Managing Winter Killed Hay and Pasture Fields

Severe winter weather can cause increased winter kill of forage stands in Manitoba. Alfalfa is prone to winterkill if the crown (the point on the plant from which all the stems grow from) is oxygen deprived due to ice cover, or if it freezes to -12 C or colder for 2-3 days.

If it is decided that a stand is sufficiently compromised that renovation is needed, some factors need to be considered. Alfalfa plants produce toxins (called medicarpins in the leaves) that reduce the germination and growth of new alfalfa seedlings.  Older stands have produced medicarpins longer and therefore have more of a build up or concentration in the soil around the plant where the leaves drop to in the fall of the year.  Generally the medicarpins are within 16” of the crown, so reseeding or over seeding alfalfa into these areas results in limited success.

Medicarpins break down over time, so a break from alfalfa for a year is sufficient time to allow for successful re-establish of alfalfa on that field.

Sod or no-till seeding can be a successful way of renovating old stands so long as the above information has been considered. These are some tips for successful germination and emergence of sod seeded forages.

  • Soil test and apply fertilizer as required, especially phosphorus (P).
  • Suppress competition from the existing vegetation, especially under drier soil conditions. 1.5 l/acre glyphosate (480 g/l formulation) will suppress the vegetation for about 60 days.
  • Use seeding equipment appropriate for sod seeding conditions.
  • Packing (in furrow or land roller) will slow drying of the soil and allow seeds to imbibe water more easily.
  • Plant shallow, i.e. ¾ inch or less. Small seeds do not have enough energy in the seed to emerge from deep plantings.
  • Check seeding depth and packing regularly while seeding.


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