Green Gold (Central): Time to assess frost damage

Here is the first release for the scissor clipping project for 2013. This year we will be reporting from various areas of the province (eastern, central, Interlake, western). For the central report, the fields that are being sampled are in the south-central and Arborg areas.

Arborg 268 212 12 36
Mariapolis 268 204 12 43
Baldur 268 173 12 34

With the later start to the growing season (similar to 2008) the fields that were samples in the central part of the province were shorter than 10 inches when the program started on May 23. The fields in the south that were sampled on June 3 have only grown one inch. The alfalfa is reported to be in the vegetative stage.

Frost was reported the morning of June 3.

As you will notice, the PEAQ and NIR readings are quite far apart, but as we have seen in the past as we move closer to the 170 target, the variability of the PEAQ will be less and will more closely follow the NIR results. You can also access reports from the MFC website.


There was frost reported in the area and although there is no significant damage expected fields need to be assessed individually. Alfalfa exposed to a light frost (-1 to -2 C) may look wilted for a few hours. Alfalfa plants experiencing light frost often show frost damage on one to several sets of trifoliate leaves that were exposed at the top of the canopy. This may set the crop back a little but it should grow out of the damage. If standing yield is great enough, harvesting at this point is not a bad idea.

If temperatures get down to around -2.8 C or lower, you can expect damage to stands of alfalfa. If the temperatures drop to -3.8 to 4.4 you can expect serious damage to not only the leaves but to the buds and growing points.

Gauging damage due to frost can be very difficult if temperatures were around -4 for an extended period of time damage could be serious but if the period of time the temperature was at -4 was fairly short damage could be minimal.

As you are likely aware the growth of each alfalfa stem takes place at the tip. A late spring frost may destroy the growing point of alfalfa, causing a stunting of the plant. A good “thumb rule” to follow is that if one-third or more of the top growth has been wilted by frost and drying up, immediate mowing will permit earlier development of a new crop. If the damage is less, the plant should recover adequately to allow harvest at the normal time. Harvest of frosted stands that were clipped should be delayed to about the mid-bloom growth stage for the second harvest to allow recovery of stored food reserves.

Growing degree days

GDD are a measure of heat unit accumulation. Because early season growth of alfalfa is related to the sum of heat units accumulated, monitoring GDD is an easy and effective way to determine when to harvest to optimize forage quality of first cutting alfalfa.

Michigan State University Extension recommends that dairy hay should be harvested at the mid-bud stage of growth which will normally provide 40 per cent neutral detergent fibre (NDF) to maximize the yield and quality of feed to lactating dairy cows. Delaying harvest after the recommended harvest time of 40 per cent NDF will result in higher yields, higher fibre, lower NDF digestibility and lower protein. Harvest of dairy-quality alfalfa that will be stored in horizontal bunkers should begin at 375 GDD. Haylage that will be stored in a vertical silo can be harvested at 400 GDD. To get GDD accumulations for your area click here.

— John McGregor is the extension specialist for the Manitoba Forage Council.



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