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 = 810 (Table 1)
- GDD last week May 25-31 = 276 or 39.4/day; long term average = 175 or 25/day
- GDD forecast for the next 10 days = 375 or 37.5/day
- Average GDD accumulation for first week of June = 177 or 25.3/day
- The 10-day forecast suggests warmer than average temperatures for the first week of June. Projected GDD is 37.5/day compared to the long-term average of 26.6/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 | 619 | 812 | 653 | 959 | 649 | 640 | 600 | 548 | 815 | -193 |
| 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
For the week ending May 31, accumulated GDD averaged 39.4/day which is well above the long term average of 25/day. The current 10-day forecast suggests a continuation of the above average temperatures and the accumulation of GDD. Spring seeded ryegrass plants are beginning to joint (1- node) and with the new 10 day GDD accumulation of 37.5/day area ryegrass fields will begin the heading stage by the second week of June.
Crop management
With ryegrass jointing in spring seeded ryegrass fields, now is the time to think about growth regulator timing. 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.
- A double additive is not recommended with Palisade as crop injury may result in certain environmental conditions (hot, dry).
Pest management
For the week ending May 28, 156 moths were captured from four traps in perennial ryegrass fields, for an average of 5.6 moths/day. Individual trap counts ranged from a low of 5 to a high of 54. Armyworm and other insect rate of development is driven by temperatures. Research data is limited to the correlation of moths captured in a trap and the infestation levels of armyworms larvae that feed on the crop. However, it takes about 8-10 days for the eggs to hatch (eggs tolerant to insecticides) and about 3 to 4 weeks for the armyworm caterpillar to pass through 6 instar stages. Data from Guppy et. al., indicates that armyworm caterpillar instar stages 1-4 account for only 6% of the feeding damage, instar stage 5 (up to 3/4-inch-long worms) approximately 15% and instar stage 6 (up to 1.25 inch) approximately 80% of the feeding damage. Field scouting will determine armyworms stages and infestation levels. The current economic threshold for larger armyworms caterpillars in grass crops is 4-5 larvae/square foot in the vegetative stage.
The southerly wind patterns of the last couple of weeks have given a ride north to many insect and disease pathogens. Armyworms and Aster leafhoppers have been observed in high numbers in perennial ryegrass fields in the last couple of weeks. As of the current date, rust has NOT been detected in area perennial ryegrass field. Pest monitoring will continue for the next few weeks.
Summer grass seed field tour - June 24
The annual grass seed summer tour is scheduled for June 24 at the U of MN Magnusson Research Farm. The field tour will begin at 5:00 p.m. 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.
Dr. Nancy Ehlke, U of MN grass seed breeder will provide an update on the U of MN ryegrass breeding program. Dr. Eric Watkins will highlight research with hard fescues. Donn Vellekson will lead a tour of the perennial ryegrass field trials to include: preemergence herbicides, fertility, postemergence herbicides, growth regulators, and a perennial ryegrass variety trial.
Next week’s newsletter will be released on June 9.