One of these pictures is a leaf on a pumpkin plant and the other is a zucchini. Showed both because they may both have the same problem? This is an organic garden with lots of compost. So far have seen only a few squash bugs and have hand picked them. What to do to save these plants?
Might be a micronutrient imbalance of some kind - have you had your soil tested? You also might go back to the listing of forums at http://davesgarden.com/community/forums/ to see if you could cross-post elsewhere.
It is possible that your plants have been invaded by squash borers...the common symptoms are yellowing leaves, turning brown followed by shriveling stems.
http://web.extension.illinois.edu/askextension/thisQuestion.cfm?ThreadID=707&catID=35&AskSiteID=34
http://www.michiganorganic.msu.edu/uploads/files/31/squash%20bug%20and%20squash%20vine%20borer%20control.pdf
The images provided by kattykorn, especially the second one, do not appear consistent with squash borer damage. I have had considerable personal experience with these pests...
maybe a watering problem, as in too much or too little......sigh. so hard to get it all right.
