Tarnished Plant Bugs
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| Immature Tarnished Plant Bug |
While the peak migration of tarnished plant bugs in central
and south Alabama seems to be over, it appears to just be starting in the
Tennessee Valley. We received reports and saw fields with 1-3x threshold
populations (2 per 25 sweeps) of adult tarnished plant bugs last week (July 7).
In almost every case, square retention was still high, which tells us that the
plant bugs had just started moving in. As this newsletter is coming out, we
suspect square retention will have significantly fallen if those fields were
not treated. With the delays in finishing planting and differences in cotton maturity
across the state, we will likely be managing plant bugs differently in
individual fields this year.
In our most mature fields (those in bloom) we need to be
sampling for immature plant bugs. This is done by placing a black drop cloth
between two rows of cotton and shaking the vigorously the plants on either side
of the cloth to dislodge any insects on the plants onto the cloth. Count the
number of immature plant bugs on each sample. Threshold is when you find an
average of 3 bugs per 5 row feet (one drop cloth sample).
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| Adult Tarnished Plant Bug |
In our later planted cotton (prior to bloom), we are still
looking for adult plant bugs migrating in. To scout for adults, the most
efficient methods are to use a sweep-net and/or monitor square retention. To
monitor square retention, look for the presence (or absence) of first position
squares on the upper 2 or 3 nodes of the canopy. Threshold is when you find an
average of 2 adults per 25 sweeps OR if square retention falls below 80%.
One thing to keep in mind when dealing with
adult plant bugs is that NO product will provide much, if any, residual control.
Adults may continue to infest fields after sprays, so if checking a field 7
days after an application, it may be possible to find the same number – or more
– adult plant bugs than the previous week. This does not necessarily mean a
control failure, just that more adults have moved into the field. As long as we
are setting squares and square retention is above 80% then we know our
application did its job.
Depending on the targeted populations, we have several
options for control of plant bugs. When going after adults in pre-bloom cotton,
the neonicotinoids provide adequate control of both plant bugs and aphids (e.g.
imidacloprid, Centric). When primarily dealing with immature plant bugs in
blooming cotton, we tend to shift away from the neonics to other chemistries. The
insect growth regulator, Diamond, is a good option that provides 2-3 weeks
residual control when used at a rate of 6-9 oz, respectively. Diamond should be
combined with a knockdown insecticide such as Transform, acephate, Bidrin or
pyrethroids (depending on resistance levels in your area) to provide more
immediate control.
Stink Bugs
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Smaller boll damaged
by stink bugs |
As some of our most mature fields are at the first couple of
weeks of bloom, it is time to start thinking about stink bugs as well. We know
that stink bugs are seed feeders and prefer bolls that are around 10 days old
(about the diameter of a quarter), however in a situation with few of these
bolls present, stink bugs will feed on even smaller bolls. Don’t slack up on
sampling bolls for damage in these earliest fields. Remember that sweep-nets
and drop cloths are
not an effective way to scout for stink bugs. In
order to scout for stink bugs we have to sample for internal boll damage by cracking
bolls open and looking for signs of stink bug feeding (warts, pin-prick marks,
stained lint). The threshold during the first two weeks of bloom is 30-50%
internal damage and 10% for weeks 3-6. In a “normal” year, we don’t worry as
much about damage during the first 2 weeks of bloom, because there are fewer
bolls at risk during this time. However, this year with fewer acres in the area
blooming and setting bolls at this point, we have the same number of stink bugs
with less acres of cotton to dilute the population. Thus, stink bugs may be in
more concentrated numbers in fields in our most mature cotton than “normal”
this year. Be sure to look at small bolls during this time while still scouting
for plant bugs. Stink bugs tend to infest field borders (
≈50
feet) and smaller fields (
≈20 acres) more heavily so keep that in mind when scouting.
Aphids and Spider Mites
We have received reports of the aphid fungus killing aphids
in parts of South Alabama over the past week. Hopefully the fungus will spread
statewide quickly and knockout any lingering populations we are dealing with
from now on. We have also gotten reports of spider mites in fields in the east
central and southeast areas of the state. For now, we are advising folks to
watch the populations and wait until the forecast shows a several of hot, dry
days in a row before spraying. We want to maximize the effectiveness of the
application and reduce the chances of a rain event reducing efficacy.
Take Home Message for the Current Cotton Insect Situation
With the varying stages of cotton (from 1st true
leaf to 3rd week of bloom) across the state (and within an
individual farm in some cases) we are going to have to do a lot of insect management on a
field-to-field basis in 2021. Proper scouting and keying in on the correct pest
for the stage of crop and time of year will be critical. We will continue to put
out information through twitter,
this newsletter and the Alabama Crops Report Newsletter,
Podcast
and on the Pest
Patrol Hotline. As always, if we can ever be of any help please don’t
hesitate to let reach out.
