Answer: What you're referring to is called "soil solarization". It works to kill weed seeds, insect eggs and some disease problems. Blossom blight is caused by Botrytis, which doesn't remain in the soil, so solarization won't be effective. A better approach would be to plant your squash in a different garden area next year, provide all day sunshine, and plenty of room to sprawl. Here's some basic information on squash blossom blight:
Blossom blight on summer squash can be identified by the bread-mold-like growth on the newly opened flowers of squash. The fungus infects the flowers, then grows into the developing fruit and causes a soft, wet rot to develop. The fungus growth which resembles numerous small pins stuck in a pin cushion, can completely cover the fruit. The disease if favored by high humidity, and ample water, which home gardeners tend to provide. Chemical control is difficult because the flowers need to be protected with fungicide soon after opening and new blossoms open daily. If you only have a few plants its better to rub off the fading blossoms and increase air circulation around each plant by breaking off a few leaves, which should reduce the humidity.
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