After 20 years of trying to get rid of the Blue flowered wild Violets (Viola papilionacea?) in my lawn here in Middle Tennessee, I have finally found a way. Two years ago while doing another web search I stumbled on to some comments that seemed to have so validity.
The chemical to use is Triclopyr, triethylamine salt*. Sold currently as Ortho Weed-b-Gone, Chickweed, Clover & Oxalis Killer For Lawns. I have found that it is very common for companies to change formulas year to year, so check the ingredient.
The instructions recommend 2 tablespoon per gallon at 8%, but I have found that 3 tablespoons per gallon works much better on Violets. This is spot sprayed on with a hand pump sprayer. One application every 10 to 14 days during the Spring and Fall when the Violets are actively growing. Followup is very important. The very first application kills off less than 25% (at best), but the second application will have a 50% to 85% kill off. After an application it can take 2 to 4 weeks for the Violet to completely die off.
After the first year my front yard was 99.9+% Violet free. It will take a year since the seeds that are left behind keep germinating. After a year I find that when I see one, digging it out by hand works best. This is important since the seeds will cause big time multiplication.
- Triclopyr, triethylamine salt = 5.74% triclopyr acid equivalant (0.49 lb/gal)