AgricultureAgricultureHoary Alyssum in Pasture and Hay
Fields in Southwest Michigan
Paw Paw, MI. Farmers and horse owners should be on the lookout for hoary alyssum, a weed species that has been found in a few hay fields in southwest Michigan which can be poisonous to horses. University of Minnesota Researchers reported that the ingestion of hay that contains a high level of hoary alyssum can cause horses to experience depression and cause a swelling of the lower legs. Fever and short term diarrhea also can accompany ingestion of the plant. Clinical signs normally subside within 2-4 days after the horses are removed from the alyssum source. In severe cases, foundering with stiffness in joints has been observed.
Hoary
alyssum is a member of the mustard family. This plant is quite often confused
with another plant species in the mustard family, pepperweed, because of the
similarity of the shape and attachment of seeds. Hoary alyssum can exist as an
annual, biennial or perennial species.
The stems are erect and tend
to branch near the top of the plant. Hoary Allysum plants can grow from 1 to 3
feet tall, although they are frequently found shorter than this in southwest Michigan hay
fields and pastures. Leaves are alternate, smoothed edged, and narrow with a
general oblong shape. The stem, leaves and seed pods are covered in a whitish gray,
short branched hair which gives the plant a pale light green coloration. The flowers
are white, and appear in a raceme (small stemlike connection) at the end of the branches.
The flowers have 4 deeply divided petals. The seed pods are round, somewhat
flattened, and contain only a few seeds. The seeds are usually held close to the
stems (unlike pepperweeds) and have a short pointed growth at the end opposite where they
attach to the stem. The plants flower from early June until fall.
Hoary Allysum is a fairly hard weed to control in the mixed species alfalfa fields that are commonly used for horse hay. Some of the herbicides that are labeled for application on established alfalfa fields (1 year or more) while the alfalfa is dormant in late fall or early spring are excellent at controlling hoary alyssum. Unfortunately, they will also likely kill any of the companion planted grass forage species in the field as well. Another spray program that is a possibility to control hoary alyssum is to apply 2,4-DB amine (Butoxone 200 or Butyrac 200 only). These herbicides are a special Butyl formulation that is the only 2,4-D that is safe to apply to alfalfa. This herbicide application should be made in early April when the hoary alyssum seedlings are in the 2- to 4-leaf stage. This control program has been rated as "Fair" in controlling hoary alyssum. Consult MSU Extension Bulletin E-434 "Weed Control Guide for Field Crops" and the product label for more information on using this or other forage herbicide products. Also, be aware that all formulations of 2,4-D have the potential to injure grape plants in the area. Portions of Van Buren, Berrien, Cass and Kalamazoo Counties have a special 2,4-D exclusion zone that bans the use of ester formulations of 2,4-D. 2,4-D amines can be applied but extreme caution should be used to keep pressures low , boom heights low and potential drift away from grapes. Producers within 1 miles of grape production should exercise extreme caution even when using the amine formulation of 2,4-D.
Hoary Allysum plant found in a spring alfalfa seeding near Lawton, MI.
