Fungicide efficacy and duration of protection against coffee leaf rust (Hemileia vastatrix) on commercial coffee farms in Hawaii

Authors: ARISTIZABAL, LUIS - University Of Hawaii; Maeda, Colby; Matsumoto Brower, Tracie; Johnson, Melissa

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2025
Publication Date: 5/7/2025
Citation: Aristizabal, L.F., Maeda, C.T., Matsumoto Brower, T.K., Johnson, M.A. 2025. Fungicide efficacy and duration of protection against coffee leaf rust (Hemileia vastatrix) on commercial coffee farms in Hawaii. Crop Protection. 196. Article 107269. https://doi.org/10.1016/j.cropro.2025.107269.
DOI: https://doi.org/10.1016/j.cropro.2025.107269

Interpretive Summary: Coffee leaf rust (CLR) is the most devastating disease of coffee worldwide, causing an estimated $1-2 billion in annual losses. In the absence of CLR-resistant coffee varieties, chemical controls in the form of preventive and curative fungicides are the first line of defense. Given the high levels of CLR infection observed on Hawaii Island coffee farms despite frequent fungicide application, a better understanding of fungicide efficacy and the duration of protection provided by these products are needed to manage CLR while minimizing costs, environmental impacts, and potential harm to farm workers and surrounding communities. We conducted a field trial in Hawaii to determine the efficacy, duration of protection, and cost of application for several preventive and curative fungicides against CLR in commercial farms under varying environmental conditions. The fungicides tested in our field trial fell into four different FRAC groups, and fungicides in these different groups were observed to have significantly different effects on CLR incidence, leaf retention, and duration of protection. We found that both treatments with the translaminar fungicide significantly reduced CLR incidence to below 2% for the duration of the trial (12 weeks of protection), and significantly increased leaf retention. The two copper-based products reduced CLR incidence below the 5% threshold in both years, significantly increased leaf retention, and provided 7-8 weeks of protection. In contrast, applications of the two biological fungicides and the botanical fungicide either had no effect on incidence or resulted in significantly higher incidence. Based on the results from this study we provide four example spray rotations for coffee growers to consider based on efficacy, cost, harvest restrictions, and management style.

Technical Abstract: Coffee leaf rust (CLR, Hemileia vastatrix) is recent arrival to the Hawaiian Islands, and quickly became the most significant challenge to the small but economically important coffee industry. Frequent sprays of fungicides and the improvement of agronomic practices (weed control, fertilization, and pruning) have been the primary management strategies for controlling this devastating disease. However, the high cost of products and labor coupled with the potentially harmful effects of chemical inputs have made frequent (monthly) applications of fungicides economically and environmentally unfeasible. The aim of this study was to determine fungicide efficacy against CLR, duration of protection, and cost of applications in field trials conducted on commercial coffee farms on Hawaii Island in 2022 and 2023. The translaminar fungicide Priaxor Xemium was the most effective fungicide tested, keeping CLR below 2% over a 12-week period. Copper-based fungicides (Badge X2 and Kocide 3000) were also effective at keeping CLR at or below the 5% action threshold, although the duration of protection was shorter (7-8 weeks) relative to the translaminar. Copper fungicides were the most cost effective of all products examined ($124/acre), followed by the translaminar ($140/acre). In contrast, the Bacillus-based fungicides (Serenade ASO and Double Nickel 55) and the botanical fungicide (ProBlad Verde) did not reduce CLR incidence and were more expensive to apply ($136-$212/acre) than the copper and translaminar products. These results suggest that conventional coffee farms in Hawaii can effectively control CLR by alternating applications of translaminar and copper-based fungicides, aiming to apply a total of 4-6 sprays between flowering and harvest to reduce negative impacts on leaf retention and yield. Without the option to use translaminar fungicides, organic farms and farms with a year-round season will need to alternate between copper and biological-based products to control CLR, aiming for 6-8 sprays between flowering and harvest.