Ostoyoae Mushrooms at the base of a dead fir.
Persistent. That’s the word to describe Armillaria. Armillaria is the genus name of a group of mushroom-forming fungi, some of which are definitely bad news for blueberry growers. Different species of this fungi cause root disease on a diverse range of woody and root crops from forestry trees and fruit trees to potatoes and blueberries.
Bill Chapman, research scientist with BC Ministry of Forests, Lands and Natural Resources is well aware of the persistence of this fungi and has spent time understanding ways to prevent its destruction. Armillaria can impact plant health and yield, potentially killing the host plant, but worse – even without the plant, the disease can still spread.
To add insult to injury, Chapman notes the fungi can’t be controlled by chemicals.
“Armillaria is a very successful and long lived disease. It can live for millennia,” he says. “At an early stage of infection there may be little observable effect as infected plants isolate and wall off the infection.”
As the disease spreads and takes over more of the host plant root, yield will drop and leaves will turn red in times of drought, often preceding death of the plant. Don’t count on mushrooms always pointing the way to an early infestation. Chapman says mushrooms usually appear around or on the stems of seriously affected or dead host plants.
Interestingly, Armillaria doesn’t always lead to death. As Chapman explains, “It is common to find Armillaria susceptible species growing happily on centuries old Armillaria infections.”
But blueberry crops aren’t centuries old and are therefore often more susceptible. With its ability to pop up years later on new crops, prevention and control of Armillaria is essential.
“Management practices which introduce susceptible hosts into contact with Armillaria which they have little resistance to can result in a disequilibrium between disease and host,” notes Chapman. “Susceptible strains planted in an Armillaria affected area die in large numbers which creates an energy source for the Armillaria to attack healthy individuals and the disease takes on an aggressive character that is not the norm in natural settings.”
Chapman notes excess use of nitrogen fertilizer, poor sanitation practices and introducing infected soil or stock may encourage Armillaria growth.
Prevention and control are not normally achieved by digging the inoculum or infected roots out – though Chapman says this may slow the progress. Obviously, ensuring soil, soil amendments and stock are disease free is paramount. Resistant strains are a positive step as is intermixing multiple strains together to vary root structure.
Hypholoma fasciculare, a competing fungi, should be encouraged through healthy soil ecosystems with fresh organic matter. Sawdust and mulches free of root disease are recommended by Chapman for blueberries adapted to high carbon to nitrogen ratio soil. He also suggests forgoing peak yields for hardier plants.
Armillaria root disease is no walk in the flowers, but with the right practices in place, it can be managed and controlled.