How do I prevent return of aphids and mildew each year on perennial verbena?

Question

I had tremendous success with perennial blue verbena when planted 4 years ago, but I did over water them. By mid or late summer they were infested with tiny whitish flies that swarmed only when disturbed and a white or light gray powdery material on leaves and stems. I am guessing powdery mildew and aphids but not positive.

It got worse each year and last summer they looked terrible by early July. Has my soil become infested and need to be replaced? I live in zone 7 but have had a colder than normal winter,

Answer 1

I heard that if you put soapy water on plants, things will go away, and this also works when plants are being eaten.

Comments

Thanks, but soap was my first and third response. Didn't work.