Understanding how grubs damage turf and using a planned, year-round approach will protect your Colorado lawn more effectively than reactive sprays alone. This article explains grub biology relevant to Colorado, outlines preventive cultural practices, compares biological and chemical controls, provides a practical seasonal calendar, and offers troubleshooting and safety guidance you can apply immediately.
White grubs are the C-shaped larvae of several scarab beetles — most commonly Japanese beetles, June beetles (also called June bugs), and masked chafer species. They feed on grass roots, causing thinning, dead patches, and secondary damage from animals that dig for them. Colorado lawns, which are predominantly cool-season grasses such as Kentucky bluegrass, tall fescue, and perennial ryegrass, are vulnerable because these turfs rely on dense, shallow root systems that grub feeding can quickly undermine.
Eggs are laid by adult beetles in mid to late summer depending on species and local weather. Larvae develop through three instars that feed during late summer and again in spring after overwintering in the soil. Most economic feeding occurs when third-instar grubs are large in late summer and early fall, and again in spring as they resume feeding. Knowing these windows lets you choose preventive or curative tactics when they are most effective.
No single tactic is sufficient long-term. Use integrated pest management (IPM): monitor, prioritize nonchemical cultural prevention, use biologicals when feasible, and apply chemical controls only when thresholds are reached and timed correctly. This reduces cost, environmental impact, and the chance of repeated outbreaks.
Proper lawn management is the foundation for grub resistance. These practices make your turf less attractive for egg-laying and more resilient if grubs are present.
Mow at the right height — for Colorado cool-season grasses, 3.0 to 3.5 inches is ideal. Taller grass has deeper roots, better drought tolerance, and can withstand some root loss.
Fertilize on a schedule tailored to cool-season grasses. Avoid high-nitrogen, late-summer applications that create lush growth attractive to egg-laying beetles. Focus fall fertilizer (after lawn recovery) to build carbohydrate reserves.
Water deeply and infrequently. Aim for about 1 inch of water per week — applied early morning — rather than frequent light sprinkling. Overly moist shallowly irrigated turf is more attractive to egg-laying females.
Dethatch and aerate. Heavy thatch and compacted soil encourage grub survival and limit beneficial predators. Core aeration in spring or early fall helps roots and improves biological control activity.
Overseed damaged areas promptly in late summer or early fall to restore turf density and reduce erosion and weed invasion.
Regular inspection is crucial before you decide to treat.
Dig a 1-square-foot plug of turf about 2 to 4 inches deep in several locations where damage appears likely (near edges, moist areas, or thinning patches). Count grubs in that square foot.
Standard economic thresholds vary but commonly used guidance is:
Also look for secondary signs: turf that lifts like a carpet, localized bird or skunk digging, and irregular brown patches.
Biologicals are effective, low-impact options — especially for homeowners who prefer to avoid synthetic insecticides.
Heterorhabditis bacteriophora nematodes are the most reliable species for grub control. Apply when soil temperatures are above about 50degF and before grub larvae move deep for winter. Nematodes need moist soil and are sensitive to UV and heat; they must be applied in the evening or overcast conditions and kept cool until use.
Beauveria bassiana and Metarhizium anisopliae are fungal biocontrols available in some products. They can reduce populations but often require high humidity and repeated applications for good control.
Encouraging natural predators helps long-term control. Birds, ground beetles, and other predators reduce grub numbers but can cause surface damage as they dig. Avoid broad-spectrum insecticides that kill beneficial insects.
If monitoring shows grub populations above thresholds, insecticide choice and timing matter.
Preventive insecticides are applied before eggs hatch in summer to protect turf through the vulnerable larval period. Neonicotinoids (imidacloprid, clothianidin) and chlorantraniliprole (a diamide) are commonly used preventive active ingredients. Preventive treatments are often more effective and require lower application rates than curative treatments because they target small larvae.
Curative insecticides are applied when grubs are already present and actively feeding. Products labeled for curative control include carbaryl and trichlorfon (note: availability and labels change; always read the product label). Curative treatments must contact the grubs and are less effective on large, deep-season larvae.
Colorado-specific timing guidance:
Always follow label directions, rate, and reentry intervals. Be mindful of restrictions related to pollinator protection; avoid treating blooming weeds and use evening applications to reduce exposure.
Spring (March-May)
Early summer (May-June)
Mid to late summer (July-August)
Fall (September-October)
Winter (November-February)
If you prefer DIY, choose products labeled for your turf type and for grubs; read and follow label instructions and local regulations. Use granular or liquid formulations as appropriate for your irrigation schedule and equipment.
Hiring a licensed turf professional can be worthwhile for large lawns, recurring severe grub problems, or when chemical application requires commercial licensing. Ask pros about their IPM plan, product choices, and environmental protection measures (pollinator safeguards, buffer zones).
Protect pollinators and beneficials: avoid treating flowering plants and apply products in the evening. Many preventive products are systemic or persistent — use them only when necessary.
Follow label rates and timing; off-label use is illegal and dangerous. Wear recommended PPE when mixing or applying chemicals.
Store pesticides in original containers, locked away, and dispose of unused product per label instructions and local hazardous waste rules.
Limit use of broad-spectrum insecticides that can harm non-target insects and soil health. Favor targeted, timed applications and biological alternatives where practical.
If problems return year after year, consider these steps:
A planned, year-round IPM approach tailored to Colorado conditions will reduce grub damage, lower chemical use, and keep your lawn healthy and resilient. Start with monitoring this season and adopt two or three cultural improvements — you will see measurable improvement in grub pressure and turf recovery.