Is this leaf spot fungus

reesesaddictSeptember 28, 2009

Hello all,

We bought this on a trip to the mountains (Tennessee I think). It is only supposed to grow there (some special color) Knowing it would probably die, we brought it back to FL, where it has been in a pot for about 4 years, refusing to die, but only producing one flower. This spring, I planted in on the south side of the house, where it gets full sun until about 11:30. Then it is fully shaded by an oak tree.

I was wondering if this is leaf spot fungus and is it to late in the year to treat. You can see from the pics that the buds? have popped out. Thanks for any help.


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rhodyman(SE PA, USDA Z6)

Leaf spots have several origins:

Brown, reddish-brown or purplish leaf spots that occur on many cultivars, including R. 'Blue Ensign' and R. 'Mrs. G. W. Leak', are physiological and not disease caused. These spots are generally purplish and are inherent in the cultivar. Environmental stress may increase their appearance. They do no harm to the plant.

Some leaf spots are caused by a virus thought to be a potexvirus, the most common ailment being called Necrotic Ring Spot. The symptoms are reddish-brown rings or spots on the leaves. It generally occurs only on the two year leaves of a few rhododendron cultivars such as R. 'Unique', or on Kalmia latifolia. It also appears on the first year foliage of some R. 'Loderi' clones. Little is known about the disease and a does not seem to spread from one cultivar to another. No control is known or generally necessary.

Leaf spotting can also be caused by chemical injury, such as drift from cleaners, paints, or chemicals used to kill moss on roofs as shown in the photo on the right. Sometimes the results of such injury may not show up for weeks or months.

There are a number of leaf spots or burns caused by fungi such as Botrytis cinerea, Pestalotia rhododendri, Phyllosticta, Septoria and others. Many are secondary infections happening after mechanical damage or environmental stress, such as sunburn, drought, winter damage or windburn. They generally occur during wet weather and many times are self limiting with drier weather. Good sanitation is helpful, so remove brown and fallen leaves. Also provide good air circulation. Spraying with Benomyl or similar fungicide can be useful, but is frequently not necessary.

Young Azalea Leafminers, Caloptilia azaleella: (also known as azalea leafroller) larvae tunnel inside leaves and form elongate blotches in April or May. These blotches may resemble leaf spot diseases. Older larvae exit the tunnels, curl the leaf tip and feed inside the curl. Large populations cause the leaves to turn brown and drop from the plant.

Here is a link that might be useful: How to care for rhododendrons and azaleas.

    Bookmark   September 28, 2009 at 6:15PM
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Thanks for the link. I think I am going to try Funginex. From the link, it is most closely described by Powdery Mildew that the Virginia Richards cultivar can get. Newb question. The Virginia Richards is a Rhododendron and not an azalea correct?
I think that my plant might be a deciduous azalea. I didn't even know that such things existed. Whenever it lost its leaves, I always thought it was dying. I guess I did learn something new today. :)

    Bookmark   September 29, 2009 at 9:16AM
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rhodyman(SE PA, USDA Z6)

Yes, Virginia Richards is a rhododendron. Rhododendrons and azaleas have very similar problems and symptoms except in the case of powdery mildew. That disease affects different rhododendrons and azaleas quite differently.

Nothing will cure the symptoms on the leaves it has affected. The only hope is that you can prevent it from getting on new leaves. Sanitation is one of the best weapons you have. The old leaves will contaminate the new leaves. It is best to collect the old leaves when they fall and either burn or throw in the garbage.

    Bookmark   September 30, 2009 at 4:13PM
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Yes it is a deciduous azalea (which are native to the US, btw). They do come in special colors (like orange and yellow). Here's my two cents worth. Those spots look EXACTLY like the spots I have on some of my azaleas. Some cultivars are more subject to this infection than others, with some completely defoliating before summers end. Some seedlings and cultivars seem totally resistant and show nary a spot. Long story short, I have no choice but to select against this in my azalea breeding program.

What I think it is? Oak blight. All over TN (and ESPECIALLY nursery stock), can and will not be controlled. It affects other ornamentals as well...spirea, cherries, hydrangea, crepe myrtles, etc.

    Bookmark   October 12, 2009 at 8:13AM
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I wanted to show an example of what I'm talking about.

Here's (two) of my seedlings that are immune to this fungal infection.

Here's one obviously susceptible to it.

Grown side by side. As you can see it's an obvious selection pressure in my breeding program.

    Bookmark   October 29, 2009 at 3:18PM
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