Ask Mr. Smarty Plants

For various reasons I urge you not to use the herbicide Ornamec 170.

1. This herbicide, a formulation of the chemical fluazifop-P butyl, is very toxic.  Extensive precautions must be made in order to avoid getting the compound on your skin or breathing its vapors.

2.  Ornavic 170 is not readily biodegradable, and no food crop can be grown on land where it was used for a full year.  It should not be used on land near a stream or ditch because runoff following a rain would bring the herbicide into contact with sensitive animals, including humans.  (I presume that the field behind your house belongs to you.  If not, you  would have to get permission from the owner before using this herbicide.)

3.  Ornavic 170 has not been evaluated for a wide variety of plants.  It may not kill all the grass species that you  have, and it may kill some of the wildflowers you wish to preserve.

4.  I suspect that some undesirable broad-leaf plants are also smothering the wildflowers in your field. These would not be killed by Ornavic 170.

Your best bet would be to bite the bullet and pull the worst of the weeds from the site yourself by hand, hopefully with the help of friends or hired neighborhood kids.

If you choose to disregard my sound advice, Ornamec 170 and a similar herbicide, Grass-B-Gon, are available from Amazon.com.  I have also seen Grass-B-Gon in some of the big box stores and in nurseries in Austin.  Skip Richter, former Travis County horticulturist, suggests using a sponge soaked in the herbicide to brush against the undesirable plants rather than spraying all the plants, good and bad.  But it would take little more effort to just pull up the individual plant or hoe it down instead.