Figure 227. White-spored gall rust displaying spore sacs and swollen branch.
Symptoms/Signs: This fungus forms round or pear-shaped galls on the main stem
or branches, which emit orange spores. There is a white-spored race
in Arizona and New Mexico that sometimes develops elongated galls.
Biology: This disease spreads directly from
pine to pine. Infection occurs on a needle-bearing twig. The fungus
stimulates the production of xylem, forming galls, which enlarge
over the years. Spores appear on the galls in late spring.
Effects: This disease is probably widespread
in the region, but at very low levels. Occasionally it has been
destructive to seedlings and saplings, following infrequent “wave
years” of new infection. Gall rust deforms but seldom kills
older trees.
Similar Diseases:Dwarf
mistletoe can cause trunk swellings (cankers) that are usually
much longer than those produced by western gall rust.