As cotton starts to square, it’s time for growers to check their fields every week for tarnished plant bugs. These pests can hurt your yield, especially early in the season. If we protect the first squares, we can help the crop grow faster and make more cotton in the end.
Don’t spray too early. Spraying when bug numbers are too low wastes money. Before cotton blooms, the threshold is:
- More than 8 plant bugs in 100 sweeps, and
- Less than 80% square retention
If square retention is over 80%, there’s usually no benefit from spraying.
Once cotton blooms, switch to using a drop cloth for checking bugs. Only spray if you find 2–3 plant bugs per sample. Even cotton varieties like ThryvOn need to be checked and sprayed if they go over the threshold.
It’s smart to plan your sprays ahead of time. We have comprehensive recommendations for different spray scenarios (skip to end of article). Start the season with insecticides that work well on plant bugs but are softer on beneficial insects. These helpful bugs eat pests later in the season, like stink bugs.
Hold off on strong insecticides like pyrethroids and organophosphates until late in the season when you really need them. Examples include:
- Organophosphates: Bidrin, Orthene
- Pyrethroids: Bifenthrin, Warrior II
Avoid using pre-mixed products (like Endigo or Brigadier) early on. They often contain pyrethroids. Unfortunately, we have documented pyrethroid resistance in North Carolina tarnished plant bug. Plus, they kill the beneficial insects we want to keep around.
A recent survey of commercial fields in North Carolina provided data verifying the long-known regional nature of tarnished plant bug (aka Lygus bug). Furthermore, recent studies have demonstrated that higher minimum temperatures and a greater area planted to wheat and soybean has likely contributed to the increase of tarnished plant bugs in North Carolina cotton. Unfortunately, we expect tarnished plant bug to continue to be a major pest in North Carolina cotton based on these results.
Because of the regional nature of this pest, some growers can count on multiple sprays for tarnished plant bug a year, while others might only spray once, or some not at all. Furthermore, insecticide efficacy varies across the year, with some insecticides becoming less effective as the year progresses. In addition, growers need to be cautious using more broad-spectrum insecticides early in the season to preserve beneficial insects. Also important, is that we have documented pyrethroid resistance in North Carolina. So these should only be used as a tank mix partner and with caution (bifenthrin is an example of a pyrethroid). We have formulated a set of recommendations to reflect these expectations.
