Coffee Leaf Rust monitoring data on Hawaii Island

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.