American Nurseryman Magazine - Horticulture Magazine and Horticulture Books - Grub infestations lure skunks and raccoonsleading - October, 2012 - DEPARTMENTS

American Nurseryman Magazine - Horticulture Magazine and Horticulture Books - October, 2012

DEPARTMENTS

Plant Health: Grub infestations lure skunks and raccoonsleading

Ah, autumn. The sizzling summer temperatures have eased, windows are thrown open and as evening falls, there's a gentle breeze that delivers a crisp hint of fall - and skunk.

There are many reasons for skunks - and their partners in crime, the wily raccoons - to be lurking, especially around this time of year when they're eager to fatten up before winter. They're omnivorous, eating practically anything that looks good at the moment, but they're particularly fond of grubs that have taken up residence just below the surface of the lawn. And with this year's unusually high white grub activity, it's no wonder these fuzzy little beasts are busy.


the extensive turf damage seen here was caused not by a small rototiller, but by Japanese beetle grubs.
M.G. Klein, USDA Agricultural Research Service; Bugwood.org

So if you're getting calls about ragged turf or skunk visits, chances are your clients' lawns are riddled with grubs. These larvae are among the most destructive of lawn pests, feeding below the surface on the roots and rhizomes of nearly all commonly grown turfgrass species and cultivars. Left untreated, they're capable of destroying the entire root system and devastating large areas of turf in a very short time.


Skunks have been frequent visitors to lawns across the country as a bumper crop of white grubs has developed.
Alfred Viola, Northeastern University; Bugwood.org

It appears this year's wacky summer weather may have contributed to a population explosion. In many areas, adults emerged earlier than usual last spring, leading to a healthy crop of pests and a longer season of destruction. A drought-stressed lawn is vulnerable, and although egg-laying females are generally attracted to well-watered turf, they'll procreate where they can. Once eggs have hatched, the grubs will feed on the roots no matter the soil condition.


Depicted here are three species of larvae among the pest complex called "white grubs." From the left: Japanese beetle (Popillia japonica); European chafer (Amphimallon majalis); and June bug (Phyllophaga sp.). All feed beneath the surface of the lawn, destroying roots and attracting skunks.
David Cappaert, Michigan State University Bugwood.org

According to Dr. Pat Vittum, turf entomology specialist at the University of Massachusetts, Amherst, egg-laying activity probably occurred as normal from mid-July through mid-August in New England states in areas that were irrigated. However, egg-laying likely was delayed in nonirrigated areas, thus delaying the development of grubs and producing an increased crop of pests that are smaller than usual. They may be small, but they're still hungry.

It's too late for white grub control by preventive means, although elimination of the current crop of grubs may forestall problems next year. There are several options for chemical control, including trichlorfon or chlorantroniliprole, which should kill grubs in less than a week. Trichlorfon is said to be the "fastest acting curative material available" to landscape professionals, according to Vittum. But because the formulation is highly soluble, it carries hefty restrictions in many areas. It's also sensitive to water with high pH.


Adorable, no? Along with their skunk friends, raccoons have an appetite for grubs, and increased raccoon activity may indicate an infestation.
Kevin D. Arvin; Bugwood.org

A few years ago, Vittum and her colleagues tested the efficacy of the neonicotinoids chlothianidin, imidacloprid and thiamethoxam - as well as trichlorfon - on an active grub population, applying the chemicals in mid-September. After nine days, only the trichlorfon had reduced the grub population (compared to an untreated area). However, at about 30 days following application, all of the neonicotinoids had made a difference. Imidacloprid was said to be less effective than chlothiaidin and thiamethoxam, but grub numbers nevertheless were reduced. Vittum's conclusion? Both chlothiaidin and thiamethoxam can reduce grub populations within 10 to 30 days following application.

Let's give a shout out to our four-footed friends. Yes, they can be destructive, but they're also alerting us to a greater threat. Get rid of the grubs, and we'll send the skunks and raccoons packing.