Higher cutting could reduce annual bluegrass contamination in tall fescue seed

Harvesting tall fescue above annual bluegrass seed heads could help reduce contamination and seed-cleaning costs. Preliminary Oregon research found that cutting at 28 centimetres rather than 5 centimetres reduced annual bluegrass collected with the crop, without consistently reducing tall fescue seed yield.

Using crop height to avoid weed seed

Annual bluegrass is difficult to remove from grass seed crops and can remain despite careful establishment, herbicide use and hand rogueing. However, most annual bluegrass seed heads sit below tall fescue panicles at harvest. Trials in 2024 and 2025 tested whether this height difference could be used to leave annual bluegrass seed in the paddock. Researchers compared:

• cutting heights of 5 cm and 28 cm
• a conventional swather and a combine used for the initial cut
• tall fescue seed moisture levels ranging from 18% to 45%.

Higher cutting reduced contamination

Annual bluegrass was absent from the 2024 trial, but 2025 results showed less contamination when the crop was harvested at 28 cm rather than 5 cm. This suggests higher cutting could complement existing weed management and reduce the burden on seed cleaning. Its effectiveness is likely to depend on crop lodging and the height of annual bluegrass plants, which can reach 40.6 cm.

Lower-moisture harvest showed potential

Tall fescue yield was not reduced when swathing occurred at 27% rather than 43% seed moisture in 2024. Cutting with a combine at 28 cm and 27% moisture produced more seed than conventional swathing at 5 cm and 43% moisture.

Results from the low-yielding 2025 crop were also broadly encouraging. However, using the swather at 28 cm reduced yield as seed moisture declined, possibly because higher reel speed increased seed shattering.

These findings show that machinery settings will be critical. Further work is needed to refine cutting height, reel speed, harvest timing and direct-combining practices.