Observations from recent course visits in Hawaii and the southwestern U.S. have revealed mealybugs and grubs are already present and feeding on turfgrass roots. Some courses are already seeing turf thinning on hybrid and common bermudagrass. As golf courses transition from overseeded ryegrass to bermudagrass, turf thinning can be misinterpreted as poor bermudagrass recovery from ryegrass competition. However, closer inspection during a few recent visits in southern Arizona revealed juvenile grubs were prolific and very likely the primary cause of the turf damage.
Mealybugs are piercing-sucking pests that feed on plant sap within leaves, stems and roots. Mealybugs have not historically been identified as a problem in the southwestern U.S. but have been an issue in Hawaii and were identified last season in southern Arizona feeding on bermudagrass. An insecticide application made in August of 2020 for mealybug control at one facility seems to have yielded benefits during bermudagrass transition this spring and early summer (see image).
Given these recent observations, I suggest scouting areas where turf has thinned or appears droughty to see if grubs are present. Note that the small grubs are typically found within the top 0.5 inch of the soil and thatch layer this early in the year. Here are a few additional suggestions for mitigating the damage these insects can cause:
- Use a systemic insecticide for extended control.
- Rotate the chemical classes used for insecticide applications. Experience shows that mealybugs are prone to developing resistance. Suggested active ingredients include chlorantraniliprole (Acelepryn), clothianidin (Arena), clothianidin + bifenthrin (Aloft), cyantraniliprole (Ference), imidacloprid (Merit, etc.), imidacloprid + bifenthrin (Allectus), and thiamethroxam (Meridian).
- Consider combination products containing pyrethroids and neonicotinoids – e.g., bifenthrin + imidacloprid – for rapid insect reduction followed by longer systemic control.
Now is the time to inspect areas where turf thinning has occurred and take action to stop the damage and prevent further turf decline if grubs are the cause.
Best wishes for a successful transition process in the Southwest and please do not hesitate to contact a USGA agronomist in the West Region for more information on managing insect pests or any other agronomic practices.
West Region Agronomists:
Brian Whitlark, senior consulting agronomist – bwhitlark@usga.org
Cory Isom, agronomist – cisom@usga.org
