I remember giving a noxious-weed presentation a few years back, during which I discussed many weed species, along with several methods and tools for controlling them. During the discussion, a gentleman raised his hand and stated that yellow starthistle didn't like water, and, in fact, he'd turned his once-infested pasture back into production with regular irrigation. I begged everyone's indulgence, and the gentleman's pardon, as I explained the myth behind his statement.
The field in question was a mixture of pasture grass, clovers and a moderate population of yellow starthistle. Having heard the myth from some passing snake-oil salesman, he heavily and regularly applied water. Over the course of a few years, the yellow starthistle diminished in density, and the grasses flourished. The logic, therefore, was that starthistle didn't like water. It all drowned!
Picture, if you will, a cross section of soil. Grasses are shallow-rooted plants, generally occupying the upper 6 to 12 inches of soil. Yellow starthistle is a tap-rooted annual, with roots extending many feet below the surface. When water was applied, the grasses intercepted the water first, depriving the starthistle of its much-needed drink. Receiving no water and being out-competed for nutrients, the starthistle died back while the grasses flourished. Voila! It's easy to see how the myth caught on, but now you know — sorry, Paul — the rest of the story.
Another myth involves the use of herbicides, and one, I admit, to which I subscribed many years ago. It went something like this: "If a little is good, a lot is better." Nothing could be further from the truth.
Herbicides, especially those that work systemically, require that they not do much damage until they've worked their way deep into the plant's roots. Keep in mind that the only way an herbicide will injure a plant is if the plant is actively growing. Therefore, spraying a plant that has senesced and died back for the season will be a waste of time and money. The cells through which the formulation must pass have dried and made further passage impossible. The same thing happens if you overload herbicide mixture with more active ingredient than needed or if you add other formulations (Never do this!).
You basically kill the initial cells upon contact, keeping the formulation from passing further into the plant's root system, and forestalling the desired result. You'll see what is referred to as "top kill," but the roots will still be viable, ready to sprout again and drive you further to the brink of insanity.
Read the label. The label is the law. Most herbicide formulations call for quite low concentrations for foliage applications. Mixtures using 2 to 3 percent are not uncommon, from which you should not deviate. This equates to roughly 2 ounces per gallon of water. Another reason to adhere to label recommendations is that injurious and unpredictable results can occur to neighboring plants if mixing recommendations are not followed.
Herbicides, when used correctly and responsibly, are wonderful tools. You'll get the desired results, the residue will generally dissipate in a short time and you can proceed to create the landscape of your dreams.
Jacksonville resident Bob Budesa oversaw the noxious-weed program with Medford District BLM and helped start the Jackson Coordinated Weed Management Area. Reach him at 541-326-2549 or firstname.lastname@example.org.