Azalea diseases ?

jjtbay(5)June 25, 2007

Last year my azalea's leaves all turned brown. The vigorous new shoots around the base of the plant died. This year I applied Bayer Tree & Shrub Insect Control Concentrate (http://www.bayeradvanced.com/product/Tree-Shrub-Insect-Control/concentrate.html) with the hope the problem was caused by insects. Now the same problem is happening again. But this time I'm hopefully catching it right as it starts and can still do something about it. I've a link to photos of the leaves below. It looks like three different kinds of diseases are happening at the same time. The azelea is a few feet from a lilac which has powdery mildew. I've been watering the azeala was applying Miracle Grow about every other week. Thank you for any suggestions you might have on how to control this.

Joe

Here is a link that might be useful: photos of leafs

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jean001(z8aPortland, OR)

Problem 1 looks like powdery mildew.

Hope someone else will help us with the others.

    Bookmark   June 26, 2007 at 2:14AM
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luis_pr(7b/8a Hurst, TX)

It could also be a form of cold/frost damage. The brown spots may be fungi that attack plants stressed by cold damage. In other words, the fungal brown spots are an oportunistic infestation caused by the cold damage.

Dispose of those affected leaves & any plant debris when they fall and put them all in the trash, not the compost pile. The fungal infection should clear up on its own as summer arrives. Luis

    Bookmark   June 26, 2007 at 7:44AM
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rhodyman(SE PA, USDA Z6)

Problem 1, Powdery Mildew:

A grayish white, powdery coating or fuzzy white growth on upper or lower surfaces is Powdery Mildew (Microsphaera azaleae). This is more prevalent on deciduous azaleas and sometimes it affects the lower surface more. Entire leaves can be covered. In late summer and fall, small black specks may be found in the white areas. Powdery mildew is more severe on shaded plants. It is favored by the high humidity found in crowded plantings and damp locations. The disease is more severe during periods of cool, moist weather. These fungi produce spores on the surface of the infected leaves which are spread by wind currents to surrounding leaf tissue. These fungi overwinter in the bud scales for initiation of infection next season. There are a number of ways to manage this disease.

* Do not overwater or overfertilize plants, as the fungus prefers succulent new growth.
* Hand-pick and destroy mildewed leaves to control small amounts of infection.
* Hose diseased plants with water when practical. This can help remove fungus and prevent new infections.
* Prune and space plantings to allow good air circulation. Do not plant in extremely shaded or damp areas.
* Rake and destroy fallen leaves year-round to reduce infection source. Do not compost diseased materials.

Chemical control is possible. Begin applications when you first notice the disease on current-year leaves. If disease appears late summer, applications are not necessary on deciduous azaleas. Do not apply sulfur products when temperature is over 85F or within a few weeks of an oil spray.

* Black Leaf Sulfur Dust
* Bonide Lime Sulfur Spray
* Bonide Remedy
* Monterey Fungi-Fighter
* Ortho RosePride Funginex
* Ortho RosePride Orthenex
* Safer Flower, Fruit & Vegetable Garden Fungicide
* triadimefon (Bayleton, Strike)
* Spectracide IMMUNOX

This fungal disease can weaken the plant. Spray when you first see the disease and then again in 10 days. Chemicals will not control the fungi that has already become established.

Problem 2, Too Much Fertilizer:

Too much fertilizer causes the edges of the leaves become distorted and turn brown uniformly over the entire plant.
Deciduous azaleas are not heavy feeders. I recommend just fertilizing once each spring with a good azalea fertilizer like Hollytone, but at half the rate on the package. Miracid is more of a problem than a cure. It is mostly water soluable nitrogen. It is probably a contributing factor to the other two problems.

Problem 3, Leaf Gall and Fertilizer Burn:

Enlarged, crabapple-like, green or pinkish galls on young leaves and flowers are caused by Exobasidium Leaf and Flower Gall. The galls become hard and turn white and eventually brown. While very noticeable, these galls will not threaten the health of the plant. This problem is more common during cool and wet spring weather. The first symptoms are swollen or puffy portions on newly expanding leaves, shoots, buds or flowers. The galls range in color from green, to pink or red depending on the part of the plant infected. As these galls age they develop a white surface growth which is a layer of reproductive spores. Eventually the infected tissue will turn brown and shrivel up into hard galls. Fungicides seldom provide control. For best control, start spraying in the early spring with Ferban or Bordeaux. Sanitation and warm dry conditions reduce infestation. It is seldom considered serious. It is most common of evergreen azaleas.

Here is a link that might be useful: Rhododendron Basics by Harold Greer, Eugene, OR

    Bookmark   June 26, 2007 at 7:48AM
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jjtbay(5)

Wow ! Thank you so much for your reply Rhodyman. I can't imagine how it could be more complete. I'm going out to pick the bad leaves for problem #1 right now...

Joe

    Bookmark   June 26, 2007 at 8:09PM
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