Weed Control in Double Cropped Corn, Grain Sorghum, or Soybeans Minimum-Till Planted Following Canning Peas

Double cropping involving minimum-till planting has become popular in many parts of the USA. In Wisconsin, double-cropping usually includes canning peas (Pisum sativum L.) as the spring crop. Trifluralin (u,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) is used for weed control in much of this pea acreage. Since effects of trifluralin residues alone or in combination with subsequent herbicide treatments on summer crops and weeds were unknown, experiments were conducted at the Univ. of Wisconsin Arlington Farm in 1977 and 1978 on a Plano silt loam (Typic Argiudoll, fine, silty, mixed mesic) with 3.5 to 4.0% organic matter. Corn (Zea mays L.), grain sorghum (Sorghum bicolor L. Moench), and soybeans [Glycine max (L.) Merr.] were minimum-till planted following canning peas grown with or without preplant-incorporated trifluralin. Effects of two herbicide combinations and an untreated control were compared in each of the summer crops. Trifluralin controlled both broadleaf and grass weeds in canning peas but did not increase shelled pea yield. Average weed growth in corn, grain sorghum, and soybeans following peas treated with trifluralin was reduced 52, 52, and 62%, and average grain yields of corn and soybeans were increased 10 and 28%, respectively, compared with the same crops following untreated. peas. Trifluralin residues reduced grain sorghum stands (44%) and yields (17%). Alachlor [2-chloro-2′, 6′-diethyl-N-(methoxymethyl) acetanilide] + atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-tri~inel + paraquat (l,l-dimethyl-4,4′-bipyridinium ion) was more effective in reducing weed growth in minimum-till corn than alachlor + cyanazine [2-chloro-4-(l-cyano-l-methylethylamino)-6-ethylamino-s-tnazine] + paraquat. There was no significant difference between the two combinations in terms of corn grain yield, however. Alachlor + cyanazine + paraquat following trifluralin in peas resulted in better weed control in minimum-till corn than a similar treatment applied to corn planted following peas grown without trifluralin. Atrazine + paraquat and 2,4-D [(2,4-dichlorophenoxy)acetic acid] + paraquat also provided excellent weed control in grain sorghum, and alachlor + linuron [3-(3-4-dichlorophenyl)-l-methoy-l-methylurea] + paraquat, and linuron + paraquat provided excellent weed control and increased grain yields in soybeans when both crops were minimum-till planted after peas treated with trifluralin. Overall, soybeans appeared to be the most successful of the three crops when minimum-till double-cropped following peas under southern Wisconsin conditions.