Q: I was wondering about grubs because my neighbor said his yard had lots of grubs last fall. When should we start to treat them?
A: How bad were the grubs in his lawn last year? Most people are caught up in the craze of killing every grub, when, in fact, most grubs do very little harm.
Almost every yard has grubs year-round. In our lawns, there are more than a half dozen species of beetles that have a grub stage in their life cycle, plus there are cicada larvae and other insects, too. They are found in lawns and flower beds. Most do very little harm, and until there are enough of them in one location, there is no need to use chemical controls. University research shared with Master Gardeners at Oregon State University says that 10 grub larvae per square foot of lawn is necessary before treatments are economical. Applying poisons to your yard when none are needed doesn’t make much sense.
In the spring, the grubs that were in the soil last fall will move closer to the soil surface from their overwintering location that was down a foot or two in the soil. They feed a little on grass roots, but rarely enough to cause enough damage to the grass. After a few weeks of feeding when the weather warms the soil, they will pupate and, depending on what kind of insect they are, become adults in the spring or summer. Lawn chemicals don’t work well on the pupa or adults. Adults fly around for miles, so killing spring grubs in your yard will not affect how many beetles will fly in from elsewhere to lay eggs for the fall portion of the life cycle.
There are chemicals sold in the spring that say they give season-long grub control. For most people’s lawns, that just means there is a season of unnecessary chemicals on their lawn.
The adult female beetles prefer to lay their eggs on lawns that are irrigated and not under trees. If you let your lawn dry out and go dormant, or if it is covered by the shade of trees, there are usually not enough grubs to need chemical treatments. Female beetles want to give their babies lush green grass roots to eat, so besides saving water, dormant lawns have fewer grubs and less need for chemical treatments.
There is no relationship between the number of grubs in a lawn from one year to the next. A lot of grubs one year has no bearing on if the lawn should be chemically treated the next year. If a lot of adult beetles are noticed in July, then a treatment in August might be warranted, but it is better to wait until August to check for grubs before deciding to treat the lawn with poisons.
During wet summers, the eggs are laid so far apart in the grass that the grubs don’t do harm. During cool summers or very hot summers, grubs die from diseases and drying out, so treatment is normally not required.
Email questions to Jeff Rugg at firstname.lastname@example.org. To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at Creators.com. Copyright 2021 Jeff Rugg. Distributed by Creators Syndicate.