White Grubs

Picture of one of our Greenbug Education Program cards that participating retailers are providing in their stores
One of the cards in our Greenbug Education Program. These and other cards are available in participating retailer’s stores.

White grubs are the white, soft-bodied larvae of several scarab beetle species, including European chafer, Japanese beetle, May/June beetles, Asiatic garden beetle, and Oriental Beetle.  They have a brown head and six well-developed legs.  When the turf is lifted and grubs are exposed, they tend to be lying on their sides in a C-shaped position.  From May through early June, white grubs pupate 2 – 5″ deep in the soil.  Adults emerge from pupae a few weeks later.  Signs of white grub damage include wilting or yellowing of grass and can result in large patches of dead or dying turf.

Life Cycle:
The adult beetle lays its eggs in the ground during the summer.  As the grubs hatch, they start feeding on the roots until cold weather drives them 2 to 8 inches deeper into the soil where they overwinter.  When Spring arrives, the grubs move up from the lower soil regions and resume feeding near the surface until they become mature and pupate from May through early June.

Management [Read & Follow All Pesticide Label Directions!]:
Curative controls are applied when the grubs are present.  Common curatives include carbaryl, which is not consistently effective, and trichlorfon.  Trichlorfon has to be applied by a licensed professional and kills, at best, 50% of the mature grubs and does not protect the lawn from the next generation of grubs.

Preventive controls target the next generation of grubs.  Most preventives are applied in June just prior to or when the target species are in the adult stage mating and laying eggs (e.g. imidacloprid, chlothianidin, and thiamethoxam).  This gives the material time to get incorporated into the feeding area.  Chlorantraniliprole needs to be applied in May well before adult flights because it needs more time to become incorporated into the plants.

Organic options include beneficial nematodes or simply letting crows, skunks and raccoons dig up the grubs and replanting grass.  Beneficial nematodes of the Hb variety (applied during the last week of August) are relatively effective compared to other available nematode varieties.  Nematodes should be used on low-value turf because their effectiveness can be spotty. [Authors: Griffin M. Dill, IPM Professional, Clay A. Kirby, Insect Diagnostician, and James F. Dill, Pest Management Specialist.  May 2012.]

Additional Information:

Here is a list of Maine’s most common beetle grubs (Family Scarabidae) that are collectively referred to as ‘White Grubs’: