Azalea spreading disease? Help!!!

julie0720August 24, 2007

I have 3 Autumn Sunset Encore Azaleas planted in one area and 6 Autumn Sunset Encore Azaleas planted in another area. All are on the same side of my house and receive about the same amount of sun. I had previously 7 Autumn Sunset Encore Azaleas but after the frost this past Spring, the leaves started turning brown and falling off. They eventually all dried up and died. I removed all of the previous azaleas except for 2 that looked like they were going to be fine, even though they did have some mild frost damage. My new azaleas are doing great except for the one that planted near the 2 old azaleas. Individual branches are just drying up. The leaves will start turning a golden brown then it just appears to dry up to the point that you can just snap off the branch. It does not affect the entire plant, just individual branches. The 2 older ones are starting to have more leaves drop too. This was only affecting the azaleas on the one side, but this morning I noticed one of the azaleas on the other side had a single branch turning the dreaded brown color. Now I am not sure if the frost is what actually killed the original azaleas or if they have some spreading disease. Please help so that my second go round with azaleas doesn't die too!!!

Front of plant.

Back of plant.

Close up of affected area

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rhodyman(SE PA, USDA Z6)

Drought, Borers or Die-Back can be possible:

1) Drought can cause entire branches or entire plants to die. We have had several years of drought here and we observe that if rhododendrons and azaleas are not watered during a drought some plants will die, but others will just have one section of the plant die. It seems to be the plants way to conserve what little moisture it has. Prolonged drought weakens plants and often results in the appearance of fungal cankers on the branches of older azaleas. Look for branches that wilt in hot, dry weather in late summer and be sure to water azaleas if drought drags on more than a few weeks. Prune out the affected branches to stop the spread of fungal canker diseases.

2) If a Rhododendron Stem Borer, Oberea myops, or Rhododendron Borer, Synanthedon rhododendri, is in a branch, the entire portions of a plant beyond (away from the roots) will wilt and die. Borers only affect the portion of the plant away from the roots from the borer. If the borer is in the main trunk, then the entire plant will wilt and die. The plant can be save by cutting off the area with the borer and letting the plant regenerate from the roots. There are no conventional insecticides that will kill stem borer larvae once they are inside the branches. The best control option for homeowners with only a few plants is to prune out and destroy wilting branches in early spring or late summer.

3) Botryosphaeria dothidea: Rhododendron Dieback is caused by the fungus Botryosphaeria dothidea. Typically, dying branches (stem dieback) begin to appear on an otherwise healthy plant. The leaves die and can remain attached to the plant until late summer. Usually a single branch on an established plant is affected. Scraping away the bark with a knife reveals a reddish-brown discoloration under the bark on dying branches of rhododendron. Dieback is difficult to control on rhododendrons in the landscape. The following rhododendron varieties are considered resistant: 'Boursalt,' 'Chionoides White,' 'Cunningham's White,' 'English Roseum, 'Le Barr's Red,' 'Roseum Two' and 'Wissahickon.' Reduce stress to the plants by planting in partial shade and watering during dry periods. Avoid wounding the plant. Prune infected branches well below all discolored wood and dispose of dead plant material. Clean pruning tools between cuts with a dilute solution of household bleach (1 part bleach to 9 parts water).

4) Phytophthora Dieback, Phytophthora cactorum: The fungus Phytophthora causes one of the most common disease problems in the landscape for rhododendrons and azaleas. This fungus is a "water mold," and thrives in poorly drained or wet conditions. A wilted plant is usually the first sign of trouble. Rhododendron leaves will curl inward and droop. Drought can cause similar symptoms. Roots of affected plants appear soggy or blackened, and the outer portion of the root easily pulls away from the inner portion.. Crown rot causes the lower portions of the stem to have a brown discoloration of the wood near the soil line. This disease is favored in poorly drained areas or when plants are set too deeply. Plants may remain without symptoms until further stressed from drought or flooding. Do not set new plants any deeper than the original soil level. Planting in raised beds is suggested. Firm the soil slightly at the base of the planting hole to prevent the plant from settling into the bed. Do not plant azalea and rhododendron plants into sites where plants have previously died from root rot. Even resistant plants may succumb under these conditions. The fungus survives in the soil and cannot be eradicated once an area is infected.

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

    Bookmark   August 24, 2007 at 4:40PM
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