Good Afternoon,

 We received your question about your sick zucchini and cucumber plants.  I’m not certain what is causing your plants to die.  The cupping of the leaves could be caused by herbicide damage from spray drift that has damaged the plants.  Depending on when you planted the plants there may be some damage from the cold if they were planted too early.  One final cause could be the dry windy weather we have had. Be sure to water on a regular basis and give them adequate water. Plants should receive 1 to 1½ inches of water per week.  It is better to water thoroughly every 5 to 7 days rather than a little each day  The following links will direct you to a document on general information about growing cucumber and squash and the second is general information about herbicide damage: 

https://extension.colostate.edu/topic-areas/yard-garden/cucumbers-pumpkins-squash-and-melons-7-609/

https://planttalk.colostate.edu/topics/weeds-cultural-problems/2101-abnormal-distorted-plant-growth/

I hope this information is helpful.  Feel free to contact us again if you have additional questions.

Linda, Weld County Colorado Master Gardener