mamashakesit, The old saying, "An ounce of prevention is worth a pound of cure" applies to mildew and other plant diseases in general. I like to spray my zinnias with a product called GreenCure®. It is safe to use and controls a long list of plant diseases, including Powdery Mildew and Downy Mildew. GreenCure is better than homemade formulas and can be used on many ornamentals, including Verbena. Incidentally, I am not in any way associated with GreenCure, other than as a user of the product. There are, of course, other products that you can use against mildew on Verbenas. ZM

Once PM develops it remains active as long as the conditions (humidity and air temps) for its growth persist. When those conditions change it begins to slow and appears to die off but the fungus remains dormant on the plant. So it is still there even if you can't see it and eventually it will kill the plant. In the meantime you can harvest from it. Fungicides only slow it, control it somewhat, they do not cure it. It can be prevented by spraying with fungicides before the fungus attaches to the leaves (so from the day of plant out or seedling emergence), but it can't be cured once it develops. Leaf removal is no problem as it doesn't stress the plant anymore than it already is stressed by the PM. Dave

Looks like aphids to me as well. To upload multiple photos in a single post you first need to upload them to a third party site such as photobucket. Then you copy and paste the HTML link from there to here. Rodney

The whiteish dusty powdery stuff might be Powdery Mildew but the yellowing of the leaves, chlorosis, probably is from another source. Sometimes just washing the plants leaves can help eliminate the Powdery Mildew while other times using something like a 50/50 mixture of fat free milk and water or mixing 1 teaspoon of Baking Soda in 1 quart of water and spraying that on the leaves will help. The chlorosis is another problem and requires a close look at the whys to determine how to correct for it. There are many reasons a plants leaves loose the chlorophyll they need. Here is a link that might be useful: plant chlorosis