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 = 850 (Table 1)
- GDD last week (May 19 - 25) = 140 or 20/day; long-term average = 151 or 21.6/day
- GDD forecast for the next 10 days = 340 or 34/day
- Average GDD accumulation for the third first week of June = 177 or 25.3/day
- The 10-day forecast suggests above average temperatures for the first week of June. Projected GDD is 34/day compared to the long-term average of 25.3/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 | 621* | 653 | 959 | 649 | 640 | 600 | 548 | 815 | N/A |
| June | N/A | 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 recent rainfall, cooler temperatures and nitrogen in the root zone has promoted ryegrass tillering. Perennial ryegrass plants that had a healthy crown this spring are a deep green color and are moving from tillering to the jointing stage of growth. Perennial ryegrass plants that experienced crown injury this spring range from dead areas in the field to plants that are tillering and are a couple of weeks behind plants that had a healthy crown this spring. The first couple days this week will be on the cool side before a significant warm up mid-week into the weekend. Look for ryegrass with healthy crowns this spring beginning to poke heads on the main stem of the ryegrass plants by the first few days of June. If the short-term forecast is correct, perennial ryegrass will enter a rapid growth phase with daily high temps in the mid-80’s and night-time lows in the mid-50s to low 60s. With this temperature regime weeds will also be in a rapid growth phase and field scouting will determine the timing of broadleaf and grass weed control treatments in perennial ryegrass production fields.
Crop management
With ryegrass jointing in spring seeded ryegrass fields, growth regulator timing is right around the corner. U of MN research has indicated that a surfactant and nitrogen source with Apogee has given increased seed yields compared to surfactant alone. With Palisade a single additive is recommended as the double additive can cause ryegrass injury, especially at the high rate of Palisade. The following conclusions are based on U of MN small plot replicated research with growth regulators in perennial ryegrass over the last decade:
- The application of a growth regulator will result in increased perennial ryegrass seed yield of 150-300 pound/acre compared to the untreated
- Growth regulators applied when the main stem is in the late boot to early heading stage will reduce plant height by 2 to 8 inches compared to the untreated
- Growth regulators reduce lodging and keep plants upright which improves seed set during pollination
- Palisade performance will be reduced if the weather turns cool. Palisade performance is enhanced when ryegrass is in a period of rapid growth
- Apogee rate of 6-8 oz/acre and Palisade at 1 to 1.5 pt/acre are recommended with a full ryegrass stand. Ryegrass with thin line growth reduce growth regulator by 20-40%
- A single additive, nonionic surfactant at 0.25%v/v is recommended with Palisade
- With Apogee a double additive, a nonionic surfactant at 0.25% v/v and nitrogen either 28%, or AMS at 2.5% v/v
- A double additive is not recommended with Palisade as crop injury may result in certain environmental conditions (hot, dry)
Additional U of MN growth regulator research can be found on the UMN Turf website.
Pest management
Lilacs are beginning to bloom, which is a good reminder now is a good time to apply an insecticide to control capsis bug in bluegrass seed production fields.
Low levels of armyworm moths were detected in pheromone traps this past week. A distribution of the moth collection from the seven traps:
- Four traps: 0 or 1
- Three traps: < 12
Canada thistle has been observed growing is perennial ryegrass fields that didn’t receive a broadleaf herbicide treatment last fall. Now is the time to monitor perennial ryegrass fields for broadleaf weeds as we are now in the window for postemergence broadleaf weed control. Field scouting will determine if a broadleaf treatment is warranted in perennial ryegrass seed production fields.
The annual Grass Seed Field Day is scheduled for June 26. Additional details will follow in future newsletters.
Next week’s newsletter will be released on June 3.