40-plus year old wild rose bush. Leaves are drying out, turn black. Is this...
40-plus year old wild rose bush. Leaves are drying out, turn black. Is this rose stem girdler? And, what can I do about it?
Hennepin County Minnesota
Thank you for the question. Without seeing a good photo of the shrub it's hard to know just what is happening with your rose and treatment depends on the diagnosis in order to cause the fewest problems to beneficial insects like pollinators. If rose stem girdler is the problem, you'll see clumps of leaves turning brown and wilting and if you look closely, you may see lumps visible on the canes where they tunnel. They kill rose canes by girdling them. The University of Utah Extension advises treatment as follows:
"The best treatment option is to remove and destroy infested canes late in the season and over the winter. There are a few insecticides that can be used to kill the eggs and newly hatched larvae, but use caution when spraying flowering plants: treat at dawn or dusk only, to avoid harming pollinators, or ideally, do not spray plants in bloom.
Treatment: Malathion, rotenone + pyrethrin (Pyrellin EC, Bonide Liquid Rotenone Pyrethrin Spray; this material is softest on bees), Diazinon. Treat every 7 days for 3 weeks". http://utahpests.usu.edu/IPM/htm/fruits/fruit-insect-disease/rose-stem-girdler/
There are other diseases and insects that can affect roses. Read this University of Minnesota Extension publication on black spot: http://www.extension.umn.edu/garden/yard-garden/flowers/rose-diseases/
Here is another U of M website called "What's Wrong with my Plant"? http://www.extension.umn.edu/garden/diagnose/plant/ You can read about diseases and see photos in an effort to diagnose the problem.
If you can't figure it out, consider submitting some photos of the problem and we'll try again.
Thank you for contacting Extension.