Virtual Museum of Canada
Jardin botanique de Montréal 
Centre for Forest Research

Rot, carpophores, canker and other problems

When a tree loses a battle, parasites move in. But only time will tell whether it will end up losing the war. Trees do have lots of tricks up their sleeves: anatomical barriers, chemical reactions, toxic compounds, and more. The tree's response depends in large part on its general state of health: a healthy, mature tree has more resources to devote to fighting off the disease than an old, sickly, dried out and malnourished one.

Since the dawn of time, each tree species has had its own list of associated diseases. And these diseases evolve, some becoming more resistant and others more infectious, until a balance is usually reached. Some experts even say that this evolutionary pressure is a major source of biodiversity.

Photo of bitternut hickory (Carya cordiformis) branches covered by round-shaped cankers, caused by the Phomopsis fungus
Phomopsis spp. on Carya cordiformis
© Frédéric Coursol

This bitternut hickory certainly looks as though it is covered in Christmas ornaments. In fact, though, each of these galls (look at one by clicking on [b]Visual Aid[b]) is a site where the tree is infected by Phomopsis fungi.