Billbugs – Our #2 Lawn Insect

The lawn looks “splotchy brown”…what could it causing it?  As you think through all of the possibilities, you are probably also thinking about what you’ve done and haven’t done this year in terms of yard care – fertilizer applications, keeping the turf roots moist, weed control, 3 inch mowing height, sharpened the mower blade – but what about bugs?

Well, the #1 bug, the white grub, isn’t set to damage the turf roots until mid to late August, and the preventative application for them is mid-July to late July, so it probably isn’t white grubs.  So, if not watering woes or white grubs, what could be the cause?  Probably 3 causes, somewhat interrelated:

  1. Billbugs.  Billbugs are weevils (actually pretty cool looking bugs, jet black with a long snout), about a quarter to half inch long.  They don’t fly, just hang out and feed on the stems of the turf plants.  If you look closely with a magnifying glass, you might not see the actual critter, but you will see a hollowed out stem and sawdust-like left behind material aka “frass”.  The adult weevils are present in mid-May; they lay eggs which hatch out over the next few weeks and begin feeding inside the stems.  The feeding larval stage resembles a small white grub larvae without legs.  There are 2 ways of controlling them; applying carbaryl (Sevin) insecticide in mid May to kill the adults or imidacloprid (Merit) acelepryn (Scotts Grub Ex) insecticide at the same time to kill the larvae as they begin feeding.  Read and follow all label directions.  Since they habituate in the thatch layer, it’s important to apply about ¼ inch of water to wash the product off of the leaves into the thatch and upper soil layer.
  2. Excessive Thatch.  Since the thatch layer is where the billbugs hang out, removing excessive thatch may improve the efficacy of the insecticide treatments, and improve rooting of the turf plants.  Take care when removing thatch, because many good turf plants may be removed along with the excessive thatch.  This is best done in late August, followed by overseeding.
  3. Summer Patch, a fungal disease.  Billbugs cause spotty damage in the lawn, while summer patch causes dead patches that are 1 to 5 feet in diameter.  If you lawn has both maladies, it can be tough to determine which is more influential.  Summer patch can be prevented or at least lessened by applying azoxystrobin, myclobutanil or propaconizole in mid-April and early May.  It’s important to read and follow all label directions, particularly watering following application with a half inch to a full inch of water following the application.
John Fech
Horticulture Extension Educator at Nebraska Extension
John Fech is a horticulturist with the University of Nebraska-Lincoln and certified arborist with the International Society of Arboriculture. The author of 2 books and over 200 popular and trade journal articles, he focuses his time on teaching effective landscape maintenance techniques, water conservation, diagnosing turf and ornamental problems and encouraging effective bilingual communication in the green industry. He works extensively with the media to extend the message of landscape sustainability, making over 100 television and radio appearances each year.
John Fech on EmailJohn Fech on Twitter

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.