Until recently, we’ve been experiencing a fairly cool, wet spring with some pretty significant temperature shifts over a short period of time. The differences in day and night temperatures can be very damaging to plant tissue and we have seen some low-temperature injury coupled with bacterial blights such as Pseudomonas syringae. Up until last year I’ve only really seen P.s. associated with low temperature event, primarily on Syringa spp. (lilac). But this year, we are seeing all kinds of leaf spots on all kinds of deciduous flowering shrubs and so far, all the lab pathology has been coming up……..you guessed it……….Pseudomonas syringae.
Usually the plants grow out of the low temperature injury and bacterial disease, the new growth comes out and covers up the injured foliage.