Raising harvest height cuts weed seed contamination in tall fescue

Preliminary Oregon research found that cutting tall fescue at 28 centimeters instead of 5 centimeters reduced annual bluegrass contamination without consistently reducing seed yield. The 2025 trial showed less contamination at the higher cutting height. Lower-moisture harvest also showed potential for maintaining yield.

The height differential between tall fescue panicles and annual bluegrass seed heads underpins this approach. Annual bluegrass can reach roughly 40 centimeters, but its seed heads typically sit below the crop canopy, allowing harvesters to leave weed seed in the field while collecting the crop. The 2025 trial confirmed this principle, though researchers noted that crop lodging and weed height variability could limit effectiveness.

Machinery configuration proved decisive in the trials. A combine cutting at 28 centimeters and 27 percent moisture outperformed conventional swathing at 5 centimeters and 43 percent moisture in 2024. However, the 2025 season revealed that higher reel speeds on swathers caused seed shattering as moisture declined, indicating that equipment adjustments require careful calibration before the practice can be recommended widely.