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 = 1,938 (Table 1)
- GDD last week (June 23-29) = 227 or 32.4/day; long-term average = 220 or 31.4/day
- GDD forecast for the next 10 days = 393 or 39.3/day
- Average GDD accumulation for the first week of July = 230 or 32.9/day
- The 10-day forecast suggests above average temperatures for the first week of July. Projected GDD is 39.3/day compared to the long-term average of 32.9/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 | 897* | 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
In the last couple of weeks pollen clouds have been observed moving across spring seeded perennial ryegrass fields. In 2025 many ryegrass production fields will have an extended pollination period, especially if areas of the field had crown damage due to cold temperatures in March and April or the excessive heat in early May. Pollen shed typically occurs first in the main culm (mother plant) followed by the tillers. This observed pollen clouds coupled with moderation in temperatures should be positive for seed set and filling of the ryegrass seedhead.
Flocks of seagulls have been observed in and around area field crops. Field scouting will determine what brings the seagulls and has them hover over crops. Historically, grasshoppers and armyworm larvae are two insect pests that seagulls feed on in agricultural crops.
Crop management
Many area ryegrass production fields are now in the full seedhead extension stage. Previous research in perennial ryegrass indicates that to maximize seed yield and quality the entire ryegrass seedhead must be protected from rust and other fungal diseases. U of MN research over a 14 year period (2009-2023), indicates the average perennial ryegrass seed yield advantage from fungicide treated compared to the untreated was 172 lb/acre. Further, the fungicide treated seed yield ranged from 31 to 409 lb/acre.
Pest management
Southerly winds of the last couple of weeks has carried several insect pests into the area. Leafhoppers have been observed in several grass crops. Last weekend with the storms and severe weather alerts brought with it the first heavy armyworm moth capture of the year. Traps around the severe weather alert had armyworm moth captures of 10 to 17 over a two day period. Field scouting in a couple of weeks will determine if ryegrass fields were a preferred source of egg laying and larvae development.
Low levels of grasshoppers continued to be observed in perennial ryegrass fields. Weather conditions and crop scouting will determine if control measures are warranted.
Crown rust, at low levels, has been observed at the U of MN Magnusson Research Farm in areas that did NOT receive a fungicide treatment. Leaf and stem rust has yet to be identified in areas NOT treated by a fungicide. These areas will continue to be monitored for rust infection, development and spread in perennial ryegrass.
Next week’s newsletter will be released on July 8.