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 = 2,438 (Table 1)
- GDD last week (July 7 - 13) = 247 or 35.3/day; long-term average = 243 or 34.7/day
- GDD forecast for the next 10 days = 328 or 32.8/day
- Average GDD accumulation for the third week of July = 239 or 34.1/day
- The 10-day forecast suggests below average temperatures for the third week of July. Projected GDD is 32.8/day compared to the long-term average of 34.1/day
| 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 | 812 | 653 | 959 | 649 | 640 | 600 | 548 | 815 | +159 |
| June | 932 | 859 | 1,064 | 959 | 1,007 | 995 | 919 | 1,007 | +73 |
| July | 465* | 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
Perennial ryegrass is beginning to turn from green to brown. This is especially true in lighter textured soils, compacted areas and fields that have naturally high gravel content in the soil (gravel streaks). As perennial ryegrass seed fields mature these fields should be monitored several times a week as when ryegrass seed moisture drops into the low 40% seed moisture losses can be over 3% per day.
One of the challenges with swathing decisions this year will be the gaps in perennial stands due to winterkill issues in the 2024/2025 crop year. These gaps tend to have ryegrass plants that produce a considerable number of late tillers. These tillers are greener and later than the ryegrass plants that were not influenced by winterkill issues. The swathing decision is a balancing act, not cutting the late-maturing seeds too early and the early-maturing seeds too late. When ryegrass is cut too early, high seed moisture content will shorten the seed filling time which leads to immature seeds and reduced seed size and weight. Cutting too late (lower seed moisture) will reduce seed yield due to increased shatter in the swathing and harvesting operations.
Crop management
With ryegrass beginning to turn from green to light brown, swathing will be right around the corner. When to swath perennial ryegrass? The following ryegrass swathing data is from the U of MN Magnusson Research Farm (Table 2). This data suggests ryegrass swathing in the mid-30s is the ‘sweet spot’. Significant seed yield losses occurred when ryegrass was swathed when the seed moisture content was over 40% or when seed moisture levels dropped into the high 20s. Perennial ryegrass seed shatter can be reduced if swathing when dew is on the plant foliage.
Sample Date | Seed Yield* (% of the mean) | Seed Moisture** (%) | Test Weight*** (lb/bu) |
|---|---|---|---|
7/30 | 96.9 | 46 | 28.5 |
8/1 | 93.8 | 43 | 29.2 |
8/3 | 107.5 | 40 | 29.3 |
8/5 | 110.2 | 38 | 29.9 |
8/7 | 121.7 | 34 | 30.1 |
8/9 | 93.9 | 28 | 31 |
8/12 | 88.8 | 26 | 31 |
LSD (0.05) | 6.2 |
Pest management
Southerly winds and thunderstorm activity continued last week in northwest MN. The armyworm moth trapping project collected a total of 107 moths with an average of 17.8 moths/trap last week. The weekly totals from six armyworm moth traps ranged from 4 to 26. The highest moth capture was in areas with thunderstorm activity accompanied by strong southerly winds.
As of last week, leaf and stem rust has not been observed at the U of MN Magnusson Research Farm in areas that did NOT receive fungicide treatment.
Next week’s newsletter will be released on July 22.