Bavaria,
Wild African Violets are pretty tricky to control, yet it can be done!
I am treating warm-season turfgrasses so the list I have to use is quite insufficient for your cooler climate turf. Here are some products to look up and do some research on. The State of N.Y. and its counties will have opposing restrictions on what you may purchase and use.
Manor or Blade (Metsulfuron)
Confront or Turflon
Triclopyr
Corsair
You will need to do some extensive reading of these chemical labels as to the use on your specific turfgrass species. The use of these chemicals may harm your turfgrass.
Usually violets require multiple applications of most chemicals to control effectively.
Weed-B-Gone is a good product for the small and actively growing tender broadleaf weeds like henbit, chickweed,etc. But these hard waxy coated flowering violets are harder to control..
Maybe someone in your location can lead you in the right direction on purchase, but maybe hiring someone with the experience will provide more control. I cannot tell you how to control these weeds in your state, all I can do is give you some different chemicals that we are suggested down south. You can do the research for your turfgrass selections, and then choose what is best..
Good Luck!
