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Tropical Gardening Helpline: Remedies to your Chinese rose beetle problem

Updated: 
May 29, 2016 - 12:30am

Jonathan asks: The leaves on my young cacao tree are getting eaten. My neighbor says he thinks it’s Chinese rose beetle damage. If so, how should I deal with these voracious munchers?

Tropical Gardener answer: Chinese rose beetles (Adoretus sinicus) often attack young cacao as well as about 250 other plants. Several low-tech and low-tox techniques have proven effective at reducing their numbers. Though rose beetle damage seldom kills plants, it can slow their growth and weaken them.

The beetles are about 0.5 inch long and usually reddish-brown in color. Their feeding reduces leaf surface and impairs photosynthesis which reduces the plant’s food supply. Though mature plants can usually resist their attacks, the growth and health of your young cacao will be compromised until you get rid of the beetles.

Chinese rose beetles feed just after sunset. They are attracted to dim light and repelled by bright light. Knowing this you can shine bright lights on your cacao for about three hours after dusk and probably discourage the attack. You might also try encircling your tree with some bright solar lights insuring that the light shines throughout the tree. If they are bright enough they may deter damage.

Neem oil and neem fertilizers also seem to discourage them. The beetles hide in the soil during the day and neem cake fertilizer in the soil and neem oil on the leaves have a deterrent odor.

One of the best methods to rid your garden of Chinese rose beetles, however, is to hunt them. They tend to feed in cycles, especially after a rain and during times when the moon is dark. These are good times to go into the garden with gloves, a flashlight and a jar with alcohol or soapy water in the bottom to kill them. Doing this a few nights a month will definitely keep the population in check.

If you want to do a one-shot trapping operation try this found on the website: www.ctahr.hawaii.edu/UHMG/FAQ/faq-chinese-rosebeetle.asp. The basic construction of the trap requires a solar lamp, a plastic or metal bowl with a hole in the bottom, some PVC pipe with threaded male and female adapters, and an “O” ring to keep soapy water in the bowl. The trap will help to keep the Chinese rose beetle population down and, combined with some of the other techniques, should prevent further damage to your cacao.

Diana Duff is a plant adviser, educator and consultant living on an organic farm in Captain Cook. Some questions that appear here were originally directed to Kona’s Certified Master Gardeners. You may contact them with questions at konamg@ctahr.hawaii.edu.

Gardening Events

Today: “Hamakua Harvest Festival,” 8 a.m. to 4 p.m. at the intersection of Mamane Street and Mamalahoa Highway in Honokaa. Exhibits, vendors, entertainment and fun for the keiki. Free. Info: www.hamakuaharvest.org.

Tuesday: “Hawaii Farmers Union Meeting,” 5 p.m. at the Adaptations warehouse in Kealakekua. Maureen Datta will conduct an informational tour of her “food hub” operation. Diane Ley, state director of the Farm Service Agency will present funding opportunities for local farmers, and Anisa from the Ulu Coop will talk about its work. Zero waste potluck. Free to members and interested public. Info: Maureen, adaptations-hi@earthlink.net or 324-6600.

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 brown bag lunch. Info: Peter at 323-3318.

Farmer Direct Markets

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

Wednesday: “Sunset Farmers Market,” 2 p.m. to sunset at the north makai corner of the Kmart parking lot.

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

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

Tuesday through Saturday: “U-Pick greens and produce,” 10 a.m. to 4 p.m. Tropical Edibles Nursery, Captain Cook.

Plant Advice Lines

Anytime: konamg@ctahr.hawaii.edu

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

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

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