UF/IFAS Okeechobee County Extension Service

458 Highway 98 North

Okeechobee, FL 34972-2578

Phone: (863) 763-6469

E- mail:  dfculbert@ifas.ufl.edu

March 29, 2006

Feature Article - for release the week of April 2, 2006

Dan Culbert - Extension Horticulture Agent  

 Got Spots?  You may have Grubs!

One of the most impressive creatures found in our Florida Yards is the Ox Beetle.  Our office is often asked to identify this one and one-half inch long dark brown beetle with one or three long horns on the front of its body.  And usually the next question asked is, does it hurt my plants?

While the majority of insects found in and around the home don’t cause significant problems to our yards, this beetle larva can cause damage to the lawn.  Turf damage begins as temperatures warm in the spring, and if they are a problem, management should begin now.

Many beetle larvae are found among grass roots.  Beetles lay eggs on the soil surface in late summer.  A low mound of soil with a hole on the end shows where the female lays her eggs.  As eggs hatch and burrow through the soil, they feeding on plant roots and grow into one to 3-inch sized white grubs.

Florida White Grubs

Several species of white grubs damage grass including the May or June beetles (Phyllophaga sp.),  masked chafers (Cyclocephala sp.), and the Ox Beetle (Strategus sp.). White grubs are, well, white, but on closer inspection their heads are brown and the rear of the abdomen is dark area. Grubs have three pairs of small legs near the head, and curl up at rest in a C-shaped position.

Between one and four years is required to for grubs complete their life cycle, and in certain years heavier infestations occur. Adult beetles do not damage grass but usually feed on flowers and foliage or ornamental plants upon emergence in the spring. 

Young landscape plants or tree seedlings are also chewed up by white grubs.  In turf areas, yellowish areas are an indicator that grass is being chewed.   In severe cases grass roots are eaten so much that a mat can be rolled back like a carpet.  If grass wilts in an area of the turf even though adequate water is available, an infestation of root-feeding grubs should be considered.

Grubs damage the grass by feeding on the roots about an inch below the soil surface.  Their feeding causes the grass to turn yellow and then brown.  The damage may first appear as spots only a few inches in diameter, but these spots will gradually become larger as feeding continues.  Heavy infestations completely destroy the roots, and the grass can be rolled back like a carpet.

Moles, skunks and armadillos feed on the grubs.  Unfortunately, they may damage the lawns or ornamental plants while searching for these insects.  To discourage their rooting activities of these forms of wildlife, best management recommendations call for the control of grubs.

To inspect for grubs, cut three sides of a one-foot piece of sod, two-inches deep with a flat spade under the grass, and lay it back.  See if the grass roots are chewed off and sift through the soil looking for these white larvae.  Replace that strip of sod, and inspect other areas in the lawn, especially those with yellowing spots.  If two or three grubs are found per square foot, use of an approved insecticide is suggested.

While there are wasps known to parasitize grubs, none of these wasps are widely available on a commercial basis.  Other grubs are being managed by bacterial-based products, but these are expensive and difficult for most homeowners to apply for grub management.

Other factors can cause off color areas in lawns, such as chinch bugs, turf diseases, sprinkler malfunctions, or fertilizer problems.  Good landscape managers must determine what the cause of the problem before corrective measures are taken.  And if an infested turf area is being converted into a vegetable garden, avoid planting root-type crops, a favorite food of grubs.

Grub Management

To help prevent contamination and reduce the destruction of beneficial insects, spot treatments can be applied when damage is first noticed and areas are small.  Treat the off-color areas and the surrounding 10-foot areas.  If damage is widespread, the entire yard should be treated.  After treatment, inspect the area two to three different times twice a week to determine if infestation is under control.

University of Florida recommendations for white grub insecticides change over time; check with our office for the latest information.  Some products are only available to lawn care professionals who must have a license to apply them to your yard. They should be applied carefully as directed on the container's label. Read and understand all directions regarding dosage rates, application information, and precautions. 

Granular insecticides and liquid concentrates are used to manage white grubs. Besides traditional compressed air sprayers, hose-end applicators are popular homeowner equipment for many grub insecticides.  Those that use 15 to 20 gallons of water passing through the hose to empty a quart sized jar are appropriate kinds of applicators.  Put the amount of insecticide in the jar as directed on the label for 1000 square feet.  Fill the remainder of the jar with water.  Spray the contents over 1000 square feet.  To insure even coverage, spray back and forth across the same area.

When spraying for control of white grubs, the turf should be moist at the time of application.  Immediately after spraying the insecticide, product labels will usually require that the turf be irrigated with a half-inch of water.  This will soak the insecticide into the soil where the insects are feeding.   

Use Insecticides Safely

Insecticides are poisons and should be handled as such.  Read the manufacturer's label carefully before opening the container and observe all instructions and precautions.  Wear rubber gloves when handling and applying insecticides.  Do not breathe mists or fumes or spill sprays on the skin.  Wash exposed parts of the body immediately after using insecticides.  Store pesticides under lock in original containers out of reach of children.  Rinse empties and put rinse water in the sprayer.  Dispose of empty containers (one gallon or smaller) by wrapping in newspaper, crush or puncture them to prevent reuse, and put in garbage can for disposal in an approved sanitary landfill.

I’ve placed more information on our Okeechobee web page, http://okeechobee.ifas.ufl.edu.  If you need additional information on white grubs, please email us at okeechobee@ifas.ufl.edu or call us at 863-763-6469.   Local residents can stop by our office at 458 Hwy 98 North in Okeechobee, and visit our Okeechobee County Master Gardeners from 1 to 5 PM on Tuesday afternoons.  

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Trade names, where used, are given for the purpose of providing specific information. They do not constitute an endorsement or guarantee of products named, nor does it imply criticism of products not named. The Florida Cooperative Extension Service - Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information, and other services to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin.  Florida Cooperative Extension Service / IFAS / University of Florida.  Larry A.  Arrington, Dean Last update: 04/04/2006 .  This page is maintained by Dan Culbert 

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