Tips for Effective Herbicide Application
Many of you are about to get into a lot of post herbicide spraying. It pays to review some of the common misconceptions and mistakes that can reduce the effectiveness of your post herbicides.
Carrier volume and nozzle selection is a key part of success. When you’re busy and have a lot of acres to get over, it is easy to skip adjusting carrier volume or changing nozzles and that leads to many of the failures we see.
All of the post herbicides commonly used fall into one of two groups. They are either a “systemic” herbicide or a “contact” herbicide. These two types have very different requirements in application techniques to assure the best chance of success.
Systemics such as glyphosate, 2,4-D, dicamba, and others kill weeds by penetrating the leaf and moving through the plant to the point of attack. The key here is to effectively get a lethal dose through the leaf. With systemics, lower carrier volumes with a higher concentration of herbicide can be effective. The correct mix of additives/surfactants is critical. These systemic products can be effective through modern “drift reducing” nozzles and maximum penetration of the leaf can be more important than total coverage.
With glyphosate and some other systemics, the concentration of herbicide in the final spray solution can be more critical than coverage. Rates of 1 to 1.5 quarts of a 42% glyphosate in 10 gallons per acre (GPA) can be effective, especially in small crops with small weeds. As the weed size and crop canopy increase, additional carrier volume may be required for penetration and to get adequate herbicide amounts on the weeds. It is a good idea to increase your glyphosate rates by the same percentage as your carrier volume. If you go from 10 to 15 GPA on your water, take the same 50% increase in your glyphosate rate.
Remember to check the herbicide label for the details. The Roundup label recommends returning to old style flat fan nozzles with larger weeds and denser canopies. You will have to be more careful about drift. In reality, most off target drift events (with the obvious exception of dicamba) are a result of too much wind in the wrong direction. The “drift control” nozzles and “drift reducing” additives are not very effective in these situations, but they make you look like you’re trying to be responsible in the event of a problem. Using these products is a lot like wetting your pants in a dark suit. It gives you a nice warm feeling but you really didn’t fix anything. Read the wind and conditions as best as you can and use the combination of rates, nozzles, and carrier that will control your weeds effectively. Resprays double your risk of a drift event.
Reflex, Cobra, Liberty, and Basagran are common “contact” herbicides. These products do not move within the weeds so coverage is critical. DO NOT go below the minimum carrier volume on the label, and use more carrier with large weeds or denser canopies. When possible, use old school flat fan nozzles. The good news is when these herbicides drift off target they usually just speckle things and rarely kill them. Most of the drift control agents have very limited real benefits, so if you are just adding them for appearances, use a cheap generic.
Additives and Surfactants
When it comes to spray additives keep it simple, cheap, and use exactly what the herbicide label recommends and not what the additive labels say. Every supplier out there has their own “proprietary” herbicide additive that will cure whatever ails you for $3-$5 per acre. Most of these are a premix of $0.75/acre worth of common ingredients blended in a jug. Keep it simple. If the label calls for NIS, the 60 cents per acre standard NIS will work just fine. If it calls for crop oil concentrate or MSO, use that. The herbicide manufacturer puts the recommended additives on the label because they give the herbicide the best chance of success. Save your money and use what they call for.
If you have water quality issues, dry AMS or dry AMS dissolved in water is still the most consistent performer. Most Midwestern water only needs 8 lbs. of AMS per 100 gallons, but you can test your water to be sure. All you need to do is bind the metals in the hard water. It is not necessary to “acidify” or “condition” the water. Avoid the low analysis “water conditioners” or “acidifiers”. Add the AMS to the water first to give it time to bind the metals before you add the glyphosate. If possible, put the AMS in the supply or nurse tank. That will reduce the risk of plugging. When you add AMS to hard water you can form some metal sulfate sludge. This is the AMS doing its job, and it is better to form the sludge in the nurse tank instead of your sprayer.
When spraying post herbicides a little attention to detail can pay off in better results.