 at hotvalleyknights.com. Cooler crops make higher yields. I'm Darren Hefty with Hefty Naturals. When your crops experience stress, you lose yield at harvest, and your crops are most vulnerable to heat and drought during the critical reproductive stages. Shield your crops from the worst summer can bring with a foliar application of heat shield. Fields treated with heat shield exhibit crop canopies up to 10 degrees cooler than untreated.