Leaf rust is caused by Puccinia recondita (synonym P.
rubigo-vera), a basidiomycete that is a heteroecious, long-cycle
rust. The fungus produces round, red-brown, spiny urediospores
with three to eight scattered germ pores. Dark brown to black
teliospores are flattened at the tips.
Wheat is the major host, but Aegilops and Agropyron
can also be attacked. Thalictrum (meadow rue), the aecial
(alternate) host, is not important in leaf rust development in
Symptoms and Signs
The first evidence of leaf rust is the development of small,
round, bright orange pustules scattered over leaf blades and
sheaths. Sometimes a chlorotic halo surrounds the pustule. The
pustules darken with age, becoming orange-brown to cinnamon-brown
as teliospores are produced (Photo 10).
Urediospores perpetuate the rust on green host tissue just as
with stripe rust, but leaf rust requires warmer temperatures
(between 59 and 72F) to develop. Teliospores remain within the
pustule and persist over the winter.
Chemical. If an epidemic develops, some of
the systemic triazole fungicides can control leaf rust. Some
protectant fungicides are registered for leaf rust, but their
use is of questionable economic value under Washington conditions.
Resistance. There is good leaf rust resistance
in the spring wheats but relatively little in winter wheat cultivars
(Table 4). Most of the club wheats can be severely damaged. Leaf
rust resistance is partially based on a "slow rusting"
characteristic. Epidemics develop at a reduced rate because of
fewer infections, a longer period of time between infection and
sporulation, fewer urediospores per pustule, and a shorter sporulation
Table 4. Resistance to stripe rust and leaf rust in Leaf
rust selected Washington wheat varieties. Adapted from the 1985
ratings of the Washington State Crop Improvement Association.