Hoary alyssum

Lifecycle: Can be an annual, winter annual, biennial, or a short-lived perennial and reproduces by seed. Hoary alyssum can spread rapidly due to the high number of seeds produced per plant.
Identification: Stems are grayish-green, hairy, one to three feet tall, with many branches near the top. Leaves are oblong, grayish-green and covered with rough hairs. Flowers are white with four deeply divided petals. Seed pods are hairy, oblong and appear to be swollen with a point on the end.
Distribution: Is commonly found throughout Minnesota, the upper Midwest, and Western States.
Habitat: Most abundant in disturbed sites but is also found in meadows and pastures and is a common weed in hay fields. It is particularly adapted to dry conditions on sandy or gravely soils. It prefers direct sunlight but can also tolerate shade.
Control: A healthy, dense stand of pasture forages can help prevent establishment or spread of hoary alyssum. Hand pulling or digging and mowing can be very effective for small infestations but should be done before flowering. There are several effective herbicides, but they may require more than one application and should be applied prior to flowering. If the weed is flowering mowing or hand pulling is recommended prior to seed production. When using a herbicide, be sure to carefully follow all grazing restrictions and other pertinent information stated on the herbicide label.
Toxin: Unknown.
When Toxic: Hoary alyssum is toxic when the fresh plant is grazed in pasture, or the dried plant is eaten in hay. Although, most horses prefer other, more palatable forages over hoary alyssum when on pasture, hoary alyssum toxicosis in pastured horses has occurred. Most hoary alyssum toxicosis occurs when horses ingest hoary alyssum infested hay.