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Landscape Pests: Grub Worms

 

They are called white grub worms and can wreak havoc on a beautiful lawn

Grub worms are the larval stage of several beetle species in the scarab family. Common offenders include Japanese, June (a.k.a. Junebugs), southern masked chafer, and tan chafer. They feature roly-poly whitish bodies that form a "C" shape when feeding.

As pests, they can ravage a landscaped yard. Even in smaller quantities, they attract wildlife (birds, raccoons, skunks, and moles) that can also cause considerable damage in their search for the tasty morsels.

They generally feed on grass roots, leaving turf easy to lift up like a rug. Once yellow and brown patches begin to show in a yard, it may be too late to save. They may also go after ornamentals in the garden, but on a less frequent basis. Other grub worm species also ingest decaying debris, which can effectively smother a plant from underground.

Not all grub worms are technically this serious and, if found in a garden bed, will probably not do much harm. Many are resistant to treatment - both biological and chemical. It is imperative to determine that grub worms are, indeed, present in the lawn before attempting to eliminate. Quite often, the symptoms can signal disease or other infestation.

Grub worms are voracious eaters as larvae, which encompasses three growth stages, or instars. They live through an annual cycle, spending much of it - nearly 10 months - in the ground. In early summer, the eggs are laid by adult beetles. Within one month, the grubs are viable and begin feeding. This generally lasts until mid-fall and well into the third instar, before they burrow deeper for the winter months. The greatest damage is accomplished in the last larval stage. When the ground warms in early spring, the grubs rise closer to the surface and feed again as they begin to pupate. By June, the adults emerge, mate, and lay their eggs - all within an approximate 30-day period. The cycle begins again.

It is wise to test for grub worms before a lawn begins to show signs of damage. This can be done by digging up a 12-inch diameter piece of turf. If it is browned already and lifts up easily, this could indicate grubs. If it resists, pull it up and dig about 2-4 inches into the soil. If more than five grubs are found in this space, an infestation is probably at more serious levels. Test again in several other spots.

Grub worms may not appear every year, with or without treatment. They prefer moist soil and if rains are plentiful, beetles may seek other places to lay eggs. When the ground is drier, homeowners tend to water more. This, in turn, attracts the beetles.

When treating with chemicals, it is essential to choose the right times. Just after the eggs are laid and in August when they are still small are recommended.

 

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