Annual and Perennial Broadleaf Weeds

bentazon (Basagran 5L and other trade names)

Rate 1 to 2 lb ai/a (1.5 to 3.2 pt/a Basagran 5L)

Time Apply postemergence to actively growing broadleaf weeds. For annual broadleaf weeds, apply when weeds are small.

Remarks Rate depends on target weed. Canada thistle should be at least 8 inches tall, western goldenrod less than 8 inches, salsify 4 to 8 inches, and common groundsel less than 3 inches tall at treatment. Make a second application 7 to 10 days later. Bentazon acts on contact, so thorough coverage is important. Use at least 20 gal/a water and at least 40 psi by ground. For aerial application, use at least 5 gal/a water and at least 40 psi. Add up to 1 quart/a of oil concentrate for ground application and 1 pint/a for aerial application. Unsatisfactory results can be expected if daytime temperatures do not reach at least 70°F in the week after application. Good soil moisture is essential for activity on weeds. May be tank mixed with bromoxynil, terbacil, or clopyralid to broaden broadleaf weed control spectrum. Preharvest interval is 20 days.

Caution Some mint leaves may burn under certain conditions. Do not apply during unseasonably cold weather or drought. Rain or overhead irrigation within 8 hours may nullify effectiveness of bentazon. Do not exceed 4 lb ai/a in one season. See various product labels for allowed tank mixes with other pesticides and fertilizers.

Site of action Group 6: photosystem II inhibitor

Chemical family Benzothiadiazole

clopyralid (Stinger and other trade names)

Rate Fall treatment (Sept. 15 - first frost): for annual weeds use 0.19 lb ae/a (0.5 pint/a product); for perennial weeds use 0.25 lb ae/a (0.66 pint/a product); for hard-to-kill perennial weeds use 0.375 lb ae/a (1 pint/a product). Spring treatment: annual weeds use 0.124 lb ae/a (0.33 pint/a product); perennial weeds use 0.19 lb ae/a (0.5 pint/a product). Max annual rate of 1 pint/a of product (fall + spring); if applying in both seasons, max fall rate is 0.66 pint/a and spring rate of 0.33 pint/a.

Time Treat small, actively growing annual weeds. For Canada thistle, apply after most basal leaves emerge but before bud stage. Fall application on winter annuals and perennials often is more effective than spring application. For difficult-to-control perennials such as Canada thistle and dandelion, a follow-up application in spring may be needed. Applying after the first fall frost usually results in reduced control.

Remarks A nonionic surfactant of at least 80% ai may be added at 1 pint/100 gal spray solution. Do not apply within 45 days of harvest. Clopyralid can cause stunting of mint growth and application to dormant mint or mint under 8 inches tall allows more time for mint to fully recover. Most weeds in the family Compositae or Asteraceae, such as mayweed (dog fennel), groundsel, dandelion, and salsify, and in the legume family, such as vetch, alfalfa and clover, are susceptible to clopyralid. Will not control broadleaf weeds such as mustards, henbit, chickweed, kochia, lambsquarters, pigweed, Russian thistle, and bindweed.

Caution Use treated mint for oil distillation only. Do not feed spent mint hay to livestock. Consult label for crop rotation restrictions. Mint straw, hay, or spent hay from treated areas cannot be used for composting or mulching on ground where susceptible crops may grow the next season.

Site of action Group 4: synthetic auxin

Chemical family Pyridine

glyphosate (many trade names)

Rate 1% to 2% solution

Time Apply to actively growing weeds.

Remarks Not all glyphosate formulations have mint on the label. Application rate and timing depend on target weeds. Apply as a spot treatment only, to no more than 10% of any acre. Can reapply in the same area at 30-day intervals.

Caution Any emerged crop sprayed will be killed. Avoid any drift outside spayed area, or those plants could be killed or injured. Allow at least 7 days between application and harvest.

Site of action Group 9: inhibits EPSP synthase

Chemical family None generally accepted.

glyphosate (many trade names)

Rate 33% solution (1 gal Roundup Ultra in 2 gal water) in rope or sponge wick applicators or a 33% to 100% glyphosate solution in porous-plastic applicators

Time Apply to actively growing weeds that are at least 6 inches taller than the mint.

Remarks Not all glyphosate formulations have this use on the label. Wiper applicator contact point with weed foliage should be at least 2 inches above crop. Weeds should be at least 6 inches taller than crop. Results improve by making two applications in opposite directions. Operate at no more than 5 mph. Do not apply to wet weeds.

Caution Contact with herbicide solution, whether by dripping from the applicator or inadvertently wiping the mint, will damage or kill the mint plants contacted. Allow at least 7 days between application and harvest. Sequential application may be made to the same area at 30-day intervals.

Site of action Group 9: inhibits EPSP synthase

Chemical family None generally accepted

MCPB (Thistrol Herbicide)

Rate Use 0.25 to 0.5 lb ae/a (1 to 2 pints/a product).

Time For field bindweed suppression, a single spring application works best. Field bindweed control improves as runners begin to exceed 6 to 8 inches. Apply in fall for susceptible winter annuals, and in spring for summer annuals when weeds are small and actively growing.

Remarks Do not apply within 40 days of harvest. Many broadleaf weed species will not be controlled at low rates labeled for use in mint.

Caution Mint may be discolored or twisted following MCPB application. Mint oil yields may be reduced if applications are made when the crop is 6 inches or taller. Do not use if minor mint injury is unacceptable. If tank mixing with other herbicides, test on small area prior to application to entire field to determine if mint injury is acceptable.

Site of action Group 4: synthetic auxin

Chemical family Phenoxy; phenoxyalkanoic acid