The Lowdown on Grubs

by Stephan Kelly, regional editor

The white grub, larval stage of the Curculionidae family of beetles, resides below the grass thatch and creates dead spots in turf.

White grubs are the larva of weevils, a Curculionidae family beetle that commonly attack the roots of turfgrasses and/or ornamental plants. White grubs grow up to become June beetle varieties, various chafer types, Japanese Beetles, Asiatic garden beetles, Oriental beetles, black turfgrass ataenius, et al.

This reminds me of my favorite story about Charles Darwin. As a youth he became infatuated with collecting beetles. One day while capturing a new beetle species for his collection he espied a beetle variety he?EUR??,,????'???d never seen. His dilemma was both hands were occupied. He solved the problem by putting one beetle in his mouth to allow him to collect the new victim.

You?EUR??,,????'???ll probably prefer not only not to place beetles in your mouth, but to eradicate the larva before they become ambulatory. Which reminds me of another true story. When explorers John Speake and Richard Francis Burton were looking for the source of the Nile, a beetle climbed in Speake?EUR??,,????'???s ear canal while he was sleeping. He could not extricate the vermin and the pain was excruciating. He ended up loosing hearing in the ear.

Examine Your Turf

The point is, you need to take care (cause the demise) of your grubs. White grubs are found near the soil surface and are identified by their three pairs of legs found close to the head of their 1-2 inch curled bodies. White grubs feed on grass, grass roots (can cause dead patches) and damage garden crops. The adults will also nibble on your pretty flowers.

Ray Bond¹ in ?EUR??,,????'??Japanese Beetles: Insect Terrorists?EUR??,,????'?? recommends the superintendent examines the grass closely to identify if there is root damage, otherwise the super may not notice a problem until the grass starts to die. The commercial application pesticide he recommends is Tempo 20 WP (cyfluthrin). White grub damage is usually most evident in August and September. Early symptoms include gradual thinning, yellowing, and weakening of the grass stand followed by the appearance of scattered, irregular dead patches.²

Grub damage on a soccer field. White grubs feed on grass and grass roots. Some insecticides (e.g., Merit .5G Systemic Insecticide Granules) contain an active ingredient that can give season long control of white grubs in a single application. It should be applied no sooner than mid-July and no later than early August, but check with your university extension to see if this schedule is different in your area. ?EUR??,,????'??Systemic?EUR??,,????'?? indicates that plant roots uptake the product. As pests feed on the plant, they ingest the insecticide.

David Shetlar³ at the Ohio State University Extension advises identifying which white grub species you have, as it will help determine a management strategy and timing for controls. This may be a good idea, in principle, but to I.D. the critters you will need, no kidding, a 10x hand lens, or even a microscope, so as to view their raster pattern?EUR??,,????'??+the arrangement of bristles and hairs on the underside of the tip of the abdomen. (Google ?EUR??,,????'??HYG-2510-94?EUR??,,????'?? for more info in this regard.)

June beetles, for instance, have a three year life-cycle. In June, the adult lays eggs in the soil and white grubs emerge within two weeks and feed during the warm months before overwintering deeper in the soil. Early the following summer, the grubs move close to the soil surface and begin feeding again. This second year is when they do the most damage. After a short feeding period during the third summer, the white grub pupates into adulthood, overwinters in the soil and lays eggs the following summer, thus completing its life cycle.⁴

June beetles have a three year life-cycle. In June, the adult lays eggs in the soil and white grubs emerge within two weeks and feed during the warm months before overwintering deeper in the soil. Many insecticides control the larval stage. Talstar, for instance, is a synthetic pyrethroid, a long lasting insecticide but with minimal toxicity to nontarget organisms. This liquid can also be sprayed on shrubs to control the adult beetles.

Science Steps In

Turf and ornamental science types are constantly coming up with new pesticides every year to handle your bug problems. For instance, in May 2005, Bayer Environmental Science (BES) received registration from the EPA for Allectus SC, a granular or liquid formulation to control of turf pests above and below the surface.⁵ Of course, the degree to which you have to deal with grubs and surface insects depends on your local. In the North the primary pest concern is grubs, with fluctuating surface insect problems. The opposite is true in the South.

According to BES, Allectus controls these white grubs and other insects:

This product was tested by more than 30 university cooperators. It combines two insecticide commonly used over the past decade?EUR??,,????'??+Merit (for grub control?EUR??,,????'??+from Bayer) and Talstar (general insect control of chinchbugs, sod webworms, cutworms, armyworms and more than 75 other pests?EUR??,,????'??+from FMC Corp.)

The SC formulation is labeled for both soil and foliar applications. For residential size properties, the product has 0.81 pounds of active ingredient per gallon; for large turf areas, the ratio is 0.63 pounds of active ingredient per gallon, but as always, refer to label for applications rates. The label says one application can provide up to 12 weeks of residual control.

And to think grubs are considered delectable in some countries! Let?EUR??,,????'???s see, I?EUR??,,????'???ll take one pound of grubs and two scorpions to go.

Biological Controls

Biological controls include some birds, such as European starlings, grackles and crows, that feed on grubs, though crows tend to pull up bits of turf when they feed on these juicy morsels. Raking the lawn exposes them to natural predators.

?EUR??,,????'??Bt?EUR??,,????'?? (Bacillus thuringiensis) is an effective biological control for Japanese beetle grubs (early fall) feeding near the surface. The Bt is applied to areas out of direct sun. Bacillus popilliae (milky spore) is also effective against Japanese beetle grubs. When the grub eats milky spore, its internal organs liquefy. The spore can remain in the soil for many years, although it may take several years for it to become effective. There are also parasitic nematodes which control white grubs, such as Heterorhabditis bacteriophora, available at garden centers.⁶

A Healthy Lawn

A healthy lawn is the best protection against white grubs. A well-watered, fertilized, aerated lawn will provide resistance against white grub attack. Good root growth is helpful as the adults prefer to lay their eggs in thin grass. If the lawn is not established or if it is being reseeded, choose a resistant grass variety, such as an endophytic grass which contains a fungus that repels white grubs. Planting geraniums in your garden will also repel white grubs.

1. Ray Bond ?EUR??,,????'??? ?EUR??,,????'??Japanese Beetles: Insect Terrorists?EUR??,,????'??
2. Michael Potter and Daniel Potter ?EUR??,,????'??? ?EUR??,,????'??Controlling White Grubs in Turfgrass?EUR??,,????'??
3. Ohio State University Extension
4. ?EUR??,,????'??Bayer Environmental Science Receives Registration on Allectus SC?EUR??,,????'??
5. The Green Lane (Environment Canada’s website)
6. University of Illinois Extension