Vascular Wilt Pathogens

The Iowa State University Plant & Insect Diagnostic Clinic frequently receives inquiries regarding trees with foliar chlorosis (yellow leaves), browning from the edge of the leaf in, and wilting appearance of limbs or whole sides of a tree.  Trees and ornamental shrubs can suffer from vascular wilt pathogens. These pathogens enter the vascular system that move water from the roots upwards. The pathogens then colonize the vascular system, and impeded water movement to the branches, resulting in yellowing and browning of the leaves, and the wilted look of twigs and limbs.

Diagnosing these pathogens is challenging. In the Clinic, we need a sample that has vascular discoloration to increase the chances of isolating the pathogen from the plant tissue. The only exception is bacterial leaf scorch, where vascular discoloration is NOT characteristic.

When sampling for vascular pathogen follow this steps;

• Select branches that are beginning to show symptoms (yellowing and browning leaves), instead of limbs that are showing advanced symptoms (completely brown or dead)
• Cut several branches from this area, then peel the bark and inspect for vascular discoloration. If vascular staining or streaking is not found, try another branch, always making sure the branch has the leaves with foliar symptoms (yellowing, browning, scorching).
• When vascular staining is found, that is the branch to submit to our clinic!. We need the rest of that branch that has not been peeled.
• Follow instructions on the Clinic website

Incorrect sampling may lead to a sample insufficient for analysis or false negative outcomes.  Avoid sending:

• Very small twigs (less than an inch in diameter)
• Samples (twig and branches) with no vascular discoloration
• Completely dead branches
• Dry samples (always refrigerate samples)
• Old samples (sample and submit a sample on the day or two form collection)

Vascular pathogens include: