[Illustration: Fruit gall showing orange colored spores on loblolly
pine.]
[Illustration: Alternate host—false toadflax.]
Comandra blister rust, caused by the fungus _Cronartium comandrae_, is a
canker disease of hard pines. The disease presently occurs in widely
scattered areas throughout the western, central, and southern United
States. In the South, the primary hosts are loblolly, shortleaf, pond,
and Virginia pine. Herbaceous plants of the genus Comandra, commonly
known as false toadflax or comandra, are also attacked.
The fungus infects pines through the needles and grows from the needle
into the branch or main stem where it forms a gall or canker. Dark
orange-colored spores which are produced on the surface of the gall in
the spring are wind-blown and infect the leaves or stems of the comandra
plants. Two to three weeks after infection, urediospores are produced on
the underside of the comandra leaf. These are wind-blown and can only
infect other comandra plants. Eventually hair-like structures known as
telia are produced on the comandra leaves and stems. The telia produce
spores which are wind-blown and infect the pine host through the needle.
The necessary combination of a susceptible pine host, the alternate
host, and the pathogen is presently known to occur only in northern
Arkansas, eastern Tennessee, and northern Alabama.
No effective method of controlling the disease in forest stands is
presently known. Silvicultural or forest management practices which
reduce the abundance of the alternate host offer promise of long term
control. Maintenance of dense stands and heavy ground cover as a means
of shading out the intermediate host plants, may be helpful in reducing
rust damage in many areas.