Perennial ryegrass growing degree days (GDD)
Perennial ryegrass GDDs will be tracked in the 2024 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 (Temperature - Base = 32 °F)
- Year-to-date GDD = 202 (Table 1)
- GDD last week (April 21-27) = 91 or 13/day; long-term average = 71 or 10.1/day
- GDD forecast for the next 10 days = 217 or 21.7/day
- Average GDD accumulation for the end of April = 86 or 12.3/day
- The 10-day forecast suggests warmer than average temps for the first week of May. Projected GDD is 21.7/day compared to the long-term average of 14.9/day
| Year | 2025 | 2024 | 2023 | 2022 | 2021 | 2020 | 2019 | 2018 | 2025 vs. 2024 |
|---|---|---|---|---|---|---|---|---|---|
| March | 0 | 0 | 0 | 0 | 131 | 30 | 0 | 0 | 0 |
| April | 202* | 296 | 93 | 95 | 236 | 183 | 211 | 184 | N/A |
| May | N/A | 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
Initial perennial ryegrass field evaluations indicate almost complete leaf desiccation down to the crown in most ryegrass fields. However, when the dead leaf tissue is removed green leaf tissue can be observed and roots are mostly white in color. More time is required to make an accurate assessment of perennial ryegrass stands. A better assessment of ryegrass winter survival can be made after the soil temperatures in bare ground and sod conditions reach the high 40s into the 50s. On Saturday, April 26 the frost was out of the ground in bare soil conditions and averaged 18 inches in sod conditions at the UMN Magnusson Farm. Soil temperatures, in turf conditions, reached 40 °F last week. Biological activity in the soil begins to increase at 40F soil temperature as does tillering in perennial ryegrass. In 2025, 40 °F soil temperature was reached on April 11 in bare soil and April 21 in turf conditions. In a twelve-year period from 2014 to 2025, the range between bare soil and turf conditions was one day in 2016 and 23 days in 2021. In 2025, the difference in bare soil versus turf conditions was 10 compared to 10.6 days for the twelve-year average.
Crop management
The following is a review of the critical soil temperatures for perennial ryegrass growth and development. This information is based on soil temperatures at a 4-inch depth that had air in the soil pore spaces (not waterlogged).
- 90 °F: Shoot growth ceases
- 77 °F: Root growth ceases
- 70 °F: Maximum temperature for expansion of root growth
- 60-75 °F: Optimum temperatures for shoot growth
- 50-65 °F: Optimum temperatures for root growth
- 40 °F: Shoot growth ceases
- 33 °F: Root growth ceases
- 20 °F: Low temperature that will kill plants if temperatures drop rapidly below 20 °F
Pest management
The perennial ryegrass armyworm moth trapping project will continue in 2025. Traps will be placed in perennial ryegrass fields after green up and will monitor armyworm movement into the perennial ryegrass growing area of northern MN.
Next week’s newsletter will be released on May 6.