Alabama Insect Situation: July 7, 2022

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.

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 1^st 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 Situation

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.