Spread of proso millet (Panicum miliaceum L.) in Ontario, Canada. II. Dispersal by combines

Seeds of proso millet (Panicum miliaceum L.) are moved between and within fields on combine harvesters. The dispersal of seeds of two biotypes of P. miliaceum by combine harvesters was quantified. The golden-seeded biotype of this weedy annual grass was known to have larger seeds and to experience less seed shattering than the black-seeded biotype. An average of 3·3% of the seeds on the plants of the black-seeded biotype was carried more than 50 m by combines, while 0·9% of the golden seeds were carried the same distance. The densities of the seed rain within 50 m of the weedy patches were 3·7 seeds m⁻² for the black-seeded biotype and 9·7 seeds m⁻² for the golden-seeded biotype. This difference was proportional to the difference in the number of seeds in the respective source patches. The numbers of seeds deposited at various points within 50 m of source patches were close to uniform for both biotypes. There was, however, a significant difference (P < 0·05) in the distributions of the seeds of the two biotypes.