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Controlling raspberry cane diseases can increase yield and reduce winter injury

Four serious raspberry cane diseases are common to Ontario. These include anthracnose, spur blight, cane botrytis and cane blight. All overwinter on infected raspberry canes. In spring, the overwintering fungi produce spores which disperse in splashing rain to cause new infections. Alternate hosts are limited to wild raspberry and blackberry.

Anthracnose lesions are round or oval, and initially grey with a distinct reddish or purple border. Lesions can develop on primocanes, leaves, laterals and fruit. Lesions on canes become sunken, infected canes become cracked and pitted as they age. Fruit from infected laterals is small, seedy and dry. Anthracnose infections occur on young plant tissue. It is important to control this disease in the spring, when tissues are rapidly expanding.

Spur blight: This disease infects old, dying leaves and from there the fungus invades the cane and buds where the leaf attaches to the cane. Early infections appear as dark triangular lesions at the base of the bud; these eventually turn silvery grey on the overwintering cane. Infected buds produce weaker laterals, smaller fruit, and are more susceptible to winter injury.

Cane botrytis: The causal agent for cane botrytis also causes grey mould on fruit. This disease infects senescing leaves and invades the cane through the leaf base. Long brown lesions spread up and down the cane, causing it to weaken or die before spring. Overwintering sclerotia imbedded in the cane produce masses of grey fuzzy spores in spring. These spores are spread in wind or splashed by rain to new canes. They can infect raspberry bloom and fruit as well as older leaves, and increase the potential for fruit rot.

Cane blight: The fungus infects through wounds in primocanes. It grows beneath the surface of the cane, eventually causing dark cankers around the wound. Canes are often brittle and break easily the following spring. Laterals and side braches which grow from infected canes wilt and die back in early-mid summer, often just before harvest.

Managing cane diseases: Because cane diseases overwinter on infected canes, pruning and good sanitation is important for good control. Prune old canes close to the ground, as diseases will be viable for several years on old stubs. Ideally, take pruned canes out of the field, and destroy them. Many growers leave prunings in the row middles and chop them up with a flail mower. Some diseases will survive on chopped up cane debris, but as this debris becomes desiccated and dry, the overwintering fungus will be less able to produce spores and rain splashed spore dispersal will be reduced. Keep rows narrow to encourage drying in the row and to reduce leaf senescence due to low light conditions. Biennial production, a system which separates fruiting canes from primocanes and helps break up the disease cycle, can be helpful in managing cane diseases. However, fungicides are still necessary in the primocane year of this system.

Fungicides for cane diseases:

Lime sulphur: Although this is an inconvenient spray to apply it is especially important where cane diseases are a problem. Lime sulphur helps to lower disease levels from the start, by killing overwintering fungi on the cane. Timing is important. Apply the lime sulphur when raspberry buds begin to swell, but no later than ¼ inch green. This coincides with early fungal activity. If lime sulphur is applied to early, the fungus will be dormant within the lesion and less susceptible to the sulphur. Application later than ¼ inch green risks injury to new raspberry tissue.

Ferbam: Apply this fungicide to protect new growth in the spring. Good coverage of new growth is important, especially in wet weather. Do not apply Ferbam after first bloom.

Captan or Maestro: These products can be applied from bloom through to harvest to control botrytis fruit rot. They will also control spur blight infections.

Tanos 50 DF: This is a new fungicide for raspberries, recently registered through the minor use program. Tanos 50 DF contains two active ingredients, famoxadone (group) and cymoxanil (group). Research trials in Quebec indicate that use of Tanos reduced spur blight ascospore emissions from overwintering canes, and significantly reduced spur blight infections on new canes. This fungicide also controlled anthracnose infections quite well in a Quebec study. Tanos can be applied before bloom, during the bloom and harvest period, and after harvest to control cane diseases. Tanos is an important tool for control of cane diseases after raspberries are harvested, a window with very few control options in the past.

Fungicide program for cane disease control (detailed recommendations can be found in OMAFRA publication #360, Fruit Production Recommendations): There are 4 important timings for cane disease control with fungicides.

1. Delayed dormant to ¼ inch green: Use lime sulphur to help reduce overwintering inoculum of all cane diseases.
2. Pre-bloom: Apply Ferbam 76 WDG or Tanos 50 DF to protect new growth. This is a very important timing for anthracnose control. Do not apply Ferbam after 1st bloom.
3. Bloom thought harvest: The priority at this timing is fruit rot control, however, choose fungicides which will also provide some control of cane diseases. Captan 80 WDG and Maestro 80 DF will control spur blight. Tanos will control spur blight, cane botrytis and anthracnose. Pristine, which is labelled and should be used only for botrytis fruit rot control, will control other cane diseases at the same time.
4. After harvest: Apply Tanos 50 DF to control cane diseases. Botrytis and spur blight infections seem to develop mostly after harvest. Late July and August are important control windows, especially if weather is wet.

Researchers have reported that survival and vigour of raspberry canes is improved when cane diseases are controlled the previous season. Controlling raspberry cane diseases can increase yield and reduce winter injury.