where the fungus
has penetrated through the stomata. These lesions then grow,
coalesce and produce uredospores with their distinctive orange
colour (Fig. 2a and c). Chlorotic spots can be observed
on the upper surface of the leaves. During the last stage of the
disease, lesions become necrotic.
Coffee rust became a concern for coffee-producing Latin
American countries mainly before (Wellman 1952) and just
after its introduction to these countries (Muller 1971; Waller
1972; Schuppener et al. 1977). At that time, the disease was
feared, because all Latin American coffee plantations grew
susceptible cultivars. However, soon after proving the effectiveness
of chemical control and due to the relatively limited
damage caused by the disease, particularly at high altitudes,
Mesoamerican coffee farmers and technical authorities began
to consider it to be manageable. This general view prevailed
until the 2008 to 2013 epidemics hit Mesoamerica, from Colombia
to Mexico, including Peru, Ecuador and some Caribbean
countries (Cressey 2013).
Despite coffee rust not being feared by the farmers, the
disease had caused significant losses even before the period
2008–2013. Most of these losses went unnoticed due to an
interaction between the disease and the coffee tree phenology.
For some (not well understood) reason, coffee rust attacks are
more severe on high yielding coffee trees (Zambolim et al.
1992; de Carvalho et al. 1996; Avelino and Savary 2002;
Avelino et al. 2006; Lopez-Bravo et al. 2012). In addition,
coffee trees exhibit a biennial production rhythm, particularly
at full sun exposure: high yielding trees normally produce low
yields the following year and vice versa. After a high yield
year, farmers therefore expect a low yield, with or without
coffee rust. However, the reduction in production may not
be attributed to the biennial production rhythm alone. Coffee
rust may also contribute to this decrease by killing severely
infected branches, such that they cannot bear fruits in the
following year (Fig. 1). These secondary losses, i.e. losses
caused by the current epidemic on productivity in the following
years, have probably always existed. Primary losses, i.e.
losses caused by the current epidemic during the current year’s
production, are less important. Usually, the fastest growth and
the peak of the epidemic are during and at the end of the
harvest, respectively (Avelino et al. 1991; Avelino and Savary
2002). Under these conditions, the current harvest is almost
unaffected. However, under certain circumstances, the epidemic
can reach high levels earlier in the season, causing the
premature death of branches, and the loss of the fruits they
bear, before the harvest. The recent epidemics, which affected
Mesoamerica, resulted in unexpected high primary losses due
to this phenomenon (Fig. 1). These apparent, direct, losses
indicated that something unusual was occurring.