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Management Alternatives

Herbicide1/

Hoary alyssum populations can be temporarily suppressed using 2, 4-D applied at label rates. Spring applications when plants are actively growing and prior to bolting will be most effective. Because hoary alyssum germinates and establishes throughout the growing season, repeated applications will be needed to target plants regenerating from the seed bank. Reports indicate metsulfuron applied at 0.5 ounce product (Escort®, Rainbowgreen Metsulfuron®, and others) per acre will control hoary alyssum, although hoary alyssum is not listed on the label. Other sulfonylurea herbicides including chlorsulfuron, and trisulfuron products as well as dicamba, and imazapic products may also be effective. Consult your Extension Agent for herbicide recommendations. Glyphosate will control hoary alyssum on seedbed preparation treatments. Studies are needed to develop herbicide recommendations for this weed.

1/Any mention of products in this publication does not constitute a recommendation by the NRCS. It is a violation of Federal law to use herbicides in a manner inconsistent with their labeling.

Hand Pulling

Hand pulling that removes the root crown is an effective method to temporarily reduce hoary alyssum on small-scale infestations and scattered plants that are either newly invading or persisting after herbicide treatments. Pulling or grubbing the root crown is most easily accomplished when the soil is moist and a shovel is used to pry-up the tap root. When the soil is dry, the plant tends to break off above the root crown enabling regeneration. Pulling should be repeated as plants regenerate from the seed bank or from remaining root crowns. Plants with seed pods should be burned if conditions permit or sealed in plastic bags and disposed of in the trash to prevent seed spread.

Mowing

Mowing will not control hoary alyssum and may increase infestations by cutting down a shading canopy and spreading seed pods. Regular, repeated mowing to a six-inch stubble height may reduce seed production when combined with irrigation and nutrient management to increase the vigor of desired plants. If the mowing equipment is subsequently used on weed-free areas, washing equipment after use will help prevent the spread of this weed.

Tilling

Shallow tilling that severs the tap root below the root crown will kill hoary alyssum plants. However, this type of disturbance will favor hoary alyssum regeneration from the seed bank. Multiple tilling or tilling followed by application of herbicide to target establishing seedlings can be used to exhaust the supply of viable seeds in the soil. Tilling is only recommended in cropland or in combination with seeding perennial competitive plants. As with any mechanical treatment, equipment should be washed after working in an infestation and before it is used on weed-free areas.

Irrigation

Hoary alyssum thrives under dry conditions. Irrigation can be used to increase the production of many forage plant species in cropland and pastures and increases their competitiveness with hoary alyssum. Good irrigation management combined with nutrient management of forage crops can prevent hoary alyssum invasion and help reduce infestations through plant competition.

Fertilization

Hoary alyssum thrives on sites with poor soil fertility. On cultivated pastures and hay meadows, nutrient management is important to maintaining the competitiveness of desired perennial grasses over hoary alyssum. Nutrient management combined with judicious use of herbicides and crop rotation is recommended where hoary alyssum invades non-native pastures and hay meadows.

Prescribed Burning

There is no information on prescribed fire effects on hoary alyssum. Fall burns may reduce seed production if seed pods are burned before seed release. Fire may create a disturbance favorable to hoary alyssum establishment and sites should be monitored for weed occurrence and follow-up weed control should be applied where weeds are found.

Grazing Management

Grazing animals have not been used to control hoary alyssum. Domestic and wild mammals consume hoary alyssum where it occurs in sufficient quantities, and poisoning has only been reported in horses. Lambs rejected hoary alyssum in a Minnesota forage field trial. Goat utilization of weed-free hay was greater than utilization of hay contaminated with hoary alyssum in a Wisconsin study. Studies specific to using these animals to manage hoary alyssum are needed. Cattle will utilize hoary alyssum in their forage areas but they generally select more digestible forages. Prescribed grazing to maintain the competitiveness of forage plants is important to prevent the spread of hoary alyssum in pastures and on rangeland, because the disturbance of overgrazing favors hoary alyssum establishment and reproduction.

Biological Control

There are no biological control insects available for management of hoary alyssum.

Revegetation

Sustainable suppression of hoary alyssum populations is more likely with desirable perennial plants that will compete for light, water, and nutrients. On disturbed sites and sites where the competitive vegetation has been lost, re-vegetation may be necessary to establish a competitive plant community. In forage crop fields, crop rotation is important for weed control and keeping the crop vigorous and competitive. For example, hoary alyssum increased in Wisconsin when five-year varieties of alfalfa replaced three-year varieties.

Species selected for revegetating disturbed sites and hoary alyssum infestations should be appropriate for management objectives, adapted to site conditions, and competitive with the weed. Management objectives will determine if non-native forage species or native species are seeded and species mixture components. The environmental conditions of the site, including precipitation, soil texture and depth, slope and aspect will affect species establishment. On native rangeland, a diversity of perennial grass and forb species that occupy many niches over time and space will most fully utilize available resources and compete effectively with hoary alyssum. Refer to Montana Plant Materials Technical Note 46, ‘Seeding Rates and Recommended Cultivars,’ and Extension Bulletin EB19 ‘Dryland Pasture Species for Montana and Wyoming’ for seeding rate guidance and revegetation species selection. State, area, and field resource specialists can help determine the most appropriate, site-specific species mix and timing of seeding for local conditions.

Integrated Pest Management (IPM)

Hoary alyssum thrives on disturbed ground with poor fertility and dry conditions. On hay ground, IPM practices include crop rotation, nutrient management, and irrigation management (where available) to maintain competitive shading forage plants. New infestations of hoary alyssum should be aggressively controlled using hand pulling and broadleaf herbicide. Based on data from Wisconsin alfalfa field trials, herbicide application was recommended as soon as possible after the last forage harvest in early fall. On pastures and rangeland, herbicide application should be combined with prescribed grazing. In farm yards, herbicide application and hand pulling should be used particularly where hay, tillage, and harvest equipment are stored. Equipment should be clean before taken to the field. Roadways, trails, and irrigation ditches should be maintained free of weeds.

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Last Modified: 11/18/2008