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 °F will be used for perennial ryegrass (T-Base = 32 °F).
- Year to date GDD = 404 (Table 1)
- GDD last week May 11-17 = 128 or 18.3/day; long term average = 124 or 17.7/day
- GDD forecast for the next 10 days = 244 or 24.4/day
- Average GDD accumulation for third week of May = 151 or 21.6/day
- The 10-day forecast suggests warmer than average temperatures for the third week of May. Projected GDD is 24.4/day compared to the long-term average of 21.6/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* | 213 | 812 | 653 | 959 | 649 | 640 | 600 | 548 | 815 | N/A |
| June | N/A | 932 | 859 | 1,064 | 959 | 1,007 | 995 | 919 | 1,007 | N/A |
| July | N/A | 1,040 | 1,119 | 985 | 1,104 | 1,174 | 1,179 | 1,067 | 1,100 | N/A |
| Total | N/A | 3,013 | 2,927 | 3,101 | 2,807 | 3,188 | 2,987 | 2,745 | 3,106 | N/A |
General crop condition
Area perennial ryegrass fields, for the most part, survived the winter and are now in the tillering stage of growth. With the recent rainfall and projected daily high temperatures in the high 60’s and daily low temperatures in the 50’s ryegrass plants will enter a rapid growth phase. Jointing will follow the tillering stage of growth. As perennial ryegrass transitions from tillering to jointing the plants enter more of a vertical growth phase and the ryegrass will begin to overtop the wheat stubble.
Lake of the Woods – Ice-Out Date
The date when lakes are free of ice (ice-out date) is an indication of the “earliness” or “lateness” of spring. In 2026, the ice-out date on Lake of the Woods was May 16 which is thirteen days later than the median date of May 3 (Table 2). The earliest recorded ice-out date is April 8 in 2012. The latest ice-out date was recorded on May 21 in 2014.
2026 | 2025 | 2024 | 2023 | 2022 | 2021 | 2020 | 2019 | 2018 | 2017 | 2016 | 2015 | 2014 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
May 16 | May 10 | April 28 | May 13 | May 16 | April 23 | May 2 | May 14 | May 14 | April 24 | May 4 | May 3 | May 21 |
Crop management
If nitrogen fertilizer has been applied and is in the root zone, ryegrass plants should be a deep green color. Perennial ryegrass plants that are not tillering, or showing a pale green color could indicate nutrient stress. If spring fertilizer has yet to be applied now is the time to get that scheduled and applied. If spring nitrogen has been applied, but plants remain yellow with non-vigorous growth, applied nitrogen may not be in the root zone, some of the applied nitrogen may have been lost, or could indicate a sulfur deficiency.
To maximize perennial ryegrass seed production U of MN research indicates that nitrogen fertilizer must be in the rooting zone prior to the accumulation of 700 GDD. As of May 17, the year-to-date accumulation of GDD is 404. The new 10 day forecast projects 244 GDD by May 27 for a projected year-to-date GDD total of 648. Spring seeded ryegrass will be in the tillering stage for the next couple of weeks.
Most of the nitrogen used by the perennial ryegrass plants is applied as dry urea. However, liquid nitrogen has potential to be used as a top dress nitrogen application in ryegrass. Previous research at the U of MN Magnusson Research Farm suggests that perennial ryegrass is tolerant to foliar applications of liquid nitrogen. Perennial ryegrass will tolerate 10 gallons of 28% applied with flat fan nozzles. Another option is to add 3 gallons of UAN when making applications of plant growth regulators and fungicides. The U of MN has over 20 years of fertility data in perennial ryegrass.
Pest management
The yellow flowers of common dandelion was observed on the south side of buildings late last week. Dandelions will soon flower and winter annal weeds will soon bolt in area perennial ryegrass fields. If a broadleaf herbicide was not applied last fall ryegrass these fields should be scouted to determine the infestation levels of winter annual weeds. With the increased soil temperatures, the cool season annual weeds will soon begin to emerge from the soil. Volunteer canola, wild mustard, common lambsquarters and smartweed species are cool season broadleaves that are the first weed species to emerge from the soil. Annual bluegrass has emerged and is growing well. Warm season weeds have yet to emerge and will take additional heat to promote germination. Redroot pigweed and tall waterhemp are examples of warm season broadleaf weeds. The foxtail species and barnyardgrass are examples of warm season grasses and will take more heat to stimulate germination. Perennial ryegrass has tolerance to several herbicides with soil activity including, Callisto, Dual, Nortron and Prowl. Herbicides with soil activity are a possibility to control late emerging weeds, especially if the perennial ryegrass stand has gaps or the stand is thin.
The armyworm moth trapping project in perennial ryegrass will continue this year. Traps will be deployed this week in area perennial ryegrass fields.
Mark Your Calendar - Annual Grass Seed Summer Field Day
The annual Grass Seed Field Day held at the Magnusson Research Farm is scheduled for June 24. Additional details will follow in future newsletters.
Next week’s newsletter will be released on May 26.