A day of devastation

I've killed all my cucurbits!   I'm absolutely devastated. 

I've got no one to blame but myself which is even worse. We have two sprayers, a middle sized and a big one. I mostly, but very seldom, use the smaller of the two. P has used the bigger one but not for some 5-10 years. I made up my potassium bicarbonate solution and put it in the midllesized sprayer which failed to pump. So I transferred the mixture to the bigger one and merrily sprayed every cucurbit leaf I had both upper and lower surface, against powdery mildew. I bet you can guess the rest of the story.  Half way through the day, which was cloudy, I noticed the courgettes were drooping then later on they were all collapsing.  I fear the big sprayer might have had weed killer residue but neither P or I have any recollection of using weedkiller in the near past,  it's just something we don't use.  I didn't think to swill out the sprayer, even if that would have helped. 

I have washed the leaves with a hose as well as possible but fear the worst. I understand cucurbits are especially sensitive to herbicides. All my courgettes, squashes and cucumbers are toast. I feel like throwing my hands up a giving up gardening.