How to Manage Pests
UC Pest Management Guidelines
Almond Brownline And Decline
Pathogens: Peach yellow leafroll phytoplasma
(Reviewed 8/17, updated 8/17)
In this Guideline:
SYMPTOMS AND SIGNS
Trees with almond brownline and decline are stunted. Leaves droop and appear wilted. Current-season shoot growth is abnormally shortened or absent. If bark is removed from the graft union, brown necrotic areas can be seen. The brown areas at the graft union may be scattered around the trunk or may form a continuous line. Check several places around the circumference of the trunk to determine whether this symptom is present. Over time, the surface of the wood at the graft union becomes mildly to severely pitted. Trees decline and become unproductive.
COMMENTS ON THE DISEASE
Almond brownline and decline is a disease that affects almond cultivars grown on Marianna 2624 rootstock. The disease is associated with Peach yellow leafroll phytoplasma, which is transmitted by pear psylla (Psylla pyricola). The phytoplasma is a microbe that multiplies and spreads within the phloem of the infected tree. When the phytoplasma reaches the graft union, cells of the Marianna rootstock die. This results in a layer of brown necrotic cells in the phloem at the graft union, which prevents spread of the phytoplasma into the rootstock but also interferes with movement of nutrients between scion and rootstock.
Brownline and decline is most commonly seen on young nonbearing trees. It has been observed on Carmel, Peerless, and Price scions.
Remove and replace stunted trees with replants. Because propagation may produce diseased trees, obtain trees from nurseries that use budwood sources tested free of the pathogen.
UC IPM Pest Management Guidelines:
J. E. Adaskaveg, Plant Pathology, UC Riverside