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 = 1,270 (Table 1)
- GDD last week (June 2-8) = 190 or 27.1/day; long-term average = 186 or 26.6/day
- GDD forecast for the next 10 days = 295 or 29.5/day
- Average GDD accumulation for the third week of June = 197 or 28.1/day
- The 10-day forecast suggests above average temperatures for the third week of June. Projected GDD is 29.5/day compared to the long-term average of 28.1/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 | 229* | 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
A steady rainfall over the weekend resulted in 0.4 to over an inch of moisture which was very welcome. The recent moisture and moderate temperatures should be positive for ryegrass growth and development. Many of the spring seeded perennial ryegrass with healthy crown this spring are in the early heading stage and are a deep green color. If a growth regulator had yet to be applied this week would be a good time to scout fields for growth regulator timing. The variable ryegrass stands in some fields will present a challenge on growth regulator timing. However, U of MN has several years of growth regulator research which suggests that a growth regulator provides benefits in both lush and thin ryegrass growth.
The next critical stage in ryegrass growth and development is pollen shed which will begin after plants are fully headed on the main stem. Perennial ryegrass typically will shed pollen in mid-morning, and these pollen clouds almost look like dust from gavel roads. Spring seeded fields with significant winter injury look to be a couple of weeks behind the spring seeded ryegrass.
Crop management
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).
A healthy crop of perennial ryegrass will be a deep green color in June. What if perennial ryegrass is pale green to yellow? Several causes would be responsible for these symptoms, but nitrogen and or sulfur deficiencies are two potential causes for the lack of green color in perennial ryegrass seed production fields. If the cause of this lack of green color is a nutrient deficiency can anything be done at this time of the year? To diagnose the problem collection of both plant tissue samples and soil samples from good and bad areas in the field will be a first step. A guide for sampling plant tissue analysis has been developed by AGVISE.
U of MN has conducted small plot research on the timing of nitrogen applications in perennial ryegrass. The optimum timing is early spring less than 400 GDD. However, a trial conducted in 2009 indicated that over a 200 pound ryegrass seed increase was realized from nitrogen applied to ryegrass between 1,000 to 1,900 GDD. Nitrogen applied this late would be considered a rescue treatment, but positive ryegrass seed yields resulted from nitrogen applied compared to the untreated. Seed Production Research - Progress Reports contain more information on U of MN perennial ryegrass fertility research.
Pest management
Armyworm moth pheromone traps continue to have low numbers thus far in 2025. Last week moth numbers ranged from 0 to 3 with a seven trap average of 1.4/trap. These pheromone armyworm moth 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. Crown rust and leaf and stem rust are two leaf diseases that can cause economic yield losses in perennial ryegrass seed production. Crown rust pustules are orange in color while leaf and stem rust are red in color. In northern MN conditions we typically can see Crown rust after 1,500 GDD’s and leaf and stem rust after the accumulation of 1,900 GDD. More on rust in next week’s newsletter.
Summer field tours
Two field tours will be held on June 26 in the Roseau area. A Hybrid Rye field tour will be held in the morning from 10:00 a.m. to 12:00 p.m. and the annual Grass Seed field tour will begin at 5:00 p.m. Complete details will follow in next week’s newsletter.
Next week’s newsletter will be released on June 17.