Field studies were conducted at three locations in the south Texas peanut growing region to compare regular agricultural calcium with power plant byproduct calcium applied at planting or peanut pegging to runner peanut at rates of 560 to 1680 kg/ha. Both calcium sources decreased Rhizoctonia and Pythium pod disease development up to 62% when compared with the non-treated control and resulted in a yield increase over the non-treated control of up to 25%. When Rhizoctonia or Pythium was not a problem, no increase in peanut yield over the non-treated control was noted with any calcium application. Peanut grade (Total Sound Mature Kernels + Sound Splits) was increased at one location with the use of both calcium sources. Calcium, magnesium, and potassium content of foliage, hull, and kernel tissue was variable and was not related to calcium source.