We have a purple leaf plum shrub in our yard out on the Redlands. I think it is sick. The leaves are a funny yellow-purple-orange-green with a lot of small purple spots. What's going on with our plant? Any other tips would be great.

— Cindy

I think you have a couple of things going on with your cistena plum. The weird, yellow-purple color is probably from a micronutrient deficiency, probably iron, which is really not all that uncommon with our soils in western Colorado, especially out on the Redlands.

Generally, we recommend people apply a chelated form of iron starting in the spring when the new foliage appears. As severe as yours is, you'll want to do a second application about six weeks later and a third application six weeks after that.

Whenever you apply iron, also apply a nitrogen fertilizer such as ammonium sulfate or a good lawn food. Iron and nitrogen really work together and doing both will enhance the effects. Apply the fertilizer to the soil in a circle with a radius about equal to the height of the plant. You don't have to dig holes in the soil or cultivate the fertilizer in. It penetrates readily; just water it well after it is applied.

From the pictures you sent, one thing making the problem worse is that the plant is next to what looks like a concrete patio under the overhang. Concrete is extremely alkaline, which makes micronutrient deficiencies much worse. There is really nothing to do about that, but it helps explain a little of what is going on.

Having said all this, sometimes there are other things going on that can cause iron deficiency symptoms. Putting the iron and nitrogen on is still a good idea, but it sometimes isn't the whole solution.

Peach tree borer is a common culprit, but if there's no gummy sap (or dried up residue) at ground level, you can probably eliminate that as a cause.

Sometimes watering issues (too much or too little) can cause this. It might be worth doing a little poking in the soil to verify the moisture level of the soil is correct.

The second thing that's going on with your plant is a fungal disease called Coryneum blight. Coryneum starts out as a small purple spot on the leaf that turns gray and falls out leaving a small hole in the leaf. This leads to the common name for this problem of "shot hole disease."

Coryneum isn't a crisis, but it can weaken the tree and spoil the appearance so it is worth paying attention to. The first step in treating the disease is to modify the environment around the plant.

Coryneum almost always crops up when a susceptible plant is in a moist, humid environment where water is spraying onto the foliage. I see your plant is next to the lawn, which probably is creating this environment.

You have to water the grass, so it may be hard to completely avoid spray and mist from getting on the plant. One thing you can do, besides adjusting sprinkler heads to minimize spray onto the plant, is to water sometime early in the morning before noon. This way the foliage dries out more quickly, which can help avoid problems with this disease.

The last thing to do is this fall when the leaves fall off the plant is to rake all of them up and throw them in the trash. Don't keep them around the yard.

This reduces what we call the "inoculum" or the material needed to start the disease cycle again next year.

The last thing you can do is after the leaves are picked up, is to spray the bare branches and the soil underneath with a copper fungicide spray.

Don't do this while the leaves are on the plant as it tends to burn and spot foliage in our climate.

You may have to do this fungicide treatment for two or three years to get on top of it, but you ought to be able to get this guy turned around and shaped up.

Dennis Hill is the nursery manager at Bookcliff Gardens, bookcliffgardens.com. Send questions to Bookcliff Gardens, 755 26 Road, 81506; or email info@bookcliffgardens.com.

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