The Q&A Archives: pruning agastache and insect treatment for ornamental

Question: We planted 2 agastache this past spring. They bloomed all summer long and were beautiful! Now that it is early November,of course, the blooms have turned brown. Should I prune them now or wait until early spring? Also, when I prune them, how much do I take off? Do I cut them down to a few inches or just take off the top of the branches and old blooms? One more question. We have a beautiful weeping cherry tree we planted several years ago. Although appearing healthy overall from a few feet away, at the end of the summer,it developed some small holes and slightly brown edges on quite a few leaves. I have seen some tiny ants and maybe spiders on the trunk here and there. I wonder if I can safely apply insect repellent to an ornamental? It does seem to fit the description of a fungus also. It did get watered every other day late spring through fall by a drip irrigation (not overhead.) Our weeping cherry still has a nice shape and lots of leaves as we are just now starting with some cold weather here in South Jersey.

Answer: Once frost has killed the foliage, trim the agastache stems back to about six inches tall. In spring, trim them back again to about an inch tall being careful not to damage the new growth. Also be on the look out for seedlings around your original plant. These can be transplanted in spring while they are still tiny, if you wish.

It is difficult to give specific control recommendations for the cherry tree foliage problems by long distance because you really need to identify the specific cause of the problem before you can treat it. Based on your description,unfortunately I am not sure what the exact problems with the cherry tree would be. The holes are likely caused by an insect. The discolored edges could be caused by incorrect watering during drought, or by overfertilizing, or some other cultural cause. In either case, it is unlikely that spraying now at this time of year would be beneficial.

As a preventive, rake up all of the fallen foliage and dispose of it in the trash to prevent possible reinfection next year. I would also suggest you consult with your local county extension (Rutgers cooperative extension) to see if they can diagnose the problem(s). It is possible a spray program during the dormant season would be recommended, but specifically what and when to spray would really depend on the specific pest.

The leaf edge discoloration is possibly related to the shallow frequent watering. The goal in watering is to soak the soil down to the deepest roots. To be sure the watering is effective, water slowly and deeply, then wait several hours and dig down to see how far the water soaked in. To know if you need to water, dig into the soil with your finger. If it is still damp, do not water yet. It is better to water deeply but less often rather than lightly every other day.

Keep the soil well mulched with a flat layer of organic mulch about three inches thick over the root area. (Do not allow it to touch the trunk.) This helps keep the soil more evenly moist and also helps feed the soil slowly over time.

I should also mention that overfertilizing can cause some foliage symptoms. Ideally, any fertilization would be done based on soil testing results to assure the correct amount is applied. Too much is actually more deletrious than using too little.

Accidental chemical exposure such as herbicide drift can also cause foliage symptoms. Again, your extension staff should be able to help diagnose this more specifically.

I'm sorry I can't be more specific for you but I hope this helps you begin to diagnose the problems. Good luck with your tree!

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