Ask the Master Gardener: Battling a rose chafer invasion on flowers

Dear Master Gardener: There are insects wreaking havoc on my rose and peony blossoms. They are one-half inch, khaki-colored beetles with orangish spiny legs. What are they and is there a way to get rid of them without using chemicals? I try not t...

Rose chafers can wreak havoc on flowering plants. Photo by Jennifer Knutson
Rose chafers can wreak havoc on flowering plants. Photo by Jennifer Knutson

Dear Master Gardener: There are insects wreaking havoc on my rose and peony blossoms. They are one-half inch, khaki-colored beetles with orangish spiny legs. What are they and is there a way to get rid of them without using chemicals? I try not to use pesticides because I am concerned about the health of bees.

Answer: It sounds like you have rose chafers, which are commonly found in areas with sandy soil, such as the Brainerd lakes area. The adults emerge from the ground in late May and early June. Rose chafers prefer sandy soil to lay their eggs, so plants located on sandy sites are most likely to be attacked. The adult beetles feed on plants for three or four weeks, usually until late June. Adult rose chafers feed primarily on flower blossoms, especially roses and peonies. Protecting your plants from rose chafers can be a challenge, especially when there are large numbers present. The non-toxic method is to pick them off your plants and drop them in a pail of soapy water to kill them. Unfortunately, they are good flyers and more may continue to fly into your garden so you will need to continually check your plants for new additional pests.

Dear Master Gardener: I've seen landscaping around commercial buildings where mulch is piled a foot high in a hill around the trees. It looks neat, but isn't it bad to have mulch piled up around trees?

Answer: Yes, having a "volcano" of mulch a foot high around a tree is bad for the health of the tree and will shorten its life expectancy or cause its death. Mulch that touches the trunk is moist from rain and/or irrigation and can rot and decay the tree. It can prevent water from reaching the tree's root system. Wood-boring insects living in the mulch can tunnel through to the softened, decomposing bark, and gain access to the vascular tissues beneath the bark. Harmful diseases can enter the interior of the plant more easily when the bark stays constantly moist. Bark-chewing rodents, such as mice and voles can tunnel through the mulch and chew through the outer bark to reach the tasty inner bark, cutting off the flow of water and nutrients, which will eventually kill the tree. Another problem is roots have a tendency to migrate up toward the top of the mulch layer during rainy periods, only to dry out when summer drought sets in (which often occurs in July). It is better to make a "donut" or ring, of mulch three inches deep around your trees, keeping the mulch at least three inches away from the trunk.

July Garden Tips


• Stop picking rhubarb early this month. The stalks grow "woodier" as they age.

• Containers of flowers need frequent feeding, as some of their nutrients wash through the soil every time you water or it rains. Use a water-soluble fertilizer at half the rate on the label every week to keep container gardens and hanging basket plants growing and healthy.

• It's important to control weeds in gardens and lawns because they compete for moisture and nutrients and often harbor damaging insects. Weeds usually spread quickly in the lawn while desirable grasses struggle in the heat. Do not apply fertilizer or herbicides during hot weather because it can burn your lawn. It is better to wait for cooler weather in late summer and fall

• Trees need 1 inch of water per week to keep roots hydrated. Trees and shrubs planted in the last three years need extra water during dry spells. Trees stressed from lack of water are more susceptible to pests, winter injury and other problems, which may not show up until months later.

• Deadhead flowers so they don't set seeds. Removing faded flowers keeps annuals blooming longer and can result in a second flush of flowers on some perennials.

• As soon as tomatoes set fruit, begin to monitor lower leaves for Septoria leaf spot. Remove infected foliage and spray plants with a registered protective fungicide if disease is severe. Mulching around the plants may help prevent disease organisms from splashing up from the soil.

• Leaf lettuce, radishes, spinach and other spring crops bolt, or turn bitter, and go to seed in the heat of July. Pull them up and use the space for a fall crop of cauliflower, broccoli, kohlrabi, cabbage and onions.

• If you have apple trees, you must control apple maggots at the beginning of July. You can spray the trees every ten to fourteen days until harvest, or two days after each rainfall of one-half inch or more. Or you could hang sticky balls (fake apples) to attract the flies so they don't lay eggs in the developing fruit. It isn't as effective but does eliminate the use of an insecticide. You can also protect your apples (perfectly!) by bagging them. Enclose each apple in a plastic sandwich bag, either a zipper closure bag or a plain bag closed with staples. Using a pair of scissors, snip the bottom corners off each bag, leaving a small opening for water to run out. At harvest, remove the bag. Although this takes some time, the apples are protected from apple maggots for the rest of the season.


• To make cut flowers last longer, pick them early in the morning before they begin to lose much moisture. Strip lower leaves, then cut the base of the stems before plunging them into a vase of slightly warm water. Change the water every day or two. If you have floral preservative, dissolve it in the water then add your flowers.

• Visit a local farmers' market for freshest produce. Support the local economy.

• A fun July project to do with children is to make a toad cottage. Dig a hole 1 inch deep in a shady spot and place a clay pot on its side in the hole. Place soil one-half inch deep on the "floor" of the pot to make a bed for your toad. Read "Frogs, Toads and Turtles" by Diane Burns together.

University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. All information given in this column is based on research. To ask a question, call the Master Gardener Help Line at 218-454-GROW (4769) and leave a recorded message. A Master Gardener will return your call.

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