USING SURFACTANTS IN WEED CONTROL
I've been talking a lot during the past two weekends about the early January weed invasion, and we recently did a tip sheet on that topic. One thing that was not discussed in detail, but probably should have been, is the use of Surfactants to help the herbicides do their job. First, let's get a bit technical and try to describe what a Surfactant is:
Definition: a linear molecule with a hydrophilic (attracted to water) head and a hydrophobic (repelled by water) end. Surfactants tend to clump together when in solution - forming a surface between the fluid and air with the hydrophobic tails in the air and the hydrophilic heads in the fluid. Often surfactants will form "bubbles" within the fluid - a small sphere of heads surrounding a pocket of air containing the tails. They can also form bubbles in air - two nested spheres of surfactant, between them a thin layer of water, surrounding a pocket of air - and anti-bubbles in fluid - a layer of air surrounding a pocket of water.
Or: A soluble compound that reduces the surface tension of liquids, or reduces interfacial tension between two liquids or a liquid and a solid.
That's obviously way more technical than your or I need to know about surfactants, but since I think they are so important in weed control in Texas, I thought it was worth starting with the basics. Almost every weekend on the GardenLine, I emphasize the point that when you're trying to kill weeds, you need to add a surfactant to the mix.
Whether its weeds, unwanted grass or brush, a surfactant is almost always essential in the herbicide mix, because most of the water here is considered "hard." And as such, hard water tends to just roll right off the leaf surfaces in question. Do the test yourself: Mix up a herbicide solution of a broadleaf weed killer and spray it on some clover or dollar weed or thistle right now. You'll see that in most cases the water beads up and rolls right off the leaf surface. Then, go back and add a surfactant, and you'll notice that there's a sheen on the leaf surface. Thus, the herbicide is actually sticking to the leaf and doing its intended duty.
There are two ways of going about adding a surfactant to most of the herbicides we use. The simple way is to add a bit of dish soap to the mix. The normal dosage is about a tablespoon per gallon of spray. By the way, to keep the suds level down when using over-the-counter soaps, first mix the rate or herbicide to half of the spray tool ( could be a trigger spray bottle or a pump-up sprayer) then add the dish soap, and fill the rest of the way by submerging the hose to below the water line.
Then, there's the professional grade surfactants like Hi Yield's Spreader Sticker or Bonide's Turbo, which won't cause any suds. However, they both will break up the surface tension so that the herbicide will again coat the leaf in question.
There is a caveat to all this; and it has to do with the Ready-To-Use/Ready-To-Spray bottles that hook on the end of the hose and mete out the herbicide dosage along with water coming through the hose. In these cases, you need to remove a small portion of the concentrate and add the surfactant in question. In this case, the dish soap usually causes an inordinate amount of bubbles - just be forewarned.
Until then, here's to great gardening from the GardenLine, heard exclusively weekend mornings 6 to 10 on Saturdays and 7 to 10 Sunday mornings on NewsRadio 740 KTRH.
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