Giant Foxtail and Velvetleaf Control in Sweet Corn

Velvetleaf (Abutilon theophrasti Medic.) and giant foxtail (Setaria faberi Herrm.) are among the most serious weed problems in sweet corn (Zea mays L.) grown in the north central U.S. While several herbicide treatments have been used to partially control these weeds, the treatments frequently leave soil residues which can injure susceptible crops commonly grown in rotation with sweet corn. Consequently, studies were conducted over a 3-year period on fields (Plano silt loam, 3.5 to 4% organic matter, Typic Argindoll fine silty mixed mesic) heavily infested with velvetleaf and giant foxtail to compare the effectiveness of 10 herbicides applied alone and in 36 combinations in controlling these weeds. Visual observations of sweet corn injury and weed control were obtained and the sweet corn was harvested to determine the effects on yields. Oats (cv. ‘Lodi’) and peas (cv. ‘NK-692’), which commonly follow sweet corn in a crop rotation and which are susceptible to residues of common herbicides, were grown over the plot areas the year following sweet corn and evaluated for carryover injury. Of the herbicide treatments included in the study, the best overall weed control and the largest average sweet corn yields were produced by a sequential application of 2.2 kg/ha alachlor [2-chloro-2',6'-diethyl-N-(methoxymethyl) acetanilide] applied premergence and 1.1 kg/ha bentazon [3-isopropyl-1H-2,1,3-benzo-thiadiazin-(4)3H-one 2,2-dioxide] applied postemergence and by a preemergence combination of 2.2 kg/ha alachlor and 0.6 kg/ha metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5 (4H) one]. Preplant incorporated combinations of butylate (S-ethyl diisobutylthiocarbamate) with atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] or cyanazine [2-([4-chloro-6-(ethylamino)-s-triazin-2-yl] amino)-2-methyl-propionitrile] and preemergence combinations of alachlor with atrazine or cyanazine provided good weed control and satisfactory yields in 2 of the 3 test years. Three-way combinations of atrazine, cyanazine, and butylate, as well as preemergence combinations of alachlor with bifenox (methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate) dicamba (3,6-dichloro-o-anisic acid) and a preemergence and postemergence split treatment of cyanazine also showed promise. Preemergence treatments failed to control velvetleaf adquately in 1973 when insufficient rainfall was received, but preplant-incorporated treatments failed similarly in 1974 following excessive rainfall. Postemergence treatments were typically best for controlling velvetleaf hut did not satisfactorily control giant foxtail. The only injury to oats (Avena sativa L.) or peas (Pisum sativum L.) from soil residues persisting until the spring following sweet corn, occurred from atrazine applied at 3.4 kg/ha preplant-incorporated in combination with butylate.