By Matt Gibson
Cane blight is a nasty fungal disease that affects raspberry, blackberry, and rose plant stems as well as the fruit of apple and pear trees. Though all of these plants are at risk of contracting cane blight, the raspberry plant (namely black raspberry) is most susceptible.
All cases of cane blight occur because of wounds on the canes of bramble plants. Wounds are usually caused by careless pruning or by insects. The first signs of cane blight are wilted foliage, usually in the form of dark brown or purple cankers that move down the cane several inches. Reddish-brown discolorations appear and then turn dark purple or black as the disease progresses.
The disease can travel from cane to cane, and though it does not typically kill the plants, it does significantly affect fruit production if not properly treated. Control of cane blight is achievable by both cultural and chemical processes if action is taken swiftly.
What is Cane Blight?
Cane blight is a fungal disease called leptosphaeria coniothyrium, which targets the stems of wild and cultivated rubus species, such as raspberries and blackberries. The disease usually targets the canes (or stems) of brambles where wounds are present, forming reddish-brown streaks that eventually take over the entire cane and cause cane death.
What Does Cane Blight Look Like?
After blooming takes place, as well as the growth of new leaves in the early summertime, plants are at risk for cane blight. The blight manifests due to wounds from pruning or damage done by insects, and then cankers, or dark brown to purple—and eventually black—spots appear on the canes below the dieback. Bramble growers may witness the sudden death of side branches or the tips of fruit bearing stems.
A greyish slime often oozes out of the wounds in wet weather, whereas in dry weather, cankers produce a powdery, fuzzy appearance. Dead stems become ultra brittle and can even break off on windy days, snapping off easily from a heavy gust.
Where Does Cane Blight Come From?
The fungus, leptosphaeria coniothyrium, remains alive through the winter as the plant is dormant, then it rears its ugly head during wet periods, as windborne spores find and infiltrate open wounds caused by pruning or insect damage or scrapes from canes rubbing against one another in the wind.
Once infected, the disease continues to spread by releasing additional spores carried by wind or splashing water. If there are wounds on other canes that remain unaffected, they are susceptible to further infection from these fungal spores. This is how cane blight spreads from cane to cane and from bramble to bramble.
Cane Blight Treatment and Control
Whatever you do, do not prune affected canes until the wintertime, when the plant becomes dormant. Doing so allows the fungus an easy, all-access pass into healthy, unaffected tissue. Be advised: patience is key when attempting to treat and control cane blight infestation, as it can take two years and perhaps longer to sanitize and prune away infected branches to reduce cane blight to manageable levels.
During mid to late winter, the dormant season for brambles, prune infected canes to the ground. If cane blight is spotted during active months, label the infected canes so that you don’t forget which ones to cut down when the time comes.
Also remove older stubs of canes that you pruned in previous seasons to cut down on abrasions that could occur on newer canes, as they can brush against the stubs in the wind. Doing all of your pruning during the dormant season is crucial, as the dormant period is the only time when the fungus is not creating new spores that could infect the plant further.
Disinfect your pruning tools after use, and only use sharp tools for the pruning process [https://www.gardeningchannel.com/pruning-tips/]. To properly disinfect tools, use a solution of 10 percent bleach or 70 percent rubbing alcohol to be sure not to spread the fungus to other branches or other garden plants.
Destroy or dispose all pruned canes by burning the debris, having the canes hauled far away, or burying them deep in the ground. This may seem like an extreme measure to take, but you can’t take a chance on allowing more spores to become airborne anywhere near your garden, as you may find yourself starting from the beginning with new infestations if you are not thorough in your efforts to eliminate the chances of further spreading this awful fungus.
Cane Blight Prevention
When planting a new bramble patch, choose an area that is very sunny and has excellent drainage. Eliminate weeds in this area regularly. Plant your brambles in rows at least 18 inches apart, and maintain the proper level of soil fertilization. Underfertilizing or overfertilizing your berry plants can result in reinfestation. Be very careful to minimize wounds, as open sores are like open doors to blight spores.
If cane blight continues to affect your plants and you feel like you are losing the fight, wait until your brambles are dormant, then apply liquid lime sulfur or copper all over the canes. Be sure to cover all of the canes thoroughly. Use liquid lime sulfur again right as new leaves sprout.
Want to Learn More About Managing Cane Blight?
This video will show you what cane blight looks like first hand on a diseased blackberry plant:
This video shows you how to properly prune infected canes during the dormant season:
This video breaks down all possible pests and diseases that affect blackberry plants: