April 19, 2002
10 Common Herbicide Mistakes
Avoiding these pitfalls can save time and money—and potentially even legal fees!
By Ellen Humphries
Each new growing season brings grass, crops and the time to treat for weeds and other undesirable plants. Whether you apply herbicide to individual plants with a backpack sprayer or to large areas with an aerial application, there are some common mistakes to avoid.
Dr. Allan McGinty, Extension Range Specialist, Texas Cooperative Service, San Angelo, came up with his Top 10 Common Herbicide Mistakes list during a long drive to give a talk on herbicide use. He has seen more than 10 mistakes but, "Over the years questions and calls I've gotten tended to fall into the same general areas." Most of McGinty's experience is as a range specialist, but many of the items on this list can apply to any herbicide user.
Starting at Number 10— Read the Label: "People hear all the time to read the label, but the problem is those labels are so long and difficult to read. The user may not know what he should look for." McGinty says first look for the DO NOTs on the label. "These will generally be in bold type and at the front. It might say something like Do Not Use Near Water, or Do Not Use Under Desirable Trees. The list is different for different products."
Second, although the label is long, look for the section which applies to your intended use. "A lot of these herbicides have multiple uses. The same herbicide might be used for forestry, non-cropland area, rangeland. Go to the section for your use," he says, to learn how to properly apply the herbicide. "This will keep the user from making a mistake that might hurt a desirable plant or themselves. However, most of the herbicides we use on rangeland have low toxicity to humans or animals."
Number 9— Broadcast Rate vs. Individual Plant Treatment Rate: "Broadcast rates and individual plant treatment rates are different," McGinty says. Broadcast treatments are applied by the use of a boom or boomless nozzle and the entire ground surface beneath the sprayer is sprayed. Broadcast application rates are expressed in pints, quarts or pounds of herbicide per acre. Individual plant treatment involves directing the spray mix at a specific plant by using a hand held spray wand. Individual plant treatment rates are expressed in terms of the concentration of the herbicide in the spray mix. "The instructions may call for a concentration of one-half percent Remedy. This means one-half gallon of Remedy in a 100-gallon spray mix. It simply requires an ability to calculate percentages to mix the right concentration."
To help determine correct quantities and percentages, McGinty and his colleague Dr. Darrell Ueckert included mixing tables in their Brush Busters literature. Brush Busters is a program developed eight years ago to educate new landowners about mesquite, huisache, Chinese tallowtree, saltcedar, juniper and prickly pear control. An additional Brush Busters pamphlet on treating yucca will be available soon. These materials are available from any County Extension Agent.
Number 8—Killed the Wrong Plant: McGinty calls this off-target damage, for example, killing an oak tree the user didn't mean to kill. This problem is very common when landowners are applying soil-applied herbicides. Different herbicides are applied in different ways. Some you spray on the leaves. Some you apply to the stems or cut stumps of plants. And some you apply to the soil under the target plant. These are called soil-applied herbicides and are usually formulated as small pellets or tablets. Rainfall is required to dissolve the herbicide and move it down into the soil profile, where it enters the plant through the roots with soil water.
"Many people understand how the wind can blow liquid leaf-applied herbicides on to non-target plants. But what gets people in trouble with soil-applied herbicides is underestimating how far plant roots extend from a desirable tree or shrub." As a general rule, McGinty says, assume the root zone to be three times the diameter of the maximum canopy of the plant. "If an oak tree is 20 feet across, stay at least 60 feet away if you are using soil-applied herbicides such as Spike or Velpar-L." When using this type of herbicide on a slope, remember they are water soluble and will move downhill with runoff and possibly kill desirable plants. "Allowing enough room from the roots of desirable plants and trees catches people," McGinty says. "That's caught me personally. I thought I knew the distance to stay away and still made a mistake which cost me several large, beautiful oak trees."
Number 7—Timing is Everything: There are certain times when herbicides are most effective on a particular plant. Most woody plants on rangelands, McGinty explains, sprout from the basal crown or roots if the top is damaged or killed. "If the herbicide is to be applied to the leaves, then we must have the plant move the herbicide down to the basal crown and roots for us. We need the carbohydrate stream to be going down to replenish the root reserves. That's when we apply the herbicide. Like a river carries a stick, the carbohydrate stream carries the herbicide." This downward movement of the carbohydrate stream happens at different times with different plants species. For example, "With mesquite we have a very specific time window in which to treat. That is 45 to 90 days after bud break. If we treat at the wrong time, we generally top kill the plant. It looks dead, but it comes back and is even harder to kill. So timing is very important."
Number 6—Use Surfactants: "The sixth common mistake or rule is a basic thing and it's simple and cheap," McGinty says. "Add a surfactant to the spray mix when using a leaf spray." Leaves are covered with wax which causes water-based herbicide mixes to bead and run off. With a surfactant, such as liquid dishwashing soap or a commercial surfactant, the surface tension of the water is destroyed and the spray mix flattens on the leaf. "Then we get maximum absorption of the herbicide through the stomata in the leaves and the leaf surface. So the addition of just a few cents worth of surfactant can be the difference between getting good results and bad results."
Number 5—Calibrate, Calibrate, Calibrate: For broadcast applications, learn how to calibrate the sprayer so you know how many gallons per acre the sprayer actually delivers. "Let's say the application rate is two quarts of herbicide per acre. If the sprayer delivers 10 gallons of liquid per acre, the user should add two quarts of herbicide for every 10 gallons of spray mix." McGinty says the Extension Service and Natural Resources Conservation Service (NRCS) can provide information on calibration. "It's not necessarily easy and it involves some math," he says, adding a reminder. "Once you calibrate a sprayer, it doesn't always stay the same. There will be wear of nozzles, so you have to recalibrate at least every season before you start spraying again." If the spray nozzles are changed, recalibrate again.
Number 4 - No Home Brews: "Landowners really need to stay away from `home-brewed' mixes," McGinty advises. "When herbicides are mixed with other herbicides, sometimes there is synergism," he says, "but sometimes the combination doesn't make the mix any more effective, and sometimes the chemicals can be antagonistic to each other and the user can get less effective results. These home brews can be very unpredictable."
They can also be illegal. McGinty explains the label on the herbicide concentrate is a legal document which outlines the proper uses of the chemical. "Texas Department of Agriculture (TDA) enforces the uses on the herbicide label. If the user is caught violating the label, TDA can file against the user and charge penalties, fines or even jail time. The user is legally bound to follow those labels." McGinty adds, "Sometimes we do mix herbicides together but those instances are based on research data which proves the mixes are safe and effective. Home brews can cause variable results and could potentially be against the label or dangerous."
Number 3—Diesel: Yes? No? How Much? There is some confusion about when diesel should or should not be added to the spray mix and how much should be added. This confusion arises because liquid herbicides can be applied two ways— to the leaves or to the stem. "When we spray the stem, we generally but not always, mix in diesel. When we spray the leaves, sometimes we add a little diesel, but not much. If we put too much diesel in a leaf spray, it becomes phytotoxic and burns the leaves off." Remember, in point Number 6, the leaves absorb the herbicide if a plant is leaf sprayed. If the leaves fall off because of too much diesel in the mix, then the plant is only top killed and comes back with a vengeance.
Never make the spray mix more than 20 percent diesel. In fact, McGinty advises staying around the 5 percent diesel level, or even better using surfactants instead of diesel for all individual plant leaf sprays.
Number 2—Hang Up The Phone: Amazing but true, there are herbicide telemarketers. "If you ever get a call from someone trying to sell you herbicide, there's only one thing to do," McGinty says. "Politely hang up. I know of no major companies I deal with in my area which sell herbicide over the phone. Most of the time when you get a call like that it's a con game. It might be legal, but they are trying to sell you a cheap mixture of a commonly available herbicide at an inflated price. If it sounds so good that you've got to try it, ask them to send you a label. Every time I've encountered a herbicide telemarketer, they will not send the label. But if you ever get their label, take it to the Extension, to TDA or to NRCS to look it over."
Number 1—Listening To Bad Advice: "The most common mistake I have encountered is landowners following advice from well-intentioned, but misinformed people on how to use herbicide." His first suggestion for sources of good advice are the folks who back up their information with research, those being the Extension Service and NRCS. Second on his list of good advisors are the sales representatives of the reputable companies. "They may recommend their product over another if the products are close in quality for a particular use, but they generally will not recommend their product for something where their product will not work. The reason is they want to protect the reputation of the company and don't want to deal with any complaints that their product doesn't work for its intended use."
McGinty recommends using care when considering the advice from retailers such as large home improvement centers or the feed store. "Those individuals working there like to be helpful, but generally they have no experience with herbicides and they really tell some wrong things. We spend a lot of our time trying to fix or correct advice received from retail outlets." McGinty reluctantly adds one other source of bad advice to his list— neighbors. "Neighbors are probably the worst source of information above even the general retail outlets. Some people don't understand that when a plant looks dead, it's not necessarily dead. Also, they don't understand the potential problems of misusing herbicide." For example, he remembers how a particular herbicide was effective killing prickly pear in West Texas, but was not labeled for this use on rangeland. One of the reasons it was not labeled was that it is toxic to livestock if they eat the sprayed plant. Because of local advice the herbicide was used anyway. It worked great—killed the prickly pear—but it also killed a considerable number of sheep which ate some of the pricklypear after spraying.
Avoiding these top 10 mistakes can help landowners be more effective, environmentally responsible and cost-efficient with their herbicide use. One last piece of advice from McGinty can help landowners from spending too much money. "Herbicide labels have three names on them. They have the chemical name (a long name most people will not understand), the common name, such as glyphosate, and the brand name, which for the example would be Round-Up™," McGinty says. If you know glyphosate is the active ingredient in the herbicide you wish to use, then you can breeze through the brand names and comparison shop the glyphosate products for the best price for your intended use.
Farming, ranching, pasture or yard maintenance, it doesn't matter—you can benefit from avoiding the pitfalls on this list of common, costly and potentially illegal mistakes.
