“Band canker is not a new disease,” said Themis Michailides, a researcher in the Department of Plant Pathology at UC Davis, talking to growers at a recent Field Day. “It was described back in the 1980s. The disease was a curiosity, very sporadic.”
But in the last five or six years, Michailides said he and his colleagues are seeing it in very young trees.
Band canker is not just one fungus, but a group of them, he told growers.
When growers see gum, by that time the infection has occurred, he said. You can scrape the bark and find canker.
How does band canker happen? Traditionally, Michailides said, there were two main things to keep an eye on: micro sprinklers wetting trees, and young trees with vigorous growth, that caused growth cracks that let fungus in.
Sonora and Padre are susceptible, and the disease tends to show up in younger trees, he told growers.
“Once you have the symptoms develop, you cannot protect the trees,” he said.
Water can spread innocolum, so growers should be careful with sprinklers once band canker is spotted.
In Fresno County, canker cropped up in a second leaf orchard by a canal with nearby willow trees. On the other end of that field, zero trees were affected.
While traditionally growers were advised to keep micro sprinklers off canopies, now the UC advises growers to apply fungicide before the disease is seen.
Another key tip: Don’t leave stumps of dead trees in affected orchards.
The bark of those dead trees can be “loaded” with inoculum.