As winter winds down, and the weather oscillates from cool to warm days, California avocado growers may notice sudden symptoms of wilt in their groves. This could be caused by Verticillium wilt.
Verticillium wilt symptoms can include the entire tree or specific branches, with leaves browning and then dying but typically remaining on the tree for several months. Brown/gray-brown streaks may be visible when the bark is removed or at the base of the trunk.
The disease is caused by Verticillium dahliae that exists in the soil and infects the tree’s xylem system through feeder roots. As a result, water movement is restricted in the tree. The fungal pathogen can be spread if infested organic matter and soil are moved about in the grove.
Infected trees may recover on their own — there is no known method for curing them — and send out new shoots a few months after initially wilting. If well cared for — pruning dead branches, irrigating and fertilizing — the tree can recover. If the tree does not, it is important to remove it from the grove. Recovered trees should not be used as a seed or budwood source.
For more information, read Dr. Ben Faber’s blog post.