Monitoring coffee leaf rust (Hemileia vastatrix) on commercial coffee farms in Hawaii: Early insights from the first year of disease incursion

Authors: ARISTIZÁBAL, LUIS - Synergistic Hawaii Agriculture Council; Johnson, Melissa

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2022
Publication Date: 5/8/2022
Citation: Aristizábal, L., Johnson, M.A. 2022. Monitoring coffee leaf rust (Hemileia vastatrix) on commercial coffee farms in Hawaii: Early insights from the first year of disease incursion. Agronomy Journal. 12(5). Article 1134. https://doi.org/10.3390/agronomy12051134.
DOI: https://doi.org/10.3390/agronomy12051134

Interpretive Summary: Coffee leaf rust (CLR) is a new fungal pathogen in Hawaii that threatens the states small but economically important coffee industry. We conducted surveys on commercial coffee farms from late 2020-2021 and observed the rapid spread of CLR across multiple growing regions on Hawaii Island. Our surveys on commercial coffee farms in Kona revealed an average CLR incidence of 36% during the 2021 harvest season, which resulted in severe defoliation on farms spanning a range of elevations. Our observation of high incidence and defoliation after just one season of CLR in Hawaii points to the need for CLR-resistant cultivars, since the reliance on fungicides to manage this disease is not a sustainable long-term solution. Cultural control practices (fertilization, pruning, sanitation, control of weeds, regulation of shade trees, etc.) that improve coffee tree health are also essential for reducing CLR pressure. In addition, monitoring CLR incidence is a key practice for establishing a rotational fungicide application program to protect coffee leaves when they are most susceptible to CLR attack (45-180 days after flowering).

Technical Abstract: Coffee Leaf Rust (CLR, Hemileia vastatrix) is considered the most damaging coffee disease worldwide, causing reduced yields and even plant death. CLR was detected in Hawaii for the first time in 2020 and quickly spread across the state. We initiated a CLR monitoring program in Kona, West Hawaii Island to track the spread of this new invasive disease across a broad elevational gradient. The goals of the program were to assist growers in the early detection of CLR, to characterize patterns of disease incidence across the region, and to collect information on farm agronomics, management practices, and costs to apply fungicides, all of which can be used to develop IPM strategies for this pathogen. We monitored 30 coffee lots in Kona, located between 204 and 875 m elevation. Average CLR incidence remained below 4% early in the season and increased to 36% during harvest. We observed no significant difference in CLR incidence between low-, mid- and high-elevation farms. A significant reduction in the number of leaves per branch was observed at the end of the harvest season, and a significant negative correlation was found between the number of leaves per branch and maximum CLR severity. Mean disease incidence and mean severity were observed to have a significant positive correlation. Incidence increased above threshold levels (5%) despite most growers applying preventative fungicides 3-10 times throughout the season, suggesting that improved coverage and timing of applications is needed along with the addition of systemic fungicides. Our study provides the first insights into CLR disease patterns under the unique and variable conditions under which Hawaiian coffee is grown and will aid in the development of IPM programs that can be used to sustain Hawaii’s coffee industry under this new threat.