Rust of pine and spruce: What should you know?

Rust is one of the most common and dangerous fungal diseases of conifers, which can lead to the drying out and death of plants. Rust affects various types of conifers, but is particularly common on pine and spruce. In this article, we will talk about the causes and symptoms of rust on pine and spruce.

What is rust and how does it occur?

Rust is a group of fungal diseases that are characterised by the appearance of multi-coloured rashes on the needles, branches or trunks of conifers that look like rust on metal. These rashes are fungal spores that are spread by wind, water or animals and infect other plants. Rust can lead to discolouration, deformation, drying and falling of the needles, and even death of the tree.

Pine and spruce rust can be either dioecious or monoecious. Dioecious rust means that the fungus has two or more plant species on which it develops and reproduces. Monoecious rust means that the fungus has one plant species on which it develops and reproduces. Dioecious rust is more dangerous because it can be transferred from one plant species to another and spread more quickly.

If a pine or spruce tree is infected with rust, then the tree gradually dries up, but at the same time, it infects other trees growing nearby, such as other pines or fruit trees on the ground. Pine rust, or bubble rust as it is also called, can develop over 2-3 years, it is a parasitic fungus that can have several host trees. If the full cycle of the fungus development is completed, the host tree dies. The rust usually affects two host trees, and 4-5 cycles of fungal development occur on the surface of these trees.

Why is pine and spruce rust actually called?

Pine and spruce rust is called so because of the appearance of the fungal fruiting bodies, which are bright orange in colour. These can be spore boxes on the branches and trunk of a pine tree or small spore bubbles on the needles. It looks like an accumulation of bright orange spores, and the area of the tree where they appear begins to corrode.

Mature rust fungus spores look like a fine powder that quickly spreads over long distances in the wind, thus overcoming tens of thousands of kilometers, which makes it difficult to determine why the plant was infected. The rust spores germinate in the smallest damage to the bark and needles of pine trees, and the disease can spread to both weakened and healthy trees.

If a pine or spruce tree is severely affected by rust, billions of fungal spores can form on the surface of the diseased tree, which, accordingly, poses a threat of infection to other types of coniferous plantations.

Rust can damage all types of pine trees, for example, cedar, Weymouth pine, lodgepole pine is more often affected by blister cancer, the causative agent of which is the fungus Melampsora pinitorqua.

Rust can cause problems such as witches’ brooms, poor tree growth, galls, and overgrowth of plant tissue.Rust spores are very difficult to spot in the early stages of the disease. Usually, it becomes clearly visible on the surface of the tree when an ugly thickening – a cancerous wound – forms in the place of their accumulation.

Black pines are particularly susceptible to rust, and these are the trees most often used in landscaping. If a pine tree is affected by rust, the crown of the tree dries up and the needles turn a bright brown colour, but the needles do not fall off immediately, so it is important to contact our specialists for help and advice in time.