5-6 weeks ago I bought a few rhodos in containers at a local nursery:
Horizon Monarch, Anna Rose Whitney, Percy Wiseman. When I planted
them I noticed that some leaf tips were cut off. I did not think much
of it at the time. :-(

Quite soon I saw that some of the leaves were developing brown spots.
The brown area always progresses from the edge (often the tip) of the
leaf inward. Eventually the all leaf turns brown. More affected by
this disease are the leaves at the base of the plant, and particulalry
the ones directly attached to the woody (older) stems.

At first I kept removing only the leaves that were in the worst shape,
with scarce results. A couple of day ago I decided to remove and
dispose of all the diseased leaves.

Could phytophthora die back be the cause? Considering I live on the
wet coast (Vancouver), do these rhodos stand a chance? Should I apply
a fungicide? I have other established (and healhty) rhodos next to
these new plants, may they be at risk?

TIA,
Luca

Luca wrote:

Quite soon I saw that some of the leaves were developing brown spots.
The brown area always progresses from the edge (often the tip) of the
leaf inward. Eventually the all leaf turns brown. More affected by
this disease are the leaves at the base of the plant, and particulalry
the ones directly attached to the woody (older) stems.

I doubt if it is phytophera. If it was, there is nothing you could do.

If a leaf has brown areas with white spots, it probably has a local
fungal infection of Pestalotia leaf spot. This is seldom controlled with
fungicides and is best mitigated by good sanitation and avoiding
excessive moisture

Another possibility is rhododendron mildew. Light green or yellowish
patches on leaves sometimes accompanies by brown spots on the back side
of leaves is a sign of rhododendron powdery mildew (Microsphaera
azaleae) . One of the puzzling aspects of this fungal problem is the
fact that two different affected rhododendrons vary in appearance.
Rhodendron cultivar 'Unique,' for instance, shows almost no upper leaf
changes, other than occasional very faint lighter yellowish areas, while
the underside of the leaves will be completely covered in brown spots.
A deep green leaf may begin to show lighter green patches, and these
areas will gradually become more yellow. Another cultivar, 'Virginia
Richards,' gets brownish purple spots on both tops and bottoms of
leaves. This common disease is named rhododendron powdery mildew
despite how little the symptoms resemble the familiar fungal disease
often seen on roses and azaleas. Usually the disease doesn't produce the
familiar white powder-like spores, although late in the summer some may
become visible. The disease manifests instead as color changes in the
leaves, followed by defoliation toward the end of the growing season.
Many rhododendrons, if basically healthy, will coexist with the disease
and seem to outgrow or at least survive the symptoms. Last year's
leaves, once they have been hit by the disease, will always have it,
with symptoms persisting from year to year until the leaves drop off.
High relative humidity at night and low relative humidity during day
with 70-80 F (22-27 C) temperatures is ideal for the disease to
flourish.

Keep rhododendrons healthy to help them manage this problem. If you
notice symptoms on last year's leaves, consider protecting the new
growth with a fungicide . Apply it now to the new growth as it expands,
before symptoms appear on this spring's leaves. Fungicides won't get rid
of the existing problem on old leaves. A new fungicide, 'Remedy,' which
is a potassium bicarbonate (made by Bonide Company), is registered for
the problem. Thorough leaf coverage is necessary with all fungicides.
Fungicides containing sulfur (such as Safer Garden Fungicide RTU) are
also registered. Others are Funginex (sold as Ortho RosePride Funginex
Rose and Shrub Disease Control Concentrate.) Be very careful to read all
label instructions, and wear protective goggles and gloves. Funginex can
be corrosive to eyes. For more information see the section above on
'azalea powdery mildew'. The symptoms are different, but the organism
and control are the same.

Rhododendrons that have been hybridized with Rhododendron cinnabarinum
as one of the parent plants do get the disease severely. Two of those
are 'Elizabeth' and 'Lady Chamberlain.' The Cornish Cross hybrids,
including 'Virginia Richards,' 'Seta' and 'Mrs. G.W. Leak' seem
vulnerable also.

--
Pardon my spam deterrent; send email to
Visit my Rhododendron and Azalea web pages at:
http://home.earthlink.net/~rhodyman/rhody.html
Also visit the Rhododendron and Azalea Bookstore at:
http://home.earthlink.net/~rhodyman/rhodybooks.html
Cheers, Steve Henning in Reading, PA USA http://home.earthlink.net/~rhodyman

Could be winter burn, but it sure sounds like Phytopthora to me. The
coalescing of the spots is unlike the leaf-spot of Rhodo I see here.

--
Mike LaMana, MS
Heartwood Consulting Services, LLC
Toms River, NJ
www.HeartwoodConsulting.net



"Stephen M. Henning" wrote in message
news
Luca wrote:

Quite soon I saw that some of the leaves were developing brown spots.
The brown area always progresses from the edge (often the tip) of the
leaf inward. Eventually the all leaf turns brown. More affected by
this disease are the leaves at the base of the plant, and particulalry
the ones directly attached to the woody (older) stems.

I doubt if it is phytophera. If it was, there is nothing you could do.

If a leaf has brown areas with white spots, it probably has a local
fungal infection of Pestalotia leaf spot. This is seldom controlled with
fungicides and is best mitigated by good sanitation and avoiding
excessive moisture

Another possibility is rhododendron mildew. Light green or yellowish
patches on leaves sometimes accompanies by brown spots on the back side
of leaves is a sign of rhododendron powdery mildew (Microsphaera
azaleae) . One of the puzzling aspects of this fungal problem is the
fact that two different affected rhododendrons vary in appearance.
Rhodendron cultivar 'Unique,' for instance, shows almost no upper leaf
changes, other than occasional very faint lighter yellowish areas, while
the underside of the leaves will be completely covered in brown spots.
A deep green leaf may begin to show lighter green patches, and these
areas will gradually become more yellow. Another cultivar, 'Virginia
Richards,' gets brownish purple spots on both tops and bottoms of
leaves. This common disease is named rhododendron powdery mildew
despite how little the symptoms resemble the familiar fungal disease
often seen on roses and azaleas. Usually the disease doesn't produce the
familiar white powder-like spores, although late in the summer some may
become visible. The disease manifests instead as color changes in the
leaves, followed by defoliation toward the end of the growing season.
Many rhododendrons, if basically healthy, will coexist with the disease
and seem to outgrow or at least survive the symptoms. Last year's
leaves, once they have been hit by the disease, will always have it,
with symptoms persisting from year to year until the leaves drop off.
High relative humidity at night and low relative humidity during day
with 70-80 F (22-27 C) temperatures is ideal for the disease to
flourish.

Keep rhododendrons healthy to help them manage this problem. If you
notice symptoms on last year's leaves, consider protecting the new
growth with a fungicide . Apply it now to the new growth as it expands,
before symptoms appear on this spring's leaves. Fungicides won't get rid
of the existing problem on old leaves. A new fungicide, 'Remedy,' which
is a potassium bicarbonate (made by Bonide Company), is registered for
the problem. Thorough leaf coverage is necessary with all fungicides.
Fungicides containing sulfur (such as Safer Garden Fungicide RTU) are
also registered. Others are Funginex (sold as Ortho RosePride Funginex
Rose and Shrub Disease Control Concentrate.) Be very careful to read all
label instructions, and wear protective goggles and gloves. Funginex can
be corrosive to eyes. For more information see the section above on
'azalea powdery mildew'. The symptoms are different, but the organism
and control are the same.

Rhododendrons that have been hybridized with Rhododendron cinnabarinum
as one of the parent plants do get the disease severely. Two of those
are 'Elizabeth' and 'Lady Chamberlain.' The Cornish Cross hybrids,
including 'Virginia Richards,' 'Seta' and 'Mrs. G.W. Leak' seem
vulnerable also.

--
Pardon my spam deterrent; send email to
Visit my Rhododendron and Azalea web pages at:
http://home.earthlink.net/~rhodyman/rhody.html
Also visit the Rhododendron and Azalea Bookstore at:
http://home.earthlink.net/~rhodyman/rhodybooks.html
Cheers, Steve Henning in Reading, PA USA
http://home.earthlink.net/~rhodyman

"Mike LaMana" fake@MikeatHeartwoodConsultingdotnet wrote:

Could be winter burn, but it sure sounds like Phytopthora to me. The
coalescing of the spots is unlike the leaf-spot of Rhodo I see here.

Winter burn would not be spreading now. It would be static.

I wonder if it could be salt damage either from fertilizer or another
salt.

--
Pardon my spam deterrent; send email to
Visit my Rhododendron and Azalea web pages at:
http://home.earthlink.net/~rhodyman/rhody.html
Also visit the Rhododendron and Azalea Bookstore at:
http://home.earthlink.net/~rhodyman/rhodybooks.html
Cheers, Steve Henning in Reading, PA USA http://home.earthlink.net/~rhodyman

"Stephen M. Henning" wrote in
news
If a leaf has brown areas with white spots, it probably has a
local fungal infection of Pestalotia leaf spot. This is seldom
controlled with fungicides and is best mitigated by good
sanitation and avoiding excessive moisture

I have 2 rhododendrons with very similar symptoms to what the
original poster described. I posted some pics here.

http://img19.photobucket.com/albums/v56/jjjggg/Sick Rhodie/ex1.jpg
http://img19.photobucket.com/albums/v56/jjjggg/Sick Rhodie/ex2.jpg
http://img19.photobucket.com/albums/v56/jjjggg/Sick Rhodie/ex3.jpg

There were three of these plants that were planted a year ago by the
landscaper. I lost one already last summer to root strangulation,
because the lanscaper did not losen the rootball. I fear I am about
to lose the other 2. These plants are north facing and I thought it
might be winter burn too, but as both shrubs growing profusely, so do
the brown spots. The other plant, not in these pics, looks the same.

Do you have any idea what's wrong with these plants and is it
terminal?

2 out of 3 English Spreading yews he planted look sickly too and show
no new growth, but that's another story.

Gary
Zone 6/7

GaryM wrote:

I have 2 rhododendrons with very similar symptoms to what the
original poster described. I posted some pics here.

You have a whole host of problems. I would guess that the plants are
stressed. If they were doing better they would be more resistant to
these problems. Some of the problems a

Pestalotia leaf spot
Wind and cold damage
Black Vine Weevil and/or Strawberry Root Weevil
Rhododendron gall midge

I wouldn't worry too much about the individual problems, but would worry
more about the general health of the plants. They need good drainage. A
wet root zone is a real killer. The need good acidic soil. They are
sodium sensative, so salt will set them way back. They like a spring
application of a good rhody fertilizer like Holytone. Residual
herbicides or lawn fertilizer will set them back.

--
Pardon my spam deterrent; send email to
Visit my Rhododendron and Azalea web pages at:
http://home.earthlink.net/~rhodyman/rhody.html
Also visit the Rhododendron and Azalea Bookstore at:
http://home.earthlink.net/~rhodyman/rhodybooks.html
Cheers, Steve Henning in Reading, PA USA http://home.earthlink.net/~rhodyman

"Stephen M. Henning" wrote in
news


I wouldn't worry too much about the individual problems, but would
worry more about the general health of the plants. They need good
drainage. A wet root zone is a real killer. The need good acidic
soil. They are sodium sensative, so salt will set them way back.
They like a spring application of a good rhody fertilizer like
Holytone. Residual herbicides or lawn fertilizer will set them
back.


Stephen, thank you for the reply. I have removed the mulch (and in
intend to destroy it). The crown fine roots look to be in good shape
for the most part, though one side is pretty brown the 9/10's of the
crown shows white fine shoots. The soil is pretty sandy but I know the
guy who planted them was pretty clueless and they could be in a puddle
below for all I know. If I remove it to look and perhaps remedy a
problem, do you think it will take it?