Weird color likely means Cistena plum is lacking iron

I have several cistena plum bushes next to our patio that are not doing well. The leaves are yellow-purple with small holes in them. I’ve checked down at the base of the plant and it looks fine. I nicked the bark and it’s nice and pink underneath. Any suggestions?

­— 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. That is not all that uncommon with our soils in western Colorado.

Generally, we’re recommending that people apply a chelated form of iron starting in the spring when new foliage appears. As severe as yours is now, you’ll want to do a second application about six weeks later and a third 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 adding 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 in well after it’s applied.

One thing that’s making the problem worse is that the plant is next to a concrete patio under the overhang. Concrete is extremely alkaline, which makes micronutrient deficiencies much worse. Nothing to do about that, but it helps explain what’s going on.

Having said that, sometimes there are other things going on that can cause iron deficiency symptoms. Peach tree borer is a common culprit, but since you’ve checked the base and it looks good, we can eliminate that. Sometimes watering issues can cause this. It might be worth doing a little poking in the soil to verify that 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.

Some of the leaves of your plant have purple spots which turn gray and fall out leaving a small hole in the leaf. A common name for this problem is “shot hole disease.”

Coryneum isn’t a crisis but it can weaken the tree and spoil the appearance, so it’s worth paying attention to.

The first step in treating the disease is trying to modify the environment around the plant. Coryneum almost always crops up when a susceptible plant is in a moist, humid environment, which usually means tap water is spraying onto the foliage. If your plant is next to the lawn, that is probably creating this environment.

You need to water the grass, so it may be hard to completely avoid spray and mist from getting on the plant. But one thing you can do, besides adjusting sprinkler heads to minimize spray onto the plant, is to water sometime between the wee hours of the morning and midday. This helps shorten the time that the leaves are in a moist environment and can help a lot.

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.

After the leaves are picked up, spray the bare branches and the soil underneath with a copper fungicide spray. Don’t do this while the leaves are on the plant because in our climate it tends to burn and spot foliage.

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, Grand Junction 81506; or email .(JavaScript must be enabled to view this email address).


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