Wilt of Strawberries and Tomatoes
Verticillium dahliae and Verticillium albo-atrum
A soil borne fungus that affects many plants.
When split, the stems show dark brown to black vascular staining but otherwise appear normal.
Tomato.Lower leaves wilt and desiccate first and eventually the whole plant may die.
Chrysanthemum.The leaves on lower branches turn pinkish or purple and wither.
Apricot.When trees are in close contact with Tomatoes or Potatoes they may be affected and leaves on the ends of branches turn yellow, wilt and fall. Fruit develops "black heart".
Raspberry and BlackberryA serious, soil borne, fungal disease of Raspberries. It causes wilting and stunting of the plant and may cause death.
Plants may be infected for a while before symptoms become visible. Initially plants wilt. Wilting tissue soon begins to yellow then turn brown and die. Internal discoloration or streaking of the sapwood occurs in most plants.
Black raspberries are usually affected more than red raspberries.
Species Affected:Brambles, Chrysanthemum, Dahlias, Eggplant, Nightshades, Noogoora Burr, Potato, Strawberry, and Tomato are very susceptible.
Over 300 different species are affected including species from the Cucurbitaceae, Rosaceae and Solanaceae families.
Blackberry, Grape, Raspberry and Strawberry are affected by both Verticillium dahliae and Verticillium albo-atrum but the latter tends to be more damaging.
Some fruit trees such as Apricot and some amenity trees.
|Trees - Susceptible|
|Botanical Name||Common Name|
|Acer negundo||Box elder|
|Elaeagnus angustifolia||Oleaster, Russian olive|
|Koelreuteria paniculata||Golden rain tree |
|Liriodendron tulipifera ||Tulip tree|
|Magnolia grandiflora||Southern magnolia|
|Prunus species||Almond, apricot, cherry, peach, plum, prune|
|Robinia pseudoacacia||Black locust|
|Ground Covers, Shrubs, and Vines - Susceptible|
|Botanical Name||Common Name|
|Berberis (Mahonia) species||Barberry|
|Campsis radicans ||Trumpet creeper|
|Cotinus coggygria||Smoke tree|
|Rhaphiolepis indica ||Indian hawthorn|
|Rhaphiolepis umbellata||Yeddo hawthorn|
|Ribes species||Currant, gooseberry|
|Rosmarinus officinalis L.||Rosemary|
|Rubus allegheniensis||Taylor blackberry|
|Rubus idaeus||Red Raspberry |
|Rubus occidentalis||Black raspberry|
|Rubus ursinus||Blackberry, brambles (Boysenberry, Nectarberry, Loganberry and Youngberry)|
|Viburnum species||Viburnum, wayfaring-tree, others|Adapted from Marilyn D. Dykstra (2000).
|Trees and Shrubs - Resistant or Immune|
|Botanical Name ||Common Name|
|Betula species ||Birch|
|Buxus species ||Boxwood|
|Carpinus species ||Hornbeam|
|Cercidiphyllum japonicum ||Katsura tree|
|Cornus species ||Dogwood|
|Crataegus species ||Hawthorn|
|Eucalyptus species ||Eucalyptus|
|Fagus species ||Beech|
|Gleditsia species ||Locust|
|Gleditsia triacanthos ||Honey locust|
|Ilex species ||Holly|
|Juglans species ||Walnut|
|Morus species ||Mulberry|
|Nerium oleander ||Oleander|
|Platanus species ||Plane tree|
|Pyracantha species ||Pyracantha, firethorn|
|Quercus species ||Oak|
|Salix species ||Willow|
|Sorbus aucuparia ||European mountain ash|
|Tilia species ||Linden|
| || |
Apple and flowering Crab Apple (Malus species), Pear (Pyrus species) an Quince are susceptible to European strains of Verticillium albo-atrum but appear tolerant of other strains and Verticillium dahliae.
Biology:Verticillium invades the root system directly or through wounds caused naturally by root growth through the soil or soil organisms. Once in plant tissues, the fungus produces toxins and invades the xylem (water conducting tissues), moving upward in the plant via spores. Where new spores lodge in the vascular tissue a new infection begins. Toxins produced by Verticillium may kill plant cells at some distance from those directly invaded. In response to invasion, the host produces substances called tyloses or gums that attempt to close off the invaded cells to limit fungal movement in the plant. This shutting down of infected vascular tissues reduces the flow of water from the roots upward. At this point, reduced water flow and toxins often result in external symptoms. Thus, the fungus often cannot be isolated from the apex of streaked wood or from wilting branches, even though damage is apparent there (figure 4) (Ash, 1994).
The fungus survives saprophytically in the soil as thread-like growths called mycelia and/or minute black resting structures called microsclerotia. In some plants the fungus may move into the leaves and persist as mycelia or microsclerotia when the leaves fall to the ground. Infected dead root systems improve the survival of these fungi in the soil.
Verticillium dahliae can survive in the soil for many years. Microsclerotia are capable of persisting for 10 or more years in the soil without a host plant. However, warm, waterlogged soils result in the rapid death of microsclerotia (Ash, 1994).
Verticillium albo-atrum will survive only as long as it takes the crop refuse to break down -- usually about two years, unless other susceptible host plants, including weeds, are grown during this time.
Most isolations from woody hosts yield Verticillium dahliae.
It is spread on implements, by soil movement, soil erosion or transport of infected plants.
The disease is usually a cooler weather disease and is most severe where there is poorly drained soil and continuously flowing cold, wet springs.
Plants that are blooming or fruiting tend to be more susceptible.
Life Cycle:The hyphae penetrate the root directly, especially if they are stressed roots or damaged by other pests of diseases. The hyphae then grow into the xylem, the water conducting tissue, and prevent the movement of water up to other tissues causing wilting and/or death. The symptoms of this disease usually appear in summer or periods of water stress.
In cane berries, the lower leaves may appear to have a dull green cast to them as compared to the brighter leaves higher on the stem. The disease usually starts at the base and moves its way up the stem. The last effects of the disease are noticed on fruiting canes that were infected the year before, because in the spring, many of the diseased cranes will be dead. If the crane is not dead, then it will most likely appear poorly developed and/or have shrivelled buds. The new leaves that grow the following year after the plant has been infected are usually yellow and have stunted growth.
Origin and History:Distribution:
World wide distribution but less important in the tropics.
Significance:Management and Control:
Soil usually needs fumigation if infected.
Plant resistant varieties.
Remove and destroy infected plants.
Do not grow susceptible plants for at least three years where susceptible vegetables were grown or where a woody plant or other susceptible plants died from this disease.
Control alternate hosts such Nightshades.
Fungicides are generally providing little control of Verticillium.
Soil usually needs fumigation if infected.
Managing trees infected with Verticillium wilt will take time and knowledge. First, confirm that the symptoms are indeed caused by Verticillium wilt. The presence of typical symptoms and streaking of the vascular tissue is fairly diagnostic, but a laboratory culture test should be run to confirm the diagnosis.
The severity of disease development will depend on the strain of the pathogen, the level of susceptibility in the host, and environmental factors. Landscape trees with recent wilt symptoms should not be removed immediately. They may "recover" and perform fairly well with some environmental manipulation. In general, the most resistant plants are those grown in moderately fertile soil in which the balance of major nutrients is tipped slightly toward high potassium and low nitrogen. Generously watered plants are often invaded less extensively than those under moderate to severe water stress.
Avoid stressing plants, especially their roots. Maintain/provide proper moisture and soil drainage. Avoid high nitrogen fertilizers - use balanced fertilizers or fertilizers with slightly higher phosphorus levels. Avoid deep cultivation around plants while they are growing. Avoid using herbicides if possible. If herbicides are used - spot treat (treat individual weeds very carefully). Remove infected plants and as much of the infected root system as soon as possible. Destroy the infected plants by burning or aerobic composting.
When replacing trees in areas where Verticillium is present in the soil, select resistant or immune trees (see Table above). Fertilize properly to promote vigorous growth and water regularly during the growing season. Remove dead and weak branches. This does not remove the fungus from the tree, but prevents infection by other fungi. Don't use the chipped wood as a mulch unless it is properly heated in a compost pile.
Trees and shrubs resistant or immune to Verticillium include Hawthorn, Oak, Pear, Pine, Poplar, Juniper, Ginkgo, Walnut, Mulberry, Willow and Honey locust. The resistance or susceptibility will depend on the cultivar and the strain of Verticillium present in the soils. Apple, pear, and quince are susceptible to the European strains of Verticillium albo-atrum.
StrawberriesPlant runners that are certified as disease free.
Fumigate affected areas before replanting.
Replant new strawberry beds every three to five years in a new location to minimize the beds from being infested with verticillium wilt.
TomatoesPlant healthy seedlings.
Use resistant varieties such as FA16, Floradale, Hybrid Surprise, Tropic, UC134, Walter.
Fumigate seed beds.
Don't plant area for at least 4 years after the last susceptible crop.
Related and Similar Species:The plant symptoms that result when this fungus attacks may be confused seasonal die-back of foliage and with other plant problems such as fusarium wilt, bacterial wilt, root rots as well as drought and damage due to excessive soil moisture.
Collated by HerbiGuide. Phone 08 98444064 or www.HerbiGuide.com.au for more information.