Effects of Selected Herbicides on Annual Weed Control and Production of Processing Peas 1

Little information is available regarding the effects of herbicides on annual weeds in processing peas ( Pisum sativum L.) and on the peas themselves. Therefore, field experiments were conducted over a 2‐year period to assess the relationship between annual weed control with herbicides and pea production. Herbicide treatments of α,α,α‐trifluoro‐2,6‐dinitro‐ N , N ‐dipropyl‐ p ‐toluidine (trifluralin), 2‐chloro‐2,6‐diethyl‐ N ‐(methoxymethyl)acetanilide (alachlor), 2‐chloro‐N‐isopropylacetanilide (propachlor) 2‐(4‐chloro‐6‐ethylamino‐ s ‐triazine‐2‐ylamino) ‐2‐methylproprionitrile (cyanazine), [(4‐chloro‐o‐tolyl)‐oxy] acetic acid (MCPA), 4‐[(4‐chloro‐o‐toyly)‐oxy] butyric acid (MCPB), and MCPB plus 2,2‐dichloropropionic acid (dalapon) were applied to ‘Alaska‐’ and ‘Perfection’‐type pea cultivars. Satisfactory control of most grass and broadleaf weeds was obtained with trifluralin, alachlor, propachlor, and cyanazine. MCPA and MCPB gave partial control of broadleaf weeds but did not improve pea yield. The combination of MCPB and dalapon gave moderate weed control and subsequent moderate yield increases in the Perfections. Significant reduction in stands of both Alaska and Perfection peas resulted from trifluralin application; substantial reduction in shelled‐pea yield, however, occurred only in the Alaska. Severe injury to pea plants was caused by cyanazine in 1970, but not in 1971 when abnormally low rainfall was received. No injury to pea plants was observed from applications of either alachlor or propachlor. Under the conditions tested propachlor at 5.6 kg/ha and the combination of dalapon and MCPB at 1.1 and 0.8 kg/ha provided the most satisfactory annual weed control with the least risk of crop injury.