Diseases such as fusarium wilt (a rare condition in these days of wilt-resistant varieties) can make peas turn yellow and die, but hot weather is more likely to kill the plants before they can produce a full crop. Peas love cooler temperatures, preferably 55° to 75°F. They won't grow well in the heat.
To solve the problem, plant earlier—anytime from four to six weeks before last frost, and no later than two to three weeks after frost. (And if it's a fall harvest that's affected, plant later—no earlier than 12 weeks before expected frost.) To avoid stressing peas, give them 1/2 to 1 inch of water each week.