Verticillium wilt is a fungus that affects nearly 85% of the woody ornamentals in the U.S. Hundreds of species are susceptible to this soil-borne fungi. Verticillium can become a serious problem as the fungi will remain in the soil forever, often without the host ever showing symptoms. This fatal disease infects the plants directly through it’s roots. It may also enter the host through naturally occurring wounds on the roots. Spores growing on the trunk are carried by wind and rain. The fungi can survive and propagate in many different types of soils and and environments, allowing for wide-spread detection in many regions. Once infected, the toxins will travel through the plant’s water system. The systemic and internal spread of the toxins means that even though a certain region or branch may express symptoms, the entire host is infected and doomed.
What to Look For:
This fungi is often difficult to diagnose because its symptoms can be confused with those caused by many other forms of damage. Damage from environmental sources, such as disease and nutrient deficiencies, can produce symptoms similar to those infected with Verticillium. Mechanical and herbicide damage can also look confusingly similar. Although symptoms can appear at any time during the growing season, they are most likely to begin in JULY and AUGUST. The severity of the infection is often most severe during or following cooler weather.
As the host fights back against the infection, it may produce “substances known as tyloses or gums that attempt to close off the invaded cells to limit fungal movement in the plant”¹. This is where symptoms start to become visible. These gums will reduce the flow of water to the affected area in order to reduce the spread of infection. Along with the toxins, this forced dehydration will produce external symptoms such as: These symptoms may appear chronically or acutely.
|Small, yellowed foliage||Leaf curling|
|Leaf scorch (marginal browning)||Drying|
|Slow growth||Abnormal red or yellow leaf coloring|
|Abnormally heavy seed crops||Abnormal red or yellowing of area between leaf veins|
|Dieback of shoots and branches||Partial defoliation|
|Wilt and branch dieback|
As external symptoms become more apparent, a cutting of a lower branch is suggested. Your certified arborist will perform a cross-section cut, likely confirming the suspected infection. Streaking of the internal tissues will appear as bluish-green, to brown or black. A chronically infected tree will express these discolorations in the growth rings of lower branches and trunks. The bark on wilting branches may also be peeled back to reveal sapwood that has been streaked with toxins, should the infection travel this high.
A soil culture test may also be performed to confirm the presence of the fungi in your soil.
FUNGICIDES WILL NOT CURE INFECTED TREES
If an infection is found to be present on your property, special care must be taken to ensure the survival of your woody ornamentals. Soil fumigants may be effective for small areas such as greenhouses, gardens, and planters. However, this is not a practical or effective treatment for properties or landscapes. Infected trees must be removed and replaced. These species of shrubs and trees are either resistant or immune to Verticillium Wilt:
We here at Fox will help you replace your infected trees! Once the soil has been infected, the fungi will remain indefinitely. Your replacement trees need to be either “resistant” or immune to this fungi. Fertilization will promote healthy, vigorous growth. Water your trees regularly and generously to combat the internal dehydration that your tree may be suffering from. Although removing weakened and dead branches wont remove the fungus, it will help to prevent infection from other fungi. Removed wood may be chipped and use for mulch ONLY after it has been properly and thoroughly heated in a compost pile¹.
If you suspect an infection, call your arborist RIGHT AWAY. This persistent fungi can damage many species on your property and must be addressed to prevent a total plant collapse. Our experienced and educated professionals will correctly diagnose and treat all of your plant and tree care concerns! From visual and manual inspection, to clinical and laboratory testing… Fox has you covered! So as always,