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A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

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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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Monday - June 10, 2013

From: Austin, TX
Region: Southwest
Topic: Diseases and Disorders, Shrubs
Title: Problems with rock rose in Austin
Answered by: Barbara Medford

QUESTION:

Hi Mr Smarty Pants, We have a Texas Rock Rose which is growing next to our gravel path in Austin, with grass growing under it. In the last week, it has stopped blooming suddenly, and all the leaves have turned brown and it looks 3/4 dead. We haven't changed our watering schedule (once/week), it's been there as long as we have (3 years) and although the temperature has increased, it should be hardy enough for that, right? Could you she'd some light on its sudden poor health? With thanks.

ANSWER:

Pavonia lasiopetala (Rock rose) is not listed in our Native Plant Database as "Texas" rock rose, but we are betting it is the same thing. According to this USDA Plant Profile Map, it is native to Tarrant County. If it was already there 3 years ago, it can hardly be suffering from heat and drought, as it has survived worse in the past.

Such a sudden decline has to be the result of some outside event. Our first thought is that a male dog might have lifted its leg on the plant, often the reason for brown spots in grass. However, rock rose gets to be quite a large plant (see pictures below) and we don't believe that would have affected the whole plant.

It sounds much more likely that this is the result of an herbicide being sprayed in the area. The rock rose is a dicot, or broad-leaf plant. Grasses are monocots, or narrow-leaf plants. Herbicides can be obtained to kill either kind of plant, and dicot herbicide is often used to kill broad leaf plants in grass. Unfortunately, there is no way to control where a spray goes, it can be inadvertently sprayed on a bush or it can drift in the wind.

The only other problem we can think of, although it should not be so sudden, is mildew. From our webpage on this plant:

"Maintenance: Cut back the shrub each year to encourage bushy growth. It may tend to become leggy during the growing season, so additional pruning may be necessary. Water intermittently to ensure blooming. Mildew is unavoidable - sometimes more sun seems to make it go away, sometimes not."

Since we can establish no clear problem nor cure, our advice is:

1. Never, EVER spray any pesticide or herbicide again.

2. Keep an eye out for dogs, and if you have any pets of your own, keep them away from your plants.

3. Trim back, as mentioned above, look for signs of mildew (University of Illinois Extension) and treat accordingly. No overhead or sprinkler watering, drip irrigation best.

 

From the Image Gallery


Rock rose
Pavonia lasiopetala

Rock rose
Pavonia lasiopetala

Rock rose
Pavonia lasiopetala

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