Perennial ryegrass growing degree days (GDD)
Perennial ryegrass GDD’s will be tracked during the 2026 growing season with comparisons to the previous eight 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 degrees F will be used for perennial ryegrass (T-Base = 32 F).
- Year to date GDD = 2,991 (Table 1)
- GDD last week July 27 - Aug 2 = 247 or 35.3/day; long term average = 234 or 33.4/day
- GDD forecast for the next 10 days = 325 or 32.5/day
- Average GDD accumulation for the second week of August = 230 or 32.8/day
- The 10-day forecast suggests average temperatures for first week of August. Projected GDD is 32.5/day compared to the long-term average of 32.8/day
| Year | 2026 | 2025 | 2024 | 2023 | 2022 | 2021 | 2020 | 2019 | 2018 | 2026 vs. 2025 |
|---|---|---|---|---|---|---|---|---|---|---|
| March | 0 | 0 | 0 | 0 | 0 | 131 | 30 | 0 | 0 | 0 |
| April | 191 | 229 | 296 | 93 | 95 | 236 | 183 | 211 | 184 | -38 |
| May | 619 | 812 | 653 | 959 | 649 | 640 | 600 | 548 | 815 | -193 |
| June | 943 | 932 | 859 | 1,064 | 959 | 1,007 | 995 | 919 | 1,007 | +11 |
| July | 1,164 | 1,040 | 1,119 | 985 | 1,104 | 1,174 | 1,179 | 1,067 | 1,100 | +128 |
| Total | 2,991 | 3,013 | 2,927 | 3,101 | 2,807 | 3,188 | 2,987 | 2,745 | 3,106 | N/A |
General crop condition
In the last couple days, a cold front that moved through the area brought scattered thunderstorms and a general rain to most of NW. This rain put a stop to ryegrass harvest and field operations. However, the short term weather points to combines moving again by mid-week. Spring seeded ryegrass harvest began last week and will continue this week. Perennial ryegrass swathing will continue this week in fall seeded fields and those with winter injury.
This will be the last weekly ryegrass newsletter for the 2026 season as after this week the majority of the perennial ryegrass fields will be swathed.