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Beginner

Scientific Name:Verticillium albo-atrum and Verticillium dahliae

Identification

• Black raspberries are most susceptible to this disease.
• The primary symptom is wilting and die-back of affected canes.
• Infected plants develop blue or purple discolouration on part or all of the cane.
• In the first year of infection, primocane leaves may turn pale.
• In the second year, green leaves will dull, turn yellow, and die.
• Canes can become stunted and completely defoliated.
• Vascular tissue may show reddish discolouration.
• Symptoms may show on only one side of infected plants.
• Fruit produced is small and crumbly.

Often Confused With
Phytophthora Crown and Root Rot
Winter Injury

Period of Activity
The disease infects in cool weather, especially in poorly drained soils or after wet springs. The symptoms develop in warmer weather, typically during the end of June and the beginning of July, and are associated with periods of water stress or crop development. If verticillium is present, symptoms typically show up in young plantings. 

Scouting Notes
Look for stunted plants with yellowed or wilted leaves. On  black raspberries, check canes for a blue or purple discolouration. Watch for fruiting canes that die just before fruit ripens. To confirm a diagnosis, dig up plants with early symptoms, and send the crown and lower stems to a diagnostic lab.

Thresholds
None established.

 

Advanced

Scientific Name:Verticillium albo-atrum and Verticillium dahliae

Identification
Verticillium wilt, also known as bluestem, is caused by the soil-borne fungal pathogens Verticillium albo-atrum and Verticillium dahliae.
Black raspberries are most susceptible to this disease. Symptoms include wilting and die-back of affected canes. Canes often develop a blue or purple discolouration. During the first year of infection, primocane leaves turn pale but the plant can recover towards the end of the growing season. By the second year, leaves turn dull green and then yellow, beginning at the base of the plant and moving upward. Over time these leaves dry up and die. Canes become stunted and completely defoliated except for a few leaves at the shoot tip. Reddish discolouration may be evident in the vascular tissue of the infected canes. Initially, only canes on one side of an affected plant show symptoms. The entire plant may die within three years.

The symptoms are similar but less severe in red raspberries. Primocane growth is reduced and plant vigour is diminished. Fruit is small and crumbly.

Both red and black raspberries are most susceptible to verticillium wilt during their first few years of development and growth.

In the case of blackberries, the canes do not turn blue but leaves turn yellow, dry-up and drop. Fruiting canes leaf out, blossom and produce fruit the next year only to collapse and die.

The economic losses associated with this disease are the result of stunted, wilted plants, reduced harvest yield, and plant death.

Often Confused With

Phytophthora Crown and Root Rot
Both diseases result in stunted, weak plants with cane die-back. However, in the case of phytophthora,  the crown and main root will exhibit a reddish-brown discolouration beneath the epidermis, while with verticillium, canes are often an off-green bluish colour.

Winter Injury
Both problems can cause poor growth and cane die-back. Winter injury shows up rapidly  in the spring and is usually present throughout the field. Verticillium mainly presents itself in a localized fashion, especially in poorly-drained soils, and shows up in early –mid summer when the plant is growing rapidly .

Biology
V. albo-atrum and V. dahliae have similar life cycles and cause similar symptoms.  They grow best at soil temperatures up to 24°C - 27°C. V. albo-atrum overwinters as dormant mycelium, while V. dahliae forms microsclerotia as survival structures. Both of these stages allow the pathogen to survive in the soil for many years.

When conditions become favourable in the spring, overwintering mycelium and microsclerotia develop new hyphae which then penetrate the plant roots. Wounds and breaks can facilitate this invasion. Verticillium wilt is systemic in the plant. Hyphae in the  vascular system damage the water conducting tissue and prevent the movement of water from the roots to the rest of the plant.  The fungus returns to the soil as dead plant tissue begins to decay.

The severity of the disease is usually directly correlated to the amount of fungal pathogen available in the soil. However, the disease may be more pronounced after especially cold winters, or during cool and wet springs. Heavy soils can also increase the incidence and severity of this disease.

Period of Activity
The disease infects in cool weather, especially in poorly drained soils or after wet springs. The symptoms develop in warmer weather, typically during the end of June and the beginning of July, and are associated with periods of water stress or crop development. If verticillium is present, symptoms typically show up in young plantings. 

Scouting Notes
Look for stunted plants with yellowed or wilted leaves. On  black raspberries, check canes for a blue or purple discolouration. Watch for fruiting canes that die just before fruit ripens. To confirm a diagnosis, dig up plants with early symptoms, and send the crown and lower stems to a diagnostic lab

Thresholds

None established.

Management Notes

• Fungicides are not effective for the control of verticillium.
• Purchase disease-free plants grown according to accredited plant propagation guidelines.
• Do not plant raspberries after tomatoes, potatoes, eggplants or peppers because these crops are good hosts for the pathogen. Do not replant raspberries where verticillium has been a problem.
• Soil fumigation before planting raspberries provides good control on soil types suitable for fumigation. Refer to OMAFRA Publication 360: Fruit Crop Protection Guide (Chapter 3 Berry Crops)for pre-planting soil fumigation treatment.