Cereal Rye Cover Crop Termination Before No-Till Corn
A 50-acre field in southeastern Pennsylvania is planned for no-till corn on May 12. A cereal rye cover crop drilled last September is now 5 ft tall with about 8,000 lb/ac dry biomass. The field has a history of common cutworm and horseweed. The grower wants to plant green into living rye to save time and retain moisture. Glyphosate is the only burndown herbicide on hand, and the rye is at early boot stage. The corn hybrid is a 105-day hybrid, and the grower plans 30% UAN at planting. He asks whether to terminate now or plant green, what burndown rate and timing to use, and how to adjust nitrogen for the rye residue.
1. Should the grower terminate the rye now or plant green? Give a recommendation with timing.
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Terminate now, not at planting. Rye at 5 ft and 8,000 lb/ac is too much biomass to plant green without risking poor corn establishment. Allelopathic compounds from rye can reduce corn emergence, and the high C:N residue ties up N. Terminating 10-14 days before May 12 gives the rye time to die and begin to dry, and it reduces cutworm activity. If the grower wants to plant green, it should have been done earlier, at 12-18 in. of rye, and with a plan for extra N and cutworm scouting. With this biomass, a burndown now and planting on May 12 is the safer choice. Do not crimp at this stage; the rye is not at the right growth stage for reliable control.
2. What burndown rate and adjuvant should be used, and what about the horseweed history?
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Use glyphosate at 1.5-2 lb ae/ac with ammonium sulfate and a surfactant labeled for the product. The rye is at early boot, still before full heading; glyphosate control is usually good at this stage but declines as the plant matures. Because the field has horseweed, add a labeled residual herbicide for horseweed if the corn hybrid and label allow it; glyphosate alone will not control glyphosate-resistant horseweed. Check the plant-back interval for the residual. Spray in the morning or evening with good coverage and low drift. If the rye is too tall for the boom, use a roller-crimper only after a burndown, not as a substitute. Scout for cutworm after planting.
3. How should the grower adjust nitrogen at planting, given the rye biomass and 30% UAN?
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The rye residue is high in carbon and low in N, so microbial breakdown will immobilize N at the soil surface. Increase the early N rate by about 30-50 lb N/ac above the normal budget, or place 30% UAN in a band 2 in. below and 2 in. beside the seed rather than surface-applied. Keep total N within the corn yield goal; the extra is a timing adjustment, not a higher seasonal rate. If the grower applies 30% UAN at planting, use a stream or knife rather than a broad broadcast over the residue. Monitor early color and tissue N at V5-V6. If the rye was terminated 10-14 days before planting, some N release may occur, but do not count on it for the first month.