Vitezslav Vylicil/Getty Images INVADERS: Spring and fall are the ideal times to control invasive species like thistles and Old World bluestems in pastures. Fighting these invaders requires a long-term battle plan. Cattle producers need to get ahead of thistles and Old World bluestem in their pastures. It starts with one, maybe two invaders in a corner of the pasture. If left unchecked, thistles and Old World bluestem can take over like an invading force, costing cattle producers valuable range their livestock could be grazing. Keith Harmoney, Kansas State University range scientist at the Hays Research Center, spoke during the April 8 Cattle Conversation hosted online by K-State Research and Extension Service. Harmoney says spring and fall are the right times to beat back these invaders, but the first step is correctly identifying the enemy.