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John Reitman

By John Reitman

Worried about grubs due to warm winter? Don't be

With winter all but an afterthought this year in much of the country, one might think such conditions might make a fertile environment for a bumper crop of white grubs. According to former University of Kentucky entomologist Dan Potter, Ph.D., golf course superintendents have little to fear this summer — at least where grubs are concerned.

According to Potter, unseasonably warm weather throughout January, February and March has nothing to do with how many grubs will emerge to plague golf courses this summer.

"When they go into winter dormancy, they go down pretty deep," said Potter, recipient of the 2010 USGA Green Section Award. "They might come out a little early, but there is no evidence to suggest we will get a second generation this summer."

Grubs operate on a biological clock.

They have what Potter described as a "natural antifreeze" that allows them to survive in frozen soil.

"They are not going to freeze in cold weather either," Potter said. "They don't freeze at the same temperature as water. You can put them in the freezer and open it later and they will still be alive."

The average daily temperature in Lexington, Kentucky where Potter is located is 37 degrees Fahrenheit. This winter has been anything but average. The daily high in Lexington exceeded 50 degrees on 22 of 28 days in February and topped 60 degrees on 12 of those day.

Then what happens in a year like this when temperatures are above normal? 

"If it's never been cold, how do they know it's time to come out?" Potter asked rhetorically. "That's a really good question. But a mild winter never seems to change their lifecycle."

030923 grubs.jpg

Potter, who has been one of the country's leading voices on white grubs, said not much has changed in understanding grubs in the past 40 years.

"I still follow the 1980s timetables for egg development," he said.

One thing grubs need for survival is moisture in the soil to ensure the viability of the eggs. If there is not enough moisture in the oil, the eggs might not hatch.

Soil moisture levels of at least 10 percent in summer when adult beetles lay their eggs will go much farther than unseasonably warm conditions at ensuring a successful hatch.

Beetles also are adept at seeking out fertile territory for depositing their eggs.

"They will seek out a moist place to lay their eggs," Potter said. 

In times of drought, moist soil can be found on irrigated grounds, like a golf course. 

"I don't make predictions about whether it is going to be a good year for grubs, because you never really know," Potter said. "I might have said that before at a field day in front of a lot of people because I wanted to sound wise.

"When there is plenty of rain in July and August there is always good egg survival. When there's drought, there is not good survival except on places like irrigated fairways and roughs. The most damage is always going to be in an irrigated rough."

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