Diseases of evergreens
Juniper/saskatoon and juniper/hawthorn rust
Juniper/saskatoon and juniper/hawthorn rusts are the most common rust in our area. Rust is a fungus which generally needs two host plants growing in the vicinity. Most need a deciduous host and an evergreen host. This fungus overwinters on a juniper, which develops brown, jelly-like telial galls on the branches in the spring. These harden in the summer, and needles beyond the galls die.
Pruning the branches of junipers back below the galls will help somewhat in reducing further rust infection. Prevention of galls on hawthorn is only possible by eliminating all deciduous hosts (juniper or saskatoon) for a radius of two miles! There is no chemical control.
Western Gall Rust
Western gall rust affects pine trees, causing a swelling in the branch that remains localized and usually does not spread to the main stem. It does not need a second host and can persist for many years without causing serious harm. Trees can become stunted or malformed and infected branches are susceptible to breakage in a storm.
Removing the galls prevents the windborne infection from spreading to nearby trees the next year. There is no chemical control.
Needle Rust
Needle rust on spruce causes powdery orange spores on the current year's needles, which drop prematurely. A wildflower, Labrador tea, is an alternate host, so affected trees are usually close to natural areas.
Cytospora canker cannot be controlled with any chemical. It can deform a spruce tree and eventually destroy it.
Cytospora Canker
Cytospora canker (also called leucostoma canker) is a common fungus on spruce trees, usually those stressed by severe drought, mechanical injury, poor nutrition, or hail injury. It begins on lower branches and moves upward, first causing dying needles as sap flow is inhibited. It causes cankers in the bark of branches that ooze amber colored sap. As it dries, it becomes a white crust.
Cytospora canker cannot be controlled with any chemical. It can deform a spruce tree and eventually destroy it.
Nectria
Nectria canker is a common secondary infection where other cankers are present. It consists of small orange spots that live on dead wood. It is not a problem in itself, but simply indicates dead wood.
Nectria canker does not harm its host. It lives on dead wood. It is a good indicator for pruning out dead wood, particularly on the inside of cotoneasters.
Armillaria root rot
Armillaria root rot causes reduction of growth and reddish discoloration of needles in pine trees. White, thready fungal growth at the base of the tree, and yellowish-brown mushrooms in the soil around the tree, are indicative. Small trees may be killed quickly, but larger ones can live for many years. The disease tends to affect already weakened trees.
Armillaria root rot cannot be controlled with a chemical. It is wise to remove infected trees and not plant pines in the affected area.