This weed is common in SW Montana and is often confused with whitetop. A member of the mustard family, Hoary Alyssum is one of the earliest weeds to appear in the spring, often beginning to flower as early as mid April. It reproduces from seeds only and can germinate and re-seed throughout the growing season. Plants flowering in May through June will germinate and produce seedlings that will mature and seed by early fall, so early treatment is recommended. Most seeds fall near the parent plant resulting in large patches of localized infestation. Contamination of forage of more than 30% hoary alyssum is toxic to horses causing laminitis, edema, diarrhea, and hypovolemic shock. Controls include herbicides and hand pulling. Mowing is effective if done frequently and kept to a six inch or less stubble. Infrequent mowing can increase infestations by spreading seed. There are no known biological control agents. It flourishes in poor, overgrazed, and dry soils. Generally, due to the seed bank and reproductive nature of the plant, it will require multiple treatments to eradicate.