Beetles and chafers, oh my!

Entomologist Dr. David Smitley explained that the pathogen used to infect the beetles to reduce their population occurs naturally and was discovered on golf course in Connecticut in 1990. Long-term trials on golf courses in Southeast Michigan showed that infected grubs are half as likely to survive winter in the soil, and female beetles emerging from infected grubs lay half as many eggs as non-infected beetles. After about five years, the pathogen significantly reduces the population. MSU has shared the pathogen with organizations in Kansas, Arkansas and Colorado.

To help spread the pathogen in Michigan, MSU gave attendees infected beetles to dig into their home lawns. The beetles were dead (which nixed my concern of not wanting to introduce beetles into my garden), but the pathogen is alive. As the beetles decompose, the pathogen is released into the surrounding soil and roots. As the grubs feed on these roots, the pathogen breaks down the bug equivalent of kidneys.

Dr. Smitley explained that Japanese beetles lay their eggs in August and they prefer doing so in moist turfgrass, like in irrigated lawns and in low-lying areas where moisture accumulates. They also like areas near linden trees.

People who took the beetles promised to keep their lawns watered (with a quarter inch of water every other day) throughout the August egg-laying season, and they will dig one-inch holes with screwdrivers and place a dead beetle in each hole. Lawns into which the beetles are introduced can't be treated with insecticides (like Grub-Ex).

If we have a dry August (like last year), that means we'll have fewer Japanese beetles the next year (with or without infected pathogens). This also explains why my own garden doesn't get a lot of Japanese beetles. I don't really have turfgrass, but weeds, as lawn. I keep them mowed but never water them, so my conditions are too dry. Yay for lazy gardening! (In case you're wondering, I passed my beetles on to someone who has the right conditions.)

However, I have seen those white C-shaped grubs in my garden, so I was curious what those were. Dr. Smitley explained that in dry lawns, these grubs are not Japanese beetles, but European chafers.

European chafer grubs damage grass roots (if you have grass damage, it's likely caused by chafers, not beetles), but they do not eat or otherwise damage plant foliage, as Japanese beetles do.

The infected beetles are all spoken for this season, but you're interested, be sure to attend next year's field day. For details, and to receive a bunch of other helpful gardening information, check out MSU's landscape alerts.

Monica Milla, the Garden Faerie, is a master gardener volunteer, garden speaker, garden coach, and author of "Fun with Winter Seed Sowing."