Cotton Insect Situation
We have been in a lot of cotton this week and much of it has needed a good rain (or two). The storms we have been getting across Alabama seem to end up being isolated and for whatever reason, dumping rain in the same areas (and missing the same areas) during each event that occurs. I am no agronomist, but I suspect these dry fields will not be needing a lot of PGRs in the coming days. Those applications may need to wait to see how the crop responds to a rain. In some fields, cotton appears to be in “survival mode” and is sending resources to the small bolls in the lower portion of the canopy instead of going back to vegetative growth after a rain event. Again, I am not an agronomist, just what an entomologist seems to be observing.
Plant Bugs
The black drop cloth is the best way
to sample for immature plant bugs.
to sample for immature plant bugs.
Based on our observations and reports we have received from across
the state, it appears we may be in the “lull” between adult and immature plant
bugs. The extended dry period we experienced seems to have caused more of a single
migration period into fields instead of a “trickle” or prolonged migration like
we observed last year. Many of the adult plant bugs that infested fields have
either died from insecticide applications or appear to have run their course
naturally. Sometimes, we see a lag time between this happening and immature
plant bugs (nymphs) hatching out. We did a lot of drop cloth samples in our
cotton that is around first true week of bloom in central AL and in the TN
Valley. Our observation was that had we been sampling a day or two earlier, we would
have found even fewer bugs. Most of the nymphs we found were first instars
(hatchlings) that are very small. In other words, most of these plant bugs were
likely just a day or so old.
Keep in mind that plant bug nymphs are extremely difficult
to find in sweep-net samples and the black drop cloth is the most effective way
to sample. If using a drop cloth, we recommend treatment when you find an
average of 3 nymphs per 5 row feet (1 sample). Additionally, some people use a
dirty square or dirty bloom threshold of 10% injury.
We are currently at a good time to get the insect growth regulator
novaluron (Diamond) in the mix. This chemical kills nymphs as they molt from
one instar to the next and is most effective when applied at the first appearance
of nymphs, which is typically around 1st bloom in Alabama. We usually
recommend a 6 oz rate, which we feel provides about 2 weeks of residual suppression.
Most times, Diamond should be tank-mixed with a knockdown insecticide such as
Bidrin (5 oz), Transform (1.5-1.75 oz), Bifenthrin (5-6.4 oz) or acephate (0.5-0.75
lb ai). This can help control any remaining adults and larger nymphs that may
already be in the field. At this point in the season (post-bloom), we no longer
recommend the neonics (imidacloprid or Centric) due to resistance management,
pollinator protection and lack of consistent performance on nymphs.
Aphids on a cotton square
Aphids
We have also started hearing about aphids building in some
regions of Alabama. Normally, we don’t see much a yield response from spraying
aphids in our research trials, but this year may be one where that trend doesn’t
hold up. In fields that are already drought stressed, we do see yield hits from
aphids compounding that stress. Treatment is sometimes recommended when
populations exceed 50 or more aphids per leaf and honeydew is accumulating, especially
under drought stress. We normally clean up aphids with plant bug sprays and don’t
need to make applications targeted only for aphids. I know we have some (very)
late cotton out there this year. If aphids are building and the cotton is drought
stressed, I would consider an application.
Spider mites in cotton
Spider Mites
Spider mites are one of the most difficult cotton “insects”
to make a management decision on. This is because thresholds are not well defined,
and weather plays a significant role in population development. Our recommendation
is to treat when 30-50% of the plants are showing symptoms, mites are present,
and no rain is in the immediate forecast (see what I mean?). Of all insect
management decisions, this one probably requires the most professional judgement.
Products with the active ingredient abamectin provide relatively good control. Coverage
is important for control and as the crop canopy develops, higher rates of these
products are recommended. Remember that populations are often worse following applications
of broad-spectrum insecticides but they can build in fields that have not been
treated recently as well.
Peanut Insect 
TSWV Symptoms in peanuts
The phone has been relatively quiet on the peanut front this
year. We are beginning our TSWV surveys with our REAs across the state and are observing
symptoms ranging from 3-9% infection so far in the Wiregrass. Of course, there
is nothing we can do at this point to reduce virus incidence.
The hot, dry weather means that we are at a risk of lesser
cornstalk borers in out peanuts, particularly in dryland fields. Dr Mark Abney at
UGA posted a good article on LCBs on the UGA Peanut Website (link).
Soybean Insect Situation
We are hearing about stink bug populations building in
soybeans. Mostly, these calls have been in fields at or around the R3 stage and
no seeds are at risk. Ordinarily, we don’t recommend treatment for stink bugs
when there are no seeds at risk. However, IF redbanded stink bugs make up a
large portion of the population, treatment may be beneficial. RBSB are not
doing much economic injury at this point, but populations are difficult to
control once they are established and immatures are present. Knocking them back
early may help. This application would need to be weighed with the risk of
flaring other pests, such as soybean loopers, later in the season. We don’t have
any data on the risk vs reward of that early of an application for RBSB, just
some experience on how damage RBSB can be and how difficult to control they can
be as well.
If you would like to provide reports or observations on the
insect situation from your region, please let us know. You can reach Scott Graham
at 662-809-3368 or scottg@auburn.edu or
Ron Smith at 334-332-9501 or smithrh@auburn.edu.
As always, if we can ever be of any help, please let us
know.
