Sacramento, Calif., (February 22, 2018) – Interplanting existing prune orchards where established trees don’t fill their space is a long accepted practice to increase grower income while limiting costs compared to complete orchard removal and replanting. This is often done in older orchards either by interplanting down the existing tree row or changing the direction of the tree rows 45° and interplanting on the diagonal between two existing trees.
Research by Dr. Themis Michailides since 2016 has shown pruning wounds on young trees are especially vulnerable to infection by Cytospora, Botryosphaeria, and/or Lasiodiplodia fungi. These infections damage developing scaffolds, potentially limiting orchard productivity over time.
Growers should reconsider interplanting prunes – or at least how they treat interplanted trees — due to the risk of pruning wound infections. The primary source of the infections in interplanted trees are the mature trees in the orchard — often in decline themselves due to those same canker and wood rot diseases.
Pruning wound infections can be minimized by
1) pruning in late summer of spring with no rain in the forecast or
2) pruning during winter and spraying Topsin-M® or Topsin-M® + Rally® after pruning and before the next rain to protect the cuts from infection. Dr Michailides reports that Topsin-M® is especialy effective against Botryosphaeria. Adding Rally® could be helpful for resistance management.
With yield and net income limited by tree spacing that is too wide and/or tree health in some older blocks, growers must choose between interplanting and removal/replanting. While pruning wound infections can speed the rate of tree decline in interplanted orchards reducing grower returns.
By Franz Niederholzer, UCCE Farm Advisor, Colusa and Sutter/Yuba Counties.
Want to learn about the recent advances in prune research and how they impact your prune management practices? Attend the UC Cooperative Extension’s upcoming meeting on Tuesday, September 26th at the Ord Bend Community Hall (3241 CA-45, Glenn, CA) from 9 a.m. to 3 p.m. The meeting will feature UC Davis Plant Pathologist Themis Michailides, who will talk about cytospora canker; UC Davis Plant Pathologist Bob Johnson, who will talk about wood rot fungi; and UCCE Farm Advisor Emeritus Rich Buchner, who will talk about his prune rootstock trial research. The meeting will follow with a Question and Answer session to help growers and PCAs plan to apply research results ahead of the pruning season. Registration is $25 online here or for $35 at the door, and includes lunch.
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With all the rain we received this winter, UC Plant Pathologist Themis Michailides warns growers that the sleeping giant of botryosphaeria and phomopsis will be awakening again. With the potential to cause severe damage in walnut orchards, Themis shared some cultural and chemical tools growers can utilize to keep it under control. Watch Themis’ brief interview with California Ag Network and read more in the March issue of Pacific Nut Producer Magazine.