Blooms turn brown rapidly. Fungus?

chas045(7b)May 25, 2011

I am in North Carolina. I have a white azalea that is growing very well and puts out a beautiful show of white blooms. Unfortunately, every year they turn yellow, then brown quickly: perhaps a week or less. I thought this might be normal but on keeping track of the many azaleas in this area, I think they last for a month or much more. I recently heard about some disease, perhaps a fungus (I forgot), that causes this.

Can you tell me what and when to do something about this. I just thought of this site. the flowers died a month or more ago.

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rhodyman(SE PA, USDA Z6)

The fungus is Petal Blight

If you are getting petal blight, then deadheading is very important. All spent flowers should be destroyed. The best way is to toss them in the trash. Petal blight is a disease that hits some rhododendrons and azaleas that bloom later in the spring. It causes the flower to turn mushy before it naturally wilts. If you look closely it forms unsightly brown spots on the flowers.

Petal Blight, Ovulinia azaleae: This fungal disease, caused by Ovulinia azaleae, primarily affects the flowers of azaleas, but mountain laurel and rhododendron flowers can also be infected. Indian and Kurume azaleas are especially susceptible. The disease starts on the flower petals as tiny, irregularly-shaped spots, giving a "freckled" appearance. On colored flowers the spots are white, and on white flowers the spots are brown. The spots quickly enlarge and become soft and watery. Flowers rot and stick to the leaves. Infection is easily spread from flower to flower by wind, rain and insects. The fungus survives the winter in the soil. The most important things that you can do to control this disease in the home landscape are to pick and destroy infected flowers and avoid overhead watering. This fungus survives in the soil, so it is important to replace the ground litter with uncontaminated mulches. Rake and remove flower debris from beneath plants and, if possible, remove old flowers still attached to plants. Apply new mulch around the base of plants to serve as a barrier to new infection. On large azalea plantings, where it is not practical to remove infected flowers, make weekly fungicide applications beginning just before bloom and continue until the last buds open.

The best fungicides are a combination of chlorothalonil and benomyl or Mancozeb or Bayleton or triadimefon. During moist seasons, control may be difficult for late blooming varieties. Sanitation practices such as deadheading and removal of diseased material my improve control. In the northwestern US, Ovulinia is present, but similar symptoms can also be caused by Botrytis cinerea which is less damaging to the flowers and easier to control.

It is important to remove diseased material from the vicinity of a planting. This means removing dead material that harbors spores of fungal disease and dying material that contains eggs of insects. Dying portions of a plant should be cut off and removed. The ground should be cleaned of dead leaves or flower parts. Pruned parts should be removed.

Deadheading flowers involves removing the structure left after blooming before seedpods form. A rhododendron or azalea flower is composed of several florets connected to the stem by a base that is easy to break. When deadheading just grab the flower near this base area and twist the flower sideways and break it off in this spongy area. Try not to break any of the buds that are around the base of the flower.

    Bookmark   May 25, 2011 at 2:52PM
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chas045(7b)

Thanks for being so fast Rhodyman. That sure sounds like what it is. I already have chlorothalonil which used to be very expensive but now is available as ortho max. I got it for iris leaf spot. The affected iris were in the same plot as the azalea. Perhahps there is a relationship although the iris fungus is Didymellina macrospora. The Ortho Max and removing all the iris, dumping them in clorox (who knows) and cleaning up, did the trick. I will deadhead, cut some low branches and rake my brains out.

I noticed that you list favoring the Pond site. That is my favored site although I don't post often. I have a pond with long stream that acts as my filter etc.

    Bookmark   May 26, 2011 at 3:28PM
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