Ask Your PCA: What are steps to protect prunes from diseases?

Issue Date: April 13, 2022
Mateo Marquez, PCA, Integral Ag Services, Durham
Mateo Marquez, PCA, Integral Ag Services, Durham

Prunes are just finishing bloom and fruit is starting to size, making water management critical. Water stress, especially as it begins to get hot in May, can cause fruit to drop. It's important to ensure the trees have ample irrigation to mitigate against Cytospora canker, a problem commonly associated with sunburn.

Wilting or flagging of a branch is an indication of Cytospora canker. The canker eventually girdles the branch, causing it to die later in the season. It's a problem that occurs year after year and can largely be prevented with sound irrigation and nutrient management.

Growers should also be on the lookout for rust. That can be a big problem. It's important to manage the disease to keep it from becoming epidemic, because unchecked, it can defoliate the trees and increase stress.

The most common symptoms of rust are bright yellow spots on the leaves, with red-brown spore masses on the lower sides of the leaf, and defoliation of the tree. Defoliation from rust can lead to tree damage.

Rust is moisture dependent. Monitor orchards from May 1 through July 15. Randomly choose 40 trees, examine each one for the presence of rust symptoms on leaves, and check low-hanging branches. Also monitor nonbearing replants in the orchard, trees with vigorous growth and known rust hot spots.

Monitor the weather for rain events, along with humidity in the orchard, and treat at the first sign of rust with a fungicide application to limit the amount of spread. Additional treatments may be necessary, especially if a treatment was required early in the season. After a treatment is applied, continue to monitor weekly or twice monthly.

This year, especially with problems such as rust, monitor for them and make applications when needed, rather than being overly aggressive. It might be better to sacrifice a few leaves and save some money.

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

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