High oil corn acreage in the U.S. has increased from less than 50,000 acres in 1992 to over one million acres in 1999. High oil corn is attractive as a livestock feed because it has greater energy value than normal yellow dent corn and can replace more expensive dietary sources of fats and proteins. The TopCross® grain production system is rapidly gaining popularity as the preferred method of producing high oil corn and involves planting a blend ( a TC-Blend®) of two different types of seed corn mixed together in the same bag. TopCross corn production may be more vulnerable to certain pest problems, including those that result in defoliation and silk clipping, than normal corn. Widely publicized yield losses in TopCross corn fields near West Liberty, Ohio in 1997, associated with insect injury and unfavorable growing conditions, have slowed adoption of this new seed technology. The objectives of this research include the following: 1) to evaluate defoliation effects on the nutrient composition of TopCross and normal corn grain and 2) to compare the effects of varying levels of defoliation at different stages of corn development on the agronomic performance of pollinator and male sterile grain parent plants, as well as their normal (and fertile) grain parent checks. Results of this project will serve as a basis for predicting grain quality and yield losses associated with leaf destruction of TopCross corn by insect feeding, and/or foliar diseases.
Three field experiments were performed to determine the impact of defoliation injury on TopCross high oil corn production. In Experiment 1 effects of early season plant injury on TopCross grain production were determined. In Experiment 2 effects of defoliation during grain fill were evaluated. In Experiment 3 effects of foliar fungicides were determined. The three experiments were established at the OSU Farm Science Review near London, the OSU Waterman Research Farm in Columbus, and the OSU-ATI farm in Wooster.
Experiment 1: A high oil TC Blend (Pfister SuperKernoil 2652-19) and its normal grain parent check (Pfister 2652) were evaluated. Early season plant injury was created using different levels of defoliation. Defoliation treatments were as follow: no defoliation, 100% leaf removal at V4 (or the 4-collar leaf stage), and 50 and 100% leaf blade removal at the V13 stage of development. The distal half of all leaves at the collar was removed to accomplish the 50% defoliation treatment. The 100% defoliation treatment entailed cutting at the collar all fully developed leaves on the plant.
Experiment 2: This experiment used the same high oil TC Blend and normal grain parent evaluated in Experiment 1. Defoliation treatments were as follows: no defoliation, and 50 and 100% leaf blade removal at the tassel emergence (VT), milk (R3), and full dent (R5) stage of development. The leaf removal protocol was the same as that described for Experiment 1.
Experiment 3 : Sixteen foliar fungicide treatments, including varying rates and application dates of Tilt and Quadris fungicides, were evaluated using the high oil TC Blend Dekalb DK 595TC.
In Experiments 1 and 2, treatments were replicated three times in a randomized complete block field design with treatments in a split plot layout. The TC Blend and grain parent check were assigned to main plots and the defoliation treatments to subplots, four rows 30 inches apart and 17.5 feet in length. Plots were planted at seeding rates of 30,800 seeds/A.
Final plant stand, numbers of plants stalk lodged (stalk breakage below the ear), and barren or with nubbin ears were recorded at maturity prior to harvest. At harvest, the center two rows of each plot were hand harvested to determine grain yield, ear moisture, and kernel weight. Ears of the TC Blend pollinator plants (SK2652 pollinator 19) and TC Blend male sterile grain parent plants were separated to distinguish effects of defoliation on these different plant types in Experiments 1 and 2. Sampled ears from the three experiments were shelled and a sub sample of grain from each plot was analyzed for grain quality composition.
To minimize possible pollen contamination from the neighboring male fertile grain parent check as well as any nearby normal corn, the TC Blend plots in experiments 1 and 2 were planted in isolation at least 100 feet from normal corn hybrids. This 100-foot buffer was planted with male sterile seed to minimize foreign pollen contamination. Plots were also planted with this TC Blend seed as border (20-50 feet) on all sides of the isolation field.
In Experiment 1, defoliation did not change the timing of pollen shed by the pollinator relative to silk emergence by the male sterile grain parents. Complete defoliation at V4 delayed pollen shed and silk emergence by 7 to 10 days. Defoliation at V13 had little effect of the timing of silk emegence and pollen shed compared to nondefoliated check. Defoliation resulted in more nubbin ears and greater stalk lodging in the TC Blend pollinator than in the TC Blend grain parent. Grain yields of the non defoliated grain parent check were not significantly different from the TC Blend. The TC Blend and Its normal counterpart exhibited similar yield response to complete defoliation at V4 and 100% and 50% defoliation at V13. Grain oil content and metabolizable energy were significantly higher in grain from the TC Blend than the grain parent check but grain nutrient composition was not affected by defoliation.
In Experiment 2, agronomic performance of the grain parent check and TC Blend were similarly affected by defoliation treatments. Yields of the nondefoliated grain parent check and TC Blend did not differ significantly. Defoliation ( 50 and 100 %) reduced yields in all treatments but 100% defoliation treatment at VT resulted in the greatest yield reduction whereas 50% defoliation at R5 resulted in no significant least yield loss. Effects of 50% defoliation on yield at VT and R3 were comparable. Yield losses from defoliation were greatest at anthesis and during early kernel development. Defoliated pollinators were characterized by a much higher percentage of barrenness and nubbin ears than the male sterile grain parents. For those pollinator plants that did produce normal ears, grain/plant, and ear weight appeared less affected by defoliation than the grain parent plants. Grain yield of pollinator plants was reduced by 50% and 100% defoliation at VT and 100% defoliation at R3, whereas all the defoliation treatments reduced yields of TC Blend grain parent plants. However kernel size of pollinators was reduced by all defoliation treatments except the 50% defoliation at VT, a response similar to the grain parent.
The oil content of grain from the male sterileTC Blend grain parent averaged 3.1 percentage points more than that of the fertile grain parent. Grain oil content was generally reduced by defoliation treatments, whereas protein content was increased. The reduction in oil content was more severe with greater defoliation at the earlier kernel development stage The oil content of the grain parent check was reduced by three of the defoliation treatments (50% and 100% defoliation at R3 and 100% defoliation at R5) with oil levels lowered by 10 -25%. The grain oil content of the TC Blend grain parent was reduced by all defoliation treatments except the 50% defoliation at VT. Decreases in oil content ranged from 5 % for 50% defoliation at R5 to 30% for complete defoliation at R3. Complete defoliation of the TC Blend grain parent at R3 and R5 reduced oil levels by 30% and 20% respectively; whereas 50% defoliation reduced grain oil levels at VT, R3, and R5 by 6%, 10%, and 5%, respectively.
In Experiment 3, there were small but significant increases in grain yield associated with certain fungicide treatments that were related to reduced disease injury. However. effects of the foliar fungicides on grain oil, protein, starch, and lysine were not significant.
Since premiums for contract production of high oil corn are based on grain oil content, the lower grain oil levels associated with late season defoliation would result in reduced premiums. Moreover, with grain yield reduced by defoliation, oil yield/A would be reduced. Additional study is needed to assess the efficacy of fungicides on kernel composition when disease pressure is more severe.
TC-Blend®, TopCross®, and Optimum® are registered trademarks of Optimum Quality Grains L.L.C.
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