Abstract:

Field experiments were established at three on-farm sites in Coshocton and Knox counties that have a history of heavy gray leaf spot pressure. A susceptible corn hybrid, Pioneer brand 3394, was used in the Coshocton experiments and a moderately resistant hybrid, DeKalb 618, was used in the Knox county experiment. The two Coshocton county experiments were planted at Riverview High School in fields that have been continuously cropped to corn. One of the Coshocton sites was established using no-tillage; the other Coshocton site was established using conventional tillage. The Knox county site was established using no-tlllage and followed soybeans.

Five treatments were evaluated in the no-tillage field experiment in Coshocton county - four plant densities: 18000, 24000, 28000, 34000 plants/A in 38-inch row spacings and one narrow row spacing planted at 34000/ A (Table 1). A randomized complete plot design with four replications was used.

Four plant densities: 18000, 24000, 28000, and 34000 plants/A in 30-inch row spacings were compared in the conventional tillage experiment in Coshocton Co. (Table 2). Treatments were replicated six times in a randomized complete block design.

Two row spacings were evaluated in the Knox Co. experiment - (1) a conventional (30-inch) row spacing and (2) narrow (15-inch ) row spacing (Table 3). A plant density of 30,000 plants/A was used in both row spacings. Treatments were replicated four times in a randomized complete block design.

Plots were monitored for disease development at silking and thereafter at two week intervals. Foliar disease severity was determined by visually estimating the percentage area of the ear leaf with gray leaf spot lesions. Two to three ratings of disease severity were performed with the first rating in late August during mid-grainfill, and the last in mid-late September at or near physiological maturity. The incidence of stalk rot was determined using the "squeeze" or "pinch" test, i.e. squeezing the stalk above the brace roots and recording the number of stalks that crushed easily. At least 10 plants in each plot were checked for stalk rot. A rind penetrometer was used to determine stalk quality when corn achieved physiological maturity. Data was also collected for grain yield and moisture, stalk lodging, test weight, and final plant stand.. Data was interpreted using standard analysis of variance procedures where appropriate.

The incidence of gray leaf spot and stalk rot was not influenced by row spacing (Tables 1 and 3). Disease development was delayed until the late grain filling stages and probably had only negligible effect on grain yields. There were no differences in grain yields between the 15-inch and 30-inch row spacings at either the Coshocton or Knox Co. site. In the no-tillage Coshocton site (Table 1) there were no significant differences in GLS or stalk rot between the varying plant populations. However, at the conventional tillage Coshocton site (Table 2), GLS was greater at lower plant densities but there were no differences in stalk rot. In the no-tillage Coshocton experiment (Table 1) yields of the three highest plant densities out yielded the lowest plant density. Similarly in the conventional tillage study (Table 2), grain yields increased at the higher plant populations.

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