Harvesting tall fescue above annual bluegrass seed heads could help reduce contamination and seed-cleaning costs. Preliminary Oregon research found that cutting at 28 centimeters (11 inches) rather than 5 centimeters (2 inches) reduced annual bluegrass collected with the crop without consistently reducing tall fescue seed yield.
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Of course. Poa is a very low heading grass. I’d be surprised if anyone harvesting it for seed wouldn’t know this.