Native Mt Laurels

Asked July 16, 2019, 10:01 PM EDT

I have some large laurels (6-8 ft tall) that are dying back and I can’t figure out why. I live in Freeland MD and looking for someone to take a look and see if they can deduce the cause. I send soil samples to Penn State and the chemistry is okay, with pH slightly high at 6.1. Nutrient are in in optimal range, so I cant figure out why they are losing foliage every year. Two of the seven have died completely. What is interesting is that there are 2 plants 8 ft away but up slope and out of the lawn drainage path that are very healthy, doing just fine (pH is the also around 6.1) I attached 3 pics. 381 is the bush next to the lawn and showing the most die-back right now. Lawn drainage is just to the left of the plant. 388 is a close up of some of the branches of the same bush. 384 is a bush behind the first bush. It is 8'. It had 2 other 6' bushes in front of it that died last year. I use Hollytone in the spring and some 10-10-10. I occasionally use Miracid (once a month), and periodically (once every couple months) apply a fungicide.

Baltimore County Maryland disease issues shrubs abiotic issues

11 Responses

It sounds like you are doing the right things to care for your plants. Mountain laurels are very challenging to grow and yours actually look quite good in comparison to many we see. They are prone to fungal leaf spot diseases, which are worse in wet weather years. They are also very shallow-rooted, so they will be sensitive to too much/too little moisture and heat in the root zone. The very wet weather we had last year and into this spring has been tough on a lot of plants. In soil that is too saturated, roots do not receive sufficient oxygen and then decline -- which leads to dieback since the plant has less of a root system to take up water.
You mentioned that the plant closest to the lawn is showing the most dieback. Have you applied anything to your lawn? Are the plants closest to the lawn receiving more sun? These plants prefer cool, moist, well-draining (not heavy clay) soil and the high heat is not agreeable for them.
You can prune out dead branches at any time during dry water. Mulch should be kept to no deeper than 2-3" and avoid putting it right up against the trunk of the shrubs. Water the plants if we get into a period of drought. It is fine to use the HollyTone also.

Christa

To the lawn, I apply lime, fertilizer and treat for weeds. Mulch is about 2-3". I drip water once a week if it hasn't rained. A local nursery recommended Fung Onil (Bonide) for leaf spots. Sound okay to apply? Any issues with applying in this heat (didn't see any restrictions on the label).

The plants get about 4 hours of direct sun. And I did cut down a larger tree about 5 years ago that was nearly completely shading them all. The first ones to die back were in the middle of the group, not the ones getting the most sun, however the one that is currently struggling the most does get the most sun.

Yes, you can use the Fung Onil product. Just be aware that a fungicide like this will help with the prevention of fungal leaf spots. It will not clear up existing symptoms. Although the label does not mention specific temperature restrictions for application, I would recommend avoiding applications when we have these excessive heat warning days. The label does indicate to do a test for phytotoxicity. Some products can "burn" foliage in high heat situations. Test the product on a small area of the shrub first and check after a day or so for symptoms before treating the whole shrubs.

Christa

I took a photo of two of the bushes next to each other. The one on the left is doing much better than the one on the right. You can see a difference from the first photo. The second is a close up of the leaves on the left bush. Dark green and upright leaves. The one on the right is a lighter green and leaves are drooping. Whatever is going on is not affecting the bushes equally. Another interesting observation is that the leaves lower and more to the left side of the right bush look better than the ones on the upper right of that same bush. Is it possible that a weed killer on the lawn could affect a bush?

You can also see some dark spots, there are some on both bushes, but it is more predominant on the right bush. Is this bad, and if so, what is the best treatment?


Typically when an entire branch or section of a plant shows symptoms, it is an indicator of a root or trunk problem (a physical injury to a trunk/branch or decline in a portion of the root system). Also, there are genetic differences between plants of the same species. Some of the visual differences you are seeing in the two plants may be attributed to this perhaps. And some plants will have a stronger resistance to disease/pest/environmental stressors than others because of their genetics. Leaf spots are common in mountain laurel plants and we do not typically recommend fungicides for them. They are not curative. The plants can tolerate some amount of leaf spot damage. These are forest understory plants that do best with cool, moist, well-drained conditions. As I mentioned before, they are shallow-rooted and will be susceptible to moisture and heat stress in the root zone. They do not like heavy soil or root disturbance. They also like soil that is more acidic than what turfgrasses like. You could try a soil test to check the pH in this area. https://extension.umd.edu/hgic/topics/soil-testing There are some lawn herbicides that can affect ornamental plants negatively due to drift or volatilization, but we do not see the symptoms of this in your plant.

Christa

I have done the soil testing pH is 6.2. I will start applying some Espoma Soil Acidifier to reduce pH.

I have not disturbed the soil or roots that I am aware of. I keep a light layer of mulch. Perhaps it is all the hotter, wetter weather we have had over the last few years. perhaps it is the overstory tree that I cut down 5 years ago. But the fact that there are healthy bushes right next to dying bushes is a mystery.

I am still seeing what appears to be leaf wilting especially on upper branches. Here is a photo (at night) of upper (some wilting or dead) and lower (looking good). I also have a photo of leaves from the bush next to it that are mostly strong and healthy looking but shows deformed new leaves.

As noted above, it is possible that there is something impacting part of the root system of the plant that has the flagging limb. Have you pulled the mulch away from contact with the trunk and examined the trunk and branches closely for any signs of damage from rodent chewing? It's also possible that voles are chewing from beneath as well.
The excess water and increased sun could definitely affect them.
This is a tricky native plant to grow that likely depends on healthy mycorrhizal fungi in the soil. We'd suggest less chemical applications in general, but perhaps a couple of inches of organic compost around the root zones to help the natural soil profile as would be available in native forests.
If you feel the need to fertilize to lower the pH some, do that in early spring.

Your stand of them is one of the best we've seen that is not a natural stand.
Leaf spots are normal and will likely be there every year. Generally we do not recommend homeowners manage them with fungicides.


Christine


now that you mention possible critter damage, I do have obvious tunneling in the root area. I can't see any damage above ground through.

Any recommendation for how to get rid of them? Attack them directly or go after the food source?

You have to do some detective work and look around the base of the shrubs. There are some types of wildlife that tunnel and you will have to look for this. You did not mention the size of the tunnels. Some possibilities include voles, moles, or squirrels.

A type of critter that makes surface runways or tunnels is a vole. They can feed on the roots of trees and shrubs. Look for silver dollar sized holes around the root system for surface runways, and tunnels. If you notice this, you can set our mouse traps baited with peanut butter and apples in surface runways or tunnels. See more on our website for photos and management. https://extension.umd.edu/hgic/topics/voles

Moles can make tunnels looking for grubs and earthworms. They do not feed on roots of trees and shrubs and do not cause damage to the shrub. No chemical control is recommended. Here is our page on moles https://extension.umd.edu/hgic/topics/moles

Also, squirrels can root around and bury acorns but do not tunnel. They do not cause root damage to the shrubs.

Marian

I have had some vole activity in the yard the past couple years. Can see their surface holes occasionally but not near the laurels. They killed a couple of my Hosta plants. Looking at the laurel patch I can detect a lot of tunneling in the most of the laurel patch, but actually none around the base of the sick laurel. (The sick laurel appears healthy at the bottom and sick at the top as shown in attachment 1. The top has much lighter green leaves and dying branches as shown in attachment 2.)

I pulled back the thin layer of mulch around the sick plant and around one of the other laurels in the middle of the patch to inspect further. There were a lot of large earth worms. I could find tunnels in most of the patch but not around the sick laurel. Inspecting the base further, I found ants but no obvious damage above surface, and not vole holes. Attachment 3 show the base. The dying leaves seem to be on the left larger vertical branch. The healthy lower leaves are on the two lower right branches.

I will put some repellent down and push the critters out of the patch unless you advise differently. Any other observations I should make?

I took a soil sample around the base of the sick laurel and will send to Penn State. The last sample, from the around the middle of the patch showed slightly high pH (6.2-6.4), good phosphate and potash, high MgO and CaO. Any optional tests or trace elements you think I should request?

Thanks again for your help!

That pH is a little low. You could consider giving an application of ammonium sulfate or iron sulfate, following label instructions.
We don't recommend using a repellent, but try putting out a few snaptraps out overnight along the trails, baited with peanut butter or bacon grease and check them in the morning. These are just regular size mousetraps. If you get voles, continue to trap for a few days which can help with populations.
Again, we wouldn't stress too much about these plants. They are doing pretty well overall and it is possible to kill them with kindness.


Christine