Over the past few days, Alabama Extension professionals have been hearing reports and have seen tarnished plant bugs infesting cotton fields across Alabama—from the Florida line, through central Alabama, and up to the Tennessee Valley.
In some cases, cotton is older (up to 12 nodes). However, in many fields the cotton is just starting to put on pinhead squares (seven to eight nodes). All of the fields have one thing in common: it is the most mature cotton in the area. These are the fields producers need to be keying in on when scouting. It will be important to scout with a sweep-net (threshold (TH) = two adults per 25 sweeps) and monitor pinhead square retention in the upper two to three nodes (maintain 80 percent of first position squares).
Depending on timing, producers may see high plant bug numbers and good square retention. However, this could likely be because plant bugs have only just moved in and the squares that have been fed on have not yet had time to show symptoms. Thus, if either threshold hits, action should be taken. Keep in mind that thresholds aren’t always a “cut and dried” number. If the sprayer won’t be back in an area for seven to 10 days and square retention is approaching (but above) 80 percent with plant bugs present, treatment may be warranted. Sometimes making the call requires some professional judgement based on previous experiences.
Scouting for Tarnished Plant Bugs
- Primary wild hosts in Alabama for tarnished plant bugs are daisy fleabane. The plant bugs will move from daisy fleabane into cotton.
- Square retention (upper two to three nodes of the plant) before an insecticide application is important because it helps to determine what kind of damage plant bugs are currently doing.
- Square retention after an application is important to help determine the efficacy of your insecticide.
Based on sampling of wild hosts (daisy fleabane), it is likely that producers will see an extended migration of adult plant bugs over the next few weeks. This gives the potential to need multiple applications to control adult plant bugs pre-bloom. If this is the case, it will be even more important to monitor square retention. Sometimes following up on an insecticide application can be tricky. Producers may scout a field seven days after treatment only to find the same number of (or more) adult plant bugs in the field. This may not mean treatment failure, but that more bugs have migrated into the field. By monitoring square retention, producers can check to see that the pinhead squares present at application were protected by the treatment.
Another thing to consider is that the adult plant bugs are also lay eggs and immature plant bugs will start showing up just prior to or at first bloom. Action taken on this migrating population of adult plant bugs can help to reduce future populations of immature plant bugs later in the year.
With good cotton prices and an already late crop, producers need to be sure they are staying ahead of insect issues and avoiding any more delays in maturity or losses yield.
If anyone has any observations of plant bugs or any other pests infesting fields, contact Scott Graham (662-809-3368) or Ron Smith (334-332-9501) for assistance.