Petal Blight

Kathy RiveraMay 22, 2012

I fear I have a nasty case of petal blight. :( This is my second spring in this home and I don't recall it much from last year. I have a ton of rhodys in front of the house (east facing) and the azaleas are in a retaining wall along the driveway (south-facing). The azaleas bloomed beautifully - the plant was covered. The rhodys were great last year - this year not much at all (though that might be due to some lacecap hydrangeas that I think are blocking the sun).

But I recently noticed the rhody flowers were wilting and browning very quickly. And then I noticed the azaleas were, too - especially my white ones. I also recall seeing brown spots on the azaleas when they were in bloom and the rhodys looking 'water logged' before blooming. So now I've done my googling and realize what we have. I can deadhead and remulch the rhodys pretty easily. But the azaleas are huge and now all the flowers are stuck to the leaves. Additionally, the ground under them is covered in pachysandra! How do I 'clean' that soil? Am I just out of luck? (unless I tear of the pachysandra - don't want to deal with that!!!)

Thank you!

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rhodyman(SE PA, USDA Z6)

You seem to be fully aware of what you have. Petal Blight comes back every year afresh from debris left from the previous year. It has little effect early in the season on the first blooms. But it build during the bloom season and the later blooming plants get the full force disease. LIttle can be done other than sanitation to remove "ALL" infected tissue.

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.

Here is a link that might be useful: Petal Blight

    Bookmark   May 23, 2012 at 5:06PM
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Until this year I had never seen petal blight in 30+ years of rhododendron growing. I believe the very early spring, early onset of hot, humid weather and the mild winter past are all contributing factors. Some varieties have remained unaffected while others, especially the late blooming whites, have been pretty severely infested.

    Bookmark   May 25, 2012 at 6:06AM
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Kathy Rivera

Interesting you mentioned that akamainegrower. I started taking notice in the area, and I'm seeing it ALL over! My red azaleas seemed pretty good - even though they bloomed before my whites. My whites were the worst. And my purple rhododendrons are hit and miss - some areas immediately wilted, some areas are still looking good (sadly, the blooms in the back that no one can see).

Any idea how to 'change the litter' of my azaleas that have pachysandra under them? Should I apply fungicide to the pachysandra? Throw some mulch over the top of it? (If I killed it all I wouldn't be sad!!!)

    Bookmark   May 25, 2012 at 8:20AM
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While low tech, low impact solutions such as changing the mulch have appeal, I'd seriously doubt whether it's very effective when you think about the zillions of spores present. I'd certainly pick off the ugly infested blooms this year, then hope for more normal weather, if there's still a "normal", next year. If symptoms appear again, an early treatment with fungicide is probably called for.

    Bookmark   May 26, 2012 at 5:34AM
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rhodyman(SE PA, USDA Z6)

Here is an article from the ARS quarterly by Dave Lewis who successfuly fought petal blight.

Controlling Petal Blight

Dr. G. David Lewis
Colts Neck, New Jersey

Petal blight is an annual problem in many of our gardens. Elepidotes, lepidotes and azaleas are all susceptible - so is mountain laurel. The early bloomers escape infection (a good reason to include lepidotes in your garden) because petal blight is a warm weather disease and normally does not become severe until May. It's those muggy, misty, rainy days that all the petal blight fungus go berserk and rot all those flowers that you waited a whole year to see.

So what can you do about this disgusting scourge of our beloved rhodies? You can spray! If you do it right you will have difficulty in finding blight in your garden. If you don't do it right, you are wasting your time and a lot of money. Any of the fungicides labeled for petal blight control will do the job. The trick is in the proper timing and the proper application.

Timing is critical. If you wait until you see petal blight, you are too late for a good job of control. Your garden will be loaded with blight spores and complete control will be very difficult. Your first spray should be applied before blight is seen. I put my first spray on when the early evergreen azaleas ('Hino-crimson', 'Delaware Valley White', etc.) are showing color - usually in the first week of May in our location. I then spray once a week for four weeks unless it is especially rainy when I close up the spray schedule to every five days. We have a number of Satsuki azaleas and late blooming elepidotes so I usually put on an additional spray in early June.

When you spray, you must get the fungicide on the flowers and buds that are showing color. Spraying leaves won't hurt but will have no effect in controlling a fungus that only attacks the flowers. Any kind of sprayer will work if you cover the flowers. Good equipment will do the right job using the least amount of fungicide, water, time and effort. You can also do the job with a stepladder and a Windex spray bottle, but I don't recommend it.

I use a powered sprayer with a high pressure pump. It has a 22-gallon (100 liter) spray tank, 50 feet (15m) of spray hose and a single nozzle spray gun. The spray pressure is set at 150 psi (I would go higher but that can damage the flowers). Low pressure sprayers are less efficient (spray droplet size is too large resulting in a need for much higher amounts of spray solution to get adequate coverage) and hose end sprayers are a last resort. My sprayer is on wheels and I tow it around our steeply sloped garden with my lawn tractor. Using my sprayer, I can spray our entire garden of approximately 1,200 rhodies and azaleas (they don't all bloom in the same week), rinse out the sprayer (be sure you rinse well if you want the machine to last) and put it away in about three hours. Depending on how much is in bloom, I put out anywhere from 50 to 125 gallons (567 liters) per application.

We have had petal blight in our garden for many years, but by using my sprayer in the manner described above I have been able to control petal blight well enough that most of you would not be able to find the occasional infected flower that does occur. You have to wait 51 weeks for those flowers. Don't let them rot on the fifty-second!

    Bookmark   May 26, 2012 at 9:00AM
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davidrt28 (zone 7)

"Until this year I had never seen petal blight in 30+ years of rhododendron growing. I believe the very early spring, early onset of hot, humid weather and the mild winter past are all contributing factors."

Same for me, I saw it all over the suburbs of Newark and Wilmington, DE, too. I think this disease is probably present everywhere Ericaceae are grown and comes and goes in severity depending on weather conditions.

    Bookmark   June 2, 2012 at 10:08AM
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