Fall Canada Thistle Control Fall is the best time to control Canada thistle. Fall conditions are well suited for greater return on every herbicide dollar spent. Fall is the best time to treat fencelines and field borders where sensitive crops prevent spraying during the growing season. Fall spraying is more effective than spring. Fall extends the spray season and spread the work load. Fall applications have less haying/grazing restrictions. You probably have got the message. Fall is the best time to treat Canada thistle. FALL SETUP - For optimum results a fall setup plan should be implemented. Plan operations to yield maximum regrowth in the fall. Options should include: Mowing - Mow to prevent seeding. Mowing produces good regrowth. Mowing works well for roadsides, grazing land, and near trees. Cultivation - Excellent program for fall regrowth in fallow. Herbicides - Low rates of 2,4-D or Roundup in early season usually produces adequate regrowth. Contact herbicides like Gramoxone Extra or Cyclone are best, especially after harvest stubble programs. BEST RESULTS - New, active growth - Treating old, mature stems is less effective. High shoot density - A high density gives better results. Shoot number is more important than shoot height. Good soil moisture - Avoid drought stress - use tillage instead. Good moisture is important for effective Canada thistle control. Treatment time is important - Applications should be made on sunny days when temperatures are greater than 50 degrees. Treat before killing frost - A sunny day with temperatures of 60 F following the first "white" frost is a good target. Early to mid September is best for Canada thistle. If the leaves are wilted and blackened then the application should not be made. Control should be attempted the following year. Tillage - Blade or sweep cultivation 10 to 14 days after spraying improves results. Herbicide rate - Do not reduce rates. Use the higher rate for greater stand reduction instead of just top growth control. This especially important for no-till. Herbicides - Herbicides that are more effective on Canada thistle are Curtail, Stinger, 2,4-D, Banvel, Tordon and Roundup. Banvel - (2-4 pt/A) Good for fall patch spraying. Residue may limit crop selection for the following year. Banvel + 2,4-D - (1 pt + 1 qt) Lower Banvel rates. Less than 1 pt/A of Banvel only gives top growth suppression. Roundup - (2-3 qt) Good choice for patch spraying. No soil residual. Roundup + Banvel (1 qt + 1-2 pt) Allow reduced Banvel rates Tordon + 2,4-D (0.5-1 pt + 1 qt) Small grain rotation. Effective long term treatment used consistently. 2,4-D (1-2 qt) Economical but less stand reduction than other treatments. Curtail - Contains 2,4-D and Stinger. Gives good thistle control. Canada Thistle Control in Future University of Minnesota reseachers have isolated a bacteria (known as Pseudomonas syringea pv. tagetis) that kills Canada thistle plants. Symptoms are leaf distortion, dwarfing and yellowing, and bleaching of upper leaves, stems, and flowers. Heavy infected plants have been killed and mildly infected plants have been prevented from flowering or producing viable seed. The bacteria also is active on other weeds:common ragweed, giant ragweed, horseweed, jerusalem artichoke, and several other weed species. Other probable weeds like black nightshade, common lambsquarters, and redroot pigweed were unaffected. Infection was consistent under extrmer temperature and humidity. However, up to five applications were necessary to achieve adequate results.