By Forrest Scharf, PAg, Provincial Specialist Fruit Crops, Regina
Blind wood occurs when buds on cherry branches remain dormant or “blind." It has been observed in Ontario, Michigan and similar regions. It results from severe winter conditions, yellow virus disease infection and genetic proclivities. When it happens in spring, few leaves develop, except in tufts at the distal end of branches. As a consequence, fruit yield, quality and plant vigour reduces over time. Fewer leaves cause lower capacity for energy production (photosynthate accumulation via photosynthesis) and lower capacity of plants to sustain strong yield or growth.
Aside from severe winter conditions that cannot be prevented or overcome; in Saskatchewan the likelihood of plants succumbing to blind wood appears to be greater when they are weakened with diseases like bacterial canker (Pseudomonas syringae), or suffering extensive sunscald. In relation to sunscald; cherry bark is relatively thin compared to many tree species and extensive splitting of the bark from this condition makes the plants more susceptible to diseases like bacterial canker. Painting stems with white paint can reduce sunscald susceptibility and splitting, but in many cases, extensive application is impractical.
Several fungal and bacterial diseases also afflict dwarf sour cherry. In Saskatchewan, the most frequently observed are cherry leaf spot (Blumeriella jappii), bacterial canker and brown rot (Monilinia fructicola). Under non-stressful growth conditions, the physical health of sour cherry is not significantly impacted by these diseases. Under stressful conditions, plant health declines and significantly reduces orchard vigour. Overwinter environmental physiological problems like sunscald, vascular damage and blind wood can further weaken plants making them more susceptible to disease infection through wounds and general weakness in immune factors. So, blind wood can weaken plants initially via energy loss, but also through greater susceptibility to disease. If initial blind wood symptomology isn’t managed, long-term orchard health and productivity is likely to decline. Similarly, if disease and sunscald are not treated there is a greater likelihood of blind wood developing as plant vascular systems struggle to maintain healthy buds. Some pest control products are registered to manage sour cherry diseases.
In Michigan, Montmorency and Balaton sour cherries have a greater tendency to suffer from blind wood than other cultivars. Balatons are more closely related to University of Saskatchewan sour cherries; and to prevent blind wood in Balaton orchards, they are treated with “an application of gibberellic acid, which stimulates the formation of spurs and increases bloom potential” (Bukovak, Anderson et al. and Northwest Michigan Horticulture Research Station). In Saskatchewan, application of gibberellins to overcome blind wood is under investigation. Growers are also testing top-growth removal strategies that have various other management efficiency gains for older overgrown orchards.
Some Saskatchewan orchardists have noted differences in cultivar or plant variety susceptibility and resiliency (overcoming blind wood as the growing season progresses). Anecdotal consensus is: Cupid cherries are most resistant; Carmine Jewel is second; Juliet is less resistant, but often rejuvenates; Valentine and Romeo are highly susceptible and Crimson Passion is the least resistant.
For more information, contact Forrest Scharf, Provincial Specialist Fruit Crops at 306-787-4666.