Trouble in paradise for coconut trees
By Jan TenBruggencate
Advertiser Science Writer
Coconut trees along the Ala Wai are dying, trees in Ha'iku on Maui are dropping their young nuts and rotting, and there are coconuts in trouble elsewhere in the Islands as well.
Photos By Gregory Yamamoto • The Honolulu Advertiser
There doesn't appear to be any single cause, said coconut researcher Jeri Ooka. Rather, it's likely something different in each area, ranging from aggressive disease organisms to simple abuse. The latter is probably the problem with the trees between the Ala Wai roadway and canal.
A couple of top-bare coconut trees tower forlornly over the mauka side of the Ala Wai Canal. There is no single cause for sick trees — it can be disease, abuse or even pampering.
"The ones along the Ala Wai have a hard time. Trees there over time have a high attrition rate from the general assault of civilization," said Ooka, of the University of Hawai'i's College of Tropical Agriculture and Human Resources research arm, the Hawai'i Agriculture Experiment Station.
The coconut is the signature plant of Polynesia, valued for its grace and beauty, for its ability to survive in salty coastal environments and for the array of products it provided early Hawaiians. The coconut remains common in Hawai'i, where today it is grown mainly as an asset to tropical landscaping. But many trees are facing threats to their existence.
Ala Wai trees have their potential feeding area limited by concrete and asphalt. Roots have been chopped to make way for roadway expansion and they are subjected to the constant shuddering of the ground from heavy traffic.
The other main problem for coconuts — particularly in wetter parts of the state — is a fungal disease called bud rot of coconut or coconut heart rot. It is caused by a fungus, Phytophthora katsurae, which appears to have arrived in the Islands in the late 1960s.
The coconut heart rot fungus comes from a notorious family. Other phytophthora species are responsible for the great Irish potato famine, for leaf rot on taro and for a serious rot on papaya.
"It's a water mold. This one is spread throughout the state. It is spread by wind and rain, as well as birds and probably rats," said Roy Yamakawa, an extension agent with the UH Cooperative Extension Service.
The fungus does best in wet conditions. At Maui's Kahanu Gardens, a coconut tree collection that once numbered near 300 is down to about 80 trees in a dozen varieties, said garden director Kamaui Aiona.
"It used to be a much larger collection. We lost a lot of trees to what we believe was Phytophthora katsurae," he said.
The garden, on Maui's wet windward side, not only gets a lot of rain, but also has a nearby river that sometimes floods.
In Waikiki, where coconut groves once thrived, a tree languishes among its healthier brethren on Kuhio Avenue.
"We've got lots of fungal issues in the garden," he said.
An early sign of infection with coconut heart rot is that young nuts will fall off; when cut open, they will be rotted inside. The tree can often survive with the fungus on its crown area until the infection finds a way into the tree's growing tip, the heart.
"It can be years before they die," Ooka said.
The fungus can get into the heart through a small crack caused by heavy winds, or through tissue made vulnerable when it is softened by excessive rain. Another easy target is a coconut tree pampered by excessive fertilization or watering.
"We first noticed this problem on golf courses. If you water or fertilize too much, the tissue gets soft," he said. Trees on golf courses and hotel properties, where the lawns are fertilized with a lot of nitrogen to make them green, and they're also watered a lot, are at risk.
"Coconuts, I think, evolved under a low-nitrogen regime," Ooka said.
When the rot gets to the heart, the first sign is that the newest leaf comes out tan-colored and dry-looking.
"If you see that, it's gone," he said.
Ooka said that an injection of the fungicide Elite or a solution of potassium phosphite appears to create a resistance to the fungus, although there is some risk to injecting the tree, since coconuts don't heal their wounds and there is a risk of a rot like thelaviopsis weakening the trunk at the injection site.
Only Moloka'i and Lana'i appear to be free of Phytophthora katsurae.
A number of other diseases and insects may attack coconuts at various times, including other kinds of phytophthora.
One of the issues for coconut trees in the Islands may be that Hawai'i is near the northern end of their range. The trees generally appear fuller and healthier nearer the equator. Hawai'i's most famous coconut groves, at Waikiki before the proliferation of high-rises and at Kapuaiwa on Moloka'i, have tended to be near sea level on the leeward sides where temperatures are warmer, Ooka said.
Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.
