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 = 2,631 (Table 1)
- GDD last week (July 14 - 20) = 193 or 27.6/day; long-term average = 239 or 34.1/day
- GDD forecast for the next 10 days = 369 or 36.9/day
- Average GDD accumulation for the fourth week of July = 234 or 33.4/day
- The 10-day forecast suggests above average temperatures for the fourth week of July. Projected GDD is 36.9/day compared to the long-term average of 33.4/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 | 465* | 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 last couple weeks have been a weather rollercoaster! Several days last week felt more like September than July. GDD accumulation last week were below the average for the third week of July. The recent rain and cool temperatures should be positive for ryegrass seed fill. The new ten-day forecast suggests above average temperatures for the end of July. Ryegrass swathing has begun and look for swathers to be out this week into next week, especially in spring seeded ryegrass fields and fields with low soil moisture holding capacity. With the projected warm temperatures perennial ryegrass will mature at a rapid pace. Monitor these fields several times a week as when ryegrass seed moisture drops into the low 40% as seed moisture losses can be over 3% per day.
Crop management
The early seeded spring wheat is beginning to turn from green to brown. Spring wheat harvest will be a few weeks out. Straw dropped from the back of the combine is the first management step to maximize perennial ryegrass seed yield potential of the 2026. If the wheat straw is spread out the back of the combine, strive for uniform straw distribution. If baling, move bales off the field so bales do not smother the young ryegrass seedlings. A light harrow after an application of P&K will help move straw clumps that can act as a blanket and smother the young ryegrass plants. When harrowing wheat straw make sure the straw flows through the harrow, if the straw clumps or balls up, the straw is too damp, so wait for it to dry out.
Seeding perennial ryegrass into fallow ground with a cover crop, or into wheat stubble after wheat harvest are both proven methods of perennial ryegrass stand establishment. Seeding date trials conducted at the U of MN Magnusson Research Farm indicate seeding ryegrass in late August gave the highest yields and dry matter accumulation the next growing season (Table 2).
Sample Date* | Seed Yield** (lb/acre) | Dry Matter** (tons/acre) |
|---|---|---|
8/23 | 1,557 | 3.00 |
8/30 | 1,695 | 3.36 |
9/6 | 1,276 | 2.43 |
9/13 | 1,128 | 2.14 |
9/20 | 892 | 1.58 |
9/27 | 508 | 0.89 |
10/4 | 116 | 0.37 |
LSD (0.05) | 319 | 0.63 |
The take home message from this ryegrass date of planting trial is 1) mid-to-late August seeding gave the highest perennial ryegrass seed production potential and 2) ryegrass seed yield declined each week in September compared to late August seeding date.
Pest management
Armyworm traps have been pulled for the season. Last week low numbers of armyworm moths were captured in pheromone traps with a range of zero to three in the six traps. Continue to monitor ryegrass fields as the heavy armyworm flights in late June and early July could possibly have larger worms by the end of July.
As of last week, leaf and stem rust has not been observed at the U of MN Magnusson Research Farm in areas that did NOT receive fungicide treatment.
Next week’s newsletter will be released on July 29.