Be aware of herbicide injury
By KRISS NELSON
NASHUA – What types of herbicide injuries are there, and what should producers look for to make a proper diagnosis?
Those questions and others were answered by Meaghan Anderson, Iowa State University Extension field agronomist, who spoke during a crop scouting school earlier this spring.
If it appears crops are suffering from an injury, Anderson said it might not actually be from the herbicide that was applied.
“Injury on crops is not always going to be from herbicide,” she said. “Sometimes we actually have injury that is caused by other tank mix components within those products. There are surfactants that we might apply that can actually heat up a mix enough to cause in injury.”
Anderson gave the example; a surfactant, when used to apply a fungicide at the wrong time to corn, can cause injury to the ears.
There can also be interactions between different chemicals that could potentially cause injury.
“Paying attention to herbicide labels is important,” she said. “We can see interactions between things like herbicides and insecticides that might actually induce injury that we wouldn’t see if we used them separately. It’s very important when we are using products to at least know the dos and don’ts of using them.”
The environment can also be a cause for herbicide injury.
“We also have to think about the environment,” she said. “Sometimes we see injury, sometimes it was the chemical’s fault and sometimes it was not.”
If the crop is stressed, for example, some injury may occur, Anderson said that should not be blamed on the herbicide.
“When I get phone calls about herbicide injury or about any injury, it’s easy to jump to herbicides for being at fault,” she said. “A lot of people do that, because if it is the herbicide’s fault they usually end up getting paid for some of it; either a re-spray or, if there’s yield loss, the chemical company or whoever made the application may pay for that. It’s easy to jump to herbicide injury, but there are a lot of other things that cause injury to our crops.”
When she is asked to investigate any potential herbicide injury, Anderson said she will start by ruling out other causes for injury.
“Asking questions and gathering up information is really important,” she said. “This is a good tip for someone that is in the field of agronomy or crop science to know.”
Some of the questions Anderson recommends asking include finding out what has happened in that field historically. If there is a pattern, does that pattern fit a piece of equipment?
“Often, it’s not just a herbicide that caused some injury,” she said. “The herbicide caused the symptom on the plant, but the herbicide wouldn’t have caused the injury if the corn wasn’t planted only an inch into the soil. Or the herbicide did cause the injury but it was cold and wet when you used the product and the corn plant was probably exposed to a higher amount of that product when it was kind of just sitting there in the soil.”
There is some good news to a herbicide injury.
“When it comes to herbicide injury, it is pretty unusual for someone to spray a herbicide and get a high enough level to where it actually ends up killing the crop,” she said. “Oftentimes, the crop ends up being injured. It looks pretty ugly, there may be a yield loss, but usually the crop does recover. To some extent, at least.”
Read the labels
Anderson said the labels on the pesticides are incredibly useful.
“Every time I get a phone call about herbicide injury, I find out what was previously in the tank and what was used so I can do some background research by looking online and I can look up some information about those products and figure out exactly how they’re supposed to be used,” she said. “There is a lot of good information on these labels.”
Some examples of the importance to reading labels could be injuries that result in the settling of a product, soil types and the sizes of the crop.
Anderson said when it comes to identifying injury, the most important thing to know is how the herbicides work to begin with.
“Are they mode of action versus site of action?” she asked. “These two terms are often used interchangeably even though they mean two different things.”
ALS inhibitors, also known as “group 2 herbicides,” are the most diverse of any herbicide group that exists, according to Anderson.
“These are, by far, the most common thing that causes herbicide injury that I see,” she said. “Most common, by far, primarily in corn is when I see this type of injury because some of them are prone to carryover from a soybean crop into a corn crop. We can also see issues if we used an ALS inhibitor in soybeans and use another one next spring before we plant corn, we can actually see an accumulation of those where the one by itself wouldn’t have caused injury to the corn.”
Herbicide resistance is also a huge concern with this group.
While ALS inhibitor injuries in soybeans are uncommon, an easy way to tell if it’s impacting the crop is to find read leaf veins on the back of a soybean leaf.
For identifying ALS injury in corn, Anderson said there are two ways symptoms show up.
“One is when then plants turn totally purple and another is the plants are yellow, but the leaf vein – that midrib down the center – is purple,” she said. “This can look like a nutrient deficiency and that’s what is interesting about this herbicide in particular. You need that shovel with you. You have to dig up the plants and look at the root systems because yeah, it looks like a nutrient deficiency, but until you look below ground, you don’t know the whole reason it shows a nutrient deficiency because the whole root system isn’t working well for that plant.”
“Get closer,” Anderson added. “Can you see the roots don’t quite look right? No hairs or fineness of them. You see very few lateral roots coming off, I call them bottle brush roots. Those are the most typical symptoms we see from spring applications of these products in corn.”