This year we have caught modest numbers of adults but in some local areas the amount of infestation is very high. Why?
-Joe Ingerson-Mahar
What those causes were seem less important now since last
year we had large adult populations and this year we seem to have very high
larval populations at least in sweet corn around the state.
As a reminder, the majority of ECB in the state has two
generations a year (and sometimes a partial third generation). One strain of ECB has only one generation a
year but if it occurs in New Jersey it is rather rare.
In 2011, while we had larval damage it did not seem extreme,
despite large numbers of adults. This
year we have caught modest numbers of adults but in some local areas the amount
of infestation is very high. Why?
Most of our prediction of the damage potential of ECB comes
from catching the adults, that is, the moths.
While this is fairly easy it can be wildly inaccurate. The adult is two stages away from the crop
damage. The adults lay eggs in small egg
masses and then larvae, caterpillars, hatch from the eggs to begin feeding on
their host plants. A lot of bad things
can happen to the ECB in this process.
Bad weather may inhibit or prevent the moths from laying
eggs. Eggs that are successfully laid
are susceptible to predators and egg parasites.
So, too, the larvae are susceptible to predators and bad weather. So even though we start with large numbers of
adults, there may be very little damage.
Conversely, if weather conditions are good, predators and
parasites are low in number or non-existent, then there may be a high
survivorship of eggs and larvae. From a small
number of moths a lot of damage may occur, and that seems to be the situation
this spring/early summer.
The best way to determine what the potential damage will be
is field scouting, where a person can look at individual plants, subsample the
field, and come up with a percentage of infestation indicating whether an
insecticide application is needed.
Lacking that, we can rely on the adult captures. This will help us to know when moths are
flying, when peak moth activity is and when most of the larval activity will
occur. We can use this information to
better time insecticide applications, but the number of adults may not produce
an accurate picture of potential damage.
What the second generation will be this year remains to be
seen.
Joe Ingerson-Mahar
