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 = 1,934 (Table 1)
- GDD last week June 29-July 5 = 258 or 36.9/day; long term average = 230 or 32.9/day
- GDD forecast for the next 10 days = 405 or 40.5/day
- Average GDD accumulation for 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 40.5/day compared to the long-term average of 34.7/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 | 181 | 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
Last week the temperatures were above the long term average. Spring seeded ryegrass is now heading and continues to shed pollen. Late summer seeding perennial ryegrass fields are a couple of weeks behind the growth and development of spring seeded perennial ryegrass.
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. The range in perennial ryegrass fungicide treated yield over this 14 year period was 31 to 409 lb/acre.
Crop management
If ryegrass is heading, is it too late to apply herbicides for weed control? Research conducted at the U of MN Magnusson Research Farm suggests that headed perennial ryegrass is tolerant to many broadleaf herbicides. The data set in Table 2 is from research conducted in 2012. Herbicides were applied to ‘Arctic Green’ that was 60% headed with minimal weed pressure.
| Treatment | Rate/acre | Seed Yield (lb/acre) | Seed Yield (percent of untreated) |
|---|---|---|---|
| MCPE | 1 pint | 1433 | 107.8 |
| 2,4-D amine | 1 pint | 1439 | 108.3 |
| Aim | 1 oz + 0.25% NIS | 1350 | 101.6 |
| 2,4-D + Clarity | 1 + 1 pint | 1320 | 99.3 |
| Basagran | 1.5 pint + 1% MSO | 1302 | 98.0 |
| 2,4-D ester | 0.75 pint | 1299 | 97.7 |
| Stinger | 6 oz | 1296 | 97.5 |
| Clarity | 1 pint | 1252 | 94.2 |
| Untreated | NA | 1329 | 100 |
| LSD (0.05) | NA | 137 | 10.3 |
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 a heavy capture of armyworm moths of the year. The total moth capture last week was 172 or 28.7 moths/trap (4.1 moths/night) The range of moth capture was 8 to 46. Highest moth capture was in areas that had thunderstorm and rain activity. Field scouting in a couple of weeks will determine if ryegrass fields were a preferred source of egg laying and larvae development.
Low to moderate levels of grasshoppers have been observed in perennial ryegrass fields. Weather conditions and crop scouting will determine if control measures are warranted.
Crown rust and leaf and stem rust
Crown and leaf and stem rust are two leaf diseases that can cause economic yield losses in perennial ryegrass seed production. In northern MN conditions we typically see Crown rust after 1,500 and leaf and stem rust after the accumulation of 1,900 GDD. Rust has not been observed in untreated ryegrass areas at the U of MN Magnusson Research Farm. Field scouting will continue this week.
Next week’s newsletter will be released on July 14.