Problems with weed control in rotations dominated by corn and potato on sandy soils

In the western part of Weser-Ems (Emsland) a rotation including 40% corn and 20% potato is prevalent. This rotation led to an obvious increase in adapted and competitive weed-species like couchgrass, panicum-like grasses, wild oat, thistles, water smartweed and black nightshade. Especially the latter species gained regional importance lately. An effective control of these weeds can only be achieved by higher costs if lower effectiveness of herbicides is not acceptable. Over yet 5 years field tests were conducted comparing the efficacy of numerous herbicides and the tolerance of crops towards them. All suitable pre-emergence and post-emergence herbicides were tested which were either registered for control of the target-species or considered to be eligible for registration. Preliminary results show that a reliable and crop-compatible control of black nightshade in potatoes is not feasible. The efficacy of pre-emergence herbicides is strongly influenced by local factors and climate, especially humidity of the soil. In case of post-emergence herbicides in almost all instances leaf-necroses in potato were induced. Use of mechanical or the combination of mechanical/chemical treatments for control of the listed weeds proved to be unsatisfactory.