Thank you Joan for your question!  I appreciate your photos. Could you send two more photos: one with the leaves and another of the whole plant. Thanks! It will help with narrowing down what might be happening! 

Thank you Joan for your additional pictures and your question!  Crooked neck squash, cucumbers melons and squash make up a group of vegetables called cucurbits. Often times they become victims of several fungal and bacterial diseases that are present in the soil. From your photos and to the best of my knowledge it appears that you may have two of the most common problems: Phytophthora blight and powdery mildew. This article may assist you if you wish to read more Diseases and Insects in Michigan Cucurbits and their Management (E3276) - MSU Extension. 

These common diseases present when the weather is hot and humid with periods of lots of rainfall, much like our Michigan summers. The pathogen/s can overwinter on plant debri;  transmitted by weeds surrounding the area; or be carried by the wind into your garden. When the rain/water hits the soil, it splashes the pathogen onto the leaves of the plant. The pathogen is very opportunistic and takes advantage of the heat and humidity to multiply. 

Some common sprays used to treat powdery mildew will contain sulfur, chlorothalonil, horticultural oil plus baking soda. Table 3 at the bottom of this article gives some brand name products for purchase, Cucumber, Squash, Melon & Other Cucurbit Diseases | Home & Garden Information Center (clemson.edu) A different product listing of oxathiapirolin is commonly used for Phytophthora. Since disease is already present these can be used on a 5 day rotational basis.

At the end of this growing period you will want to clean up any infected material and throw it out in the trash - do not compost! Do not grow any cucurbits in this area of your garden for at least 3 years. 

Here are some cultural practices that seem to work for this grouping of plants: Plant disease resistant varieties - they will be listed on the seed envelope. Sow seed/plants into nutrient dense soil spacing 2-4' across giving your plants lots of room for air circulation. Consider growing them vertically. Water at the base of the plant - limit overhead irrigation - maybe plant in a mound to further water draining off the plants. Apply a horticultural oil or fungicidal oil every 10 days. When disease is seen these can be applied every 5 days. This article had a further suggestion of using a mustard cover crop planted in spring to ward off common  diseases. Biofumigation for Managing Phytophthora Blight and Other Soil-Borne Pathogens (cornell.edu)   

May you enjoy a bountiful harvest!