Start Thinking About White Grubs

This is the time of year when most people aren’t thinking about white grubs, but it’s a good time to start, according to Rick Brandenburg, turfgrass entomologist, North Carolina State University, Raleigh, N.C.

The main reason for this is that white grubs, such as the larvae of Japanese beetles, masked chafers, green June beetles and others, often don’t cause any visible damage until late in the summer. “However, with many of the newer products available for grub control, early application is critical,” Brandenburg advised.

Most white grubs have similar life cycles, Brandenburg said. “The adults are generally present for about a month in the summer,” he shared. “This is quite obvious in the case of Japanese beetles, which can be seen feeding on various ornamental plants during June and July in North Carolina, for instance. Others, such as masked chafer, are less obvious. When the beetles are observed, it provides us a bit of an early warning that they may be laying eggs in nearby turf, which can be subsequently infested with white grubs (the larvae of these beetles).

"The larvae feed the rest of the summer and early fall, go deep in the soil to overwinter, feed awhile in the spring and then complete development into the adult beetles in the late spring. A grub infestation can only be determined by digging down into the upper 4 inches of soil.” 

Some of the older grub control products had a fairly large window of application – in others words, you could apply them in June through September and get good control, Brandenburg said. With some of the newer products, the timing window is a little narrower and best results are obtained when the products are applied during egg laying and egg hatch in June in July. “Knowing the life cycle of the pest and how to best use each product is very important,” Brandenburg emphasized.“While some products are fast acting and can work against larger grubs late in the season, they may provide little residual control.”

Dry weather adversely affects white grubs. Many beetles, such as Japanese beetles, actively seek out the lush green turf areas because that indicates good soil moisture. Good soil moisture is critical for egg survival. Under very dry conditions, grubs that are present will generally be deeper in the soil and this makes control very difficult, Brandenburg pointed out. “Pre-irrigating the area may help, but nothing can replace the benefits of good rainfall to keep the grubs near the soil surface,” he said. “Control of white grubs is difficult and should only be a last resort in situations of severe damage.”

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