It is not unusual for squash plants to wilt in hot sun, particularly if they have not been recently watered. A thorough soaking will revive the leaves by sending water through the plant. If watering does not fix wilting, your plants may have squash vine borers. These are the larvae of wasps that laid their eggs on the stems or foliage.
About this Author
Aileen Clarkson has been an award-winning editor and reporter for more than 20 years, earning three awards from the Society of Professional Journalists. She has worked for several newspapers, including "The Washington Post" and "The Charlotte Observer." Clarkson earned a Bachelor of Arts in journalism from the University of Florida.