Billbugs & Grubs

Lawn & Turf Tips: Bluegrass Billbugs & Grubs

Bluegrass Billbugs

Although not as common, bluegrass billbugs can be responsible for severe turfgrass damage.They seem to cluster in neighborhoods, especially where intensive bluegrass management is occurring. Adult bluegrass billbugs are weevils, or snout beetles, with mouthparts located at the end of a curved snout or bill. Although bluegrass billbugs rarel fly, they may rapidly spread through continuous lawns of a neighborhood.

Life Cycle

Billbugs have a one year life cycle. They winter over as adults in sheltered locations in and around turf grass areas.

The adults are active in late April and May, when soil temperatures are above 65 degrees.
They lay their eggs at the crown of blurgrass stems.
When hatched, the larvae begin feeding on those stems which, in some cases, kills the plant.
As the larvae grow, they leave the stems and and move into the soil feeding on the roots of the plant.
Once they have completed their feeding around mid-July, the larvae pupate in the soil or the thatch.
In late July, the Adults emerge from the soil and move to the overwintering sites.

Symptoms or Signs of Damage

The adult billbugs feed on the stems and blades of the grass but do not cause much damage.
The young, newly hatched larvae feeds on the inside of the grass blade or stems. They hollow out the crown and stem of the plant and leave behind fine sawdust like plant debris and excriment.
As the larvae grow and get larger, they feed on the roots of the plant as deep as 2"-3" below the surface of the soil. This is when they do the most damage to the plants. When the number of larvae is large, root systems can be almost completely destroyed killing the grass.
The damage caused by the billbug larvae is often mistaken for grub damage, sod webworm damage, disease, heat or drought stressed turf.
The greatest damage from billbug larvae is during late June to late August.
Where the grass has been killed by the larvae, it comes loose from the soil and separates easily.

White Grubs

Grubs are white to cream-colored C-shaped insects (1/4"-1 1/4" long) that feed on the fibrous roots of grass and sometimes other plants. Their bodies are white with six legs and a hard head and usually lie in a curled or C-shaped position. They are immature (larvae) stages of May/June or Japanese beetles from the scarab family. Turf grass damaged by white grubs has a reduced root system and is easily pulled away from the soil.

Symptoms and Damage

It is mormal to find a few white grube per square foot in lawns. The mere presence of grubs is not necessarily a cause for concern, because healthy turf can easily outgrow the root loss caused by a small number of white grubs. They are one of the most destructive insects of turf because they feed on grass roots causing severe wilting and eventually death of affected lawns. The damage appears first as drought stressed.

When the turf is heavily infested, it may first appear off color them wilts quickly but with continued feeding, the furf dies off in large irregular patches.
With the tunneling and burrowing of the grub, the furf tends to feel sponge and rolls back like a carpet.
Another indication that white grubs may be present is moles, skunks, raccoon, or flocks of blackbirds finding the turf attractive.

Life Cycle Stages

The scarab family has a complete life cycle starting with eggs, larvae, pupae and adults. The May/June beetles have a 3 year life cycle. Japanese Beetles have a 1 year life cycle. Most scarab beetles winter over in the soil, however, the May/June beetles winter over as adults.

Eggs: The eggs are a creamy-white and about 1/16-inch long. They are slightly oval when they are first laid in the soil. Once laid, they absorb water from the soil and become slightly swollen and rounded.
Larvae: The larvae is c--shaped and referred to as grubs. They are thick with creamy-white bodies. They have a brown head capsule and short legs. The larvae have 3 instars meaning they molt 3 times.
Pupae: These tend to be slightly longer than the adults. Their bodies are formed in chambers approximately 1-2 inches below the soil surface. They start out cream colored and then darken before emerging as adults.
Adult: The adults are oval shaped with the atennae ending in a large club of flattened plates. The May/June and Japanese beetles are the most common types of scarab in our area.

Identification

The best way to identify if you have grubs is to cut three sides of a 12 by 12 inch square (30 x30 cm) and 4 inches (10 cm) deep piece of sod. You may notice that the sod just rolls up like carpeting. Once you have lifted the sod piece. Check through the top 4 inches of the turf you pulled up. If you have 3 or more grubs in a 12x12 inch area you should consider treatment. Do this same process in several spots throughout your lawn.

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