Spiraea

November 19, 2016

Replaced azaleas, across the front of my house facing NW, with Spirea about four years ago.  Each summer small black spots have appeared, and in July and August most all the leaves fall off.  Some new ones come back, but from that time on, it looks like a skeleton.  I sprayed several time before with a fungicide but the spots started showing up and still it happened.  The nursery said they needed nutrients and so while spraying fungicide I also put fertilizer two to three times.  It seemed to slow it down, the plants really grew but, it just happened at a later time in the summer and the end results were still the same.  Any ideas why the black spots and why the leaves fall off about the same time each summer?

I am assuming you have summer blooming spireas instead of spring only bloomers.  I have never had any issues with diseases on spirea. While spirea is in the rose family and could be susceptible to several leaf-spotting diseases, we usually don’t see them.  But since you are having issues, here are some strategies.  Practice good sanitation this fall.  Rake up and dispose of all the leaves around the plants after they have all fallen.  Spray with a dormant oil to try to smother any overwintering fungal organisms.   Make sure the area where they are planted is not getting too much water.  Spirea are fairly drought-tolerant.  You could do one preventative fungicide spray as they are leafing out, but no more.  If the leaf spots appear again next year, the minute you spot them, take a sample in to your local county extension office so they can send it in to our disease diagnostic lab so we can pinpoint which fungus you have.  I do not think it is nutritional.  They are fairly tolerant of a wide range of well-drained soils and not too particular about nutrition.

November 2010

We have a "bridal wreath" (sorry I do not know the official name for it) which we pruned after it bloomed this past spring. Since then it has grown "dramatically" and has some tall shoots on top. It is quite large and located in our front yard near the street. Can I prune it NOW for appearance and not affect its blooms next year? We "inherited" the plant when we bought the lot on which we built our new house and I have no experience with bridal wreaths.

Bridal wreath is the common name for the white blooming spring spirea. Pruning now WOULD affect the flowers for next spring. Flower buds are set for all spring blooming plants now. The time to officially prune is in the spring after bloom. Don’t just prune it to the size you want it to be, because any new growth would then make it larger. Prune it by at least 1/3 more to allow room for new growth. If you have a few wild shoots, taking them off now would not impact your spring display all that much.

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