Perennial ryegrass growing degree days (GDD)
Perennial ryegrass GDDs will be tracked during the 2025 growing season with comparisons to the previous seven years. The accumulation of GDDs will begin after the snow has melted from the perennial ryegrass fields and continue through swathing. A base temperature of 32 °F will be used for perennial ryegrass GDD model.
- Year-to-date GDD = 311 (Table 1)
- GDD last week (April 28 - May 4) = 109 or 15.6/day; long-term average = 104 or 14.9/day
- GDD forecast for the next 10 days = 315 or 31.5/day
- Average GDD accumulation for the second week of May = 124 or 17.7/day
- The 10-day forecast suggests much warmer than average temps for the second week of May. Projected GDD is 31.5/day compared to the long-term average of 17.7/day. A GDD accumulation of over 30/day is typical for the end of June in the Roseau area.
| Year | 2025 | 2024 | 2023 | 2022 | 2021 | 2020 | 2019 | 2018 | 2025 vs. 2024 |
|---|---|---|---|---|---|---|---|---|---|
| March | 0 | 0 | 0 | 0 | 131 | 30 | 0 | 0 | 0 |
| April | 229 | 296 | 93 | 95 | 236 | 183 | 211 | 184 | -67 |
| May | 82* | 653 | 959 | 649 | 640 | 600 | 548 | 815 | N/A |
| June | N/A | 859 | 1,064 | 959 | 1,007 | 995 | 919 | 1,007 | N/A |
| July | N/A | 1,119 | 985 | 1,104 | 1,174 | 1,179 | 1,067 | 1,100 | N/A |
| Total | N/A | 2,927 | 3,101 | 2,807 | 3,188 | 2,987 | 2,745 | 3,106 | N/A |
General crop condition
The rain early in the week, increased soil temperatures and daily high temps in 70s to low 80s °F over the weekend should bring ryegrass plants out of dormancy. In many fields, the brown desiccated leaf tissue is still visible. More time is needed to make an accurate assessment of perennial ryegrass stands. More on perennial ryegrass stand assessment in next week’s newsletter.
Crop management
Perennial ryegrass critical growth stages, based on GDDs in Minnesota growing conditions, are listed below. This data averaged over years, locations and planting dates of ryegrass fields grown in the environmental conditions near Roseau, MN. These ryegrass plant stages are a benchmark to help in the scheduling of various field operations and monitoring pest infestations throughout the growing season.
- Greenup: 100
- Tillering: 200
- Early Jointing: 700
- Late Jointing: 900
- Early Heading: 1,100
- 50% Heading: 1,300
- Pollen Shed: 1,600
- Swathing: 2,700
As of May 4, the year-to-date accumulation of GDD was 311. The new 10 day forecast projects 315 GDD by May 14 for a projected year-to-date GDD total of 626. Spring-seeded ryegrass will be tillering stage for the next couple of weeks.
When should spring nitrogen applications be made in perennial ryegrass? Ideally, after the frost is out, the ground is firm enough to support application equipment, and green ryegrass rows are visible. In the environmental conditions of northern MN, perennial ryegrass will go through three distinct phases in the uptake and utilization of nitrogen. These three phases:
- Phase one: Slow nitrogen uptake, up to 700 GDD
- Phase two: Rapid nitrogen uptake, 700 to 1,300 GDD
- Phase three: Nitrogen redistribution, 1,300 GDD to physiological maturity
The best management practices (BMPs) listed below are for perennial ryegrass spring fertility management based on over two decades of U of MN research.
- Spring-applied nitrogen should be in the rooting zone prior to 500 GDDs with no previous nitrogen and up to 700 GDD if 30 to 50 units of nitrogen was applied in the fall.
- Delay applications of spring nitrogen until the frost has come out of the ground and the fields have firmed up to reduce chances of rutting the field with heavy equipment.
- Spring-applied nitrogen should be based on yield goal, but 140 pounds of nitrogen has given consistent results after a good wheat crop with average residue. This nitrogen rate should be reduced in prevented planting situations, high residual nitrogen (N), or if a below average wheat crop was harvested.
- Positive ryegrass yield response observed from up to 20% Environmentally Smart Nitrogen (ESN) with urea.
- Spring applications of ammonium sulfate (AMS) produced ryegrass plants that were taller, greener, and more vigorous compared to urea alone.
- A positive response yield response has been documented from AMS up to 20 pounds/acre when added to spring nitrogen, especially in course textured soil, heavy residue, and cool soils.
- Try to schedule applications of spring fertilizer before a forecasted rain event. If rain is not in forecast, consider the use of a nitrogen stabilizer and/or rolling fields.
- If soil test for phosphorus (P) is in the low to medium range, additional P (40 pounds) in the spring has shown ryegrass seed yield increases compared to no additional P.
- If plants show nitrogen stress mid-season, perennial ryegrass is tolerant to foliar 28% nitrogen.
- Additional perennial ryegrass fertility data is available on the UMN Turf Website.
Pest management
Winter annual broadleaf weeds have a rosette of leaves near the soil surface. Field pennycress, cockle, shepherd’s purse, and marestail are examples of winter annual broadleaf weeds. Winter annual weeds grow fast in the spring and will soon be in the bolting stage. If these winter annual broadleaf weeds were not controlled last fall, field scouting will determine if early season herbicide treatment will be needed this spring.
Next week’s newsletter will be released on May 13.