Comandra Blister Rust
Cooperative
Extension, College of Agriculture & Life Sciences, The University of Arizona
Written by
Deborah Young, Associate Director, Cooperative Extension
Mary W. Olsen, Plant Pathology Specialist
At a Glance
- Mondell pine should not be planted within a mile of Comandra populations.
- Infection of pine occurs through needles by spores produced on Comandra, but spores produced on pine cannot re-infect pine.
- There is no effective control for Comandra blister rust, and infected trees should be replaced with non-susceptible native trees.
Fig 1. Comandra blister rust on Mondell pine.
Comandra blister rust is a native disease in Arizona on ponderosa pine.
It also occurs on Mondell pine, a pine species introduced for landscapes
and Christmas tree production in Arizona. Comandra blister rust can cause
death of ponde-rosa saplings, but it is not an important disease of mature
ponderosa trees. However, infections kill Mondell pine, and they should
not be planted within a mile of Comandra.
The alternate host for the rust is Comandra pallida, for which the disease is named. Comandra pallida, commonly called bastard toadflax, is a small herbaceous perennial plant found in close association with oak. It has small light pink flowers in terminal clusters and nutlike fruit. It is found throughout Arizona at elevations of 4,000-8,000 ft.
Pathogen - Comandra blister rust, Cronartium comandrae.
Hosts
Pinus eldarica (Mondell pine, Afghan pine), Pinus ponderosa
(ponderosa pine) and
Comandra pallida, bastard toadflax.
Symptoms/ signs
On Mondell pine, Comandra blister rust causes branch dieback and death of trees of all ages. Swollen areas develop in branches and trunks, and the bark and underlying sapwood die. On pine, orange "blisters"develop on trunks and branches as the bark splits and ruptures. Infections on Comandra, the alternate host, appear as orange or rusty colored pustules on leaves after summer rains.
Disease
Fig 2. Generalized life cycle of Comandara Blister rust
Like many rust fungi, Comandra blister rust is a very specialized
pathogen. It requires two specific hosts (pine and Comandra) to
complete its life cycle and has five different spore forms. Infection
occurs in pine needles after rains in late spring or after the summer
monsoon in late summer by spores (sporidia or basidiospores) produced
on the alternate host, Comandra. These are delicate spores that
can travel in air currents only about one mile. During the first year,
the fungus becomes established in pine bark, and swollen areas with fruiting
structures (spermago-nia) develop in branches and trunks.
The following year a different spore stage, the aecial stage, develops
on pine in April and May. Aecia develop into bright orange blisters, then
rupture and produce spores (aeciospores). The bark cracks and dries out,
resulting in death of the bark and sapwood. The aeciospores produced on
pine infect Comandra when there is enough moisture for germination.
Aeciospores do not re-infect pine. They remain viable after being air
borne for long distances, and can infect Comandra many miles from
the nearest ponderosa pine.
During the summer, other spores (urediniospores) develop on the Comandra and infect only Comandra. This stage is known as the repeating stage since the urediniospores re-infect Comandra throughout the rainy season and cause an increase in disease in Comandra. An overwintering or resting stage, the telium, develops on Comandra in summer and fall. After spring and summer rains, the cycle begins over again the following year as telia on Comandra germinate and produce spores (sporidia) that infect pine.
Fig 3. Rusty colored pustules (aecia) on pine
Environmental conditions
Disease is favored by high humidity and moisture. Infection of pine usually occurs after spring rains in April and May or the summer rainy season from July through September when spores produced on Comandra are carried by air currents for short distances. These spores do not effectively move more than one mile from their host. However, the potential for disease occurs wherever Comandra grows and susceptible pines such as Pinus eldarica are introduced. Landscape environments and Christmas tree plantations afford a good microclimate for disease since low branches and close proximity of trees increase humidity.
Fig 4. Swelling and cracking of trunk of Mondell pine infected with Comandra blister rust.
Prevention/ Control
Susceptible pines such as Mondell pine should not be planted within a mile of Comandra populations since the spores that infect pine must come from Comandra. Disease has been severe on Mondell pine in areas of oak habitat near Prescott and Sedona where Comandra is common, but has not been observed in Christmas tree plantations in the Sulfur Springs Valley. Although fungicide applications may suppress development of the fungus on pine, they have not been shown to kill the fungus and are, therefore, not recommended. In landscape pines, removal of lower limbs and use of drip irrigation may reduce humidity and disease but are not reliable strategies for control.
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Document located http://cals.arizona.edu/pubs/diseases/az1310/
Published February 2003
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