Insect Pest Management in High-Oil Corn
G.C. Brown, Department of Entomology
Introduction
We measured the economic impact of
insect pests on two quality-enhanced corns, high-oil and “waxy” corn. Both of these crops are cultivated using
conventional corn production procedures but they bring a premium over
traditional #2 yellow dent corn and that premium is based on the oil or wax
content. The objective of this research
was to determine whether the insect pests affected the qualitative characteristics
of the crop and, consequently, whether different management procedures should
be used for insect pests of these crops.
Two insects were particularly
studied, corn leaf aphids and European corn borer. The corn leaf aphid affects pollination,
which was a particular concern for high-oil corn, while the corn borer disrupts
many aspects of the crop’s grain-producing capacity and is the most serious
corn pest in Kentucky.
The research was conducted in a
series of controlled field and greenhouse experiments during the 2000, 2001,
and 2002 growing seasons in Central Kentucky and Princeton,
KY. The
high-oil hybrid was Beck’s 5405 while the waxy hybrid was Patriot’s WX4060,
both agronomically good choices for Kentucky.
Results
The principal results were:
- Wax
content in “waxy” corn was not affected by either type of insect. Both the concentration and quality of
amylopectin were unaffected, although there was a quantitative yield loss that
was not statistically different from traditional corn. Thus, traditional insect management
guidelines can be used for this corn.
- For
high-oil corn, seed oil content is sensitive to stalk-boring Lepidoptera
such as the European corn borer but relatively less sensitive to
foliage-feeing insects such as corn leaf aphids. High corn borer populations depleted oil
content to below 6%, below the premium threshold.
- For
TopCross® varieties, corn leaf aphids seriously interfered with
pollination, reducing yield of these varieties much more than observed
with conventionally-pollinated corns.
For these varieties, the corn leaf aphid must be considered a
significant pest, unlike with conventional corn varieties that are rarely
impacted by this insect.
- There
is a strong inverse relationship between corn leaf aphids and European
corn borer on high-oil corn but not on waxy or conventional corn
hybrids. Higher European corn borer
populations apparently degrade phloem sap quality in the tassel, thereby
limiting aphid reproduction. Plants
with three or more corn borer galleries had, on average, about half as
many aphids compared to plants with no corn borer galleries. The physiological basis of this
interaction is unknown.
- Based
on these studies, a new general economic threshold model was
assembled. This threshold will make
it possible to determine action thresholds for any crop that has a
quality-based premium as a component of its valuation. This will be increasingly relevant as
more quality-enhanced crops appear in the near future.
- New
thresholds for these insect pests are about 25% lower for European corn
borer and 50% lower for corn leaf aphids in high-oil corn. Based on historical records, high-oil
corn producers can expect to require an insecticide application for corn
borers nearly every year and an “over-the-top” application for corn leaf
aphids about twice as frequently as they now experience. This increased management cost
significantly increases the insect management expenses for this crop. Waxy corn producers can use existing treatment
guidelines for dent corn and their insect management expenses will be
unchanged.
- Because
of the increased management expenses on high-oil corn, TopCross® varieties
should be avoided and the newer self-pollinating high-oil varieties used
instead. These varieties may not
have quite as high of an oil content but the aphid effects will be
negligible and the insect management savings will offset the slight
reduction in oil content.
