Pine tree infections: White Pine Blister Rust
The Eastern White Pine, our symbolic tree, is integral to our province’s ecosystem but is now threatened by invasive pine tree infections.
One of the most dangerous pine tree infections threatening Eastern white pines in Ontario is White Pine Blister Rust (Cronartium ribicola). There is no cure for White Pine Blister Rust once it has taken hold within an infected tree. As such White Pine Blister Rust poses a substantial risk to the native white pine populations in Ontario.
What is White Pine Blister Rust?
White Pine Blister Rust is a non native, invasive pine tree infection caused by the fungus Cronartium ribicola. It infiltrates the trees and forms cankers, causing their bark to burst open. Cankers appear first on branches and move to the trunk once the disease has taken hold. Once cankers appear on the trunk, the eventual death of the tree is inevitable.
Which trees are affected by White Pine Blister Rust?
White Pine Blister Rust targets white pine species, with the Eastern White Pine (Pinus strobus) being the most susceptible in Ontario. The Eastern White Pine is the largest species of tree in our area, growing to 30 m in height with a crown spreading to 12 meters. However, all five needle pine species can be affected. Due to the dominance of white pines within our forests this is one of the pine tree pests and diseases most threatening to our local ecosystem.
Damage Caused by White Pine Blister Rust
White Pine Blister Rust causes significant damage to infected trees, impacting their growth, reproduction, and overall health. The fungus disrupts the normal physiological functions of the tree, leading to reduced photosynthesis, nutrient uptake, and water transport. The development of cankers on branches interferes with the flow of essential nutrients, resulting in weakened and stunted growth. Eventually, the cankers reach the trunk of the tree, where they completely encircle it, leading to the death of the tree. Ultimately, if not addressed, White Pine Blister Rust can lead to the decline and mortality of white pine populations.
White pine blister rust symptoms
Infection takes place in the late Summer or early Fall, but the disease takes several years to complete its life cycle, so you will notice progressive symptoms over a number of years.
White pine blister rust life cycle
White Pine Blister Rust needs two unrelated hosts to complete its life cycle. The first stage of this pine tree infection begins in the spring when white blisters, called aecia, appear on trees infected the previous year. Within the blister, fungal spores are produced, which are released into the air when the blister eventually bursts.
These spores cannot infect other pine trees – they require a different host – species of the genus Ribes, which includes currants and gooseberries. The fungus forms infections on their leaves and stems but does not tend to do much damage to this host and may not even be visible. The infection develops on the plant, finally producing basidiospores that can only infect pine in the Fall.
The spores are carried on the wind, and if they find a suitable species of pine within a few kilometers will infect them by entering through the needles. The fungus then will spread from the needles into the twigs and branches over the next 12 to 18 months. White blisters will begin to appear on infected branches the following spring.
Meanwhile, the fungus on the originally infected tree has spread into living bark on the branch. Each year more aecia are produced in spring, release their spores, the bark on which they were living dies back and the fungus moves on to living bark. It keeps spreading until the branch or stem is girdled and killed.
