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 = 2,191 (Table 1)
- GDD last week (June 30 - July 6) = 253 or 36.1/day; long-term average = 230 or 32.9/day
- GDD forecast for the next 10 days = 366 or 36.6/day
- Average GDD accumulation for the second week of July = 243 or 34.7/day
- The 10-day forecast suggests above average temperatures for the second week of July. Projected GDD is 36.6/day compared to the long-term average of 34.7/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 | 932 | 859 | 1,064 | 959 | 1,007 | 995 | 919 | 1,007 | +73 |
| July | 218* | 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
Many spring seeded ryegrass fields have pollinated and are in the seed filling stage. Late fall seeded ryegrass fields and fields that had crowns injured are in various stages of pollination. Hybrid rye and winter wheat fields are beginning to turn from green to brown. Spring seeded perennial ryegrass fields will soon be at physiological maturity (maximum dry matter accumulation). After physiological maturity, the plant begins the dry down phase which ends in seed maturity and ryegrass swathing.
Flocks of seagulls continue to be observed in and around area field crops. Field scouting will determine what brings the seagulls and has them hovering over crops. Grasshoppers and armyworm larvae are two insect pests that seagulls feed on in agricultural crops.
Crop management
Perennial ryegrass fields will be ready to swath in a few weeks. Previous research indicates swather choice can influence seed shattering in perennial ryegrass. The choice of swather type could be an important management decision in 2025 with the variable perennial ryegrass stands.
Several considerations for swathing the 2025 perennial ryegrass seed crop include:
- As swather width is reduced (discbine) a short ryegrass plant may not produce a windrow that can be efficiently picked up with the combine
- The lack of biomass from gaps in the field will result in more movement of the ryegrass plant from the swathing operation, especially when traveling at speeds over 10 mph which will increase seed shatter.
- The lack of dew in the morning will result in more seed shatter, especially with more aggressive cutting operations.
- Ryegrass seed shatter increases as seed moisture moves from the mid-30’s into the 20’s.
- Wider swather widths, when operated at lower speeds, will produce a window that should be more efficiently picked up with the combine.
Pest management
In the last couple of weeks low level jet streams and south winds have carried a flush of armyworm moths and other pests (leafhoppers, leaf rust) to northern Minnesota. Last week the armyworm moth trapping project collected a total of 162 moths which is an average of 27 moths/trap. The range was a low of 4 to a high of 56 moths/trap. The highest moth capture was in areas with thunderstorm activity accompanied by strong southerly winds. Armyworm moth captures were low in the entire months of May and most of June. In years past heavy armyworm flights have been documented in late May into June. The heavy moth flights in the 2025 season are about a month later than the previous three years. The six site average armyworm capture data is listed below.
- May 19: 5
- May 26: 3
- June 2: 2
- June 9: 1
- June 16: 14
- June 23: 12
- June 30: 38
- July 7: 162
A couple thing to remember: 1) just because moths are caught in a pheromone trap doesn’t guarantee a worm outbreak (field scouting will determine the actual infestation level) and 2) armyworm eggs are tolerant to most insecticide treatments, so it is important to wait to apply insecticides until the eggs have hatched into worms.
Low levels of crown rust has been observed at the U of MN Magnusson Research Farm that did NOT receive fungicide treatment. The number of days since the last fungicide application, product used, and rate will determine if a sequential fungicide will be needed to protect the seedhead through swathing.
Next week’s newsletter will be released on July 15.