PEST FACT SHEET:

White Pine Blister Rust (Cronartium ribicola)

1. White Pine Blister Rust is caused by a fungus.

2. It is a disease of five-needle (a.k.a. white) pines, including Sugar Pine.

3. It is an obligate parasite, meaning it needs a living host to survive.

4. The complete life cycle of the pest requires two host species. It spends part

of its life on the pine, and the other part on plants of the genus Ribes, which

include gooseberry species.

5. The disease cycle is as follows: cankers, or sores, on the pine release spores,

which land on a Ribes plant and infect it. Eventually the fungus on the

Ribes plant produces another type of spore that returns to and infects the

pine, landing on the needles and growing to the branch, eventually forming a

canker.

6. The spores are spread from plant to plant by wind.

7. Moist, cool conditions are needed for spores to germinate and infect the

host.

8. Signs of disease on the pine are:

a. Brown spots on the needles;

b. Dead branches, called “flags”, in the crown; and

c. Fungal growths, called “cankers”, on the trunk.

9. The disease is more likely to attack and kill young trees.

10. Control strategies:

a. In the 1950’s, an effort was made to eradicate (completely eliminate)

all Ribes plants, but it was unsuccessful.

b. Now, breeding for pines that are naturally resistant to the disease is

the main strategy.

Left photo: Fruiting bodies producing spores on a pine

branch

Center Photo: Spores on the alternate host Ribes

Right Photo: A damaged branch, called a flag