Scattered reports are coming in from across the province of alfalfa winterkill in some of the higher risk older stands and fall harvested stands. Extensive winterkill has occurred in eastern Ontario, from Arnprior south, east to Quebec and west to about Brockville. There are reports of 75% winterkill in some of these areas, particularly on flat, heavier clays in the Ottawa Valley. This winterkill includes some new seedings, as well as orchardgrass. A cool, wet spring has delayed green-up and spring seeding, further complicating how to manage the situation. Forage inventories are exceptionally low for this time of year, and record high hay prices continue to be reported.
Alfalfa fields should be scouted for winterkill and heaving by digging plants and assessing roots and crowns for plant health and disease. Fields that showed signs of stress or disease last year, fall harvested fields, and fields that are slow to green-up should especially be monitored. Using a shovel, dig alfalfa roots, rinse the soil off in a pail, and use a knife to cut open the root and crown. Watch for crown and root rots, brownish disclouration, spongy texture and lack of secondary roots and nodulation. Plant health is often more significant than plant density to a successful yield. The minimum number of healthy plants per square foot should be 12 – 20 for 1st year stand, 8 – 12 plants for 2nd year stands and 5 plants for a 3rd year or older stand. Refer to “Check Alfalfa Stands This Spring and Make A Plan” https://fieldcropnews.com/?p=5845.
If winterkill is identified early enough, the best option is often to simply replace the winterkilled stand by seeding a new forage stand in a new field in the crop rotation. Corn can follow the winterkilled alfalfa to take advantage of the nitrogen credit and rotational yield benefit. A direct seeding can be done, or by using a companion forage crop such as cereals or cereal-pea mixtures. (Forage Production From Spring Cereals and Cereal-Pea Mixtures http://www.omafra.gov.on.ca/english/crops/facts/98-041.htm) If an alfalfa stand is uniformly thin or weakened but the grass content is good, an application of nitrogen can significant increase yields and increase protein levels. Do not try to repair a stand by interseeding alfalfa into an alfalfa stand because of autotoxicity and disease, unless the stand was seeded the preceding year. (Alfalfa Autotoxicity https://fieldcropnews.com/2013/04/alfalfa-autotoxicity/) Where winterkilled areas are large and patchy, some farmers attempt to repair these areas by no-tilling in red clover and/or annual ryegrass. These species are difficult to dry for hay, but can make quality haylage.