Q. I have a few gravel areas around my house and part of my driveway is gravel as well. Every year I need to apply some sort of vegetation killer to prevent the grass, dandelions, etc. from going crazy. I seem to remember reading in your column about some sort of organic herbicide that was a by-product of the wine making process. It lowered (?) the pH level of the soil so nothing would grow for quite some time. This sounds appealing to me and would appreciate any info you may have as to it’s use and availability. Thanks. Buck Nieraeth – Tacoma, WA
A. Back in 2001 a product called Blackberry & Brush Block came out. Acetic acid, which was one of the main ingredients, is a byproduct of the wine industry in the sense that all wine contains trace amounts of acetic acid, and it increases when the wine goes “bad” and become vinegar if not stored properly. Vinegar that we buy in the store is about 5% acetic acid. The initial claims of the Blackberry & Brush Block discussed the fact that it could be used to reduce the soil pH to 3. In theory a soil with a pH of 3 would be very inhospitable to many forms of life including plants. Researchers at WSU extension questioned this mode of action. They sited that the acidity of the product was not strong enough to achieve this pH (when using reasonable amounts) because of the inherent buffering capacity of most soils. I agreed with their analysis and stopped recommending this product for use in this “soil pH” mode of action. Acetic acid can also be used as a contact herbicide. Early research indicated good control of annual weeds and less consistent control of perennial weeds, which may need multiple applications. You may find that your current control methods are as good or possibly better than those you might get with acetic acid based herbicides. It all depends on the weeds you are trying to control. For example, dandelions would likely need multiple applications because of its storage taproot that will not be killed by the acetic acid based herbicide.