July 1998

What's Bugging You From Last Summer

David M. Kopec, Extension Turfgrass Specialist

Last summer was an awful season for white grubs on turf. These are the larvae of certain kinds of scarab beetles which lay their eggs as adults on the turf in June, and then die on your porch. The hungry young larvae are what cause the damage to the turf. They chomp away at the roots and severely thin the turf. The turf has no capacity to go more than one day without water. In some cases, it's worse than that!

How can you tell if you have them in turf on the golf course? The turf will have patches that appear thin and are yellow in color. The turf will peel up in some places and you will find the grubs. White grubs have six legs and outside jaws for biting on the roots. If you find more than three grubs in a square foot area, you may want to treat. If you are out in the country, the javelina will find them for you. They root where there is food. They "got a nose for that stuff" better than Jimmy Durante did! At this time, you need to apply an insecticide labeled for grubs as soon as possible. However, you should determine that the patches are not being caused by poor irrigation patterns. If your irrigation is okay, there is usually some turf still alive and the soil is moist.

In late May and early June, the adults fly around at night looking for Mr. or Mrs. Right! Their purpose is to copulate, so that the female can lay eggs in the turf. The eggs hatch and the tiny larvae start eating away. They grow rapidly and get big. One way to estimate if the population may be severe is to use bug lights (trap lights) and see how many adults you can catch each night. Or simply sit outside at night and see how many there are (relative from week to week). About four weeks after the peak of adult activity occurs (when you see the most adults at night), treat the turf with an "active" insecticide. Most of the egg laying has been done and the larvae are small and most susceptible to control at this point. "Traditional" insecticides for turf (ex., Oftanol, Dursban, etc.), are most active when you first apply them. The insecticide "Merit" is systemic and moves to the root, therefore, it should be applied about 3-4 weeks when the most damage is expected. When using this product, apply it one week after you see 3-5 adults at the light, at night. You can supplement chemical control agents as well.

If you treat early in the spring, last years larvae are more mature, and less responsive to the insecticide. At this point, they change into adults, leave the lawn, and start flying ....and its "Prom Night" for 7-10 days. As a general rule of thumb, it's best to treat in the beginning of August.

Companies are looking to develop natural products which will control grubs. So far BT strains are not commercially available that control these specific types of insects. Insect growth regulators are being looked at hot and heavy. They will probably be available some day soon.

--Products listed are not intended for endorsement, nor is exclusion of other or similar products intentional. Products are used for purposes of example only. Always read the label.-- 

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