Leaf rust columnar buckthorn
I have three beautiful buckthorn columnar shrubs in our Northern Fort Collins yard. Two are thriving. One has what appears to be leaf rust (leaves have dark orange spots). They were planted in clay soil 2 years ago. How do I treat the one with the leaf rust, and how do I prevent the other two from getting sick?
Larimer County Colorado
That doesn't look like rust to me, more like necrosis or general dieback of the leaf tissue. You didn't mention how much of the plant is affected, but it looks like a small percentage. It may have gotten nipped by frost, hail, weather or other environmental/cultural issues.
At this point, I think it's a "wait and see" and keep up on good cultural practices. If the leaves look unsightly to you, you can prune them off.
Thanks fo your response!
I would guess that about 30% of the leaves are affected to a small degree. The plant doesn't look too bad, just different in height and density of leaves from the other two. It just does not appear to be thriving like the others.
What are the "good cultural practices" I should be following? Should I fertilize them? All three are on a drip system for irrigation. I think they're each on a separate 1 GPH drip line.
Yes, proper watering. I wouldn't fertilize--it can cause additional stress. The third shrub may have been planted at a different height, the soil might be too wet, too dry, etc.
How long are you running the irrigation? How many days per week? Is there more than one emitter per shrub? Are the emitters located directly at the base of the shrubs? If so, you're probably not targeting the roots that are absorbing the water. As shrubs and trees grow, their roots spread 3-5 times the width of the canopy. You'll need to move the emitters out as they grow and possibly add more emitters. Also, are the emitters actually working? Sometimes lines get chewed or plugged.
But check the soil moisture...for two, it might be perfect moisture. The other might be too wet or too dry.