Ortho Weed Finder

Grubs:
To determine whether or not there is a significant number of grubs to warrant control practices, remove a square section of lawn 6 inches by 6 inches and 4 inches deep. Turn the section of lawn unto a flat surface, use a trowel to break up the soil, and place any grubs you find in a cup. A healthly lawn can usually tolerate 8 to10 grubs per square foot without showing signs of distress.
Most conveniently turf/soil plugs are sampled with a standard golf course hole cutter (4.25" diam ~ 0.1 ft2).
Damage thresholds vary considerably with grass species, management type, and climatic conditions. The better maintained the turf and the more extensive the root system, the higher are the damage thresholds.
Among the coolseason grasses, tall fescue is the most grub tolerant species whereas perennial rye grass is the least tolerant.
If a lawn is being dug up by skunks, raccoons, or crows, particularly in March through May or in September or October, or if moles are creating a network of tunnels under the grass, it is likely that the lawn has a significant population of grubs which the animals are feeding on.

Due to the White Grubs' (WGs) tunneling activity, infested turf feels spongy underfoot and can be pulled up like a carpet, exposing the C-shaped WG.
If soil sampling has revealed high WG populations, treatment may be necessary. This curative control approach works best if applied while the grubs are still smaller (i.e., mid August to early September). Once the grubs have reached the 3rd larval stage, they are much harder to control.
Spring applications (late April through May) are generally the least effective and rarely justified because the grass can outgrow most grub populations.

Chemical control - curative:
Insecticides available for curative WG control include the organophosphates trichlorfon (Dylox(R), Advanced Lawn 24 Hour Grub Control), diazinon (Diazinon(R); not for golf courses, sod farms, turf areas > 1 A), and chlorpyrifos (Dursban(R); only on sodfarms), and the carbamate carbaryl (Sevin(R)). For late applications and thatchy lawns, trichlorfon is the usually the best choice.

Chemical control - preventive:

Advanced Lawn Season-Long Grub Control) and the molt-accelerating compound halofenozide (MACH 2(R), GrubEX). Due to their long residual, imidacloprid and halofenozide can be applied as early as May and June, respectively. If applied that early, various other insect pests may also be controlled (billbugs, annual bluegrass weevil, greenbugs; halofenozide also cutworms, sod webworms).
If WG are the primary targets, the optimal application time for imidacloprid and halofenozide is June/July when the female beetles are laying eggs. As the larvae grow, they become less susceptible to these insecticides.
Scott's GrubEX and Bayer Advanced Lawn season-Long Grub Control will contol grubs without killing beneficial earthworms.

Biological control:
Presently available products containing the insect parasitic nematode species Heterorhabditis bacteriophora (e.g. HeteromaskTM, GrubstakeTM Hb), Heterorhabditis megidis (e.g. Nemasys(R)H, GrubstakeTM Hm), or Steinernema glaseri can provide very good control of Japanese beetle, but are not effective against oriental beetle, Asiatic garden beetle, or European chafer grubs.

Links:
Weed Control
Japanese Stiltgrass
Grubs at massaudubon.org
An Integrated Approach to Insect Management in Turfgrass: White Grubs, Rutgers Cooperative Research and Extension Fact Sheet (FS1009) at somerset.nj.us


last updated 26 June 2006