Lawn damage from grubs
I feel your frustration. It took us a couple of years of better pasture/lawn management, but we seem to have significantly reduced our grub population without the use of chemicals. Albeit, with a little help from our friendly neighborhood skunk. Here’s the information you requested and some additional information to keep you headed in the right direction:
How to know you’ve got a Grub Problem
Grubs feed on the roots of grasses, so lawns will show wilting and browning in an irregular area. Lawns can brown for other reasons so it’s best to check the roots of the affected area(s) and locate the c-shaped grubs. Carefully pull back your sod in an area where you suspect they are located, in particular the marginal areas where brown grass meets green, and look for the grubs. Usually a population of about 10 or more grubs per square foot will contribute to your lawn browning. Skunks (and perhaps even raccoons) will dig up and damage your lawn in grub infested areas looking for a free meal. A skunk will usually stop in for a quick meal after dark and dig up areas of the lawn in search of the grubs. Moles are not a reliable indicator of grub problems.
Once you have a few of those grubs in hand, you’ll be able to identify them with a magnifying glass and the key found at the Ohio State University Extension website at: http://ohioline.osu.edu/factsheet/hyg-2510
Grub management should include cultural practices but can also include biological and chemical control strategies. Unfortunately, there are no known turfgrass species or cultivars resistant to white grubs; however, Kentucky bluegrass and Creeping Bentgrass can fill in thin spots caused by the damage. Although not resistant, drought tolerant grasses such as fine fescues and tall fescue and perennial ryegrass may recover more quickly.
Good cultural practices such as adequate irrigation and fertilization can also help offset grub damage. Actively growing turf with healthy roots has been shown to tolerate populations up to 50% higher than recommended thresholds without showing damage.
· Fall fertilization can help with recovery of grub damage.
· High nitrogen applications in the spring will encourage shoot growth at the expense of root development which can make the turf more susceptible to spring and summer grub damage.
Biological Control of Grubs
There are at least three biological control agents commercially available for white grubs in turf: (entomopathogenic) nematodes, (entomopathogenic) fungi, and the milky spore disease bacteria.
These alternatives have relatively poor or inconsistent results in the field. However, there may be situations where a turf manager wants to try a biological due to insecticide restrictions. When purchasing these products it is important to be assured that they be handled in an appropriate manner and that you carefully follow all the directions during and after application.
Spring treatment are not recommended. Usually, the grubs are large enough to be tolerant of insecticides. If you plan to use chemical controls later in the season, refer to the following link “Identifying and Managing White Grubs in Turf” by Sid Bosworth, Extension Agronomist, UVM
Thanks to S. Bosworth, Extension Agronomist, UVM, the University of Illinois Extension, and Ohio State University Extension for their expertise.
Hope you find this helpful!
UVM Extension Master Gardener Program Volunteer