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 = 1,080 (Table 1)
- GDD last week (May 26 - June 1) = 230 or 32.9/day; long-term average = 177 or 25.3/day
- GDD forecast for the next 10 days = 293 or 29.3/day
- Average GDD accumulation for the second week of June = 186 or 26.6/day
- The 10-day forecast suggests above average temperatures for the second week of June. Projected GDD is 29.3/day compared to the long-term average of 26.6/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 | 39* | 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 month of May, in northern MN, has been unusually warm. The NDAWN weather station at the U of MN Magnusson Research Farm near Roseau, MN recorded 4 days over 90 and 6 days over 80F. The warm temperatures coupled below average rainfall has “pushed” perennial ryegrass growth and development. The drought index currently lists northern MN in the moderate drought category. The total accumulated GDD in May of 2025 was 812 compared to 653 in May of 2024. The new 10-day forecast suggests a continuation of the above average temperatures with the projected GDD accumulation of 29.3/day compared to the long-term average of 26.6/day. Spring seeded perennial ryegrass with healthy crowns are in the late boot to early heading stage. Ryegrass fields with significant winter injury are a couple of weeks behind the spring seeded ryegrass with healthy crowns.
Many grass seed fields require an isolation strip in the certification process. Kris Folland is the local Field Supervisor with the Minnesota Crop Improvement Association (MCIA). If you have questions or concerns, please contact your grass seed agronomist, seed conditioner or Kris with MCIA (218-791-2156).
Crop management
With warm temperatures in May and the projected warm temperatures this week many perennial ryegrass fields will soon be heading. In the growing conditions of northern Minnesota, perennial ryegrass biomass production has ranged from less than a ton to over four tons/acre. Ryegrass biomass production of less than two tons/acre could be classified as “thin line” growth and biomass production of over 3 tons/acre would be more “lush,” or even classified as rank growth. As of the end of May of 2025, many perennial ryegrass fields would be considered “thin line” rather than “lush” growth. Even in years of thin line growth previous U of MN research would indicate that the application of a plant growth regulator will produce a positive response in perennial ryegrass seed yields. However, the application of the growth regulator may have to be delayed until the ryegrass plants have more vertical growth. Check with your agronomist or seed conditioner for local experience.
Pest management
Many ryegrass production fields have gaps or thin growth. One of the strategies for extended weed control is to add a preemergence herbicide when making the normal post emergence weed control treatments. Callisto, Dual, Nortron and Prowl H2O are soil applied products that that can be applied as a delayed pre herbicide treatment to help control weeds that emerge later in the season. Talk to your agronomist or seed conditioner for local experience.
Low levels of armyworm moths were detected in the seven pheromone traps last week. Traps will be monitored until early July.
Cereal Rust Bulletin: The USDA-ARS tracks rust development and movement from the Gulf of Mexico to the northern plain states. As of early May, crown rust (Puccinia coronata) was observed in buckthorn in southern MN. Buckthorn is an alternate host for rust that infects oats, wheat and other grasses. Perennial ryegrass is susceptible to crown rust. Historically, in the environmental growing conditions of northern MN, crown rust can be observed in ryegrass after the accumulation of 1,500 GDD.
Summer grass seed tour
The annual grass seed summer tour is scheduled to begin at 5:00 p.m. on June 26. This field tour will be held at the U of MN Magnusson Research Farm. Directions to the U of MN Magnusson Research Farm. At the intersection of MN Hwy 11 and 310, proceed north on MN 310 for two miles, turn left (west) on Roseau County 16 and proceed west for approximately three miles. The U of MN Research Farm is located on the north side of Roseau County 16.
Field trials on the tour include ryegrass fertility, ryegrass weed control, ryegrass variety trial, ryegrass herbicide plant back, ryegrass competitive space plant nursery, MNHD hard fescue time of establishment, MNDH fertility and a hybrid rye and winter wheat frost seeding project.
Next week’s newsletter will be released on June 10.