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SOUTHERN CONE RUST
Swollen first-year conelets of slash pine infected with the southern cone rust fungus. Note brightly-colored (yellow) aeciospores.
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| Pathogens: |
Fungus Cronartium strobilinum |
| Common Hosts: |
Slash pine Pinus elliottii
Pines Pinus spp. |
| Alternate Host: |
Various Evergreen Oaks |
Significance: |
Southern cone rust is generally insignificant as a damaging disease of pines. It can, however, be of some economic importance in commercial forestry operations as a destroyer of cones and highly valuable, genetically improved seed in seed orchards and seed production areas. The disease is common in Florida, although it varies from year to year in its incidence and distribution. In particularly active outbreaks, southern cone rust is often very showy as the swollen, diseased cones on infected pines produce masses of bright yellow-orange spores. |
Recognition: |
Infected, first-year conelets of susceptible pines swell rapidly and by April are often three to four times larger than their disease-free counterparts. The scales of infected cones typically exude a sweet, sticky fluid (actually a spore stage of the pathogen) which is attractive to nectar-loving insects (especially cone moths, Dioryctria spp.). In the late spring (April - June) infected cones become readily visible, even at long distance, due to production of large powdery masses of yellow-orange spores (aeciospores) on their surfaces. |
Infection Biology: |
First-year female flowers (young pine cones) of host pines are susceptible to infections by the southern cone rust fungus from the time they emerge from bud scales until the end of the natural pollination season (late January to mid-February for slash pine). Infections are initiated by minute airborne spores called sporidia. Sporidia are produced on the infected foliage of several evergreen oaks including live oak, running oak, and dwarf live oak which serve as alternate hosts of the pathogen. As the disease progresses on infected cones, the showy masses of fungal aeciospores are produced. Aeciospores initiate new infections on the foliage of alternate host oaks. |
Control: |
In most situations controls are not necessary. In high value seed orchards or seed production areas southern cone rust can be controlled adequately through the regular application of certain fungicides during the period of conelet susceptibility (January - February). |
Bulletin No. 196-A | Printed October, 1983 | Contact the
Forest Health Section 
