Mountain laurel dying
We live on a ridge in Allegany County x ~35 yrs. Laurel has been grad sickening. We tried thinning some trees around them (after disc w forester). Last year, at least the new growth at the bottom of the plant, where it was reshooting, looked ok. This year is worse, and they are very sick w no healthy new growth. Some shrubs entirely dead. The reference I have, Common Problems of Mountain Laurel S. M. Douglas, says to remove fallen leaves, etc. Obviously can't do that in the woods. Sprays recommended include Trichoderma harzianum Rifai strain KRL-AG2, Streptomyces griseoviridis strain K61, and Bacillus subtilis strain QST 713 may be effective as protectants. Do you have any preference about these products or better ideas. I hate to see them all dying. We try to protect all the native plants. Let me know if you want other pics. Thanks so much. Judy
Allegany County Maryland
The fungus is not unusual. Yes, if you can remove some of the worst-infected leaves and/or any of the old infected material, that would lessen the amount of inoculum that is reinfecting the plants. Good garden clean-up, as much as possible. If possible, you could even rake up below plants and put down a light layer of clean mulch.
You also can prune off dead wood back to healthy or a bit more, in an effort to stimulate new growth. If you have a great deal of mountain laurel with new shoots, prioritze the new shoots if you spray a fungicide. A couple of years of new clean growth may be able to revitalize the roots.
We don't have a preference for the fungicides. You'd have to start when leafing out begins and continue through bloom. (Avoid flowers as much as you can.)
A little fertilizer would not hurt.
Thanks. Just to clarify, the laurel is in the forest, so cannot rake and lay down new mulch.
Does that change your rec re spraying? Should we cut back the shrubs?
Since it sounds like these are wild plants (as opposed to planted garden plants), then we suggest letting nature run its course with regards to the fungus and dieback. Natural selection will permit the more resistant individuals to survive and those with less vigor or resistance to succumb to the fungus. Fungicides can be of benefit as preventatives, but will not cure existing infections. In addition, there is concern that fungicides negatively impact beneficial soil microbes. Weather plays an important role in disease spread and severity; the past two springs were very wet and likely contributed to the preponderance of the disease. If this spring's weather is drier - especially as new growth is emerging and maturing - then it's possible they will be minimally affected. With time, older and damaged leaves are shed, so they can grow out of the worst of it. We would not recommend cutting them back given the slow rate at which Mountain-laurels grow; forcing new growth closer to the ground could also make it easier for them to get infected, as spores can splash up off of the soil surface and leaf litter onto vulnerable foliage.