Cane Blight

Yesterday, I harvested my first sun-warmed, tangy-sweet raspberry of the season.

Raspberries

For me, raspberries rank right up there with tomatoes for good reasons to grow your own. Store-bought raspberries rarely have the flavor or plump texture that fresh, homegrown raspberries provide. That being said, cane blight can take all the fun out of growing raspberries at home. If you know what to look for, you can prevent this disease from spreading.

Cane blight is a fungal disease. The fungus responsible for cane blight goes by the name Leptosphaeria coniothyrium. It is also known as Paraconiothyrium fuckelii. [Apparently, someone hates this disease even more than I do!] Cane blight can also attack blackberries. The same fungus also causes a rose canker and root rot on strawberries. Unaffected host plants include bamboo, juniper, stone fruits, blueberries, and currants, so you may want to keep them at a distance from your blackberries and raspberries.

Symptoms of cane blight

This disease starts by looking similar to fireblight, spur blight, and anthracnose, but it progresses differently. Canes infected with Leptosphaeria coniothyrium will develop purplish-black lesions at wound sites. These lesions will develop into black or brown cankers that encircle the cane, causing wilt and twig dieback. Infected canes may also twist around other stems rather than grow normally. The bark may split, and the wood becomes very brittle. Leaves and fruit on those canes will wither and die but stay attached. If you look closely, you can see tiny, black fungal bodies on the wood. [Sadly, I was unable to find any photos.]

Unripe raspberries growing on healthy canes

Preventing cane blight

Fungal spores can blow in on the wind and be splashed onto plants by rain, sprinklers, and overhead watering. Spores enter healthy canes through injury sites. Jagged pruning cuts, growth cracks, and damaged roots can all provide points of entry, so keeping plants healthy and protected is the best way to prevent this disease. Use these tips to help prevent cane blight on your raspberries:

• Wait until the weather and the canes are dry before pruning.
• Space plants out for good airflow to help them dry more quickly.
• Provide good drainage.
• Avoid over-fertilizing. [Regular soil tests are always a good idea!]
• Mulch around the canes and irrigate regularly to prevent the soil from becoming hydrophobic.
• Control pests, such as borers,, that may create injury points.
• Quarantine new plants before adding them to an established raspberry bed.

How to control cane blight

The only control is the removal of infected canes. The cane blight fungus overwinters on the canes, so infected canes should be removed and destroyed. Be sure to dip your pruners in a household cleaner between each cut. Remove severely infected plants. Fungicides are not effective against cane blight.

Keep your raspberry plants healthy for many years of summer deliciousness!