injury to seedling alfalfa, red clover, and birdsfoot trefoil. Dalapon was also included as a mixture with 1 lb/A of an ester and of an amine. The second part of the work reported in this paper was designed to compare the effect of an ester formulation of 4-(2,4-DB) at 1 and 2 lb/A in combinations with dalapon at 2 and 3 lb/A and TCA at 8 lb/A.