INVASIVE PLANT Hoary alyssum, a perennial mustard plant, has the potential to cause problems on farms in the Okanagan and Similkameen. (Photo submitted)

Mustard plants invading agricultural areas in Okanagan Similkameen

Two species of perennial mustards causing problems within region

  • Aug. 12, 2019 2:57 p.m.

By Lisa Scott

There are a significant number of invasive plants in the mustard family that grow in the Summerland area.

Members of the mustard family have successfully adapted to a world disrupted by mankind. These Eurasian imports appear to have followed migrants to North America, many species brought purposely for use in cooking or medicine.

Mustard plants can be readily identified by the flower, which has four petals that give the appearance of a cross and are responsible for the scientific family name, Cruciferae.

The seeds of all mustard species can be dried or used fresh as a substitute for black pepper.

Most of the mustards are opportunistic annuals that have found their niche in cultivated fields, including tumble mustards, shepherd’s purse and pennycress, all of which are commonplace in the Okanagan-Similkameen.

Of greater concern are the perennial mustards.

There are two perennials occurring in our region that weed experts are closely monitoring, hoary cress and hoary alyssum.

Both of these species have the potential to invade agricultural fields and rangelands, where they can cause a serious environmental and economic impact.

Hoary cress flowers earlier in the spring and has now gone to seed in most locations.

In April through May, white masses of flowers are evident in dense patches along many of our roadsides and adjacent agricultural fields.

Also referred to as white top, hoary cress spreads both by seed and creeping roots.

Roots have been recorded to penetrate as deep as nine metres in the soil, although they typically do not exceed depths of one metre.

Mature hoary cress plants grow up to 50 centimetres tall. Alternate leaves are greyish-green and lance shaped.

This mustard species invades a wide variety of environmental conditions, commonly growing on dry roadsides, fields and other disturbed habitats.

In the Okanagan-Similkameen, it has moved off roadsides into sagebrush grasslands, an expansion that has caught the attention of weed experts in the province.

It grows well on alkaline soils that are wet in late spring and does best in areas with moderate amounts of rainfall.

Hoary alyssum is an annual to short-lived perennial that is currently in bloom.

It is a tap-rooted plant with stems that reach heights of up to one metre. It spreads only by seed.

Plants vary from simple, slender and unbranched to fully branched and rounded.

This variation in form is likely due to site-specific conditions such as soil type, nutrient availability, moisture levels or competition with other plants for these limited resources.

While it is most common on sandy or gravelly soils, hoary alyssum establishes in dry, disturbed habitats, such as roadsides and railway embankments. It is also found on meadows, pastures and hayfields.

Hoary alyssum is covered with star-shaped hairs. The grey, upper leaves of hoary alyssum are elliptic and clasp the stem, while lower leaves have short stalks.

Its white flowers appear in June and can continue blooming into the summer months, especially if plants are mowed. Hoary alyssum tends to increase in forage crops following drought or winterkill.

Of significant importance is the impact hoary alyssum can have with horses. If they consume large quantities of this plant, horses may be troubled with fever, limb edema and laminitis.

Most poisonings occurring when hoary alyssum is mixed in alfalfa hay.

If your property supports either of these mustard species, it is important that infestations be eliminated whenever possible.

Small patches of both species may be destroyed by hand pulling or digging.

While mowing can prevent seed production, this action tends to encourage hoary alyssum to shift from being an annual to a perennial.

For hoary cress, mowing two to three times a year for several years may slow the spread and reduce seed production; mowing should be conducted during the bud stage.

As with all invasive plants, disturbed areas should be seeded or planted to provide competition.

For further information on invasive species visit www.oasiss.ca or facebook.com/invasivespeciessociety or contact the Executive Director for the Okanagan-Similkameen, Lisa Scott, at 250-404-0115 or oasiss@shaw.ca.

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INVASIVE PLANT Hoary alyssum, a perennial mustard plant, has the potential to cause problems on farms in the Okanagan and Similkameen. (Photo submitted)

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