how to treat diseased rosemary, lavender and raspberry shrubs - Ask Extension
Hello, I have a community organic garden plot with three mature shrubs - a rosemary bush, a lavender bush, and a small area of raspberry vines. all th...
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how to treat diseased rosemary, lavender and raspberry shrubs #905738
Asked June 13, 2025, 8:33 PM EDT
Hello, I have a community organic garden plot with three mature shrubs - a rosemary bush, a lavender bush, and a small area of raspberry vines. all three developed a wasting disease at the same time in mid-May. they were in flower, and then sections of the bushes branches turned brown and shriveled up to die. About a quarter of the raspberry canes had tiny dried up berries, discolored shriveled leaves and striped canes that died. I've removed most of the dead parts from these plants. What else can I do to help them recover? What can I do to prevent this in the future?
Montgomery County Maryland
Expert Response
Hi- sorry to learn of your plant issues.
Rosemary- this looks like winter injury. All old/dead/dying growth can be pruned out. As long as the crown and roots are healthy, it will make new growth. If the plant was healthy and green coming out of winter and then started to decline, there may be a root rot problem. This is more likely if the soil remains wet due to poor drainage or a leaking water pipe. You didn't include a photo of the lavender plant but the same would apply- possible winter injury and/or root damage from a disease or waterlogged soil.
We don't see symptoms of fungal leaf spot diseases. The leaves appear scorched. Is it possible that a chemical or pesticide was applied to the 25% of canes showing symptoms?
Some possible causes for the cane dieback:
Leaf/cane disease- there are a number of fungal diseases that can cause cane death. These are progressive diseases that don't infect and kill canes in a few weeks time. You would have seen early symptoms on the canes and leaves:
https://extension.umn.edu/plant-diseases/raspberry-cane-diseases#symptoms-of-cane-blight-1789361
Root rot disease- these cause cane dieback, especially where the soil tends to stay wet.
Viruses- several affect raspberry but the symptoms in your photos don't match the more common viruses to our region, like tomato ringspot virus:
https://blogs.cornell.edu/berrytool/raspberries/raspberry-viruses/
Borers- split open dead canes and look for signs of borer activity.
We suggest pruning out all of the injured canes close to ground level, bagging them up, and removing them from the garden. We would not recommend composting them on site since we don't know the symptoms' specific cause(s).
Contact us if the symptoms spread or change and monitor the healthy canes for developing symptoms.
Jon
Rosemary- this looks like winter injury. All old/dead/dying growth can be pruned out. As long as the crown and roots are healthy, it will make new growth. If the plant was healthy and green coming out of winter and then started to decline, there may be a root rot problem. This is more likely if the soil remains wet due to poor drainage or a leaking water pipe. You didn't include a photo of the lavender plant but the same would apply- possible winter injury and/or root damage from a disease or waterlogged soil.
We don't see symptoms of fungal leaf spot diseases. The leaves appear scorched. Is it possible that a chemical or pesticide was applied to the 25% of canes showing symptoms?
Some possible causes for the cane dieback:
Leaf/cane disease- there are a number of fungal diseases that can cause cane death. These are progressive diseases that don't infect and kill canes in a few weeks time. You would have seen early symptoms on the canes and leaves:
https://extension.umn.edu/plant-diseases/raspberry-cane-diseases#symptoms-of-cane-blight-1789361
Root rot disease- these cause cane dieback, especially where the soil tends to stay wet.
Viruses- several affect raspberry but the symptoms in your photos don't match the more common viruses to our region, like tomato ringspot virus:
https://blogs.cornell.edu/berrytool/raspberries/raspberry-viruses/
Borers- split open dead canes and look for signs of borer activity.
We suggest pruning out all of the injured canes close to ground level, bagging them up, and removing them from the garden. We would not recommend composting them on site since we don't know the symptoms' specific cause(s).
Contact us if the symptoms spread or change and monitor the healthy canes for developing symptoms.
Jon
