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 = 710 (Table 1)
- GDD last week (May 12 - 18) = 208 or 29.7/day; long-term average = 151 or 21.6/day
- GDD forecast for the next 10 days = 243 or 24.3/day
- Average GDD accumulation for the third week of May = 175 or 25/day
- The 10-day forecast suggests slightly below average temperatures for the end of May. Projected GDD is 24.3/day compared to the long-term average of 25/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 | 481* | 653 | 959 | 649 | 640 | 600 | 548 | 815 | N/A |
| June | N/A | 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
It would not be an understatement to say the temperatures last week were on a rollercoaster. In the early part of the week record high temps were recorded in many locations. A couple of weather reporting stations had daily high temps in the high 90s and 100 F. Temperatures in that range are more typical for the end of July. By the end of the week, daily high temps were in the 40s and frost was recorded in several weather reporting stations. The updated 10 day forecast suggests the temperatures will be back in the normal range for the end of May.
Perennial ryegrass plants that had healthy crown this spring are in the late tillering to moving into the jointing stage of growth. When ryegrass enters the jointing stage, the plants will begin to exhibit more of a vertical growth pattern and will soon overtop the wheat stubble. Perennial ryegrass plants that experienced crown injury range from dead plants to plants that are just beginning to tiller from the crown region.
Crop management
If nitrogen fertilizer has been applied and is in the root zone, ryegrass plants should be a deep green color with vigorous growth. Perennial ryegrass plants that are not tillering, or showing a pale green color could indicate nutrient stress. If spring fertilizer has yet to be applied now is the time to get that scheduled and applied. If spring nitrogen has been applied, but plants remain yellow with non-vigorous growth, plant applied nitrogen may not be in the root zone, some of the applied nitrogen may have been lost, or could indicate a sulfur deficiency. With the hot dry weather, one if the questions that are being asked is how much of the applied nitrogen was lost? Data from a recent AGVISE newsletter suggest that after a week of hot weather without rain nitrogen losses can range from 0 to 60%. The dry soil conditions and humidity levels in the teens may have reduced the potential for nitrogen loss.
Previous research at the U of MN Magnusson Research Farm suggests that perennial ryegrass is tolerant to foliar applications of liquid nitrogen. Perennial ryegrass will tolerate 10 gallons of 28% applied with flat fan nozzles. Another option is to add 3 gallons of UAN when making applications of plant growth regulators and fungicides. The U of MN has over 20 years of fertility data in perennial ryegrass.
Pest management
An armyworm moth trapping project will be conducted in the 2025 season. Two traps were placed near hybrid rye fields on May 2. Hybrid rye was selected for this early monitoring as these fields were the greenest of any fields in the area. This week additional armyworm trapping sites near perennial ryegrass fields will be added to this trapping network. Total moth captured from the two moth traps near hybrid rye fields.
- Week ending May 11 = 4
- Week ending May 18 = 18
These armyworm moth traps will be monitored through the end of June. A couple thing to remember when trapping armyworm moths: 1) just because moths are caught in a trap doesn’t guarantee a worm outbreak, (field scouting will determine the actual infestation level), and 2) armyworm eggs are tolerant to insecticide treatments, so it is important to wait to apply an insecticide until the eggs have hatched into worms. More information on armyworms larvae in future newsletters.
Many winter annual weeds are bolting, clovers are growing well, and dandelions are flowering. Cool season annual weeds emerging include wild buckwheat, wild mustard, wild oats, smartweeds and common lambsquarters. Field scouting will determine the infestation levels of winter annual weeds. Now would be a time to get these fields sprayed before bolting and flowering is complete in these winter annual weeds. A second application for broadleaf weed control may be necessary depending upon the level of infestation of warm season broadleaf weeds.
Next week’s newsletter will be released on May 27.