Wherever coffee is produced, the discovery of ‘coffee leaf rust’ can be devastating news for growers. With its detection in Hawaiʻi late last year, CLR quickly became a serious threat to the second highest-valued crop in our state.

“In other coffee-growing areas worldwide, CLR is managed by maintaining plant health, planting resistant varieties, and applying systemic fungicides – but in Hawai‘i, resistant varieties and systemic fungicides are not yet available,” explains Zhiqiang Cheng of the Dept. of Plant and Environmental Protection Sciences.

“Local growers,” he continues, “currently have copper products and a few biological products available for use, but these products mainly work as preventative or contact protectants, and mainly when infection levels are low. Systemic fungicides typically provide longer-term control through penetration and  movement in the leaf tissue.”

But since 2017, the Hawai‘i IR-4 Program has been preparing for the day when CLR might reach our Islands. Then-PI Michael Kawate (now emeritus), Zhiqiang (current PI), Julia Coughlin, and James Kam have been working to generate the data required to register Quadris^®Xtra, a systemic fungicide, to control CLR.

“Although Hawai‘i didn’t have CLR at that time, this was a pre-emptive strategy – we wanted to have a systemic product available, if and when CLR arrived,” says Julia. “This hasnʻt been labeled yet, but we are continuing efforts on this project.”

When CLR was first detected in Hawai‘i, Julia immediately contacted the national headquarters of IR-4. Since 1963, this federally funded program has been a primary resource for helping specialty crop growers with their pest-control needs by developing data to support the registration of pest-management products.

IR-4’s plant pathologist quickly reached out to product registrants, hoping to identify an effective fungicide with data on international residue, efficacy, and crop safety – data needed to support an emergency registration.

A potential product was identified, and a multi-agency team (Hawaiʻi Coffee Growers, Hawaiʻi Dept. of Agriculture, BASF, and others) took it from there, successfully obtaining an emergency exemption for the use of BASF’s fungicide product Priaxor® Xemium®. IR-4 supported this effort by preparing the residue data summary needed for EPA’s dietary risk assessment. IR-4 will also prepare the Sec. 3 petition to EPA to add coffee to the Priaxor® label. This will count as progress toward registration, a requirement to renew the Sec. 18 emergency exemption for Priaxor® next year.

While the Sec. 18 submission was in preparation, BASF requested crop safety data. In response, the Hawaiʻi IR-4 Program conducted two field trials testing Priaxor with three different adjuvants to see whether sprays caused any burning or adverse effects on the plants.

“No adverse effects were observed,” says Zhiqiang, adding, “Our field program is currently conducting field efficacy and crop safety trials to screen other potential fungicides. We look forward to more fruitful collaboration as we generate additional field efficacy data and submit proposals to control CLR.”

Read the article, Coffee Rust Attacks Hawaii Coffee Trees; IR-4 Fights Back.

CLR photos courtesy of Forestry Images.org