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How does European corn borer damage corn? What is the impact of European corn borer on silage yields? Does European corn borer feeding affect silage quality? What is an economic treatment threshold and how are they used? Determining the economic threshold for ECB damage in corn silage.
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Assessing
the Impact of European Corn Borer on Corn Grown for Silage by
Scott W. Myers, Michael
Ballweg, and John L. Wedberg The European corn borer (Ostrinia nubilalis) is potentially a serious pest of corn grown for silage. In Wisconsin, the European corn borer (ECB) generally produces two generations per year. Overwintering larvae typically emerge as adults and begin depositing egg masses in early June, while the second generation is usually seen in late July or early August, depending on weather conditions. How does European corn borer damage corn? Damage to corn occurs as
larvae feed on the leaves and bore into corn stalks and ear shanks.
European corn borer tunneling (Figure 1) results in reduced yield potential,
broken stalks, and dropped ears. Economic ECB treatment thresholds for
use with corn varieties grown for grain have been developed. However,
little information is available to dairy farmers and silage producers on the
effects of European corn borer on corn grown for silage. Recently, three years of
research evaluating the impact ECB on silage corn yield and quality were
conducted in Wisconsin. In these studies, various levels of ECB infestation
were tested using laboratory-reared corn borers. Plots were evaluated to
determine what level of infestation would reduce corn silage yields to the
point where control measures would be economically warranted. What is the impact of European corn borer on silage yields? We evaluated three
popular dual-purpose grain/silage hybrids. While hybrids varied in
yields and quality, the impact of corn borer feeding remained the same for
each hybrid used in these field research plots. Significant yield
losses were seen in plants infested with corn borers. For plots infested
with 1st generation corn borers, yield losses were as high as 25% when 84%
of the plants were damaged. Similarly, up to 18% yield losses were
measured in plots where 84% of the plants were infested with 2nd
generation corn borers. Does European corn borer feeding affect silage quality? What is an economic treatment threshold and how are they used? An economic treatment
threshold is a pest density at which control measures need to be initiated
in order to avoid economic losses because of damage caused by insect feeding. In the case of ECB damage
to corn grown for silage, the economic treatment threshold is the percentage
of plants infested with corn borer egg masses sufficient to cause silage
yield losses that would exceed the cost of an insecticide application. Using
data from research studies, economic thresholds have been calculated for 1st
and 2nd generation ECB on corn grown for silage and are presented in Table
1. Determining the economic threshold for ECB damage in corn silage. Select Table 1 for 1st
generation ECB scouting or Table 2 for 2nd generation infestations. Next,
select the treatment cost - the cost of an insecticide application needed to
control ECB - from the upper row of the table. Then choose an estimate of
corn silage value from the left-hand column (silage values are based on a
“wet weight” of 65% moisture). Follow the selected row and column to
where they intersect to determine the economic treatment threshold level for
your field. When the number of corn borer infested plants is equal to or
greater than the value in the table, an insecticide application is
warranted. Infested plants are those
corn plants that have ECB egg masses deposited on their leaves or with
leaves showing feeding scars such as “window paning” caused by early
instar corn borer larvae. Insecticide applications to control European corn borer are most effective when they are applied after eggs begin to hatch and before the larvae begin to tunnel in to leaf midrib, sheath, and stalk tissues. Insecticides that provide residual control for a few days after application are preferred, as they will kill late hatching larvae. The values provided in the table are based on 80% efficacy of an insecticide application, and does not account for any additional costs of scouting fields to detect corn borer population densities. Our research shows that economically damaging levels of ECBs can be found in corn grown for silage. Corn silage growers need to consider the potential for economic damage when producing this crop. An effective ECB control program starts with early season scouting to detect initial populations of ECB egg masses or early signs of feeding. Then, if warranted, insecticides need to be applied in a timely manner to provide maximum control of corn borer larvae. Table
1.
Economic treatment thresholds for 1st generation ECB
infestations
Note:
When the percentage of infested plants is equal to or greater than the
number indicated in the table,
an insecticide treatment is warranted. Table
2. Economic treatment
thresholds for 2nd generation ECB infestations
Note: When the percentage of infested plants is equal to or greater than the number indicated in the table, an insecticide treatment is warranted. |
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