Verticillium Wilt (or Collapse) is caused by Verticillium dahliae, which can be present in the soil for years and spread through organic matter or soil that is moved elsewhere. The fungus then infects an avocado tree’s feeder roots and moves through the xylem system where it restricts water movement to foliage. As a result, a tree’s leaves can suddenly turn brown and die. Brown and gray-brown streaks also may be present on the trunk.
There is no known cure for this condition, but a well-cared for tree may recover and produce vigorous shoots within a few months of the initial wilting. If growers identify infected trees, it is important to monitor the tree and, if the tree recovers, to monitor for recurrences of the infection.
For infected trees, prune off dead branches when dieback ends and new growth begins. Continue to properly irrigate and fertilize the tree. Going forward, avoid using a once-infected tree as a source of budwood or seed. If a tree dies from Verticillium Wilt, be certain to remove it from the grove.
Verticillium is known to infect other plants — berries, flowers, cotton, eggplant, olive, pepper, stone fruit trees, strawberry and tomato — so avoid planting these crops with avocado trees. In addition, avoid planting avocado trees in soil sections that are known to have been infected.
For additional information, read Dr. Ben Faber’s Vertiginous Collapse blog post.