APRIL
1990

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

04-13-90

Here a Grubworm, There a Grubworm

Editor's Note: In the fourth paragraph, the reference to "Junebugs” is correct as is, even though it may not match your dictionary.  Scientifically speaking, since a Junebug is NOT a true bug, the words “June” and “bug” are combined into one word.  Most dictionaries list this reference as two words.  A future column will address this subject in more details.  

Most lawn owners and home gardeners are eternal optimists, at least in the springtime.  During the first warm days of spring, these creatures emerge from their domiciles armed with rakes, spray cans and fertilizer bags.  With the accumulated energy of winter relentlessly driving these people onward, they prepare to battle Mother Nature over the appearance of a bit of real estate called the lawn.  The eternal springtime dream of an insect-free lawn is quickly shattered through the specter of a grubworm infestation.

Grubworms, sometimes just called white grubs, are the scourge of the green-lawn enthusiast.  The insects are the larvae of beetles known as Junebugs or May beetles.  Japanese beetle larvae are also called white grubs.

These insects deserve to be called grubs.  They spend their life underground grubbing around for food.  Some, including an insect called the masked chafer and the Japanese beetle, spend only one year in the larval, or grub, stage.  Other grubs may spend two to three years underground.

Grubs feed on plant roots, especially the roots on grasses, such as those found in lawns.  Most feeding occurs during the warm months of the year.  During cold or dry periods, the grubs burrow deeper in the soil and stay there until the soil returns to desirable temperatures or moisture.

Grub feeding does horrible things to the grass plant.  They deprive the plant of its ability to produce water and nutrients, so it dies.  This, of course, results in brown spots in the lawn.

Neighbors have the uncanny ability to notice grub-induced brown spots in lawns and immediately begin to talk:  “Guess who has the grubs?”   Of course, the social disgrace of having grubs is more than most lawn owners can take, so they do what they can to solve the problem.

Where there are grubs, there are also grub eaters.  Moles, blackbirds and skunks are grub eaters of the first order.

While moles and skunks can rid a lawn of grubs, the solution might be worse than the problem.  Indeed, no one is certain how many skunks per lawn it takes to eliminate white grubs.  In addition, this control method carries with it the risk of exceeding the clean air standards for some cities.

Insecticides are useful tools in dealing with grubs.  But applications need to be properly timed, which is tricky.  Also, the use of insecticides carries with it some environmental hazard.

There are other methods.  Some folks have tried walking around on the lawn with spiked shoe, lawn “aerators” attempting to spike the grubs.  No one is sure if this method is effective, but it gives the owner satisfaction of having gotten even with at least one grubworm.

 

Writer: Tom Turpin
Editor: Carol McGrew