Tropical Gardening helpline: Battling the Chinese rose beetle

Alice asks: I am plagued with Chinese rose beetles. They are eating the leaves on all of my rose bushes, some of my herbs, my cacao and my hibiscus. What can I do to get rid of them?

Tropical Gardener answer: Actually several methods are available to control Chinese rose beetles (Adoretus sinicus). Their appetite is very wide ranging. They enjoy eating the leaves on more than 250 plant species, so until you reduce their population, you are likely to see lots of damage. Severe beetle damage causes a reduction in photosynthetic leaf surfaces which can weaken the plant significantly.

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It sounds like you know what Chinese rose beetle damage looks like but for those who don’t, their feeding results in the leaves on target plants looking like they’ve been shot with buckshot. Severe infestations can cause leaves to look like lace or in some cases only the leaf veins will remain.

The beetles spend their days in the soil or hiding in leaf litter. You are not likely to see them unless you go out just after sunset with a head lamp to look for them on your plants. They are about a 1/2-inch-long and dark brown. Hunting them is actually a good way to reduce the population. Take a jar with alcohol or soapy water and remove the beetles from the plant with gloved hands and place them in the jar. Either of these solutions will kill them. If you have a severe problem you might want to do this repeatedly until you see fewer beetles. Follow up by going out once or twice a month to get any new ones that arrive.

If you do want to kill the beetles but are not into hunting, you could build a simple trap to catch them. Information on the beetle plus a YouTube and directions about building a trap can be found at http://www.ctahr.hawaii.edu/UHMG/FAQ/faq-chinese-rosebeetle.asp. Trapping Chinese rose beetles will definitely reduce the population and the damage.

Several practices have proven successful in discouraging these beetles from attacking your plants. Using neem cake fertilizer around the base of targeted plants or spraying the soil and leaves with neem oil can help, since beetles don’t seem to like the odor. You can also discourage them by shining bright lights on the plants for two to three hours after sunset. Some good results have been reported using several solar lights around the plants. The brighter, the better.

Since the beetles often fly to their next meal, physical barriers can also dissuade attacks. A tall cylinder of garden fencing covered with weed, shade or other fine mesh cloth will prevent flying beetles from reaching protected plants. Make these lightweight and portable and you can move them from plant to plant. Just be sure they are as high as the plant for complete protection.

These techniques can be quite effective, especially when several are employed. They are really the only way to get rid of Chinese rose beetles on plants whose fruit or leaves you eat. For ornamentals like roses or hibiscus you could use systemic chemical insecticides that will kill any beetles that eat the leaves on treated plants. If you are an organic gardener, there are no OMRI approved pesticides that have proven effective against the rose beetles.

A readily available insecticide, Sevin, will kill Chinese rose beetle when applied according to directions but it washes off in rain. Systemic insecticides with the active ingredient imidacloprid will also work when directions are followed correctly. Neither of these should be used on edibles and in both cases reading and following directions is essential to success.

Email plant questions to konamg@ctahr.hawaii.edu for answers by certified Master Gardeners. Some questions will be chosen for inclusion in this column.

Diana Duff is a plant adviser, educator and consultant living in a dryland forest north of Kailua-Kona.

Gardening Events

Monday: “Rapid Ohi‘a Death Seed Banking Initiative,” 1-4 p.m. at Kuhio Hale, Department of Hawaiian Homelands 64-756 Mamalahoa Hwy (Mile Marker 55) in Waimea. North Hawaii Workshop to teach ways to collect, handle, and process ohia seeds in response to the ROD crisis. Free. Info: Visit www.ohialove.com or contact Marian Chau at (808) 988-0469 or mmchau@hawaii.edu or visit www.rapidohiadeath.org.

Saturday: “Work Day at Amy Greenwell Garden,” 9 a.m. to 12:30 p.m. Meet at the Garden Visitor Center across from The Manago Hotel in Captain Cook. Volunteers will be able to help with garden maintenance and are invited to bring a brownbag lunch. Water and snacks provided. Info: Call Peter at 323-3318.

Farmer Direct Markets

Wednesday: “Sunset Farmers Market,” 2 to 6 p.m. in the HPM parking lot at 74-5511 Luhia St. in Kailua-Kona (across from Target)

Wednesday &Friday: “Hooulu Farmers Market,” 9 a.m. to 2 p.m. at Sheraton Kona Resort &Spa at Keauhou Bay

Friday: “Pure Kona Market,” 9 a.m. to 5 p.m. at Amy Greenwell Garden in Captain Cook

Saturday: “Keauhou Farmers Market,” 8 a.m. to noon at Keauhou Shopping Center

“Kamuela Farmer’s Market,” 7 a.m. to noon at Pukalani Stables

“Waimea Town Market,” 7:30 a.m. to noon in front of Parker School

“Waimea Homestead Market,” 7 a.m. to noon at the Waimea Middle and Elementary School Playground

Sunday: “Pure Kona Green Market,” 9 a.m. to 2 p.m. at Amy B.H. Greenwell Garden in Captain Cook

Plant Advice Lines

Anytime: konamg@ctahr.hawaii.edu

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Tuesdays &Thursdays: 9 a.m. to noon at UH-CES in Kainaliu – 322-4892

Monday, Tuesday &Friday: 9 a.m. to noon at UH CES at Komohana in Hilo 981-5199 or himga@hawaii.edu

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