by Joel Bagg, Forage Development Specialist & District Sales Manager, Quality Seeds Ltd
Forage crops in Ontario have generally over-wintered very well, but there are scattered reports of some alfalfa winterkill, winter injury and alfalfa heaving. The normally higher risk area of the Ottawa Valley seems to have minimal winterkill issues. Some alfalfa winter injury has been observed in fields that broke dormancy in December and early spring and were subsequently frozen. While this does not necessarily kill alfalfa plants, new crown buds have to be formed, resulting in uneven growth and reduced yields. Some fields harvested in late-fall are showing delayed green-up and growth this spring. New forage seedings are underway in good soil conditions. Some alfalfa fields seeded last year appear poor to fair, and may benefit from overseeding with a no-till drill or be reseeded.
Successful establishment of a vigorous, uniform, weed-free stand is important to provide quick growth and high yields during that first year and for the life of the stand. Key management factors are:
- seed early,
- ensure adequate soil fertility & proper pH,
- seed into a firm seedbed, packing before and after seeding if needed,
- place seed at a uniform ¼ - ½ inch depth, and
- control weeds early – 2,4D-B at the 1st – 3rd trifoliate stage.
New forage seeding crop insurance is an inexpensive way to manage the risk of unsuccessful establishment. (www.bit.ly/1EWmkes). Refer to “Successful Forage Establishment” (www.qualityseeds.ca/blog/9-successful-forage-establishment) and “5 Forage Establishment Mistakes To Avoid” (www.qualityseeds.ca/blog/12-5-forage-establishment-mistakes-to-avoid).
Repairing Poor Alfalfa Seedings
There were some poor new seedings in 2015, particularly in western Ontario, due to the very dry May, excessively wet June and subsequent poor weed control. Some of the very poor fields were reseeded or overseeded last summer. Fields seeded last year with poor results should be walked and assessed on an individual basis to determine if reseeding or overseeding is required. In a predominately alfalfa stand, you want to see at least 12 healthy seedlings / square foot to have an acceptable yield potential at this stage. These stands may have to be rotated earlier than normal. Alfalfa autotoxicity is usually not a concern for about a year after the initial seeding, but the window of opportunity will soon be closed.
The use of a no-till drill to overseed into a thin new seeding is much more effective than using a conventional drill or brillion. Broadcasting forage seed into an existing stand is usually unsuccessful. Driving a no-till drill across the stand will kill a few plants, but with low alfalfa plant counts the gain should be much more than the loss. Soils must be fit so there is good seed-to-soil contact with minimal traffic damage. If some healthy alfalfa is present but needs to be thickened, a reduced seeding rate should be used that is inversely proportionate to what plants are there (down to about 10 lbs / acre). Grass seed can also be included if required. Refer to “Repairing New Alfalfa Seedings”. (www.qualityseeds.ca/blog/1-repairing-new-alfalfa-seedings)
Winterkill Assessment & Decision Making
Make decisions based on yield potential on a field-by-field basis. Walk alfalfa stands, dig some plants and use a knife to cut open the root and crown to assess for plant health. Watch for crown and root rots, brownish disclouration, spongy texture, a lack of secondary roots and nodulation, and assymetrical crowns. Plant health can be more significant than plant density to a successful yield. Assessment should not wait until after the corn is planted, since dealing with winterkilled forage stands may alter the crop rotation significantly. A minimum number of healthy plants per square foot guideline is 12 - 20 for 1st year stand, 8 - 12 plants for 2nd year stands and 5 plants for a 3rd year or older stand. As a general rule, at least 55 stems per square foot provide a maximum yield. The critical level of 40 stems per square foot or less will result in a 25% yield reduction and should be rotated. Refer to “Check Alfalfa Stands This Spring and Make A Plan” (www.qualityseeds.ca/blog/11-check-alfalfa-stands-this-spring-and-make-a-plan).
Although not a major issue, there has been some frost heaving of alfalfa reported. Assuming otherwise healthy plants, if the crowns are heaved less than 2.5 cm (1 in), the taproot is probably not broken and the stand is salvageable. These stands will likely reseat themselves over the season by natural settling and secondary root growth. Do not cultipack these fields, as this does more damage than good by damaging crowns. If crowns are heaved more than 3 cm (1 in), the taproot is likely broken. Broken plants will green up, but then die, depending on how deep the break is. Refer to “Frost Heaving of Alfalfa” (http://fieldcropnews.com/?p=6344)
Alfalfa winterkill is observed more commonly in older stands, fall harvested stands, stands with very little stubble, and stands with poor drainage or low fertility and pH issues. 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 100 lbs/ac nitrogen credit and 10 – 15% rotational yield benefit. A direct seeding can be done, or by using a companion forage crop such as cereals or cereal-pea mixtures. Do not try to repair an established stand by interseeding alfalfa into an alfalfa stand because of autotoxicity and disease, unless the stand was seeded the preceding year. Where winterkilled areas are large and patchy, some farmers attempt to repair these areas by no-tilling in Italian ryegrass and/or red clover. These species are difficult to dry for hay, but can make quality haylage. Refer to “Forage Options When Winterkill Strikes” (www.qualityseeds.ca/blog/13-forage-options-following-alfalfa-winterkill).