What is in this article?:
- There is an increase in canker-caused trunk disease in California almonds which can result in large financial losses for some growers.
- UC farm advisor David Doll says the increasing canker problem is caused in part by almond tree cultural management practices which focus on high vigor.
- One Merced County almond grower lost more than $16,000 to canker disease in a 15-acre field.
Doll’s preliminary results from the studies suggest that large cuts made on primary and secondary scaffolds are more detrimental to tree longevity. Aldrich and Padre appear to be more susceptible to canker damage than Carmel, Nonpareil, and Butte. More field data is needed to confirm this.
“The take home message is large cuts made on primary and secondary scaffolds can impact the long-term sustainability of the orchard,” Doll said.
Pruning cuts are necessary in almond production to train the tree for growth and production, plus to remove branches so equipment can pass through the orchard.
In recent years, the almond industry has shifted to less pruning to boost tree vigor and yields.
“I really believe we are seeing more canker disease due to shifting cultural practices,” Doll said. “We are growing larger trees which means farmers prune less, but when farmers do prune larger cuts are made. This creates a larger target for fungi and possible infection.”
Doll says the almond industry needs to change cultural management in the early parts of tree development for better canker control. He has several thoughts.
First, make maintenance pruning cuts further from the trunk of the tree.
“This will help keep infection from moving into the trunk and risking the structural integrity of the tree,” Doll explained. “If farmers can prevent infection of the trunk and the original scaffolds coming off the trunk, I think they can do a pretty good job managing cankers.”
Another point, Doll says, is perhaps farmers should re-think the tree vigor issue.
“Maybe farmers shouldn’t grow the trees so fast,” Doll said. “It is a very hard argument to make to an almond farmer but it is something to consider since it impacts the number and size of the cuts along the tree trunk.
Additional research is needed to study the impact of rain events when cuts are made. Instead of making cuts during the summer months, research needs to weigh the impact of cuts during the early spring and late fall.
University of California plant pathologist Themis Michailides of the Kearney Agricultural Research and Extension Center is currently examining the healing time of pruning cuts as it relates to infection susceptibility.
Overall, Doll considers trunk canker disease a low risk to the overall almond industry. Yet control strategies should be developed and implemented early on as fungi infection impacts orchard longevity.
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