1025 GMT - Wheat prices trade at a three-year high as investors grow increasingly wary of a supply shock caused by the deteriorating Black Sea situation. Russian and Ukrainian wheat exports are effectively stalled following a series of strikes on both grain-laden ships and export terminals. A slowing in supply from the region is supporting prices as together Russia and Ukraine account for nearly 30% of global wheat exports, Rabobank's Andrick Payen says. Both countries are seeking other routes for their wheat, but any alternatives "are unlikely to offset the port capacity lost at Odesa and Novorossiysk," Payen writes. Chicago wheat contracts rise 0.1% to $7.49 a bushel after jumping around 5% in the last session. Prices have jumped by around 30% since June.