How to Manage Pests

Pests in Gardens and Landscapes

Blackline

Blackline is caused by cherry leaf roll virus. First symptoms of blackline are poor terminal growth, yellowing and drooping leaves, and premature defoliation. Trees may show dieback of terminal shoots and decline, often accompanied by profuse suckering of the rootstock. Small holes and cracks in the bark at the graft union can be seen. If you remove a piece of the bark on black rootstocks, you can see a narrow black line or strip of dead tissue at the union. On Paradox rootstocks, blackline may spread into the rootstock as a canker. Trees die.

Solutions

The blackline virus is transmitted mostly by pollination; very little transmission is made by grafting. There is no known cure. English walnuts on English rootstocks will get the virus, but will not die. Black walnut rootstocks are not susceptible to blackline.

Line of dead tissue at graft union
Line of dead tissue at graft union

Spread of disease into a canker
Spread of disease into a canker


Statewide IPM Program, Agriculture and Natural Resources, University of California
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