Intra‐ and cross‐field dispersal of Beckmannia syzigachne seed by a combine harvester

BACKGROUND Beckmannia syzigachne (Steud.) Fernald has become a dominant weed that has evolved resistance to major herbicides used in the wheat fields of rice‐wheat double cropping areas of the middle and lower reaches of the Yangtze River, China. Seed dispersal occurs over long distances via irrigation water. As mechanical harvesting services popularize, there is concern that combine harvesters could play an increasing role in B. syzigachne seed dispersal. RESULTS Random sampling of 30 combine harvesters at wheat harvest determined that an average of 8000 B. syzigachne seeds remain in the combine after wheat harvesting, predominantly on the metal plate. These seeds could potentially be transported into adjacent fields. A double exponential model predicted that seeds remaining on the metal plate could be dispersed over 7885 m 2 into the next field. Within a field, the number of fallen seeds and their dispersal distance were positively correlated to panicle density. Combines spread seeds away from the source potentially creating new weed patches. During irrigation and rotary tillage ploughing, 70% of B. syzigachne seeds scattered in the field floated on the water surface and were moved away by the wind. CONCLUSION Both wheat combine harvesters and water flow effectively spread B. syzigachne seeds. Areas with high B. syzigachne population density should be carefully harvested separately, and the metal plate should be carefully cleaned to prevent spreading the weed across fields and region. Floating B. syzigachne seeds displaced to field edges by water can be physically removed with nets to prevent further distribution by water.