Spring has arrived, and many ranchers' thoughts turn to killing weeds. Before you hook up the trusty (or in some cases, rusty) sprayer and give er a go, think about the following things:
Identify the weeds
Is your weed a cool-season or warm-season weed? If it is a cool-season weed and it's April or May, there's not much point in killing it with herbicides when hot weather will do the job for free in a month or so. Weed identification is also essential to know which type of herbicide to apply and when to apply it (covered in following sections).
Should I spray?
Before you hook up the sprayer, scout your pastures and decide whether you have enough weeds to justify spraying. If you had a lot of weeds last year, you'll probably have a lot again this year, unless you've lessened your grazing pressure or introduced an alternative management approach to decrease weed numbers. You should not try to achieve 100-percent control of all weeds in a pasture. It is seldom cost-effective.
Calibrate the sprayer
Possibly the number-one reason for control failures of herbicides is incorrect sprayer calibration. If your sprayer is not properly calibrated, you have no idea how much herbicide you're applying. Applying too much herbicide wastes money and applying too little gives poor control of weeds. Before you begin spraying, check to see how many gallons of liquid per acre the sprayer is delivering. Also, check each nozzle in the boom and make sure they're putting out the same amount.
Spray the right product
Many times I hear a comment like, "I've sprayed those grass burs with 2, 4-D every year for five years and I've still got them." There's a good reason for that grass burs (sandbur) are a grass, and 2, 4-D does not have good activity on grasses. The best way to kill sandbur with 2, 4-D is to set the container down on the plant and leave it there. Always read the label for the list of weeds controlled by a product before you spend money on it.
Spray at the right time
After poor sprayer calibration, the second biggest cause of herbicide failure I see is spraying at the wrong time. What is the wrong time? Let's look at some examples:
One example of spraying at the wrong time is spraying a leaf-absorbed herbicide before the weeds emerge, for instance, spraying 2, 4-D on ragweed on May 1. You've done it for years and it's worked. Then you have a year when it doesn't work. One possibility is that the spring was colder than normal and the ragweed is late emerging. Spraying them when they're not there is a poor way to use 2, 4-D. Be sure to scout to make sure the weeds are up before you spray in early spring unless you're using a product with residual control.
Another example of spraying at the wrong time involves the size of the plants you want to kill. Most weeds are easiest to kill when they are small. Almost all weeds are easier to kill when they're young and actively growing than if they're mature or drought stressed. One exception to this rule is Carolina horsenettle. It is easier to control when it has developed berries than when it is very young.
Does mowing work as well as herbicides?
No. We rarely recommend mowing pastures for weed control, and there are several reasons why. One, it costs as much or more to mow as it does to spray. Two, mowing cuts down the forage grasses you want the cattle to eat as much as it cuts down weeds. Three, almost all major weeds and brush will re-grow after mowing (cedar is an exception). Mowing makes the place look better for a while, but that's about it.
Make sure your herbicides get on your weeds on your property and nowhere else. Having your herbicides kill the neighbor's garden, flowers, trees, etc., is unlikely to make that person friendly toward you. Check the wind before you spray, and don't apply herbicides when the wind is too strong or is blowing in the direction of your neighbor's plants. Calibrate your sprayer for coarse droplets instead of fine sprays coming out of your nozzles. This can also reduce drift.
Follow the label
The label is the representation of a federal law. If you do something out of compliance with the label, it is a violation of federal law. On a softer note, the things written into the label are there to help you get the most out of a product. Pay attention to the safety information, it can save your health. Look at the list of weeds controlled, it can keep you from using the wrong product. Check to see if a surfactant or additive is needed it can make the material work much better.
This is not a comprehensive article on how to control weeds, but it is intended to make you think before you spray. Taking a little time to think before you spray can help you do a better and safer job.