Insect Note #2 (Revised)
Prepared by:
K. A. Sorensen, Extension Entomologist
Dated 1/94
Placed on the Web 4/95 by the Department of Entomology, NCSU
Revised: 3/05
European Corn Borer in Potatoes
Ostrinia nubalalis (Hubner). Lepidoptera: Pyralidae
The foliage and stems of Irish potatoes grown in eastern North
Carolina are frequently damaged by larvae of the first generation
of the European corn borer. The damage occurs primarily during the
month of May. The first moths usually appear between April 15 and
May 1.
I. Damage
The damage to Irish potatoes may cause reduced yields and poor
quality.
- Reduced yields may result from damage due to larvae
in the stems. The injury reduces the movement of plant nutrients.
The invasion of disease organisms such as blackleg may cause stems
to collapse or rot.
- Poor quality results from discolored stem ends of the
tubers. This is due to disease organisms, especially blackleg,
entering at the point of injury and moving down the stem and into
the tubers.
II. Life Stages
The European corn borer has complete metamorphosis, which means it
goes through four life stages, namely: egg, larva, pupa, and adult.
A few comments about each stage follow:
- Egg: Female moths lay eggs in groups of 5 to 50 on
the underside of leaves. These greenish-colored eggs overlap
lightly and look like fish scales. About two days after the eggs
are laid, the black heads of the developing larvae may be seen.
The eggs hatch in about one week, depending upon temperature and
other factors.
- Larva: The larvae or "worms" damage potato foliage.
After hatching, they search for a protected area in which to hide
and feed. After feeding a few days on the exposed surface of
leaves and stems, they bore into the hollow potato stem.
The larvae are approximately 1/8 inch long when first hatched, but
after passing through several growth stages, finally reach about 1
inch in length. Larval development takes about 30 days.
- Pupa: The pupal period, passed inside the potato
stems, takes about 14 days for the first generation.
- Adult: The adults (moths) emerge from the pupal
stage, mate and soon the females begin to lay eggs. Each produces
400 or more eggs during her lifetime, which is 2 to 3 weeks in
duration.
The moths are the first active stages to be noted in potato-growing
areas. Each spring, they emerge from overwintered larvae that were
in carried-over cornstalks or weeds of the previous year.
III. Detection
The proper time to begin a control program can be determined by the
presence of European corn borer moths or eggs.
- Adults - The emergence of the first moths can be
determined by using light traps, screened cages or sex pheromone
traps or walking field borders.
- Light trap - The black-light trap is stationary and traps
moths that emerge naturally in a local or limited area.
- Screened cages - Cornstalks from several areas of the
county can be put into a screened cage at one location. This will
give the first date of emergence and the rate of emergence of the
moths. Screened cages in local areas or for a single farm may be
used.
- Sex pheromone Traps - Use the New York sex pheromone
attractant and place in H. zea or screen trap in the field.
Male moths will be attracted and can be counted.
- Field Scouting - Walking potato fields when checking
for other insects or diseases will often flush ECB moths from field
borders.
Once the moths emerge, growers should be alerted so that they will
be prepared to begin spraying 7-10 days depending upon the
temperature and other factors that influence the rate of
development of the European corn borer.
- Eggs - Another method of determining when treatments
should be applied is the examination of Irish potato leaves or
leaves of the weed dock for European corn borer eggs. Following
adult emergence, potato leaves must be examined daily. Once the
eggs are found they can be flagged and checked for egg hatch.
Treatments should begin with 5 days.
IV. Control
European corn borers infest Irish potatoes each year in eastern
North Carolina. Because of their habits, it is impossible to
predict which fields will be infested. Therefore, since fields in
some areas are infested every year, all fields in the area should
be scouted and treated beginning 7 to 10 days after a significant
emergence of moths.
Apply insecticide to the foliage weekly from the time the first
application date is determined (usually first week in May) through
significant moth flight. Since the objective is to kill the larvae
in the two- or three-day period from the time they hatch until the
time they bore into the potato stem, frequent and thorough
applications are needed.
