Lettuce and kale sales have dipped in recent weeks in response to an unusual number of rat lungworm cases on Maui that have left many visitors and residents questioning where produce is grown.

“Everybody is really sensitive to where the produce is coming from,” Neil Hasegawa, general manager of Hana’s Hasegawa General Store, said Friday. “People rather eat lettuce from the Mainland — it never used to be that way. It’s always been the fresher it got or closer it was, the better it was.

“People are really conscious about that now.”

Growing concerns have spurred some grocery stores to buy produce off-island, which could spell disaster for local farmers, a Maui farmers union representative said. The recent outbreak also could increase biosafety control costs for farmers, who already get little governmental help.

“I hope people aren’t scared to eat local anymore because that’s really going to hurt our farming industry whether you’re organic or not,” said Simon Russell, president of the Hawaii Farmers Union United Haleakala Chapter.

As of Tuesday, the state Department of Health had confirmed six cases on the island this year and was investigating three others. The disease, caused by a parasitic worm that affects the brain and spinal cord, has hospitalized at least three people.

There is no cure for the disease.

“This is the first kind of scare that we’ve had where we got to really watch what you eat,” Hasegawa said. “The last time I’ve seen this kind of scare was the dengue fever outbreak.”

Rats host the worm and pass the larvae through their feces, which slugs feed on. Humans can get infected by consuming raw produce or water contaminated by the slug, or by eating raw or undercooked snails, slugs, prawns and land crabs.

Health officials have linked the recent outbreak to increased numbers of the semi-slug, which carries the parasite 70 to 80 percent of the time. Maui Invasive Species Committee officials said that the slug appears to be most pervasive from Nahiku to Kipahulu.

As a result, lettuce sales have dropped 20 percent at the century-old Hasegawa General Store — even though the store does not sell lettuce from Hana, Hasegawa said. The store gets its lettuce and kale from Kula Produce, which ships it from the Mainland, and advertises it that way to assure customers.

“Lettuce would be the hardest hit,” he said. “We mark the signs with U.S. and check the invoices to make sure whatever we’re buying matches the signs.”

Restaurants and stores have posted signs telling customers that their salads and vegetables are safe to eat, and remind them to wash produce thoroughly. Some store managers declined to comment Friday.

A spokeswoman for Whole Foods in Maui Mall said in an email: “Out of an abundance of caution, our Maui store is currently using only greens and lettuces from the Mainland for all prepared food items and has posted reminders for customers on proper care of fruits and vegetables.

“We are closely monitoring this issue and working with the Hawaii Department of Agriculture to develop a plan that allows us to continue to support local agriculture while ensuring the safety of our customers and Team Members,” public relations official Janette Rizk said.

Kevin Clarke, assistant manager at Down to Earth, said that store officials contemplated getting produce from the Mainland as well, but met with supplier Kumu Farms. He said that the farm manager had already issued a handout to stores and reassured them that the farm was safe from the semi-slug.

The farm, located at Maui Tropical Plantation, is on the leeward side of the island and is too dry and arid for slugs to thrive, Clarke said.

“It would be terrible to have to ditch the local farmers because they would be losing a lot of production,” Clarke said.

Jesse Yancey, assistant manager at Pukalani Superette, said that the store has stuck with its local farmers and has not seen produce sales drop “one bit.” All produce is cleaned, weighed and prepackaged, but the store still encourages customers to wash it again and even sells vegetable wash solutions for those who are extra cautious.

“We keep our produce pretty clean, but farmers also clean it because they know it’s going to go straight out,” Yancey said.

One way farmers can help rectify the problem is by controlling rat and slug populations. That can be tricky, though, for organic farmers who have to use mechanical traps and other nonchemical alternatives to protect their farm, Russell said.

Russell, who grows organic fruits and vegetables in Makawao for restaurants, said that farmers already take extreme precautions to ensure their crops are safe from invasive species and safe to eat. Increased costs for biosafety control would further hurt local farms competing against large Mainland ones, he said.

“We need to inspire confidence really quickly in the consumer base,” he said.

Russell said that the issue could benefit some local farmers, who have proved to be safe and reliable, but he lobbied for more support universally by state legislators and media agencies. Russell serves as the Maui representative on the state Board of Agriculture and said that the Department of Agriculture only gets 0.38 percent of the total state budget.

“Almost every other state in the country, aside from like Rhode Island, has a way higher ag budget than Hawaii, and we’ve got three growing seasons a year,” he said. “We can put robots on Mars. Why can’t we get rid of rats?”

Hasegawa encouraged residents to have confidence in local farmers and stores, but they should still ask questions and check signs.

“I think that’s the biggest thing you can do and if you’re not sure, ask more questions because the store is important,” he said. “I think now all the farmers have stepped up their game so they’re making sure their slug eradication programs are up to par and even better than what it was before this.”

* Chris Sugidono can be reached at csugidono@mauinews.com.