Entomopathogenic Nematodes and Grub Control Over the Winter

Grubs are the larvae of a variety of beetles.

Nematodes are tiny, almost microscopic, worms. There are bad nematodes, like the root-knot nematode, that infect plants and cause a great deal of damage and plant loss. Entomopathogenic nematodes, however, are good nematodes that parasitize harmful insects. Some species of beneficial nematodes can be used to control grub populations, but both nematodes and grubs go into a dormant state for the winter. Nematode application must be carefully timed for effective elimination of grubs.

Grubs

Black vine weevil grubs can be a serious problem for rhododendrons.

Chafers, Japanese beetles, June bugs and oriental beetles are some of the most common species responsible for grubs found just beneath the grass. These larvae eat the roots of grasses and other plants. A severe lawn grub infestation will destroy so much of the root system that the lawn can easily be lifted up like fresh-laid turf grass. Black vine weevil grubs prefer the roots of landscape and fruit plants such as yew shrubs and strawberries.

Grub Lifecycle

Damp soil beneath well-watered lawns is the most favorable environment for egg development.

Grubs mature into beetles in late spring and remain active until mid-summer when they lay their eggs in the soil. The grubs hatch and begin feeding on small roots in late summer, working their way up to larger roots as they grow. In autumn, they burrow down farther into the soil where they remain until the soil warms in the spring.

Nematode Application

Lawn and landscaped areas should be watered often for several weeks after nematode application.

Treatment with entomopathogenic nematodes should take place in late summer just as the grubs are hatching. Late August and early September is the best time for nematode application in most areas. The nematodes kill the newly hatched grubs until the weather begins to cool. They burrow into the soil in the fall and awake from dormancy in the spring as the soil warms. The nematodes resume feeding on any remaining grubs from the previous season. The lawn and landscaped areas must be well-watered before and after Entomopathogenic nematodes are applied. They cannot move around and work their way into the soil without moisture. Follow the supplier's application recommendations carefully. Inappropriate application or lack of water will render them useless.

Grub-Killing Nematode Species

Heterorhabditis megidis and Steinernema kraussei nematodes are effective at killing black vine weevil grubs. Heterorhabditis megidis nematodes are effective in soil temperatures of 53 degrees F and above, while Steinernema kraussei nematodes are effective in soil temperatures down to 41 degrees F. Steinernema scarabaei nematodes were studied in a three-year project at Rutgers University to determine their effectiveness in the control of the white grub larvae with good results. "S. scarabaei is highly effective as a curative white grub control," reports Albrecht M. Koppenhofer, Ph.D., Specialist in Turfgrass Entomology at Rutgers.

References

• University of Illinois Extension; Root-Knot Nematodes; March 1993
• Cornell University Department of Entomology; Nematodes; David I. Shapiro-Iian
• University of Connecticut IPM; Control of White Grubs; Dana Karpowich & Tim Abbey
• Global Horticultural Inc.: (Black) Vine Weevil
• Missouri Botanical Garden: Kemper Center For Home Gardening: Taxus x Media 'Gwen' (Yew)
• American Rhododendron Society; Practical Black Vine Weevil Management; Richard S. Cowles