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View Full Version : Cause of rhodie leaf damage/loss?


lakesregionscapes
05-19-2012, 04:50 PM
Hope this is the right sub-forum. I was hoping a different set of eyes might help us determine what went wrong... 5 large healthy rhodies, planted last summer, came through the winter fine; early April they looked good - no damage, or winter burn. Got a call from the customer today - shrubs look terrible - need to be replaced.
No one has been there this spring, except maybe a carpenter. We're in Central NH, and we had a really dry spring (no rain in March and April), but it has been raining a lot since. Went over to look, and take pics. Two shrubs are 2/3 damaged, 3 are just about wiped out.
I added the landscape photos from last fall to show their location and environment. Mostly shady, hemlocks and moss, bottom end of a steep hill with odd, talcum powder fine, orangy-beige soil, we amended before planting with better loam and hydrogel. Rhodies generally do really well around here and are very common.
Hubby is feeling like it looks like chem burn, but from where? New buds seem green and developing. Fungal? Soil issue? Drought stress?(hard sell after 3-4 weeks of rain, but no-one has been there in 6 weeks)
To me the really weird part is that there were OK 6 weeks ago...

phasthound
05-19-2012, 06:48 PM
Don't guess, send samples (an entire plant with roots if possible) to the U of NH in Durham. http://extension.unh.edu/agric/AGPDTS/PlantH.htm

There is nothing like having a lab report to show your client you are a professional.

bamaturf
05-21-2012, 08:57 AM
rhodies dont like wet feet. either elevate or move them further up the hill in the bed, or trim trees to let more light in. my 2 cents. had a similar situation
last year & rhodies looked bad, then a storm got a near by tree. this year
rhodies look a lot better w/ more blooms

Dr.NewEarth
05-21-2012, 01:10 PM
How was your winter?

I am guessing your problem is from ground water and the native soil.
It is possibly "Armillaria" root rot.

I wonder if you are also seeing "allelopathy" from the Hemlock roots?

Get a lab test as Barry has suggested.

It's some-times difficult for us to see all of the factors that could contribute to plant decline, from a picture.

I always have many more
questions, inspections and tests that I can do in person.

lakesregionscapes
05-26-2012, 10:31 PM
Figured I'd follow up with an expert's conclusion so if someone else is searching this issue they get the final input, for our specific case.
Since thanks to the state budget cutbacks our cooperative extension is under-funded, under-staffed and over-worked and in the peak of their busy season, I decided to first pester our local Barlett Tree expert, who consults with landscape contractors quite willingly, and cares for trees on several of our other clients' properties. He got out there to take a look and got back to me within a couple of days...
He's quite sure it is winter burn, despite the very late manifestation. We had a dry fall, minimal snowfall (no snowmelt in spring) and a two month drought (March-April). There has been record rhodie damage all around the region, often on shrubs that never suffer usually.
He explained that although the stress damage occurs over the winter, the signs don't appear until the growing season starts, and on this location that is nearly a month behind the rest of the area. Painted ferns onsite were up barely an inch, while they're fully leafed out everywhere else in town. The shrubs in the shade were less damaged, roots are all sound (shrubs have been pulled) and what new growth there is looks healthy... The rhodies were pulled yesterday. Since we first saw them 2 weeks ago, the rest of the leaves had dropped, and they actually look more like we are used to seeing in spring, after a tough winter (horrible). We seem to have just caught them earlier than usual in the progression of symptoms, while the burns were still working their way up the leaf length.
The salvaged plants are going in our yard, and the replacements will be getting wrapped for the winter at least until they are well established. We're planning to replace at cost, to split the pain. Bartlett felt the location was a bit shady in the top (thin the canopy a bit), but otherwise fine (we selected specifically shade tolerant varieties). The location is tough and there aren't any better evergreen candidates, so rhodies remain the choice... The hill is too steep for wet feet to be a concern.

Thank you to all of you who weighed in, I always appreciate the range of knowledge in this forum.

Dr.NewEarth
05-28-2012, 08:33 PM
I still believe you should get a test. Have you pulled out one of the plants to check the rootball. If you can do that, get another picture please.

Smallaxe
05-29-2012, 06:36 AM
Winter burn is another way of saying, drought... protecting the plants from dessicating winds is fine, but the real issue with struggling landscapes is, water...

I learned from fruit tree farming that the water available in September determines the size and vigor of the fruit in the following season... I keep landscapes soaked as much as possible until the ground freezes...

rlitman
05-30-2012, 01:43 PM
Drought is not the total answer. Rhododendrons can't just soak up water from the ground when the ground is frozen. You can't water them in the winter, so watering isn't going to help this. By the spring, the damage is long done, and watering then is just too late.
Watering well in the fall does indeed help, but only to a degree.

Protecting from desiccating winds helps. Another option is to spray with a product that helps seal the stomata, such as Wilt Pruf, or an oil product.

Smallaxe
05-31-2012, 09:35 AM
Drought is not the total answer. Rhododendrons can't just soak up water from the ground when the ground is frozen. You can't water them in the winter, so watering isn't going to help this. By the spring, the damage is long done, and watering then is just too late.
Watering well in the fall does indeed help, but only to a degree.

Protecting from desiccating winds helps. Another option is to spray with a product that helps seal the stomata, such as Wilt Pruf, or an oil product.

Winter kill occurs with plants that go into the winter, with less than robust water reserves... if they don't get snow cover they are reliant upon roots below the frost line to access moisture, so there needs to be moisture down there before winter comes... correct preparation is done automatically by the plant itself as long as it has enough water to prepare...
Winter kill is drought and drought alone... if there is another cause, then we need to know that...
Just because some plants, like Japanese Yews, can never prepare for a Zone 3 winter, especially if planted out in the open; doesn't mean there was something other than lack of water causing the winter kill...

Mark Oomkes
05-31-2012, 09:59 AM
I would hazard a guess that you also have some Phytophthora going on as well.

Trees Too
11-19-2013, 07:56 PM
I noted 2 things in your original post. 1) You're in New Hampshire, 2) These are large leafed Rhodos which don't tolerate the cold/dry temps of northern environments. This winter injury/burn diagnosis isn't that far off base, as it doesn't necessarily manifest itself first thing in the spring. If you going to plant Rhodos up north, but to go with the small leafed PJM Rhodos. ;)

32vld
11-20-2013, 09:44 PM
I had 4 rhododendron's that my mom had planted.

They showed the same damage. I cut out all the bad sections.

That helped some. Then when weeding the beds I noticed that the soil directly underneath the plants to be compacted hard with surface rhododendrons roots.

Loosing the soil up with a hand cultivator in the root zone brought the plants back to good health. Doing good after two full years now.

Smallaxe
11-21-2013, 07:14 AM
I had 4 rhododendron's that my mom had planted.

They showed the same damage. I cut out all the bad sections.

That helped some. Then when weeding the beds I noticed that the soil directly underneath the plants to be compacted hard with surface rhododendrons roots.

Loosing the soil up with a hand cultivator in the root zone brought the plants back to good health. Doing good after two full years now.

Excellent... that is the first thing I do when bushes start to look peaked... next I check for rodent/insect damage to the bark...
Keeping the soil loose, moist with plenty of air space prevent most problems to begin with... :)

Trees Too
11-22-2013, 12:05 AM
As a general rule of thumb. As with the large leafed Rhodos that were shown in the above pics. In areas of harsh winter climates. It is a must to ring these large leafed Rhodos in the fall with burlap to guard against Winter Injury. You can take it a step further by also spraying an anti-desiccant such as Vapor Gard or Transfilm. Although I am not totally sold on the effectiveness of these products.

Smallaxe
11-22-2013, 07:48 AM
Winter injury is largely evidenced through dessication... if the plants can survive the freezing temps, then adequate water will certainly help... keep them well watered right up to the freezing of the soil...
We have always been a little cold for Arborvitaes to do well out in the open, where the sun and wind can brutalize them... however with just using adequate irrigation practices, especially in the Fall we can grow arbs, w/out worry and w/out special covering... :)
Burlap covering all the way to the ground encourages rodents, so keeping it up a ways is usually safer... :)