AMARILLO — With cotton production’s gradual move north into the Texas Panhandle, Dr. Brent Bean, agronomist with the Texas Agricultural Extension Service wants growers to take good care when this crop is planted near corn and sorghum.
Crop injury can occur whenever 2,4-D or dicamba are applied in neighboring fields, according to Bean. Both products, used for years, offer good economical control for a wide range of broadleaf weeds.
But cotton is extremely sensitive to these herbicides, especially 2,4-D. Severe injury can and does happen whenever it drifts in from other fields.
“This can lead to economic losses, and result in lawsuits and payment of damages between traditionally good neighbors,” he cautioned. While the potential for drift cannot be completely eliminated, it can be reduced by using proper equipment and spraying techniques.
Chemical drift, usually in two forms, volatilization (vapor) and physical can occur. Volatilization is associated with the phenoxy or 2,4-D type herbicides.
“When material ‘volatilizes’ it is changed from a liquid to a vapor (gas),” Bean said.
Wind currents have the capacity to carry the vapor long distances. Under the right conditions, cotton can sustain severe damage, even when grown several miles from the application site. The old ‘ester’ formulations of 2,4-D were particularly vulnerable to volatilization.
Today only 2,4-D amine and low-volatile ester products are sold. The amines are the least vulnerable to volatilization, followed by the ‘isooctyl’ and’butoxyethenol’ esters.
Producers do have many options to minimize the risk from volatilization. Use 2,4-D amine formulations or dicamba rather than the low volatile esters when cotton is within range.
The 2,4-D amines are only slightly more volatile than dicamba under normal conditions. When possible avoid application when temperatures are above 90 degrees.
Physical drift can occur with any herbicide, according to Bean.
“This is the most common type, and many variables impact drift,” he said. One study by researchers at the University of Mississippi showed that wind speed, boom height, and distance downwind to susceptible vegetation as having the greatest effect.
When wind speed doubles, the potential for downwind drift increases seven fold. Avoid herbicide applications when the wind speed is more than 10 miles per hour, the agronomist said.
Sprayer boom height plays a role; if doubled, the risk for drift increases 350 percent.
“Keep booms as close to the target as possible,” Bean said. Spacing 20 inches apart is the norm for standard flatfan nozzles.With this spacing when using 80-degree tips such as an 8003 nozzle, the boom should be placed 17 to 19 inches above the target.
For 110 series nozzle tips, the height needs to be set at 15 to 18 inches over the target. Thus, lowering the boom also reduces excessive drift.
Distance away or downwind from a spray zone is critical. Researchers involved in the Mississippi study saw a five-fold, or 80 percent reduction for drift when the distance downwind was doubled.
“Planting a buffer strip between a sprayed field and any susceptible vegetation is recommended,” he said. A safe zone, 200-300 feet across, is usually adequate, if used with other good drift control practices.
“Droplet size is important factor for control, the smaller it is, the greater the risk.” Bean said. Using a larger orifice size on the nozzle tip helps, for example; an 8004 tip emits fewer small droplets than the 8003.
“Increasing water volume is important,” the agronomist said, “for example 15 gallons per acre is better than 10 gallons.”
Use the lowest possible pressure setting within a nozzle’s ideal range. More pressure increases small droplet emissions. The type of nozzle and tip used governs the amount and size of liquid produced. The drift guard and new air induction tips were designed to lessen the amount of small droplets.
“Spray equipment dealers have good information on those that emit larger, more uniform droplets,” the agronomist said.
Finally, everyone from the grower to the herbicide applicator needs to know about a weather condition called thermal inversion.
“Never spray if an inversion is present,” Bean advised. The anomaly occurs anytime warm air is trapped between two colder layers. While difficult to identify, it is most common during early morning under cloudy, still conditions. Dew and fog close the ground are good indicators that one is present.
Another good indicator for an inversion — dust that lingers in the air, Bean said. This can cause drift to move several miles, and extra caution is warranted. Once the temperature starts warming and the air starts mixing, a thermal inversion will dissipate. Bean urged growers and applicators to be vigilant.
“If cotton is growing nearby, use as many drift control practices as possible. Keep in mind that 2,4-D or dicamba are contained in many herbicide premixes. Always check container labels,” the agronomist said.
County extension agents keep a list of the most common products containing these compounds. They can also make suggestions on herbicide alternatives.