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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Thursday - May 05, 2011

From: Round Rock, TX
Region: Southwest
Topic: Diseases and Disorders, Watering, Shrubs
Title: Powdery mildew hits Rock Rose in Round Rock Texas
Answered by: Lleslie Uppinghouse

QUESTION:

My beautiful Rock Roses have gotten spots of white fuzzy "fur" on their leaves in the past month. This is not something they have ever had before and I'm worried its some kind of disease. Is it something I should worry about and if so is there some way to treat it? I love my Rock Roses they are one of the few plants that survived Austin's two weeks of freezing temperatures this last winter. I dont want to lose them. I bought them from the LBJ Wildflower Center Spring plant sale two years ago. Sigh.

ANSWER:

Powdery mildew is almost unavoidable with Pavonia lasiopetala (Rock rose). Many plants with woody stems and fuzzy leaves struggle with this nuisance. Powdery mildew is a common fungal infection. Hot sun helps reduce the chance of mildew forming so if your Rock Rose is not in the full sun you might want to think about moving it. Also it is important to make sure that this plant has good drainage. Although poor drainage isn't the cause of mildew, the combination of soggy roots with mildew can stress out the plant enough to kill it. Pavonia also likes to be cut back every year, keeping it from becoming leggy. Some theorize that if you do this twice a year rather than once, it helps keep the mildew away.

We are suspecting that it is the cloudy days combined with early hot temperatures that is exacerbating the situation. Once mildew develops you may find that it returns again and again, even in the hot sun of summer.

The good news is that powdery mildew can be beat with household ingredients. Use one half tablespoon of baking soda and a couple of drops of dishwashing soap (something natural if you can) mix it up with one half gallon of water in a spray bottle and spray the leaves. This changes the PH on the leaves slightly making it tough for mildew to form and spread. You might have to do this every now and then to keep the mildew away. Other than being susceptible to powdery mildew, Rock Rose is a tough little plant. Well, worth fighting for.

 

From the Image Gallery


Rock rose
Pavonia lasiopetala

Rock rose
Pavonia lasiopetala

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