Tall phlox problem
For the past 2-3 years my tall phlox have developed a mid season yellowing of the leaves. The leaf veins remain green, and the edges and inter-vein areas are yellowed. All the leaves are affected,, but there is no significant browning, leaf drop or dead leaves. They still flower but somewhat sparsely. I have tried an anti-fungal ( daconil) spray in June before any yellowing had started. I have powdery mildew on some nearby lilacs that I control with that, so I tried it back in June on the pholx even thouugh I hadnt seen any of the fuzzy gray mildew patches on their leaves. Could my problem be plant nutrients?
Worcester County Massachusetts
You could have your soil tested (www.soiltest.uconn.edu) but mine do the same. I think it is nutrient deficiencies due to drought stress combined with maybe powdery mildew. This happens every August. I'n not sure spraying would make a difference. The plants look awful but I just cut them back a bit after they flower and they've been coming back for 30 years. I have found that 'David', a white cultivar that is not as susceptible to powdery mildew always looks the best. So if their bad appearance really rankles you, I would look for disease resistant cultivars and keep them well watered.