How can I control Phytophthora root rot in organic cherries?
Answer: Cherries are notoriously susceptible to root rots in wet, poorly drained soils. Clay soils should be avoided, though some soil drainage problems can be mitigated by berming, ditching, or tiling. Sandy or sandy loam soils are best.
Phytophthora root rot can be a serious obstacle anywhere?East or West?where the soil remains saturated or very wet for any appreciable period of time. The causal organisms can be any of several species in the genus Phytophthora, but they all share one important trait: the spores spread and are infective only where and when the soil is saturated with water.
The main symptom is often an indistinct unhealthiness or lack of vigor. An infected tree might simply grow poorly or exhibit off -color foliage. Sometimes a tree will die quickly, especially after a period of soil saturation, but it’s just as likely that a tree will linger and die over a period of seasons. If Phytophthora is suspected, a better diagnosis can be obtained by pulling back the soil from around the crown and shallow roots and, using a knife to cut away the bark, looking for a reddish-brown discoloration of the cambium. Infected tissue may also smell sour.
The major controls are good site selection or site modification. Pick sites with light, well-drained soils and/or ditch and berm to ensure good drainage. Cherry roots are especially susceptible; thus, the oft-repeated warning, “Cherries don’t like wet feet.” Though there is no high level of resistance among the various cherry rootstocks, some, like Mahaleb, are especially susceptible to Phytophthora, whereas Mazzard, Morello, and Colt are moderately resistant.
Cornell researchers recommend that if planting in a heavy soil or in any situation where drainage is suspect, plant the trees on 12-inch-high berms and/or ditch and tile the planting site.
Ready to learn more? The ATTRA publication Cherries: Organic Production focuses on organic pest and disease control and other topics relevant to organic production of both tart and sweet cherries. It introduces the Canadian bush cherry and discusses climatic considerations for cherry production. Information on marketing is included, as are further resources and sources of trees and pest-control materials.
In addition, Cherry Diseases Identification Sheet serves as a handy guide to help identify some cherry diseases and to learn more about causes and solutions.