A new plant disease could threaten more crops across our islands. Papaya farmers may know about ring spot, but a new affliction called papaya mushy canker disease has been identified in Guam.
Mushy canker disease can kill a healthy papaya plant in less than two weeks. It's caused by bacteria that hitches a ride on invasive snails and slugs. It can also spread through rain and wind. So far, there's no way to treat an infected plant.
Glenn Dulla, an assistant professor of plant pathology at the University of Guam, recently published the territory's first report of the bacteria. He said the disease has been present in the Pacific for several decades.
"Typically, the bacteria will enter the plant tissue and start to degrade and hydrolyze the tissue," Dulla said. "So what it produces is these dark lesions that kind of look like they're water-soaked. It looks like a dark green or dark black spot on the plant, so it affects the leaves, the stems, and eventually just rots it to the point where the plant itself will lose integrity and flop over and die. It can also rot the fruit itself."
He said that if the disease spread to Hawaiʻi, there would be serious economic implications. According to the state Department of Agriculture, the value of utilized papaya production in Hawaiʻi was estimated at $8.5 million in 2021.
"We've heard stories where farmers have given up on growing papaya because the pathogen or the disease spread so quickly, and it rots out their papaya seedlings," Dulla said. "Even if it is in a mature papaya field, the fruit isn't of a quality that is sellable or marketable."
He said invasive species found on Guam usually make their way to Hawaiʻi, or vice versa.
"I believe probably quarantine practices, no illegal smuggling, movement of clean plant tissue products, clean seeds would be the best way to prevent the spread to other islands," Dulla said. "Within an agricultural field, the only way you could stop it is to prevent the leaves from getting wet and to prevent snails and slugs from entering your nursery or field, which is almost impossible, quite honestly."
To keep the disease away from the islands, it's important for people not to transport fruit and plants into Hawaiʻi, Dulla said.
"For quarantine officials, it's a huge nightmare, and it scares us because it's so easy to sneak a piece of fruit in with no malice or malintent and then chuck it out into a trash can or into the environment, and it just releases another invasive species or introduces a new plant disease," he told HPR.
This interview aired on The Conversation on Aug. 26, 2024. The Conversation airs weekdays at 11 a.m. on HPR-1.
