Late fall herbicide applications can be a good alternative to early spring for control of several introduced biennial forbs or broadleaf weeds in southeast Nebraska. A few of these biennial forbs are considered noxious weeds in Nebraska including musk thistle, plumeless thistle, and spotted knapweed while bull thistle, common mullein, and poison hemlock are just troublesome weeds in pasture. Some of the herbicides recommended for these weed species are restricted used pesticides that require private pesticide applicator training and license to buy and apply. However, there are some general use pesticides that can be used to control these noxious and troublesome weeds. Mechanical and cultural control options can be effective at low densities or to prevent future infestations.
There are two Extension publications that are helpful resources when it comes to plant identification and herbicide control options. The first publication is the Extension Circular 118: Common Forbs and Shrubs of Nebraska Rangeland, Prairie, and Pasture published in 2017 that helps identify common forbs. The publication provides key information about each species including a distribution map of the plant in Nebraska, when it flowers, how tall it gets, where it prefers to grow, uses and values, and other important information. The publication is free to download at extensionpubs.unl.edu as a pdf or a print copy can be ordered for $12.00 plus applicable tax and shipping. The second publication is the 2022 Extension Circular 130: Guide for Weed, Disease, and Insect Management in Nebraska. There are several sections that are useful including weed control in non-crop areas, noxious weeds, and troublesome weeds and woody plants. We still have some free copies available in the Saline, Jefferson, and Gage County Extension offices.
For musk, plumeless, and bull thistles, and spotted knapweed, a late fall treatment of a general use herbicide like Milestone or restricted use herbicides like Tordon 22K or Grazon P+D are effective. For common mullein, Cimarron Plus, Escort, or Overdrive are general use herbicide options or restricted-use Grazon P+D. For poison hemlock, 2,4-D ester plus dicamba is a general use herbicide option or restricted-use Grazon P+D. Additional herbicide options by weed species are provided in the 2022 Guide for Weed Management in Nebraska along with recommended rates, remarks, and approximate cost. An alternative to herbicides is a sharpened spade that can be used to cut the taproot below the rosette but can be impractical for large infestations. Well managed pastures that are fertilizer and not overgrazed along with monitoring can help reduce and slow infestations of these noxious and troublesome biennial forbs.
For inquiries about these and other agronomic resources from Nebraska Extension, contact me at or 402-821-1722. Know your crop, know your tech, know your bottom line at croptechcafe.org.
