Ask SAM: Organic herbicides enter the market

This column is provided by Larimer County Extension's Small Acreage Management (SAM) Program to assist rural residents.

Dear SAM,

Can vinegar be used to kill weeds?

Andrea P.

Dear Andrea,

The thought of using a salad dressing ingredient as an herbicide has a certain appeal.

Several acetic acid herbicides have entered the marketplace recently. These products have received special attention because some have been approved for use by organic farmers. Common household vinegar also contains acetic acid, but at a lower concentration. Acetic acid herbicides usually contain 10 to 20 percent acetic acid while vinegar contains about 5 percent acetic acid.

But do these herbicides work?

Acetic acid products are contact herbicides and work by burning plant tissues. Above ground plant parts can be severely damaged or destroyed, but roots are left unscathed.

Acetic acid herbicides are generally nonselective, meaning they damage all plants they come in contact with, though some plants may suffer more than others. Compare this to a selective herbicide such as 2,4-D, which kills broadleaf weeds without damaging grasses.

Single applications of acetic acid herbicides will not give good control of perennial weeds such as Canada thistle, bindweed or leafy spurge. These weeds have extensive root systems and will send up new shoots, seemingly before you even get back to the garage to put away your sprayer.

Control of perennial weeds with acetic acid requires multiple applications. As soon as the plant generates new growth, it must be sprayed again. This practice must continue until the plant expends its energy trying to produce new shoots and finally dies. With some weeds, this could take several years.

Because acetic acid is nonselective, most plants will be destroyed in the treated area. Thus, if you are successful in controlling your target weed you will also have killed most of your desirable plants and created a bare area. Most likely, weeds will invade this area creating a new problem.

Acetic acid herbicides might be best suited for areas where you want no vegetation. Walkways or edges of driveways can be kept bare with periodic applications.

If you have a garden, you could use an acetic acid herbicide to eliminate weed seedlings in the spring before planting your vegetables. This stale seedbed approach can be very effective at reducing weed problems later in the season.

Be very careful when handling acetic acid herbicides. The acids can cause severe skin irritation or eye damage. Even though they carry an organic label, these products can cause serious injury if not properly handled.

SAM

Have a question about rural living? Write to Ask SAM, Larimer County Cooperative Extension, P.O. Box 543, Fort Collins, CO 80522.