Reduce Drift Potential

Follow these recommendations to minimize drift into peanut fields.

By Peter Dotray, Todd Baughman, James Grichar,
Texas AgriLIFE Research and Extension Service

Soon, the spraying of postemergence herbicides to control weeds in production fields will be in full swing. The majority, if not all, of our peanut fields are in close proximity to either Roundup Ready cotton, corn or soybean fields as well as other crops, including small grains and horticultural crops.

Over the past few years, we have seen a number of peanut fields with damage due to Roundup (glyphosate) drift. Therefore, we thought that a list of things to consider to help minimize spray drift might be a timely reminder at this busy time of year.

1. Avoid spraying in windy conditions! High wind speed is the No. 1 cause of herbicide drift. When wind speed doubles, the horizontal distance spray droplets travel will also double.

Conversely, do not spray when winds are extremely calm because of potential herbicide movement due to temperature inversions (more information following).

2. Larger droplets reduce drift potential. The smaller the droplet, the longer the time it takes to travel from spray tips to the target (weeds or soil) and the farther it will drift. Larger and more uniform droplets reduce the potential for drift. The ideal droplet size is 400 to 800 microns.

Smaller droplets also evaporate faster, and herbicide efficacy will be reduced. Therefore, use a larger nozzle orifice size. Larger orifice nozzles with high delivery rates produce a thicker sheet of spray solution and larger droplets than nozzles with a small orifice size.

3. Increase the carrier volume. The driving force behind herbicide uptake into plant leaves is the concentration gradient. Increasing the carrier volume will decrease the water droplet concentration, minimizing the risk of drift damage.

Increasing the carrier volume may help improve the efficacy of some herbicides (e.g. Ignite), but decrease the activity of other herbicides (e.g. Roundup).

4. Decrease spray pressure. Increased spray pressure can cause the spray sheet to be thinner. This thinner sheet will break into smaller droplets than a thicker sheet produced at lower pressure.

5. Use drift reducing-type nozzles. Many nozzles on the market today that are designed to produce a higher percentage of large spray droplets and lower percentage of spray “fines.” Select nozzles that work best with your sprayer and production practice.

6. Consider using a drift retardant agent. There are several drift retardant products that can be added to spray mixtures to reduce the percentage of “fines” in herbicide applications.

Check labels and make sure that these products are compatible with the spray mixture. It is generally not recommended to use both reduction tips and retardant agents at the same time.

7. Lower your boom height. When the boom height is set too high, droplets must fall further, increasing the chances for drift. Setting the boom at the lowest possible height while maintaining proper spray overlap will reduce the risk from herbicide drift.

8. Spray during times of high humidity and low temperatures. Weather conditions can affect the potential for herbicide drift. The optimum conditions for low risk are higher humidity levels and lower temperatures. Droplet evaporation is most severe when conditions are hot and dry.

9. Avoid spraying during a temperature inversion. A temperature inversion occurs when a layer of warm air gets trapped between two layers of cooler air. Spray particles can get caught in the layer of warm air and move long distances.

10. Minimize potential of spray drift to come in contact with sensitive plants. Make applications when sensitive plants are not present, avoid applications near sensitive plants by using unsprayed buffer rows, and spray when the wind is moving away from sensitive plants. Use a shielded sprayer. Avoid aerial applications near sensitive areas.

Most herbicides will not volatilize (a conversion from the liquid state to a gaseous state), but all herbicides move by means of physical drift (the liquid state moving to non-target plants).

Be aware that over-the-top applications of Roundup in Roundup Ready crops have the potential to damage adjacent crops including peanut. Conversely, applications of Cadre, Pursuit, Cobra and 2,4-DB made to peanut can damage adjacent cotton fields.

Always carefully read and follow herbicide label instruction to maximize herbicide effectiveness and minimize herbicide movement to non-target plants.