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Ask Your PCA: How can farmers protect prunes at bloom?

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Issue Date: April 14, 2021
Mateo Marquez, PCA Integral Ag Services, Durham
Mateo Marquez

At bloom, brown rot and russet scab are a concern for prunes. If there are aphid problems in the orchard, the first aphid colonies will start showing up as well.

Brown rot causes flower mortality, and it can go into the shoot and cause shoot dieback. As far as the Prunus species go, prunes appear to be fairly tolerant of brown rot, especially compared to almonds.

Russet scab hasn't been a major concern for the last several years. Even so, sprays are applied during bloom for brown rot and russet scab. Because prune bloom happens so rapidly, with generally only one or two rain events, it makes it easy to rotate chemistries and reduce the risk of resistance building.

Prunes do better with rain at bloom than hot, dry temperatures, and when there are these conditions, it's advised to irrigate.

Aphids have become slightly more difficult. In years past, one treatment or even a dormant spray was sufficient, but now dormant sprays aren't working and frequently after a treatment there will be a resurgence more often than in the past. Resistance is most likely the issue, and there aren't any new chemicals coming down the pike.

Aphids build up in large numbers on the under surface of leaves in spring and cause them to become slightly curled and stunted. High populations will severely disfigure and stunt the leaves, which results in reduced shoot growth. Aphids will also reduce sugar content of fruit, and honeydew dropping on fruit can cause fruit cracking. There is also the potential to reduce yield the following season, as shoot growth is one of the primary areas where the tree maintains good yields by growing new flower sites.

Current recommendations for aphids are scouting the field, timing of treatment and treating only when necessary, to reduce the need for retreatment.

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

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