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John Fulton

John Fulton
Former County Extension Director

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In The Backyard

Horticulture columns and tips done on a timely basis

Grub Check

Posted by John Fulton -

The first indicator of grub numbers to come is the number of adults. Right now we are starting to have the June bugs out and laying eggs. There are actually three types of grubs that can be found in turf areas. These would be larvae of the Japanese beetle, the June bug, and the green June bug. All of these insects cycle annually, and the green June bug is not really a turf pest, but rather is found in areas with high organic matter such as compost piles and flower beds.

Don't pull the trigger and treat for grubs at this time. We are about a month early. I usually say to treat at Logan County Fair Time. I know that the insects don't know what time it is, but people do. By timing treatments around the fair, it provides an easily remembered "marker" for us. Most publications indicate early August as the time to assess grub numbers and apply treatments if warranted. Most turfs in good condition can stand 8 or so grubs per square foot without damage becoming noticeable.

Looking at adult numbers right now just gives us a very rough idea of how many adults there are to lay eggs. By waiting another month, we give the eggs time to hatch to a stage where they can be counted and controls would be effective. Many controls are not timed at "first sight" but rather at "complete hatch." Controls applied when the first actual grub is seen can be a month or so ahead of the last egg hatching. In this case we want to allow for a complete hatch to assess numbers and, if needed, apply one grub control treatment. Even the early-apply products should be applied close to this August time period. A good example is the product Oftanol. It was promoted at first as a product that could be applied in May for grub control. It worked well a few seasons and then the microbes that break the chemical down began to build up to the point where it also had to be applied in the August time frame.

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