Pitchers with 20+ IP, 3.00 ERA or lower in May & June
Matt Cain (Giants) 1.81, 0.75
Chris Carpenter (Cardinals) 2.53, 1.71
Yovani Gallardo (Brewers) 2.31, 2.25
Clayton Richard (Padres) 3.00, 1.80
Did any of them also have an ERA of 3.00 or lower with 20+ IP, in April? Yes, but just barely: Clayton Richard had an ERA of 3.00 in April over 30 IP. If you wondering about Ubaldo Jimenez, he has an ERA of 3.46 in June covering 2 starts, although he has won both starts.