Re-vegetation

Sustainable suppression of diffuse knapweed populations is less likely without desirable perennial plants to compete for water, nutrients, and light. On disturbed sites, and sites where the competitive vegetation has been lost, re-vegetation may be necessary. Successful establishment of desirable vegetation can be improved by selecting a site-adapted seed mix, preparing a firm weed-free seedbed, controlling weeds, and seeding at a time that optimizes moisture availability to establishing seedlings.

Species selected for re-vegetating disturbed sites and diffuse knapweed infestations should be appropriate for management objectives, adapted to site conditions, and competitive with the weed. Management objectives will determine if 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 diffuse knapweed. 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 re-vegetation 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.

An ideal seedbed for re-vegetation is one that has pulverized soil on the surface with moderate amounts of mulch or plant residue, firm soil below seeding depth, and free of residual competitive plants. Although following this seed-bed preparation protocol may be practical on agricultural land, a no-till drill may be the best method to seed into diffuse knapweed infestations that have been suppressed on uncultivated rangeland. On sites inaccessible to machinery, broadcast seeding with little or no seedbed preparation is often the only option. Increasing seeding rate can increase the establishment of seeded species that are broadcast. Weed infested sites burned by wildfire have been successfully re-vegetated using aerial seeding. Refer to Montana Plant Materials Technical Note MT-58, ‘Seedbed Preparation and Seeding’ for more information.

In most cases, herbicidal suppression of diffuse knapweed is needed for re-vegetation of infested lands. The herbicides listed in Table 2 will control diffuse knapweed and reduce competition during the establishment period with little or no injury to emerging grass seedlings. Picloram provides the most persistent diffuse knapweed suppression of the herbicides listed in Table 2, and therefore provides the greatest window of competition-free establishment. This is especially important for species that are slow to establish, such as many of the native grasses. However, where herbicides have been applied, chemical carryover should be assessed prior to planting permanent vegetation, particularly if forbs, shrubs, or trees are included in the planting plan.

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Last Modified: 06/02/2008