Establishment of Crownvetch with Herbicides 1

A number of herbicides were evaluated preplant, preemergence, and postemergence as aids to the establishment of crownvetch ( Coronilla varia L.) in the field. In five experiments, during the four years of the study, the degree of weed control and the density of the crownvetch stands were evaluated during the seedling year. Yields of crownvetch and weeds were determined the year following establishment. Preplant applications of S‐ethyl dipropylthiocarbamate (EPTC), α,α,α‐trifluoro‐2,6‐dinitro‐ N,N ‐dipropyl‐ p ‐toluidine (trifluralin), N ‐butyl‐ N ‐ethyl‐α,α,α‐trifluoro‐2,6‐dinitro‐p‐toluidine (benefin), and a mixture of l,l‐dimethyl‐4,6‐diisopropyl‐5‐indanyl ethyl ketone and l,l‐dimethyl‐4,4‐diisopropyl‐7‐indanyl ketone (64‐296‐B) nearly eliminated all weed grasses and were somewhat better than preemergence and post emergence applications of 2,2‐dichloropropionic acid (dalapon) for controlling weed grasses. Mowing, in addition to the use of these herbicides, was necessary to control broadleaf weeds and to insure good stands of crownvetch. Stands of seedling crownvetch and yield the year following establishment were increased when herbicides and mowing were used during establishment. Postemergence treatments with an amine and ester of 4‐(2,4‐dichlorophenoxy)butyric acid (2,4‐DB), 3,5‐dibromo‐4‐hydroxybenzonitrile (bromoxynil), and 3,4‐dichloro‐4‐hydroxybenzonitrile (chloroxynil) controlled broadleaf weeds but the herbicides injured seedling crownvetch and reduced its vigor. Bromoxynil and chloroxynil were more injurious to crownvetch than 2,4‐DB. Injury from 2,4‐DB, bromoxynil, and chloroxynil was such that use of the herbicides could be justified only where stands would be lost without practices to control broadleaf weeds.