Ask Your PCA: What is best way to combat diseases during almond bloom?

Issue Date: February 12, 2020
Jed Walton PCA, Big Valley Ag Services, Gridley
Jed Walton

Rain during almond bloom means a higher risk of disease. Depending on whether it's a short or a long, drawn-out bloom, that could mean two to three fungicide applications. If it's dry and no rain, one application will be sufficient.

The main diseases at bloom are brown rot, shot hole and anthracnose.

Brown rot will kill the multiple flowers and fruiting spurs, which impacts next year's yield.

Shot hole creates lesions on the leaves that begin as tiny, reddish specks that turn into spots with tan centers and purplish margins. If it becomes severe enough, it will cause leaf drop.

Anthracnose causes flagging and kills the leaves or the flowers/spurs. Because it can kill multiple spurs and fruiting wood, it can also impact yield the following year.

Fungicides are used to treat these diseases, and most fungicides registered for bloom are safe for bees. If there is concern, spraying at night is advised, when the bees aren't active.

Ground application is the preferred application because it provides the best coverage. With a wet bloom, the orchard floor could be saturated, making that impossible.

The next option is air. Because there are limited helicopters and only so much ground can be covered in a day, it's advised to plan in advance as much as possible.

Nutrition is important at bloom as well. Though it is generally applied in the fall based on leaf and/or hull samples, weather or harvest may prevent a fall application. It can be applied at bloom, and research has shown it should be applied at pink bud before full bloom.

Irrigation is another important consideration heading into bloom. With a dry winter that depletes the profile, it's advised to irrigate early to rebuild it. Not only does it impact this year's crop, but the set for the following year as well.

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item.

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