Glyphosate increased the drydown rate of annual ryegrass, preserving its nutritive value, reports University of Florida animal scientist Gbola Adesogan.
The herbicide was applied to standing ryegrass when it reached peak quality. When the crop had dried to 45% dry matter, it was harvested and ensiled. Growers accomplish the same thing by mowing and windrow drying, but drydown takes longer and quality is lost, Adesogan points out.
Ryegrass plots were sprayed with glyphosate at 0.25, 0.5 and 1 lb of acid equivalent per acre, while control plots received no herbicide. Forage drydown rates were about 2.5%, 2.8% and 3.7% per day for the low, medium and high glyphosate rates, respectively. The 45% dry matter target was reached in nine days with the high rate, 11 days with the medium rate and 13 days with the low one.
Control plots didn’t dry for nine days after the others were sprayed, then dried 1-2%/day from days 10 to 18. After 20 days, unsprayed ryegrass was mowed and wilted overnight to reach 45% dry matter.
More than 90% chlorosis (loss of green color) was seen in high-herbicide-rate plots within five days of spraying. Ryegrass treated at the medium and low rates reached that chlorosis level a few days later. No chlorosis was observed in control plots throughout the trial.
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Silage from ryegrass treated with the highest glyphosate rate tested 18% protein vs. 14% for untreated silage, Adesogan reports.
He also treated forage sorghum with the herbicide, but those results haven’t been analyzed yet.
Adesogan thinks the method shows potential for use on single-cutting annual crops in humid areas where weather often interferes with field drying. But he says more research is needed before it can be recommended to growers.
“One thing I wish we had done was measure the glyphosate residue in the forage,” he says. “The animals aren’t eating the forage right away; it’s being ensiled. So I don’t really think it’s an issue.”
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