The stinkbug is not a good guy in the garden and can cause damage, especially to the fruits.
But, unfortunately, I think eric is right about the downy mildew:
https://www.apsnet.org/publications/imag ... 000044.jpg
note the "dried" edges.
earlier in the process, it looks like this:
https://www.maine.gov/agriculture/pestic ... ke-big.jpg
Here's the article the second picture came from:
https://www.maine.gov/agriculture/pestic ... mildew.htm
But downy mildew is much more virulent than powdery. Plants often survive with powdery mildew for a long time, often long enough to be killed by fall frost instead. Downy mildew kills plants.
At this point, given how badly affected your plants are, I think they are toast and I would pull them and trash them (in a bag in the trash, NOT in your compost pile) to keep from spreading it to more of your garden.
For future reference, here's things you can do to try and prevent it:
1. Despite some strains of downy mildew overcoming currently available genetic resistance, the use
of disease-resistant or tolerant cultivars is still highly recommended as some degree of resistance remains. A list of these can be found at the North Carolina State University Cucurbit Breeding web site at https://cuke.hort.ncsu.edu/cucurbit/cuke/cukemain.html
2. Select growing sites with good air drainage, full sunlight, and low humidity.
3. Avoid overhead irrigation to prevent leaf wetness.
4. Insure adequate, but not excessive fertility.
5. Monitor the crop frequently, and make use of the North American Plant Disease Forecast Center at https://www.ces.ncsu.edu/depts/pp/cucurbit
to monitor reports of downy mildew throughout the country. Local updates are also available on VegNet (https://www.ag.ohio-state.edu/~vegnet/
6. If early in a downy mildew epidemic, removal of infected plants may help to slow the spread of the
disease. When doing this, make sure not to spread the disease by hand or infested equipment.