Written by Tianna DuPont, WSU Extension. Aug 21, 2019
Sampling and removal of infected trees is critical to slowing the current outbreak of Western X and Little Cherry Virus. Infected trees can not be cured. The disease is spread throughout the tree even when symptoms are obvious only in one section. Infected trees must be removed. Any infected trees that remain in the orchard are a reservoir of disease for your orchard and your neighbor’s.
Little Cherry Disease is caused by a virus Little Cherry Virus 1 and 2 or a phytoplasma called Western X. In addition to insect vectors, root grafting can move the disease from tree to tree and threatens new infections in replacement trees. When removing infected trees apply an herbicide to kill the roots which then can no longer infect new roots via root grafting.
Treat the interface of the bark with the wood, the area called the cambium or sapwood (the outer ring of wood, next to and including the bark) (Figure 1). This is the living part of the tree which moves water and nutrients and will be most likely to move the herbicide. Treat when the tree is actively growing. Herbicide must be applied immediately after cutting.
Multiple glyphosate labels allow application in stone fruit and as a ‘cut stump treatment’ (eg Glystar pg 29, Buccaneer pg 24). Check your glyphosate label. Most labels say to apply a 50 (mixed with water) to 100% solution of the glyphosate product. Applications can be made with a small hand/backsprayer or a paint brush to fully cover the entire cambium (Figure 2). Some labels also allow a frill/injection application (eg Glyphosate 4DS pg 28) (Figure 3). A hatchet, chainsaw or drill can be used to notch the tree. The notch/drill holes need to extend into the living tissue in the cambium but do not need to extend deep into the heartwood. A 50 to 100% glyphosate concentration is applied at the equivalent of 1 ml per 2-3 inches of trunk (Glyphosate 4DS). Follow your label’s directions.
Currently a research collaboration between WSU, GS Long and the Washington State Tree Fruit Research Commission is investigating most appropriate rates, timings and products and we will share new information as soon as it is available.
Removal of infected trees is critical to successful management of this disease. Be aggressive.