Grub control options

By John Fulton

[August 18, 2008]  We have discussed the timing of grub control treatments in past columns. As a reminder, the date would have been early August for annual white grubs. We are now approaching treatment for grubs coming from the Japanese beetles. Knowing when to treat grubs is one thing, and knowing what product to use is another.

Many grub control treatments are combined with fertilizer products, and this is the appropriate time to apply a fall fertilizer treatment. It seems each year provides more "stand-alone" treatment options as well. Diazinon used to be the product of choice for many homeowners, but the cancellation of home horticulture uses of the product created confusion in selecting a product. The other wild card was that the use of diazinon helped eliminate mole problems (by driving them to the neighbor's yard) since the product killed grubs and reduced earthworm populations. Many of the products currently used do not affect earthworm populations, and on the whole that is a good thing since earthworms greatly benefit lawns. There are now some "soft baits" available for mole control that are effective.

Current recommended products include halofenozide (Mach 2), Heterorhabditis bacteriophora (Cruiser), imidacloprid (Merit) and trichlorfon (Dylox). Many of the chemicals have other brand names in addition to the ones listed in parenthesis. It is also recommended to drench treated areas with a half-inch of water within 30 minutes of application, and this is especially important with liquid applications. Application just ahead of a rain is usually best. Granular applications buy a few days of time but still need to be watered into the root zone where grubs are active. The products with Merit will take three weeks or so to activate. Some reputable sources also list carbaryl (Sevin) granules as an option for grubs from green June bugs and Japanese beetles. Carbaryl does reduce earthworm populations to some degree.

In good growing seasons, it normally takes at least 10 grubs per square foot of lawn area to justify treatment. In less favorable seasons, this number can be reduced to six to eight grubs per square foot. As your gasoline bill for the lawn mower can attest, this has been a good growing season to date.

Consider many factors when selecting a product. These would include combination with fertilizer, effectiveness, species controlled, cost and the effect on the environment. The Cruiser product is actually a nematode and would be the most environmentally safe. It also costs about $55 to treat about 3,000 square foot of lawn. The other organic product sometimes mentioned for control of the Japanese beetle grubs is milky spore. This product is a bacteria that takes several years to become very effective and can cost around $35 for 2,500 square feet of lawn. You can't apply any other controls with milky spore since you need high populations of grubs to increase the bacteria populations to high levels and provide transmission between grubs.

Good luck as you decide your attack plans against grubs. The choices are many, and the attainment of the "perfect" lawn is a goal many strive for. Remember, you can live with some grubs. However, too many can be devastating to a lawn. With Japanese beetle populations at very high levels in many areas, odds are great there will be grubs to battle.

[By JOHN FULTON, University of Illinois Extension, Logan County]