In the battle against pests and diseases, those who fight the fight are never without problems to solve.
Luke Milliron, UCCE Orchards Advisor in the Northern Sacramento Valley, has his hands full this season worrying about both a physiological condition, leafing failure -- “I’m seeing lots more of it this year” — and almond leaf scorch, a disease — “I’m worried there will be more scorch problems this summer following a relatively mild winter.”
Leafing failures in the Monterey variety were first noted in 2018 with University of California advisors reporting leaf-out issues in several varieties in 2020, especially in younger Bennett Hickman trees.
“Our understanding of this is still evolving,” Milliron said. “We don’t know how significant almond leafing failure and leaf scorch will be in 2021 as it may depend on what weather conditions we experience. With both problems recently increasing in prevalence in parts of the Central Valley, I wouldn’t be surprised to see them both again this year and suggest that growers mark affected trees and monitor their progress.
“Be wary of premature removal, increased fertilization, or increased irrigation of the affected trees.” Milliron said. “Give them time to show whether they are declining, plateauing, or heading towards recovery.”
With responsibilities in Butte, Glenn, and Tehama Counties, he acknowledged: “It’s tough because we really don’t know what’s causing the leafing failure problem seen foremost in Monterey, the second most important almond variety, but branching out to other varieties, too.
Many possible causes
There’s the possibility it’s a bunch of different causes affecting different varieties. We had a good chill this year and yet we’ve had problems like blank wood and dormant buds. It could be related to previous stress or some component of winter temperatures, but at this point, we really don’t know it’s cause.”
Some Monterey have been observed lacking leaves, but flowering and fruiting. And yet, when you cut into living wood, it ultimately dies by year-end resulting in a loss of branches and no new growth.
“If you’re losing branches, you’re seeing your future yields go down and that’s scary. It’s a concern about what trees look like today and their implications on growth which will impact yield over the next couple of years,” he said.
Researchers are making a distinction between leafing failure and non-infectious bud failure experienced in Carmel and other varieties.
“There is no perfect variety (although the closest thing we have is Nonpareil). It’s always a conversation of risk, different issues with different varieties,” he said.
“We’re seeing the same Monterey trees with leafing failure get worse each year, not better, and some growers have tried severely pruning back the tree although it’s too early to say whether or not that’s a fool’s errand or whether it will help some.”
Also of continuing concern is almond leaf scorch. “I sent off a lot of samples last year suspecting leaf scorch, although most came back negative,” he said. “Another farm advisor during that super heavy crop year attributed similar symptoms in one orchard to extreme potassium deficiency. I encourage growers to make sure they take July leaf samples so we can rule out some other problem rather than a nutrient deficiency or a salt excess brought about by the drought.
“You should be doing leaf analysis anyway, checking your nutritional program and water quality,” he said. “It’s so much cheaper than having to do a pathogen test.”