Volume
3 Issue 2
May 23, 2006
Hoary Alyssum in Hay, Pasture and
Forage
 Hoary
alyssum (Figures
1,
2 and
3) is a
weed common to Minnesota, the surrounding states, and
Canada. It is particularly adapted to dry conditions such
as occur on sandy or gravely soils. Hoary alyssum is a
member of the mustard family and is perennial in its
growth habit. Hoary alyssum tends to increase in forages
following drought or winterkill,
regardless of the soil type of the field.
 As with any weed control program, proper pasture and
hay management is the first consideration. This includes
annual fertilization of pastures, seeding adapted species,
and controlled grazing to avoid overstressing desirable
forages. For hayfields, proper soil fertilization and
seeding to insure adequate
forage stands that are vigorously growing and competitive
will help to prevent high levels of alyssum developing.
Winterkill can open some alfalfa stands
 to invasion by
alyssum, in which case the most appropriate method of
control would be to re-establish the hay crop. Remember,
adequate alfalfa stands should contain 5 plants per square
foot in the third year or older stands to have adequate
populations remaining to merit continued economic hay
production.
If herbicides must be used, the most effective in pure
alfalfa are products applied to dormant stands or
following first cutting. There are no other good herbicide
options for controlling alyssum beyond the first cutting.
For grass pastures, of the various broadleaf herbicides
available, the most economical approach would be to apply
2,4-D in the spring or fall to suppress hoary alyssum.
Re-treatment will likely be necessary. No broadleaf
herbicides are labeled for use on grass/legume mixed
pastures that do not have significant injury potential to
the legume as well.
Hoary alyssum is not a known poisonous plant as we
typically think of plants such as hemlock, bracken fern,
nightshade and white snakeroot. Considering the widespread
distribution of alyssum in Minnesota and the lack of
reported toxicity to animals, it is of relatively low
toxicity to livestock in that sense. Complete avoidance of
hoary alyssum in hay or forage is not an economical or
environmentally sound goal.
For ruminants, the buyer should be aware of potential
concerns when feeding hay containing hoary alyssum, though
horses appear to be at greater risk. The buyer should be
aware of the clinical signs and monitor ruminants for any
indications of toxicity, and remove alyssum-infested hay
if problems develop.
For horses, hay producers and horse owners both should
be aware of toxicity symptoms and management needs
regarding hay that may contain low levels of hoary
alyssum. Buyers should be alert for clinical signs of
toxicity development and immediately remove
alyssum-infested hay if symptoms develop. Hay containing
greater than 30% hoary alyssum should not be fed to
horses.
Other Resources for identification and management
of plants toxic to livestock:
Plants Poisonous to Livestock.
L. M. Axton and B. R. Durgan. U of MN Extension
Service Circular FO-05655
http://www.extension.umn.edu/distribution/livestocksystems/DI5655.html
Horse Extension: Weed Identification, Plants
Poisonous to Horses, Weed Identification and Control,
Weed Seedling Identification, Hoary Alyssum: Toxicity
to Horses, Forage Quality, and Control
http://www.extension.umn.edu/horse/components/weeds.htm
Will R. Yliniemi
Hubbard/Becker Extension Educator
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