White flies. From what I know management with insecticides is very difficult. You did mention you had ants. Ants do interfere with the beneficial bugs that would help prevent or minimize and outbreak.

Whiteflies hang out on the undersides. And they fly up in your face when disturbed, then soon settle on the leaves again.

It's much more likely these are aphids and their cast skins. Lots and lots of both!

My first thought was "whiteflies" but I then caught sight of the little green leaf to the left of center and I can just make out a bunch of green aphids. So yes, aphids (green) and their cast skins (white). The ants were probably farming the aphids. You can wash them off repeatedly with the hose, spray them with various sprays (both toxic and not), order up some beneficial insects (but generally you want to do that before an infestation explodes), and you can find more information on all those techniques by using the search function. The best prevention of an infestation like that is vigilance. I don't mean that you have to whip out the insecticide the moment you see an aphid, but keep an eye on your plants and if a pest insect's population seems to keep growing unchecked take action. Cheers!

Thanks to everyone for your responses.

Pulled out a magnifying glass for a much closer look. Googled Aphids and Whiteflies and Aphids it is. Found a pic of the exact one (http://www.naturescontrol.com/image/aphids.jpg) because of the distinct dark "horns" on the back of the critters.

I checked the underside of the leaves and they are just coated with the aphids. Because of the close proximity of the other plants I think I'll nuke this one and be very diligent in checking all the others in the days to come. That little factoid of the the ants farming the aphids is very interesting. I've got ants on other plants and will watch very carefully moving forward.

Thanks again for the rapid replies and the good information.

-Mark

With aphids, whiteflies and most other insects, the key is to get them as soon as you first see them. I had major problems with spider mites this year, a new pest in my garden, because I let them get out of control before treating them. Of course, like you, I didn't know the early warning signs.
Knocking aphids off with a hard spray of water each morning works well if you catch them before their numbers get out of control. Also the bugs don't seem to like foliar sprays of seaweed, compost tea, etc. plus the plants are being feed. For larger things like cucumber bettles, stink bugs and leaf-footed bugs, try a hand-held vaccum or shop vac or the squish-em method(but be quick before they fall to the ground(: For all insects, break their life-cycle early on and they can be held in check or eliminated. If you let them run rampant and take over they often overwinter, especially in mild climates, and attack hard the next year.

Pete

Thanks for the information, Pete. I will try the foliar sprays next time.
As a followup, I sprayed the leaves (esp the undersides) of the plant adjacent to this one with a soap solution (2 tsp Dawn + 2 cups warm water) as I found a very manageable amount of aphids on some of the leaves. I found out that the soap solution removes the waxy covering of the aphids and they dehydrate until dead. 24 hours later there is no sign of aphids on my plants.

-Mark

I got a very bad infestation of black aphids on my cowpeas this year. As soon as I noticed it, and it was from one day to the next that the vines were just covered, I sprayed the plants with a heavy jet of water, spraying until they were all knocked of as far as I could see. I did this daily for three days, each day seeing a dramatic decrease in the population. That was all I had to do. As the above posters say, it's about getting right on it when you see a problem. I have not sprayed insecticides for aphids on anything in years and years.