Ask Your PCA: How do moist conditions affect almond trees?

Issue Date: February 9, 2022
Justin Nay PCA, Integral Ag Services, Durham
Justin Nay

Dry conditions started the 2022 season. This has resulted in a few almond orchards starting to push flowers in Northern California. While dry conditions aren't ideal for the overall season, they do have benefits during bloom.

A dry bloom reduces the risk of disease and saves money on fungicides. This is advantageous to growers with the price of chemical applications and supply-chain issues making it expensive and difficult to get fungicides.

But a dry January doesn't guarantee a dry February. If the weather patterns change, growers will have to apply fungicides to prevent disease.

In recent years, the more prevalent diseases have been bacterial blast, jacket rot and anthracnose in Northern California and the Central Valley. Moisture in the orchard drives these diseases. Some are spread by wind, some by raindrops. Dew can also be problematic. For the most part, moisture and almond trees do not mix.

With a wet bloom, brown rot is a concern for older orchards. For younger orchards that are more tightly planted, jacket rot is of greater concern.

Brown rot takes time to build up inoculum in an orchard. It directly reduces yield by killing flowers, and it becomes very unsightly. With prolonged periods of rain, flowers become infected, and the disease moves into the stem, killing multiple flowers and nuts. Infections can move into low branches or scaffolds and kill or create a canker that produces disease in the following years. Flowers are most susceptible when fully open.

Jacket-rot-infected petals develop water-soaked brown spots, and some may fall onto the leaves, causing secondary infections. The infection can spread to floral tubes or flower jackets causing them to wither and stick to developing fruit. As fruit sets and grows, brown spots develop where the jacket sticks to them. It can kill nuts, cause deformation, and even get into the into the peduncle and kill the spur.

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

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