What is the white foamy goo on my blueberry bushes' leaves?

This is definitely not being caused by aphids. Heavy rain washes a lot of it off, but some still remains. I've never seen this 'goo' before. We take excellent care of this berry orchard, and I definitely do not want to use any chemicals on my 10 blueberry bushes, but I would like to have some at harvest. Right now (June 26, 2011, Zone 5A), there are at least 200 berries on each bush. Appreciate any info to get rid of this 'goo.'