Seed Production Newsletter – June 23, 2026

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 = 1,458 (Table 1)
• GDD last week June 15-21 = 175 or 25/day; long term average = 197 or 28.1/day
• GDD forecast for the next 10 days = 325 or 32.5/day
• Average GDD accumulation for fourth week of June = 212 or 30.3/day
• The 10-day forecast suggests close to the average temperatures for the end of June. Projected GDD is 32.5/day compared to the long-term average of 30.3/day 

General crop condition

Last week continued the cool trend of the past few weeks which is a welcome change from the hot temperatures in late May and early June. The new 10 day forecast points to seasonal temperatures which should be positive for perennial ryegrass growth and pollination. Spring seeded ryegrass is now heading and the next critical stage in ryegrass growth and development is pollen shed. Perennial ryegrass sheds pollen in the mid-morning. As these pollen clouds drift across ryegrass fields, it looks like dust from gravel roads. 

Crop management

As of June 19, leaf rust has NOT been observed at the U of MN Magnusson Research Farm in plots that have not received fungicide treatments. Leaf rust is carried into the perennial ryegrass growing regions of northern MN by southerly winds. Low level jet streams transport rust spores and these spores tend to be deposited in association with thunderstorms and rain events.   

The USDA-ARS tracks rust development and movement from the Gulf of Mexico to the northern plain states. Rust movement on air currents from southern states has been called the Puccinia Pathway.

Pest management

For the week ending June 19, 42 armyworm moths were captured from five locations (average of 1.2/day) in northern MN. So far in 2026 four significant moth captures have occurred:

• May 25: 112
• May 28: 156
• June 5: 129
• June 12: 149
• June 19: 42

If we assume an average of 35 days from egg laying to fully developed larvae, moth flights at the end of May should have larvae in the 5^th to 6^th instar stage by the end of June into the first week of July. Larval instar stages 5 and 6 account for over 80% of the foliage consumed by armyworm larvae. Moth flights in the first week of June will have 5^th to 6^th instar larvae in mid-July and moth flights in mid-June should have 5^th to 6^th instar larvae at the end of July. The multiple armyworm moth capture and egg laying is primary reason that we can see worms of various sizes in perennial ryegrass fields. Field scouting will determine if the projected larvae stage correlates to the actual larvae in the field. 

Crown rust and leaf & stem rust

Crown and leaf and stem rust are two leaf diseases that can cause economic yield losses in perennial ryegrass seed production. Crown rust pustules are orange in color while leaf and stem rust are red in color. In northern MN conditions we typically see Crown rust after 1,500 and leaf and stem rust after the accumulation of 1,900 GDD. More on rust in next week’s newsletter. 

Summer grass seed field tour – June 24

The annual grass seed summer tour is scheduled for June 24 at the U of MN Magnusson Research Farm. The field tour will begin at 5:00 p.m. Directions to the U of MN Magnusson Research Farm. From the intersection of MN Hwy 11 and 310, proceed north on MN 310 for two miles, turn left (west) on Roseau County 16, and proceed west for approximately three miles. The U of MN Research Farm is located on the north side of Roseau County 16. Perennial ryegrass field trials include: preemergence herbicides, fertility, postemergence herbicides, growth regulators, and a perennial ryegrass variety trial. 

Next week’s newsletter will be released on June 30.