Tall phlox problem

Asked August 21, 2020, 12:28 PM EDT

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

1 Response

Hi,
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.