Lawn Pests & Fungus

Billbugs are root-feeding weevils that damage Kentucky bluegrass, perennial ryegrass, and occasionally tall fescue in Colorado. Larvae feed inside stems and roots, causing dead patches that resemble drought or heat stress. Damage appears late spring through mid- summer.

Chinch bugs are sap-sucking insects that cause patchy, drought-like lawn damage, especially during hot, dry summers. They thrive in sunny, dry areas and weaken turf by removing plant juices and injecting toxins. Damage appears quickly and often mimics heat stress or drought scorch.

Cranberry Girdler is a root- and crown-feeding caterpillar that damages Colorado turf, especially Kentucky bluegrass, fine fescue, and bentgrass. It causes large thinning areas, brown patches, and poor late-summer lawn recovery. It is one of the most destructive sod- feeding insects in Colorado turf.

Cutworms are night-feeding caterpillars that chew through grass blades, stems, and crowns. Damage appears as small brown patches, chewed stems, or sudden thinning, especially in newly seeded lawns. Adults are the brown or gray moths often seen fluttering around porch lights.

Japanese beetle grubs are root-feeding white grubs that cause severe turf damage, especially in irrigated Colorado lawns. They are similar to other white grubs but tend to be more aggressive, more numerous, and more destructive. Damage appears late summer through fall and often requires preventive treatment in areas with known infestations.

Sod Webworms are grass-feeding caterpillars that chew turf blades and crowns, causing patchy brown spots that worsen in hot, dry weather. Adult moths are the small tan moths that fly up when you walk across the lawn. Damage usually appears mid–summer through early fall.

Turf mites are tiny, sap-feeding arachnids that cause dry, straw-colored patches, usually during late winter to early spring when grass is stressed and moisture is low. In Colorado, winter turf mite damage is extremely common, especially on south- and west-facing slopes.

White grubs are root-feeding beetle larvae that damage lawns by chewing through the turf’s root system. This causes large brown patches, spongy turf, and easy peel-back of sod. Grub damage typically appears late summer through fall, but the insects develop underground year-round.

Ascochyta Leaf Blight is a rapid-onset turf disease that causes lawns to appear straw-colored almost overnight, especially after periods of heat + drought stress, mowing injury, or irregular watering. Despite its alarming appearance, Ascochyta is usually temporary and non- lethal.

Dollar Spot is a common summer lawn disease in Colorado, especially in Kentucky bluegrass, fescues, and ryegrass under low nitrogen or drought stress. It forms silver-dollar-sized spots that merge into larger brown patches. It is destructive if unmanaged but responds well to proper nutrition and watering.

Fairy Ring is a soil-based fungal complex that causes dark green rings, dead rings, mushrooms, or a combination of these. It is very stubborn, especially in Colorado’s dry, compacted soils and thatch-heavy bluegrass lawns. Management requires soil modification, deep watering, and sometimes fungicide + aeration programs. 4

Necrotic Ring Spot is one of Colorado’s most common and destructive lawn diseases, especially in Kentucky bluegrass. It causes rings, dead patches, frog-eye patterns, and thinning that worsens with drought, heat, and excessive thatch. Usually appears late spring through fall.

Powdery Mildew is a cosmetic fungal disease that affects Kentucky bluegrass in shady, damp, low-airflow areas. It appears as a white, powdery coating on grass blades. It rarely kills turf and is usually a sign of too much shade, poor airflow, or prolonged moisture, rather than a serious infection.

Snow Mold is a cool-season lawn disease that appears after long snow cover, especially on north-facing lawns, shaded areas, and yards with heavy thatch. It causes matted, bleached patches in early spring. Most cases are cosmetic and recover quickly with light raking.

Summer Patch is a serious, root-destroying turf disease in Colorado, primarily affecting Kentucky bluegrass and occasionally annual bluegrass. It thrives in hot soil temperatures, poor drainage, and compacted or overwatered lawns. Damage is often mistaken for drought stress, but watering does not revive affected patches.

Rust is a very common late-summer lawn disease in Colorado, especially during dry periods, slow growth, or nutrient deficiency. It coats grass blades in orange dust, weakens the lawn, and can stain shoes and pets. Rust is usually non-lethal and easy to manage with proper fertilization and watering.

Heat Stress occurs when turfgrass experiences prolonged high temperatures, intense sun, dry soils, or shallow rooting, causing wilting, browning, and thinning. It is extremely common in Colorado during mid-summer, especially on south- and west-facing lawns, slopes, and compacted soils.