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.
Over the last several years, two new types of cankers have appeared – cankers which infect the tree’s pruning wounds and cankers which target tree cracks, festered by the wind.
These cankers are caused by the highly destructive fungal pathogen Botryosphaeria spp.
These latest cankers typically grow throughout the summer and are more commonly found in the Padre and Fritz almond varieties, but are also found in Nonpareil, Avalon, Carmel, and Aldridge.
“Usually when a farmer first sees this disease it is not very noticeable,” Doll said. “Suddenly the canker enlarges and it’s very obvious. Then the tree starts falling apart and the crop yield eventually declines.”
Doll has studied cankers, including those with Botryosphaeriaceae fungi, in almond plantings across Merced County. One photo he shared was of a tree with the bark removed which revealed a bright yellow-colored canker at the pruning wound site.
“You can see this nice beautiful canker on this tree. Don’t call it a beautiful canker to a farmer. They don’t like that very much,” Doll laughed.
Beauty is in the eye of the beholder.
The fungal infection causes a weakening of the tree scaffolds. Later, the tree splits from the crop weight and must be replaced.Damage is more common 3-6 years after planting.
“Essentially, the tree is worthless to the farmer,” Doll explained. “The farmer loses the crop on the tree, but also faces the added costs to replant and bring the tree back into production.”
Doll has conducted studies in six Merced County almond orchards, looking for Botryosphaeriaceae fungi-caused cankers, the amount of damage to trees, and possible management changes to help reduce the problem.
Of the six fields studied, tree losses varied. The lowest loss was 7 trees in a five-acre area planted in Nonpareil and Carmel in a 18X22 feet spacing (110 trees per acre). About 50 trees had canker damage.
The worst damage and loss was in a 15-acre Nonpareil-Butte-Padre orchard with the Buttes and Padres at the 5thleaf stage where 116 trees were lost to canker disease. The financial loss to the grower was $16,112, using the UC Tree and Vine Loss Calculator.