White grub problems in Kentucky turfgrass are usually a combination of Japanese beetles and masked chafers (Figure 1). Flights of these species have been above normal this summer, according to Dr. Dan Potter, UK Research Entomologist. On one hand, that could mean intense damage and dead spots in turf in about 5 to 6 weeks. On the other hand, not much grub damage may show up. Weather over the next few weeks will determine which hand prevails.
Impact of Weather
Precipitation patterns have a major impact on white grub damage to turfgrass. Under dry summer conditions, Japanese beetles and masked chafers are attracted to low-lying or irrigated areas where soil moisture is adequate to stimulate egg hatch and grub development. Female beetles will be attracted to these sites. White grub damage in these scattered oases can be severe, even if beetle numbers are low.
Our rainfall pattern so far this summer makes most grassy areas suitable for white grubs. Even though beetle flight is high, their eggs will be spread over a large area and may keep numbers below damaging levels of about 10 or more grubs per square foot. However, if rain shuts down, then a shallow root system may not be adequate to pick up deeper soil moisture, so turfgrass is more vulnerable to grub damage.
- Most products used for white grub control (imidacloprid, chlothianidin, thiamethoxam, or chloranthaniliprole) are effective against small grubs. Applications made between now and the end of July should be effective.
- Products containing chlothianidin or trichlorfon can be applied later as rescue treatments, if necessary.
- If using liquid formulations for grub control, do not overspray flowering plants.
More thorough information on white grub control is available in the following fact sheets:
- Insecticides for Control Of White Grubs in Kentucky Turfgrass (ENTfacts-441)
- Controlling White Grubs in Turfgrass (ENTfacts-10)
By Lee Townsend, Extension Plant Pathologist