Date: May 19, 2009
Author:
Glenn Friesen, Forage Specialist, Crops Branch, Manitoba
Agriculture, Food and Rural Initiatives, Ph: 204-745-5672
Unseasonably wet conditions last fall combined with
above average precipitation and cool conditions this spring, some
hay stands are dealing with excessive moisture. Additionally, some
areas of Manitoba experienced frost conditions over the past week. If you are concerned
about your hay stand and its production potential this season, below
are some tips to assess the damage.
Hay Fields
Just as in annual crops, the concern with forages is protecting the
growing point. At this time of year, growing points in grasses are
all at the soil surface or below ground, and protected from frost
injury. On the other hand, legumes elevate their growing points as
the growth stage advances, leaving them susceptible to frost injury.
The crucial advantage perennial crops have over annuals are the
crown and root reserves. Although growing tip damage may occur, the
plant will always have the capability of sending out new growing
points, as long as the crown is not damaged. Temperatures needed to
affect alfalfa crowns vary depending on slope position, amount and
type (“wet or dry”) of snow cover, soil temperature, soil moisture,
companion crop, and wind. Most studies estimate that alfalfa crown
damage may become an issue when air temperatures reach -5C for more
than 4 hours. Stand assessment should take place 3 to 5 days after
the frost.
Producers can expect to see some minor leaf burn due to frost
damage; however, there is much less concern for crown injury.
Established fields
- Established alfalfa seeded last spring or earlier will recover
to take advantage of the additional moisture quite nicely. Plant
tops that remain green and upright will keep growing as normal.
- However, plants in younger stands (1-3 years) generally have
fewer crown buds developed and available for rapid re-growth. Yield
potential may be affected. Plan on monitoring the stand for plant
stand reductions into the early summer.
- If the top 4" or more on a plant is wilted, if plants are drying
out, and/or if they're becoming discolored, they will stop growing
for a short period of time. Eventually, new shoots will develop --
some from branches on the main stem and some from the crown. Growth
will be set-back slightly, and yield may be affected.
Below is a guideline to use when assessing stand damage:
- If less than 30% of stem tops show wilting/browning from
frost, do nothing. Enough stems remain to provide good growth
and yield of first cutting. Stand will have some yield reduction
of first cutting but will recover completely on second cutting.
- If most or all stem tops are damaged and stand is less than
10” tall, do nothing. The growing points have been killed but
the alfalfa will form new buds at lower leaf junctures
(ancillary buds) and continue growing (first cutting might be
delayed). Alfalfa may demonstrate some horizontal growth. Mowing
existing top growth will not enhance recovery. If stand is over
12” inches tall, harvest and allow to regrow.
- If all stems on a plant are frozen back to the ground, the
plant is dead. This extent of frost damage has not occurred in
Manitoba to our knowledge. However, if observed and fewer than 5
plants per square foot remain, consider rotating to another crop
and replanting alfalfa in another field to avoid autotoxicity.
Seedling fields (Seeded in spring of 2009 or fall of 2008)
- At emergence, alfalfa and most winter hardy forage grass and
legume seedlings are extremely tolerant to cold. But, frost
tolerance changes with age. Four or more hours of temperatures
around -5C may kill new seedlings, especially once the seedling
has reached the 3rd – 4th trifoliate stage. Heat from the soil
often protects them from brief, cold temperatures. Seedlings
frozen so that all trifoliate leaves are discolored and dying
will not re-grow. Seedlings with 1 trifoliate remaining should
regrow. Alfalfa seeded with a companion crop survives lower
temperatures and longer exposure times before showing frost
damage. Reseeding your stand should not be required if more than
20 plants per square foot are remaining; however, less than 15
plants per square foot should trigger a consideration to reseed
or broadcast additional seed on the field. Since the plants are
less than two years old, autotoxicity is not an issue.
- However, as most spring seeding of forages takes place in
late May to mid-June, few if any fields are in the germinating
to emerging stage at this time of year. Therefore, field
conditions should be excellent when the time comes to seed a new
forage field. In fact, this extra moisture received might also
give producers a chance to clean up that last flush of
weeds.
Pastures
Pastures can be thought of in the same manner as established hay
fields. Since most pastures are mainly grass, frost injury is not a
significant concern. Much like the hay fields, the added moisture
will improve stand health and may increase productivity, depending
on the amount of overgrazing that has taken place and the fertility
program.
Spring Flooding
Excessive moisture last fall, significant snow fall in some area,
and spring rains have left the moisture level of many forage stands
at field capacity. Flooding a forage stand limits the amount of
oxygen in the soil profile, and since plant roots require oxygen to
remain healthy, plant productivity and survival is reduced when soil
moisture levels are too high. Below is a list of the flooding
tolerance of a few common forage crops.
Spring flooding tolerance levels of a few common forage crops.
- Alfalfa: 2 weeks
- Alsike Clover: 2 – 3 weeks
- Smooth brome grass: 2 – 3 weeks
- Timothy: 5 – 7 weeks
- Meadow Foxtail: 5 – 6 weeks
Producers are recommended to monitor their pastures for flooding
damage in lower areas. If plants have died, re-seed the area by
broadcasting or sod-seeding with a double disk press drill.
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