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The Honolulu Advertiser

Posted on: Friday, January 18, 2002

Invading bug a threat to farms

By Beverly Creamer
Advertiser Education Writer

UH extension agent Randall Hamasaki collected these aster leafhoppers from an infested crop at the Gushing Waters Watercress Farm in Waipahu. The insects are as small as the diameter of the lead core of a pencil.

Deborah Booker • The Honolulu Advertiser

It took a year of sleuthing that involved a dozen scientists and advanced DNA analysis but University of Hawai'i agriculture officials have uncovered a new threat to O'ahu watercress farms: a teeny leafhopper that could also prove ominous for other vulnerable crops, including lettuce and papaya.

The critter — a /-inch bug called an aster leafhopper — carries a mysterious disease called "aster yellows" that's new to Hawai'i but infects 300 species on the U.S. Mainland and in Canada. Carried by the wind, the hopper can easily cross state lines, infecting crops and even weeds as it moves.

While the bug can be killed with malathion — the only pesticide approved for use — it may already be so entrenched in Hawai'i that it's impossible to eradicate, with the possibility of wiping out watercress and attacking another 100 plant varieties, say the experts.

"It has serious potential for our diversified agriculture industry," said Steve Fukuda, the UH College of Tropical Agriculture and Human Resources extension agent tracking the bug. "It will hit things like lettuce and tomatoes, cabbage, papaya, and maybe some crops like cucumbers, watermelon, pumpkin, zucchini, carnations."

State Agriculture Department chairman James Nakatani is concerned enough to be looking for money to study the potential impact.

"The lucky part is it hasn't spread," he said.

Mystery of the yellow leaves

Tracking down the organism has taken a year and involved extension agents, scientists and even state workers to unravel the mysterious yellowing of some O'ahu watercress, one of the 12 most profitable vegetable crops in the state. (According to the most recent statistics from the year 2000, Hawai'i watercress earned more than $1 million for its growers and provided the local market with 95 percent of all the cress consumed in the state.)

"This story is a good example of the teamwork of people from our college, all with different expertise," said John Hu, associate professor of the Plant and Environmental Protection Sciences branch of the agriculture college. "The research went from physiology to pathology."

Only when extension agents had checked everything else, including water salinity, plant nutrition, bacteria, viruses and other pests did they turn to Hu's laboratory experts and a DNA analysis technique that the department perfected several years ago for just such an emergency.

Stumped no more

As watercress farmers fight to save their businesses, both the industry itself and the state have been critical of how long it took to find the problem.

"We have one farmer who's essentially been out of business since September," said John McHugh, from Watercress of Hawai'i, an industry association. "Part of the reason has been that it has taken so long to identify what's causing the problem."

"This has been the worst that the watercress industry has seen as far as anyone can remember in 50 years-plus," said Fukuda. "There are farms that have totally shut down their production. They're trying to get clean planting materials and trying to control the vector from coming in and infecting their present crop."

One of the farms hardest hit is owned by Nakatani and his brother, Don, and it's a family operation started by their grandmother 75 years ago. James Nakatani said that because of his sensitivity about the issue, as Agriculture Department chairman, he told his staff: "Treat this like an agriculture problem and not my problem."

To keep the disease from spreading, Don Nakatani followed the advice of extension agents and pulled out all his plants.

With the losses, he was forced to lay off his five employees and is now starting from scratch with fresh cuttings from the Sumida watercress farm makai of Pearlridge. Sumida, the island's largest cress farm, has lost about 10 percent of its crop.

Watercress a big deal

Department of Agriculture research statistician Ronald Nakamura said watercress is one of a dozen vegetable crops with over $1 million in farm sales annually. For comparison, zucchini sales are

$1 million; cucumber $2.5 million; head cabbage $2.8 million.

The total sales value of the state's diversified agriculture — everything except sugar and pineapple — was $45.5 million in 2000.

It was Wayne Borth, a junior researcher with a background in the bacteria-like organisms called phytoplasma, previously unknown in the Islands, who finally identified the disease, now called "watercress yellows."

Using the polymerase chain-reaction technique — finding the DNA from the disease within plant tissue — he pinpointed the problem in two days. It's the same technique used to first identify dengue fever.

The rarity of phytoplasma in the Islands is part of the reason scientists were puzzled, said Randy Hamasaki, a second UH extension agent pursuing the mystery. "This would be low on your suspect list because it's not here," he said.

Only one phytoplasma has been known in Hawai'i and it attacks an indigenous tree on the Big Island.

Fighting back

There's no way to know how the aster leafhopper and the disease it carries arrived in Hawai'i, but now that they're here, the only choice is to develop techniques to handle or stop them.

"Once it's established, it's a real problem," Borth said. "It has a very wide host range of other crops. Organisms of this type have been reported to also infect barley and lettuce and cucumbers and flower crops like chrysanthemums and asters." And corn.

So far, only the Pearl City area watercress farms seem affected, but with high winds coming in the next few days, the bugs may spread further.

Extension agent Hamasaki said farmers can spray with malathion, although farmers worry about the bug becoming resistant to it. McHugh said any pesticide residue is washed off, or disintegrates, before the cress goes to market.

Other control mechanisms include "roguing" or pulling diseased plants from a field, keeping weeds under control so it can't thrive in them, and making sure the root stock used for replanting is undiseased.

Reach Beverly Creamer at bcreamer@honoluluadvertiser.com or 525-8013.