Verticillium wilt is a very harmful fungus that infects the vascular systems of many woody and herbaceous plants. It stops water from getting to the plants and eventually kills them. Some tree species, on the other hand, are naturally resistant to or immune to verticillium wilt. This makes them perfect for landscapes where this soil-borne pathogen is present.
Understanding Verticillium Wilt
Verticillium wilt is caused by two related soil-borne fungal pathogens – Verticillium dahliae and Verticillium albo-atrum. The microscopic fungi enter plants through the roots and then spread through the water-conducting xylem tissues, forming blockages This prevents water and nutrients from reaching the stems and leaves Affected plants display wilting, yellowing, defoliation, and dieback symptoms, usually starting on one side.
The fungi can persist in soil for years. Once a plant is infected, there is no cure. Verticillium mostly affects annual herbs and vegetables, but it can also hurt many trees and shrubs.
Gymnosperms – Naturally Resistant Conifers
An entire division of woody plants the gymnosperms, are broadly resistant to verticillium wilt. Gymnosperms have naked seeds and include conifers like pines firs, spruces, redwoods, junipers, cedars, and more. Their resinous sap, thick bark, and other defenses make them poor hosts for the Verticillium fungi.
Any species of pine, fir, spruce, cedar, redwood, cypress, or other conifer can be planted in areas affected by verticillium wilt. They’ll grow unaffected by the disease.
Dicots – Select Deciduous Trees With Resistance
Among deciduous woody plants, there are certain species with proven natural immunity to verticillium wilt. These resistant species mainly come from the rose, legume, birch, and oak families.
Oaks
All species of oak trees have strong resistance, including white oaks, red oaks, live oaks, willow oaks, etc.
Birches
River birch, paper birch, yellow birch and European white birch are unaffected
Black Locust
A legume tree resistant to the disease. Fixes nitrogen in soil.
Mulberries
Both red and white mulberry trees are immune. The berries are edible.
Buckeyes
Ohio buckeye and yellow buckeye are resistant trees.
Willows
Weeping willows, black willows, pussy willows resist verticillium.
Dogwoods
Kousa dogwood and Cornelian cherry dogwood are resistant varieties.
Smoke Tree
An ornamental tree with airy puffy blooms.
Catalpa
Southern and northern catalpa trees are unaffected.
Black Gum
Also known as tupelo or pepperidge tree.
Monocots – Palms, Yuccas, Agaves
Verticillium wilt can’t hurt monocots like palms, yuccas, and agaves. In hot, dry places where verticillium wilt is common, these make striking vertical accents.
Palms
Queen palms, date palms, fan palms, etc.
Yuccas
Stiff, spikey yucca plants resist the disease.
Agaves
Large sculptural shapes and succulent leaves.
Key Facts on Resistant Trees
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Conifers, oaks, birches, willows, dogwoods and other trees have natural genetic immunity to verticillium wilt.
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Once infected, there are no fungicide sprays or cures for susceptible trees like maples, ashes, elms, etc.
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Remove and destroy infected plants to limit the spread of fungal inoculum in soil.
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Verticillium can persist in soil for over 10 years after susceptible plants are removed.
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Rotate herbaceous crops, but resistant trees can be continually planted in affected soil.
Planting Advice for Landscapes With Verticillium
Here are some tips for incorporating resistant trees in garden beds or landscapes where verticillium wilt is a problem:
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Test soil to confirm verticillium is present before planting.
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Remove dead plants and till soil deeply to disrupt fungal resting structures.
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Solarize soil by moistening and covering with plastic sheeting in summer.
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Add resistant varieties of both woody and herbaceous ornamentals.
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Incorporate organic matter to encourage beneficial microbes that suppress fungal pathogens.
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Use raised beds for herbs and vegetables if drainage is poor.
By choosing tree types that are genetically resistant to verticillium wilt, you can grow beautiful, healthy gardens even in places where this harmful pathogen is present. Pay attention to conifers, oaks, birches, dogwoods, willows, and palmettos that are naturally resistant. If you know about plant immunity, verticillium won’t be a problem for your landscaping plans.
Frequently Asked Questions
What crops does verticillium wilt not affect?
The best protection against verticillium wilt is growing plants with resistance or immunity to the disease. Verticillium-resistant tomato varieties carry a “V” on the plant tags or labels. Birch trees naturally resist the disease, and verticillium wilt doesn’t affect conifers such as pine and spruce trees.
What plants are resistant to verticillium wilt rhs?
The Royal Horticultural Society produces a list of resistant plants: Alnus (alder), Gleditsia (honey locust), Betula (birch), Ilex (holly), Carpinus (hornbeam), Liquidamber (sweet gum), Cercidiphyllum (katsura), Morus (mulberry), Crataegus (hawthorn), Platanus (plane), Eucalyptus (gum tree), Populus (poplar), Fagus (beech), and more.
Are any maples resistant to verticillium wilt?
Although maples are generally thought to be highly susceptible to Verticillium wilt, red and sugar maples appear to be much more resistant than Norway maples. ‘Jade Glen’ and ‘Parkway’ are reported to be more resistant than other cultivars of Norway maples.
Are dogwoods resistant to verticillium wilt?
A partial list of resistant shrubs includes dogwood, firethorn, flowering quince, holly, and rhododendron.
Reduce fungus in soil
To prevent Verticillium from attacking fruit trees, try to reduce the amount of fungus in the soil. You can do this in the following ways:
- If you want to plant new stone fruit, make sure the land has been grass-free for at least a few years. Also, don’t plant stone fruit where potatoes, tomatoes, or strawberries were grown in the past.
- It is best to plant apples or pears if you have to plant fruit trees in soil that has Verticillium in it because they are very resistant to the disease. It is also possible to plant apricots grown on plum rootstocks when other options are not available. These trees are somewhat resistant to the disease.
- Use only high-quality, disease-free planting material, because transmission of V. dahliae in vegetative planting stock is significant.
- It’s best not to plant blocks of young stone fruit next to tomatoes, potatoes, peppers, strawberries, or melons, because these plants can make the Verticillium population in the soil grow faster.
- To stop Verticillium from growing quickly in the soil, get rid of weeds after planting or sow the block down to grass and clover. There are three main types of weeds that host Verticillium. These are Chenopodiaceae (fat hen), Solanaceae (nightshade), and Amaranthaceae (red-root amaranthus).
- Take down as many of the trees’ roots as you can that are badly damaged or not producing fruit. Before planting again, fumigate or treat the area in some other way (for example, by heating the soil) to kill any fungus that is still there.
- Young plants shouldn’t be put through too much water stress, root damage, or fertilizer.