Planning Ahead for the Rose Chafer

First published in the Observer
By Russell Rolffs, Gathering Ground executive director

Recently I saw a sign at the entrance of a garden that read: “If nothing is eating your plants, your garden is not part of the ecosystem.” The message to gardeners, I think, is to be proud when your plants are preyed upon as it means they are contributing to the web of life. This is a noble idea, and I admire it for many reasons, but when your peonies are covered with dozens of little brown bugs munching away, it is hard to be noble-minded!

If you are a gardener on Washington Island, you likely experienced or heard others mention the rose chafer infestation last June. Rose chafers are tan and pale green beetles with a dark brown head and orange legs. They live for only about one month in their adult form. On the Island, this is from about the second week of June to the first week of July. Then, they lay eggs in grass with sandy soil, their preferred habitat, where the larvae hatch and burrow deeper, eating roots as they go. They do not pose a serious threat to lawns, but as adults, they do serious harm to flower gardens and fruiting plants. Last year, Gathering Ground lost over 80 percent of its flower buds to rose chafers. And, of course, without flowers there are no fruits. It was a rough year in the vineyard.

By all accounts, 2018 was an unusually bad year for rose chafers. We counted over 150 of the beetles on a single vine one day, and the average daytime count at the peak was over 50. Other gardeners on the south side of the Island where sandy soils are more dominant reported similar experiences. Grapes and roses are favorite foods of rose chafers. Neither will they pass by a meal of peonies, strawberries or raspberries, both flowers and foliage. They even eat tough natives like the ox-eye daisy. On Gathering Ground’s grapes, they began by skeletonizing the leaves, and when blossoms developed, moved to them.

Rose chafers are, in other words, a formidable foe, made only worse by their toxicity to birds, including chickens! And considering that we have nearly pure sand more than six feet down at Gathering Ground, I sometime despair of ever getting a crop of grapes or any other fruit there again. But I remain hopeful.

When it comes to controlling an infestation, generally speaking, your options are to deter, deflect, or destroy. There are a number of conventional pesticides out there that do a good job of destroying rose chafers, but many of them are quite toxic environmentally. Neonicotinoides are commonly used against rose chafers and other beetles, but they are equally poisonous to bees and other pollinators – beneficial insects, as they are sometimes called. Carbamates and organophosates are also used in commercial orchards and vineyards and are available to home growers, but they are both neurotoxins and therefore dangerous to humans. They also are broad spectrum, meaning they kill a wide range of insects. Even organically approved pesticides like pyrethrum and spinosad are toxic to a wide range of insects, killing bees and other pollinators along with the pest, and therefore best avoided.

Using poisons to grow food is, in my opinion, surprisingly uncontroversial. The truth is, most of the fruit that we buy and wine we drink was grown with the aid of one of the above pesticides. Orchardists in California even spray some of these pesticides and fungicides during periods that overlap with pollination of bees, accepting as a fact of life that a good percentage will die as a result. It’s true, no grower wants to spray pesticides, but that doesn’t mean their priority is finding a spray program that has the lowest ecological impact while still allowing

them to get a harvest. And yet, the need for larger ecological awareness only grows. Scientists are observing dramatic declines in global insect populations, some predicting widespread die-offs in mere decades. If this seems farfetched, consider the Sichuan Province of China, where pollination of fruit trees is performed by hand due to local decimation of pollinators by insecticides.

Last year at Gathering Ground, we primarily used neem oil products to deter rose chafers. Neem oil is ecologically benign, but it is not strong enough control an infestation of rose chafers. We also underestimated our pest and did not have equipment to spray until peak infestation. Do not give up on neem oil, however; if rose chafer numbers are down this year, it will be more effective.

This year at Gathering Ground, we are going to get creative and try several new methods of controlling the beetle. We plan to start our control efforts before the beetles emerge from the soil, in May when they are still grubs. We will do this with a beneficial nematode that preys upon the grubs in the soil. Soil disturbance through tillage will also disrupt the grubs’ development. We also hope to experiment with a very narrow spectrum control (effective only on beetles) called BeetleGONE, another form of biological control but this time a bacteria, a strain of Bacillus thuringensis, that is sprayed on the plant and is consumed by the adult beetle.

I am also interested in ways of deflecting rose chafers. This can be done with a physical barrier and is a good option for home growers. Drape cheesecloth or a product called Protektnet over your plants to keep the beetle from gaining access. Large orchardists also use such netting to protect from insects and birds, but that represents a significant investment, something Gathering Ground is not prepared for. An alternative way to deflect pests that we do hope to employ this year is Surround, a finely ground clay that is mixed in solution and applied as a protective coat to the plant. It would be like eating a burrito coated in sand – not so appetizing!

Home gardeners take heart, though; the rose chafer is only out for a few weeks. Knowing that provides a light at the end of the tunnel. If you are trying to protect just a few plants, I recommend using a protective netting in combination with handpicking. Rose chafers are easily picked or shaken from plants and dropped into a bucket of soapy water. If using a net, they will likely congregate on the outside of the net and can then be easily collected by balling up the netting and soaking it in soapy water. Do this during the day when they are more active and you can get a larger harvest. And while it may be hard to enjoy your peony bloom when it’s hidden beneath a net, you could always protect them just long enough to cut and enjoy inside in a vase where rose chafers are sure not to find them.

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