White grubs are the larvae of beetles such as Japanese beetles and masked chafers and are among the most destructive lawn pests in Kentucky entomology.ca.uky.edu. They chew off grass roots, reducing the turf’s ability to uptake water and nutrients entomology.ca.uky.edu. Here’s what Louisville homeowners need to know:
Grub species vary in their life cycles. Japanese beetles, masked chafers and May/June beetles all lay eggs in turfgrass, but their egg‑laying periods and vulnerability to insecticides differ. Adults emerge and mate in late June and July, then females deposit eggs in sunny, irrigated areas. Newly hatched grubs feed on roots through late summer, burrow deeper to overwinter and resume feeding in spring before pupating entomology.ca.uky.edu. Because symptoms often appear in late summer, monitoring and early intervention are crucial. Combining cultural and chemical control methods produces the best results.
Signs of Grub Damage
- Thinning and yellowing patches: Damage often appears in August or September as irregular, thinning areas that can coalesce into larger dead patches entomology.ca.uky.edu.
- Spongy turf: Heavy infestations cause turf to feel spongy; sod may roll back like a carpet due to root destruction entomology.ca.uky.edu.
- Animals digging: Skunks, raccoons and birds may tear up the turf to feed on grubs.
Life Cycle & Timing
- Egg laying: Adult beetles emerge in June–July and lay eggs in mid‑summer entomology.ca.uky.edu.
- Feeding: Grubs feed on grassroots through late summer and fall, overwinter in the soil, then resume feeding in spring before pupating entomology.ca.uky.edu.
- Threshold: Eight or more grubs per square foot in August sampling indicates a need for treatment entomology.ca.uky.edu.
Control Strategies
- Water deeply: Healthy lawns tolerate some grub feeding; proper watering (1 inch per week) encourages deep roots daviess.ca.uky.edu.
- Use insecticides responsibly: Preventive insecticides applied in June or July provide season‑long control; curative products applied in August target actively feeding grubs. Only treat when grub counts exceed thresholds entomology.ca.uky.edu.
- Overseed after damage: If grubs have thinned your lawn, overseed in early fall (mid‑August to early October) to repair damage publications.ca.uky.edu.
Integrated Control
- Maintain lawn health: Healthy, well‑watered lawns can tolerate light grub populations without visible damage. Follow proper mowing and watering practices to promote deep roots daviess.ca.uky.edu.
- Monitor early: In July and August, peel back small sections of sod to check for C‑shaped larvae. Economic thresholds are about eight grubs per square foot entomology.ca.uky.edu. If numbers are below this threshold, treatment may not be necessary.
- Choose the right product: Preventive insecticides such as imidacloprid, thiamethoxam or clothianidin are applied from late June to early July. They target young grubs and provide months of protection. Curative products containing trichlorfon or carbaryl kill larger grubs but provide shorter residual control. Always read and follow label directions.
- Consider non‑chemical options: Parasitic nematodes and milky spore disease products are biological controls that infect grubs, but performance varies with soil temperature and moisture. Consult your county extension office for recommendations.
- Repair and overseed: After controlling grubs, rake out dead patches, top dress with compost and overseed. Water frequently to establish new seedlings publications.ca.uky.edu.
Understanding grub biology helps you time control measures effectively. For severe infestations, contact Rise Pest Pros for professional lawn inspection and treatment.
