We have a property that was over grazed and the hoarhound has taken over. What chemical product will kill it?
You asked for a chemical to kill this and I have several on a link below. A less expensive and organic method that will not kill grass is listed below. I found this at http://www.gardenguides.com/68256-rid-horehound-weeds.html
Mark all of the areas where the horehound weed has been appearing in the summer. You can use spray paint or tiny flags to mark these locations. Keep these locations marked until December when you can use a solution to prevent the weeds from growing again in spring.
Wait until winter to try to kill the horehound weeds. Snow or cold temperature will not affect the solution to the soil, but don't spray the solution in below zero weather. Prepare the solution at the end of December or the beginning of January. This will assure that the solution is fresh and active to kill the weeds before they can start to grow.
Pour 1 gallon of cool water into a large bucket, and then add 12 oz. of white vinegar. Stir the mixture with a wooden spoon or paint stick. Add 2 oz. of orange essential oil and 1 tsp. of liquid dish detergent to the mixture and stir well.
Pour the mixture into a garden sprayer. Do not overfill the sprayer. If you don't have a garden sprayer, use a water bottle, but you will need to continually refill it.
Spray the solution all around the area where the horehound weed has been growing. Soak the area well and then dispose of any leftover solution. The orange essential oil and vinegar are the key ingredients that specifically kill horehound weeds. Also, this solution is safe for your soil and lawn. When spring comes, the grass will grow back without any sign of horehound weeds.
Chemical methods are found on this site. http://www.gardenguides.com/68256-rid-horehound-weeds.html Most of the other sites that I researched recommend waiting until fall to apply the chemical. Common chemicals that affect growth are 2,4-D which has many names; Diacamba aka Banvel, Clarity; Picloram + 2,4-D Aka Grazon P+D, Gunslinger; Triclopyr aka Garlon 3A, Garlon 4 Ultra. Another chemical that works differently by affecting the plants amino acids is Metsulfuron aka Escort. The link that I provided will give you more details, and visit your local garden center to see which products they recommend for your area.
Thank you for the opportunity to learn about the Hoarhound plant. I do not think I have seen it. It sounds like a major annoyance. Best wishes with controlling this pest.