Garden Thyme: Grub Worms

This month we will focus on an often-overlooked pest in your lawn, the June Bug, or its larvae, the grub worm. I print this article every year at this time because for you to get good grub control, timing of the chemical application is critical.

White grub damage can be detected by the presence of irregular shaped areas of weakened or dying grass in the lawn. Damage may appear any time between the months of June and October. Turfgrass damaged by white grubs has a reduced root system and is easily pulled from the soil. At least one turfgrass disease, Take-all Patch, can sometimes be mistaken for white grub damage.

To confirm whether you need to treat for grubs, examine several soil sections at least 3 to 4 inches across and 4 inches deep (sample sandy soils to greater depths). A good rule of thumb is to examine several soil plugs (up to one square foot per 1,000 square feet of turf) from widely scattered parts of the lawn. Take care to include areas at the edges of suspected grub damage. Finding more than five white grubs per square foot justifies treatment, although some lawns with even higher numbers of grubs may show no damage.

Chemical control

Proper timing and chemical application are critical to suppressing white grubs. New white grub insecticides are more persistent and less toxic to beneficial arthropods and earthworms. However, these treatments must be applied early enough to kill the smaller (less than 1/2-inch long) larvae. Once white grubs reach the third-instar life stage, they are more difficult to control. Around here the best time to apply grub control products is mid to late June.

Post-treatment irrigation is essential for all grub control products. Irrigate granular formulations within 24 hours to wash the insecticide into the soil and minimize the chance for exposure to people, pets and wildlife. Two or more irrigation applications may be needed if the soil is wet or difficult to penetrate. For dry soils, apply 1/4 to 1/2 inch of water the day before a treatment to improve penetration of the soil and to encourage white grubs to move closer to the soil surface. This makes grubs easier to contact with the insecticide treatment.

Environmental Considerations

Unnecessary insecticide applications sometimes create more problems than they solve. Pesticides can have detrimental effects on beneficial organisms, like earthworms, that help decompose thatch. Most insecticides do not discriminate between “good” and “bad” bugs and may kill beneficial insects that help control other pests. Also, unnecessary pesticide applications can increase the risk of insecticide resistance developing among white grub and other pest populations. For these reasons, routine, “preventative” insecticide applications to lawns for white grub control are not recommended.

Heavy rainfall can wash recently applied pesticides out of lawns, especially if the ground is saturated with water when the treatment is applied. Avoid treating lawns just before a heavy rain is expected. Also try to avoid application of pesticides to street gutters and sidewalks. Drop-type spreaders are less likely to scatter pesticide granules off of the target site than are rotary-type spreaders. Pesticide runoff from improper pesticide applications reduces the effectiveness of a treatment and can pollute above-ground and underground water supplies.

Organic Tip

I had a customer tell me about a great organic approach to control grubs in your lawn. Once the grubs turn to the June Bug beetle they start flying around and within a few weeks they return to the soil to lay their eggs. The customer said that what you do is place a bucket with some soapy water under whatever lights you have on at night around your home. The beetles will fall into the bucket and will not be able to fly out. What a clever idea?

A Garden To Do List for the month of June for our area will include the following:

  • Be watching for chinch bug damage that usually starts in your grass adjacent to concrete walks and drives.
  • Look out for spider mite damage on things like junipers once it starts getting hot.
  • Now is a good time to plant vinca and portulaca. These are great heat lovers and easy to take care of summer annuals.
  • Any of your roses that are prone to black spot should be treated on a bi-weekly basis with a product like Bonide Infuse. Don’t wait until the black spot occurs before treating. Once black spots form they will not go away.
  • If you haven’t already done so, re-mulch your trees and shrubs with a good quality mulch like Landscapers Pride Black Velvet mulch or pine bark mulch.
  • Check your herbs and veggies on a regular basis for any damaging insects.
  • Be on the lookout for whiteflies, mealy bugs and aphids. These can damage your investment in plants.
  • Be alert for slug and snail damage. Come by the Growers Outlet and pick up the correct products to use. We carry a great effective organic product that is safe for people and pets.
  • If you have any stubborn broadleaf weeds you can spray them with Bonide Weed Beater for Southern Lawns now that temps are well above 80.
  • If you are ready to apply your second application of lawn fertilizer use Microlife 6-2-4 organic fertilizer, Nitro Phos SuperTurf or Nitro Phos Sweet Green before the end of June.

For great gardening products and information, come by the Growers Outlet and visit with any member of our team to get the help you need or go to our website at We have the products and knowledge to help you have the prettiest yard on the block.