Fall is an excellent time to control invasive weeds with herbicides. Late summer and fall rains provide land managers with a good opportunity to extend their application season.
This varies depending on your target weed species, location, elevation, aspect and other climatic conditions. Generally, fall applications can be made once herbaceous plants have expanded overwintering rosettes or perennial plants initiate new basal growth. A light frost may have occurred. It is a good idea to wait for moisture to stimulate growth of rosettes or regrowth of herbaceous perennial plants.
Field trials conducted in Montana show that spotted and diffuse knapweed with can be controlled with Milestone® herbicide at 5 or 7 fl oz/A applied in fall. This application timing provided greater than 95 percent control of both established plants and seedlings for up to 2 years. Applications can be made until the soil freezes*.
Milestone® herbicide at 5 or 7 fluid ounces per acre (fl oz/A) is highly effective for controlling Russian knapweed. Applications of Milestone can be made on Russian knapweed until after the foliage has died back (leaves are brown and dead!) until the soil freezes or is covered with snow. Milestone will provide residual control of plants that try to re-grow and emerge after the initial application*.
Field research has shown herbicide applications can be made in the fall as long as there is live Canada thistle foliage. Even though Canada thistle leaves will begin to senesce, Milestone herbicide at 5 to 7 fl oz/A will provide good control up to late October as long as there is some green foliage*.
Fall herbicide applications may be applied to rosettes over a longer period in the fall than in the spring. An additional advantage is that fall treatments reduce the potential of injury from spray drift to foliage of nearby desirable plants since sensitive crops have been harvested or desirable plants are dormant. Fall application of Milestone® herbicide at 3 to 5 fl oz/A provides excellent control of biennial thistle (e.g., musk, bull, and plumeless thistle).
Fall is an excellent time to control blackberry. Opensight® herbicide at 3.3 ounces product/acre (oz/A)/A, or Milestone plus Garlon® 4 Ultra (5 fl oz/A+2 pt/A) provide optimal control of blackberry when applied after bloom and before frost. It is recommend that after mowing, shredding, or burning, applications should be delayed until the next season and enough re-growth has occurred for good uptake and translocation.
Basal bark applications with Garlon® 4 Ultra or Pathfinder® II can control undesirable or invasive brush species year round, extending your vegetation management program.
*Opensight® herbicide at 2.5 to 3.3 ounces of product per acre can be applied in fall if other weed species such as whitetop, poison hemlock, common tansy, or annual or biennial mustards are present.
Celestin Duncan contributed to this article.
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Milestone and Opensight herbicides are not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. When treating areas in and around roadside or utility rights-of-way that are or will be grazed, hayed or planted to forage, important label precautions apply regarding harvesting hay from treated sites, using manure from animals grazing on treated areas or rotating the treated area to sensitive crops. See the product label for details.
State restrictions on the sale and use of Garlon 4 Ultra, Milestone and Opensight herbicides apply. Consult the label before purchase or use for full details. Always read and follow label directions.©2021 Corteva
Published 9/2012; Reviewed and updated 6/2019
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