SOUTH AFRICA CORN EXPORTS COULD BE REDUCED-USDA Despite earlier optimistic indications, the South African corn crop is at a critical stage in its development and recent reports of heat stress could reduce production and therefore exportable supplies, the U.S. Agriculture Department said. In its report on Export Markets for U.S. Grains, the department said South Africa's corn exports in the 1986/87 (Oct-Sept) season are estimated at 2.5 mln tonnes, up 40 pct from the previous year. The re-emergence of South Africa as a competitor follows a period of severe droughts, which at one point required South Africa to import 2.7 mln tones of U.S. corn in 1983/84, it said. Since those imports in 1983/84, the U.S. has been facing increased competition from South Africa in Taiwan and Japan. But if South Africa is perceived as lacking available supplies, purchases of U.S. corn may be further stimulated, the department said.