WEED CONTROL IN SWEET CORN

Charles E. Stanger and Joey Ishida
Malheur Experiment Station
Oregon State University
Ontario, Oregon, 1995

Purpose

Several herbicides were applied at various rates alone and in tank-mix combinations as preplant incorporated and postemergence applications to evaluate Jubilee of sweet corn herbicide tolerance and control of common problem weed species in corn production.

Procedures

Herbicides evaluated in the trial included Dual II, Frontier, Axiom, and Axiom tank-mixed with Atrazine or Bladex applied as preplant incorporated applications. Herbicides applied postemergence to both corn and weeds included Peak, Tough, and Basagran. Tough was evaluated as wettable powder and emulsifiable formulations. Postemergence tank-mix combinations included Peak/Atrazine and Tough/Basagran. Crop oil concentrate (MorAct) was added to Peak, Tough/Basagran, and Basagran herbicides.

The trial site for this study had been planted to Stephens winter wheat in October 1993. Following wheat harvest in August of 1994, the straw was shredded with a flail chopper and the field double disked and furrow irrigated. In October, before mold-board plowing, 100 lb/ac of phosphate and 60 lb/ac of nitrogen were applied broadcast. After plowing, the soil was tilled, bedded, and left to overwinter. Soil texture was silt loam with 1.3 percent organic and a pH of 7.2.

On May 9, 1995, the beds were harrowed using a spike-tooth bed harrow. The preplant herbicides were applied and incorporated in the top 2 inches of soil using the spike- toothed bed harrow. Jubilee variety of sweet corn was planted with a John Deere flexi planter. The trial area was furrow irrigated after planting to furnish moisture for seed germination and seedling emergence. Air temperature was 68°F; soil temperature at 4-inch depth was 58°F; wind was calm, and skies overcast when herbicides were applied.

The postemergence herbicide treatments were applied on May 29. Corn plants were 4 inches tall and had 4 to 6 leaves. Emerged weed species included lambsquarters, redroot pigweed, hairy nightshade, kochia, and barnyardgrass. Broadleaf weeds ranged from plants with cotyledon leaves to plants one-inch tall and one-inch rosettes. Barnyardgrass plants had 1 to 3 leaves. When postemergence herbicides were applied, the wind was calm, air temperature 72^oF, soil temperature 62^oF at 4-inch depth; skies were clear, and the soil moist on the surface.

The herbicides in both the preplant incorporated and the postemergence treatments were applied with a single bicycle wheel experimental plot sprayer. Individual plots were 4-rows wide and 25 feet long. Distance between rows was 22-inches. Each treatment was replicated 3 times using a randomized strip-type experimental plot design. The spray boom covered 4 rows with a spray nozzle centered over each plot row. Teejet fan nozzles size 6502 were used. Spray pressure was 42 psi, and water was applied at a volume of 20 gallons per acre.

Results

Jubilee sweet corn was tolerant to all the preplant incorporated herbicides and to the postemergence applied Basagran and wettable powder formulation of Tough. Jubilee corn was not as tolerant to the 0.94 lb ai/ac emulsifiable concentrate formulation of Tough which caused some temporary yellowing of the corn leaves. Corn was less tolerant to Peak which caused severe leaf chlorosis and some stunting of growth to the corn plants. The symptoms occurred within 3 days after herbicide application and persisted for 10 to 14 days before the corn resumed normal growth. The herbicidal activity of Peak increased when the rate of crop oil concentrate increased from 1 to 2 pints. The best treatments for broadleaf weed control included Frontier, Axiom, and the tank-mixes of Axiom with Atrazine or Bladex. Axiom alone did not completely control hairy nightshade. Tough, Tough plus Basagran , and Basagran plus a crop oil concentrate controlled most broadleaf weeds. The preplant incorporated herbicides controlled barnyardgrass, but barnyardgrass was not controlled by the herbicides applied postemergence.

Table 1