Powdery mildew is a fungus--neem is to repel bugs. You can also use a spray made from corn meal for the mildew (check out the dirt doctor site for that--you soak corn meal for a while then spray the liquid and it's great against mildew and also has great fertilizer qualities).

Here's what Garrett says about Neem:

April 24, 2003
By Howard Garrett

Neem is the extract of a tree native to India and other warm climate areas. It's kin to our chinaberry. Neem doesn't kill insects but works as a repellant. It works on a wide range of insects and is quite effective.

Neem is a botanical insecticide extracted from the seed of a tropical neem tree from India. Neem works by preventing molting, suppressing feeding or repelling the bugs depending on the insect. It does not harm humans, birds, plants, earthworms, or beneficial insects and is registered for use against aphids, whiteflies, thrips, hornworms, mealybugs, leafminers, gypsy moths, weevils, webworms and loopers and probably lots of other bugs. Tests conducted by the USDA showed neem extracts repel cucumber beetles for up to 6 weeks. Neem is most effective against insects that have a complete metamorphosis - eggs, larvae, pupae and adults. I love these products because they don't hurt our firends, the birds, bats, frogs, lizards, snakes, and other beneficials.   

We have a great little nursery in west Arlington called Hare's that I pass on my way home from work if I take back roads. I stopped and spent $18 today buying a flat of salvia, peppers, squash, watermelon, verbena and lantana. (I also picked up two 1-gallon penstemons that will be gorgeous out front, along with some big purple bell peppers.) I've already put in the squash and watermelon. The other stuff will go in the ground over the next couple of days. The soil is good for digging now--we had five inches of rain over the weekend. I'm going to put in another layer of flower garden out in the front and stick in some red, white, and blue verbena. No flags for me, but I'll be in great shape by July 4th. :)

SRS