White stuff killing my gherkin?

[lifesahaze]

I have 2 gherkins growing in my greenhouse, but one of them has become really poorly.  The stem close to the top has been covered with a thin layer of white foamy stuff, and the plant above the white has died off.  A number of the leaves have curled over and stuck together, and the gherkin fruits have just turned yellow and are dying off. 

Has anyone seen anything like this before? I've cut the plant off at the stem just below the whitening and destroyed it - but don't know whether it's going to come back or attack something else!

Off for a calming cuppa now...  happy Saturday x

[lifesahaze]