Early Detection Key to Managing Ceratocystis Canker in Almonds
Ceratocystis canker, caused by the fungal pathogen Ceratocystis fimbriata, is one disease among a complex of fungal canker diseases that infect almond trees.
Based on a statewide survey out of the Department of Pathology at University of California, Davis, canker diseases are the primary cause of tree death in almond orchards, and Ceratocystis canker is one of the most prevailing canker diseases found in California. This canker disease is aggressive, but it doesn’t have to mean disaster.
“If you know what to look for, the disease is manageable,” says Florent Trouillas, UC Cooperative Extension Specialist, Department of Plant Pathology, University of California, Davis.
The key to successfully managing Ceratocystis canker is accurate diagnosis, which means knowing specifically which canker disease you’re dealing with. A quick visual diagnosis may not always be correct, leading to inappropriate management practices, Trouillas says.
“There’s a lot of overlap in what the various canker diseases look like, so it’s easy for Pest Control Advisors (PCAs) and growers to assume when they see profuse gumming on a tree’s trunk that they’re dealing with one type of canker over another,” he says.
A specific amber gumming pattern at the site of shaker injuries caused by mechanical harvesting is a prime indicator that Ceratocystis canker has infected your tree. The pathogen is unique in that it develops mainly around the cambium tissue at the point of injury.
Cause and Spread
Unlike other types of canker diseases, Ceratocystis canker is spread by insects and not by rain or irrigation water. One of the pathogen’s main entry points is shaker injuries, where the pads of a shaker injure a tree’s bark. Once the bark is compromised, the tree emits specific compounds. Insects, including beetles and the drosophila fly, are drawn to these compounds, spreading the disease as they feed on the pathogen’s spores.
Pruning cuts also provide entry points for Ceratocystis canker. If you remove a branch to get it out of the way of field equipment, for example, you may want to protect it with a fungicide. Your PCA can help you choose the right product for your tree.
Bark injuries and pruning wounds are susceptible for up to 14 days, Trouillas says, and cankers are most active during the spring and summer growing season.
“Trees in the third and fourth leaf are most likely to die from an early infection. Older trees are not as prone to decline,” he says.
The disease may be managed by avoiding bark injuries from mechanical shakers. If the bark is injured, remove the damaged tissue to the edge of the injury to promote callus formation.
“In theory, large pruning cuts and shaker injuries can be treated with the same fungicide. However, our fungicide experiments were only conducted on pruning cuts, not shaker injuries. The fungicide Thiophanate-methyl appears to be efficacious against a broad range of canker pathogens, including Ceratocystis,” Trouillas explains.
He goes on to explain that tree surgery has proven effective on shaker injuries because of the different nature of the wound. The thought is to remove the infected tissues of the trees that already are affected and showing gumming symptoms. Cleaning the damaged bark can be done before infection occurs — as a means of prevention. The idea is to remove the broken bark and expose the cambium to promote callousing and the trees’ natural healing process.
Trouillas says the best way to manage the disease is to prevent it from occurring. “This comes down to good operator training to avoid shaker injuries in the first place.”