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Coffee leaf rust management ‘a learning process’

LIHU‘E — Coffee leaf rust, avocado lace bugs and beetles with a potential connection to rapid o‘hia death were among topics under the microscope Wednesday, during an online conference dedicated to Hawai‘i’s invasive pests.

The Kaua‘i Extention Office of the University of Hawai‘i College of Tropical Agriculture and Human Resources hosted the event, which featured speakers from throughout the state and mainland.

CTAHR Extention Agent Andrea Kawabata, based in Kona, Hawai‘i Island, claimed researchers in Portugal recently identified the coffee leaf rust found in Hawai‘i as Race 24.

It’s one of 50 races of CLR currently found throughout the world.

“Race 24 affects many of our commonly-grown varieties, and literature on this race shows it to be prolific, quick to germinate, infectious and aggressive,” Kawabata said. “Knowing this, we will need to be aggressive in our management areas and find varieties that are resistant to this particular race.”

The presence of CLR, caused by the fungus Hemileia vastatrix, was confirmed on Kaua‘i last June. The local discovery came less than one year after the state’s first reported case on Maui.

Kawabata is recommending coffee growers stump one-third of their CLR-infected farm and selectively prune the remaining two-thirds, in conjunction with a prescribed fungicide schedule and other mitigation efforts detailed on her website,

“Coffee leaf rust is new, so it’s a learning process on how to best manage this disease,” Kawabata said.

She closed by reminding farmers the Hawai‘i Department of Agriculture CLR subsidy program, announced last autumn, remains up and running.

Qualified applicants to the program can receive 50% back on the cost of fungicides, with reimbursements up to $600 per acre.

Lace bugs and ambrosia beetles

The avocado lace bug (Pseudacysta persea) is another recent arrival to Hawai‘i, first appearing on O‘ahu in December 2019, and reaching Kaua‘i by May 2020.

The insect is now considered widespread on Kaua‘i and the major islands, causing leaf yellowing and dieback.

“I think everybody has seen this, probably, on their avocado trees,” said Jensen Uyeda, an extension agent on O‘ahu.

Uyeda is part of a team conducting small-scale pesticide trials on ALB-infected trees, to evaluate certain sprays’ efficacy.

Finding pest-resistant varieties and quantifying avocado orchards’ yield losses will come next, Uyeda said.

“It may be more practical, at least from an organic standpoint, to identify varieties that are more tolerant to damage,” he explained. “Meaning, they’ll still get damaged, but they still can produce relatively-good yields.”

Uyeda and his colleagues have already noticed differences in susceptibility between tree types, but have yet to see if these trends hold statewide.

Kylle Roy, of the U.S. Geological Survey Pacific Island Ecosystem Research Center and Purdue University, discussed invasive beetles that preliminary research indicates play a role in the spread of ROD.

“We have found five ambrosia beetles on Hawai‘i Island that are commonly associated with ROD,” Roy said. “…We’ve found all (but one of) these same ambrosia beetle species associated with ROD on Kaua‘i.”

Roy and others are preparing to submit their findings to the international, peer-reviewed Journal of Plant Pathology.

The CTAHR Kaua‘i Extension Office’s next online conference is slated for Wednesday, March 23, at 9:30 a.m.
Source: The Garden Island

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