Several management practices may be effective in reducing the severity of local European corn borer infestations. However, to have significant impact, some of these management practices must be conducted over a community or county-wide area.
The effect of planting date on European corn borer infestations will vary, depending on the number of larval generations in the corn production region and the corn hybrid planted.
Early planting of borer-resistant corn hybrids will normally result in minimum infestation, larval tunnels, and broken stalks; but presently, the yield potential will be lower than yield from susceptible hybrids. If most growers in a given location follow a comparable planting date, it will provide conditions for uniform dispersal of ovipositing female moths and thereby reduce the number of egg masses deposited in certain fields. However, abundant action sites in and around a specific field will allow larger aggregations of moths and will result in larger numbers of egg masses being deposited in that field. Fields planted extremely early by an individual grower also will provide conditions for concentration of ovipositing female moths, which can result in a heavy European corn borer infestation.
Early planting of resistant hybrids also is considered a practical management approach. Extremely early planting (or earlier than other producers) of resistant hybrids may result in heavier than average infestation of first-generation larvae for that specific field, if moths are present during the tasseling and silking period. Late planting also will be attractive to concentrations of ovipositing females and will result in above-normal infestations and damage to late whorl-stage corn by second-generation larvae. Except for a few tolerant corn hybrids, heavy second-generation infestations in corn planted early or late will result in broken stalks, dropped ears, and reduced yields. Keep in mind that most resistant corn hybrids lose their resistance when the corn reaches tasseling and silking stages. Most hybrids are susceptible when second-generation larvae attack. Early-planted corn that has kernels initiated (Table 2) when the second-generation European corn borer is present has a better chance of avoiding serious loss.
In the three- and four-generation regions, all planting dates are subjected to a minimum of two generations of larvae. Earlier plantings receive infestations from first and second generations. Later plantings receive infestations from second and third generations. But, similar to the two-generation regions, earlier planting is a viable and practical management option.
Early harvesting is a management option that will effectively reduce yield losses resulting from broken and lodged plants and dropped ears. Most corn produced in the Corn Belt is subjected to infestations by two generations of larvae. After boring into the plant, the second-generation larvae feed primarily in the lower portion of the plant (Table 10). This feeding is responsible for stalk breakage and dropped ears. Early harvest, combined with early planting, will reduce yield losses. In the southern portion of the Corn Belt (Kansas, Kentucky, and Missouri), and in other southern regions where more than two generations occur, early harvesting of heavily infested fields is recommended. If the corn can be mechanically dried on the farm, it probably will be profitable to dry it. If no on-farm drying facilities are available, it usually will be better to harvest early, sell the corn, and take a moisture dockage.
Research in Delaware has indicated that the highest survivorship of overwintering larvae occurs when stalks are disked; it is lowest when stalks are left aboveground on the field over the winter and plowed down in the spring before larvae pupate. Disking seems to provide some degree of protection for larvae because fewer larvae survive when stalks are left aboveground over the winter, presumably because of exposure to diseases, predation by birds, and other natural enemies. The most effective reduction of overwintering larvae occurs when stalk residue is exposed over the winter and plowed down in the spring before pupation. However, this method must be practiced on an area-wide basis in order to have a significant reduction in the overall European corn borer population.
Table 10. Location of second-generation, fifth instar European corn borer on susceptible field corn in the Corn Belt (Iowa, W. B. Showers; Nebraska, J. F. Witkowski).
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Iowaa Nebraskab
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Percent Percent
Plant area Borers/plant of total Borers/plant of total
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Above the ear 0.94 29 2.0 31
On the ear 0.29 9 1.12 18
and shank
Below the ear 2.02 62 3.21 51
Total per plant 3.25 100 6.33 100
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aIowa-Each mean composed of 360 observations (10 plants 3 36
replications),
August 1968.
bNebraska-Each mean composed of 80 observations (10 plants 3 8
replications),
August 1978.