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John Reitman

By John Reitman

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Some grub behavior remains a mystery


Timing is everything when it comes to controlling white grubs. Catch them early enough and they barely offer a challenge. Wait too long, and there is sure-fire trouble ahead, prompting Ohio State professor emeritus Dave Shetlar, Ph.D., to once say the best control for larger mature grubs is a 20-pound bag of insecticide. The brand or active ingredient is really irrelevant.
Dave Shetlar, Ph.D."Then you take the bag and drop it on them, because thats the only thing that is going to kill them," Shetlar has said.
Reports are circulating on the eve of white grub season that populations might be up this year in some parts of the country. There is no clear consensus among experts on the accuracy of that statement.
Some have said mild winters actually can hinder population growth, and harsh winter conditions, like those that prevailed through much of the country this year, can make grubs stronger.
"I think that is mostly b.s. Insects can handle just about anything winter throws at them," said Dan Potter, Ph.D., entomologist at the University of Kentucky and the winner of the 2011 USGA Green Section Award. "They have many adaptations to buffer them from the vagaries of a given winter."
Other than when to kill the juvenile versions of critters like Japanese beetles, masked chafers and green June beetles, little is known about what makes these bugs tick, especially the factors that influence swings in population. Or, if such variations even exist at all.
"I think thats just hearsay. Nobody has any real data on grub numbers increasing or decreasing, and doubtless it depends what region of the USA you are in" Potter said.
One thing that some of the leading researchers in the field of grub control can agree upon is the soil conditions that promote population growth.
Dan Potter, Ph.D."In my opinion, the most important variable that affects grub distributions is soil moisture," Potter said.
Beetles lay dehydrated eggs that need soil moisture levels of 10 percent to 11 percent to hatch. 
"The beetles seek moist soil with grass roots in which to lay eggs. They will not lay eggs in very dry soil," Potter said. "When summer is very dry, my sense is that a higher percentage of the eggs are laid in irrigated turf. In essence, the grub population is concentrated in irrigated areas in such years."
Ohio States Shetlar says prolonged wet periods through the summer during the past several years have made for prime grub-laying conditions.
"Over most of the eastern third of North America, the March through early July window has been wetter than normal for the last two to three years," Shetlar said. "This means that the soil conditions for the grub egg hydration has been excellent and has led to a steady increase in their populations."


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