What's bugging you? …… a plethora of crop insects in 2001 Mike
Rankin
It's one of those scary types of years.
Wet weather leaving just enough time to get the field work and other
necessary work done and precious little time to actually monitor what's
going on in those fields where a crop is already planted and growing.
Based on reports from across the state, it appears that it may be
well worth your while to take a few minutes and walk corn, soybean, wheat,
and alfalfa fields to make sure crop insects aren't eating away at what
yield potential currently exists. Here's
a rundown on some of the major insect pests being reported around the state. Soybean aphid update
We talked a little about soybean aphids in the last newsletter, but since that time confirmed spottings of soybean aphid have been made in Rock and Columbia Counties and southeastern Minnesota. The next two to three weeks will tell the story as to what kind of year this will be from an aphid standpoint. The period for rapid population growth of the soybean aphid is from early to mid-bloom. This is also the time when they do the most damage. Finding a few aphids on leaves now is no reason to panic and begin spraying. A few colonies on even the majority of leaves are not serious. However, diligent monitoring from that point forward is necessary to insure population growth doesn’t explode to yield reducing levels. Late planted fields (and we have plenty of those!) are most susceptible to large aphid outbreaks. Armyworms
Moths, in general, are abundant in 2001 and many of them belong to
the armyworm clan. There is
perhaps no field crop insect in Wisconsin that causes dramatic damage to the
extent of armyworm. Walking
into a field invaded by this insect is an unforgettable experience.
You can hear them chew, they crunch under your feet, and leave
nothing standing but stalk and leaf veins.
Armyworm moths are attracted to grassy areas for egg laying.
These can be within or adjacent to a field.
Small grain crops are prime targets but uncontrolled grassy weeds
within a corn field are also attractive to moths for egg laying.
There are typically three generations of armyworms per season in
Wisconsin with the second one being the most damaging.
There have already been reports of armyworm problems around the
Midwest (including Wisconsin). Locally, we have many corn fields with grassy weeds that were
not initially controlled because of wet soil conditions. If you have fields in this category, monitor the situation
regularly until the grasses are controlled and you see no signs of armyworm
feeding in the corn. Also scout
wheat fields regularly until harvest.
With the end of the alfalfa weevil season comes the beginning of the
potato leafhopper show. It's no
longer a question of "if", but rather one of "when and how
many?". To date, leafhopper have not been present at economic levels to
treat, but with the recent stretch of sunny and warm weather that could
change very quickly. Typically, we are cutting second crop at about the time
treatment thresholds are reached and our greatest cause for concern comes at
the beginning of the third growth cycle. This year, a number of fields had a
delayed first cutting and could be at risk prior to a second cut.
Glandular-haired (i.e. leafhopper resistant alfalfa varieties) are
getting better. The third generation of these varieties is certainly superior
to the initial releases. However, of
the varieties that have been tested by the University of Wisconsin, none are
able to withstand heavy levels of leafhoppers and perform similarly to those
where an insecticide application was made.
Dollar return on seed investment for glandular-haired varieties will
be greatest for producers who don't want to field scout, don't want to pay a
scout, or in years where leafhopper pressure is at marginal threshold
levels. Stalk and Hop Vine borers
Both of these insects seem to be more commonplace with each passing
year. Damage is usually limited
to corn border rows along grassy ditches and waterways; however, we have
seen damage throughout some corn fields where grassy weeds (usually
quackgrass) were a problem last fall and again this spring.
Remember that the stalk borer feeds above ground and the hop vine
borer confines its activities to the below-ground portions of the stem. Symptoms of these two insects are characterized by wilting corn plants (usually hop vine) and whorl feeding (common stalk borer). Both species eventually end up in the stalk. Chemical control is very difficult and must be based on growing degree day accumulations. Once borers are in the plant, your ability to control the infestation drops off. Hop vine borer move to the plants quickly after emergence. By the time you notice the injury it is usually too late for insecticide intervention. The best long-term solution for both borer species is to improve the weed management program for the field and deny the moths a place for egg laying during late-summer and early fall.
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