We hit the tarnished plant bug threshold for the first time this season on July 15 at the Tidewater AREC, in Suffolk. Reports of threshold numbers are rolling in from collaborators as well. Here are a few key reminders for successful plant bug management this year;
1. Use economic thresholds
These economic thresholds are the point at which you will see a return on investment from spraying for plant bugs.
Pre-bloom threshold;
8 plant bugs/100 sweeps AND less than 80% square retention
Many of our cotton fields here on the research farm and in on-farm trials are beginning to flower this week. Once you reach 50% of plants in a field with flowers, switch to using a drop cloth to sample plant bugs. The drop cloth should be placed on the ground between two rows and the plants on either side vigorously beaten over top of the sheet. Take a sample in 6-8 spots throughout a field and average to determine the number of bugs per drop cloth sample. Making the switch from sweep net samples to drop cloth samples during bloom is critical for making informed management decisions on plant bugs.
Threshold from the 1st week of bloom on;
3 plant bugs/5 row feet
Even if you are using a Thryvon cotton variety, it still needs to be scouted and treated for plant bugs at the recommended thresholds. Weekly scouting will provide the best insight on when and where insecticide applications are needed.
2. Insecticide rotation
Hold off on using strong broad-spectrum insecticides until late in the season. These include pyrethroids and organophosphates;
Organophosphates: Bidrin, Orthene
Pyrethroids: Warrior II, Bifenthrin, countless generics (look for insecticide MOA 3A on the label). Many premixed products, including Endigo or Brigadier include a pyrethroid.
Plant bugs have developed resistance to pyrethroids, and these products eliminate beneficial insects, which may keep other pests in check later in the season. An early pyrethroid spray can often flare spider mites, aphids, and bollworms later in the year.
A good option for your first spray for plant bugs is Transform @ 2 oz/ac. Diamond @ 4-6 oz/ac can be included as well, where there are nymphs present. This product is an insect growth regulator and will not have activity for adult plant bugs. If timed correctly, it has been shown to increase the time before another plant bug spray is needed. Neonicotinoids (Centric, Admire) can also be effective early in the season, but need to be combined with other products to get good control as the year progresses. Be sure to check the label for restrictions on use patterns during bloom (e.g., application restrictions because of risk to bees and other insect pollinators).