Grace asks: The bark at the base of a grapefruit tree on my property has started to peel off. The tree does not look very healthy either. Is this something that could kill the tree? In any case is there anything I can do about this?
Tropical Gardener answer: Several causes for the peeling bark at the base of your citrus tree are possible. Some more lethal than others.
These symptoms can be caused by the tree’s natural growth process or rapid changes in temperature. If this peeling is not accompanied by other symptoms like oozing of gummy material, bark discoloration or tree dieback, it may not be something to worry about.
Because you report the tree doesn’t look healthy, the problem may be more severe. If leaves or branches are dying, the roots may be rotting. Irrigation emitters placed too close to the tree can cause root rot. A season of heavy rainfall could be a cause, especially if your tree is planted in a lawn that gets frequent irrigation or that has been heavily mulched.
Some of the most serious root diseases are caused by phytophthora fungi. One form frequently seen here is phytophthora stem canker. This soil borne disease thrives in wet conditions and can cause the bark to peel at the soil level. You may be able to determine the existence of root rot by digging back the soil a bit on one side to check the roots. If you see some rotting, you might want to remove any grass or mulch in the root zone, pull back the soil a bit, water less frequently and only water in the morning so the roots can dry during the day. If you are just seeing the peeling bark, the disease may be just starting and you may be able to arrest its progress.
In advanced cases, the trunk can become girdled with wound tissue, branches and leaves may dieback and fruit may drop. Uncontrolled, root rot can eventually cause death.
Phytophthora stem canker can spread to other plants in the same species when conditions are very wet. If you suspect the fungi phytophthora is present, Scot Nelson from the University of Hawaii recommends drenching the roots of the infected plant(s) with Phosgard, a high phosphorus fertilizer or with Rampart, a fungicide with high phosphorus acid. Either or both may be available locally at gardening stores, BEI Hawaii or Hawaii Grower Products.
Nelson’s “The Plant Doctor” app is available for iPhone and Android in English and Spanish. Go to http://hawaiiplantdisease.net/index.php or email snelson@hawaii.edu for more information.
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
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. Bring a brown bag lunch. Info: Peter, 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
Tuesday and Thursday: 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