I have never seen that before but maybe it is some type of mold or fungus. If that is the case then the diluted bleach spray should help. A copper spray might also help. If it is not anything to worry about then the bleach or copper spray should not do any damage to the plants if applied properly and late in the evening or very early in the morning. Read up on the use of the diluted bleach spray before using it and check for the strength of the bleach to make sure you get a proper solution for spraying.
http://tomatoville.com/showthread.ph...t=bleach+spray
Bill