Southern cone rust is caused by the fungus _Cronartium strobilinum_. It
has been reported to completely destroy slash and longleaf pine cone
crops in Georgia and along the Gulf Coast from Florida to Texas.
[Illustration: Cone rust symptoms on slash pine.]
[Illustration: (cont.)]
Like most other rusts, the fungus requires oaks and pines to complete
its life cycle. Although infection of oak leaves occurs annually, no
significant economic damage is done to the oaks. Fungus spores produced
on oak leaves infect the mature female pine flowers about the time of
pollination (January-February). The fungus grows through the developing
conelet causing it to swell abnormally. By early April or late May the
infected cones are three to four times larger than the normal first-year
cones and even exceed the maturing second-year cones in size. The
swollen cone scales are reddish in color. Cavities in the cone filled
with orange-yellow spores burst and the cones become orange-yellow. The
swollen orange-yellow cones in the tree crowns can be easily
distinguished from normal cones by an observer on the ground. By late
summer most of the diseased cones have died and fallen.
Control at present is confined to seed orchards. Hydraulic spraying of
the flowers with fungicides gives a significant reduction in infections.
Consult your local forester, county extension agent or the nearest
Forest Pest Management Office for current control recommendations.