by William and Mary Weaver
“The horse is already out of the barn,” said Dr. Douglas Doohan, Herbicide Specialist at Ohio State University of the widespread use of 2,4-D and dicamba-resistant corn and soybeans. There is already a lot more 2,4-D being used in corn and soybean fields to burn down marestail and other weeds that have become resistant to glyphosate. Drift happens all the time, but herbicide drift damage is reported in only five to 10 percent of instances.
“One group of scientists reported that 2,4-D and dicamba are 75 to 100 percent more toxic to certain plants” such as grapes and tomatoes, than glyphosate, according to Dr. Doohan. New formulations and application technologies have been carefully worked out to reduce the likelihood of droplet drift, the most common type of drift. However, as more phytotoxic chemicals are used more frequently, the number of drift damage reports would be expected to rise.
“There are still a lot of things we don’t understand about atmospheric conditions that can result in drift, but what we do know can give us some measure of management,” explained Dr. Doohan. The factor among atmospheric conditions that is easiest for growers to overlook is atmospheric stability.
“It has taken me decades to come to this conclusion,” Dr. Doohan continued, “but I believe the absolute worst time to spray is early in the morning, around 5:30 a.m., when there is no wind. No wind in spring and summer and little cloud cover can create an inversion, where the surface of the ground is colder than the air above because of the irradiation that took place over night.
“With an inversion, small spray droplets that inevitably form don’t necessarily fall to the ground. Instead they can float, and can move farther than usual. This is a confusing concept. Generally, though, spraying at 5:30 a.m. with no cloud cover and no wind is not a good idea. Wait until you have at least three mph of wind.
“If you believe you see herbicide damage in a crop, time is of the essence,” continued Dr. Doohan. First, take plant tissue samples from leaves exposed to the drift and any new leaves and shoots that have since developed. “I’m not giving recipes—we don’t really know—but you probably have four to five days to get a sample with 2,4-D.” Scout regularly when grain farmers are spraying.
“A biochemist in my department told me that after seven days in hot weather (75 to 80 degrees), you can’t find 2-4 D in plant tissue, although I haven’t done the experimental work to know for sure that this is true. I know that within three to four hours after a foliar application of 2,4-D, I can see herbicide damage on newly developing leaves of treated plants. If drift occurred, and the amount of deposit was large, one might see the same time span.” Some herbicides cause damage very quickly.
If the damage is severe enough to end up in court, “Document, document, document,” said Dr. Doohan. Although this should not be construed as legal advice, here are some suggestions that could be sensibly followed. Ask a neighbor to witness you taking the sample and sign and date a statement saying he witnessed it. Make sure your camera is set to print the date on each photo of the damage. Take lots of photos of damaged and undamaged plants. Keep a record of custody of the samples. Notify the Department of Agriculture and your Extension Agent.
“Since prevailing winds are generally south/southwest, look for ‘footprints of damage’ between the suspected location of the drift and your vegetables. Wild grape, hickory and locust in hedgerows will be very quickly affected by 2,4-D.
“Perhaps, to establish potential ‘footprints of damage,’ you could grow potted cotton and/or tomato plants, which are very susceptible to drift damage from auxinic herbicides such as 2,4-D and dicamba, in your greenhouse and set them on the southwestern side of fields that could be in jeopardy from drift. I don’t know how practical that is, but it’s not practical to lose a crop from herbicide drift and have no idea where it came from.”
However, Dr. Doohan said, “Drift Happens. If someone sprays under less than ideal atmospheric conditions including weather, wind speed and even atmospheric stability, some drift will happen with even the best formulations and equipment,” and even extremely small amounts can have serious consequences. For this reason, even before the crop year begins, start working on the prevention of future problems.
“Your best prevention/defense is communication. Talk to your neighbors every year,” to ask about their cropping plans, and to explain what you will be growing in each field adjoining theirs. Explain the high costs involved and the high value of specialty crops you grow and the devastation that drift damage can bring to that small area. The alternative to regular communication could be spending a lot of money on lawyers and time in court.
Register the location of your sensitive crops on the appropriate websites. Driftwatch.org has been renamed fieldwatch.org . Commercial applicators pay attention to this website. They don’t want lawsuits.
“Keep in mind, though, that not all plant damage is herbicide drift, according to research we’ve done in the greenhouse. The damage you’re seeing could be from chemicals you yourself have used in your field and conditions, such as flooding that have magnified their effects.”
For example, you may have applied Sandea to your tomatoes, for which it is labeled. Sandea will injure tomato plants a little, mostly causing a little chlorosis. But if your tomatoes have been flooded for 24 hours, you can see Sandea’s effects on tomato plants all over the place. “If you have 48 hours of flooding, which we can get in Ohio on our heavier soils, the root system can be reduced by 40 percent compared to a plant that has not been flooded.”
You can get hormone-like symptoms similar to those caused by 2,4-D if Sandea is used, followed by flooding of the field for an extended period.
Or you may have sprayed Pursuit preplant on a soybean field adjacent to your own tomato field. Nobody would deliberately spray a tomato field with Pursuit, which is a toxic herbicide that makes 2,4-D look like ‘Mr. Nice Guy,’ but even if the amount of drift is very small, affected tomato plants can be half the size of normal.
It’s also possible that symptoms you’re seeing could be caused by a pathogen.
In your own defense, keep good records. “There’s an old adage, ‘If it isn’t written down, it didn’t happen.’ If an auditing agency comes to your farm, the first thing they will ask for are your records.” Know the typical symptoms of damage from the drift of the various herbicides. Also important—know what your crop plants normally look like at different stages of growth.
For more information, check out The Ohio State University Extension (OSUE) factsheet intended for vegetable and fruit growers, http://ohioline.osu.edu/factsheet/hyg-6105 .
Understanding and preventing drift damage from 2,4-D and dicamba
by William and Mary Weaver