As we get further and further into post-emergence herbicide application season, there is an elevated risk for herbicide movement. The biggest concern is movement of growth regulator herbicides onto soybeans. Find out how to determine if your soybeans are at risk and what to do if they are.
Factors to Consider
Weed management has been a challenge for growers and 2018 is no exception. Many challenges exist from short planting windows to shorter pre and post emergence herbicide application windows to early soybean flowering. We are now approaching the end of growth stage cutoffs for herbicide application. This leads us to ask, can we expect any damage from herbicides?
The response is typically the age old cop-out, “It depends.” To be more specific and relieve some headaches, there are five factors that are important to consider in determining this answer.
- What growth stage was the soybean crop at?
- What geographical region are you in?
- Was the crop stressed before or after application?
- What rate, a.i., adjuvants, carriers, tank mix partner, etc are we dealing with?
- What soybean variety did you plant?
While these are not the only factors, they are a good step in getting your answer. Generally, as soybean approaches flowering risk for yield loss increases. However, this does vary by region.
Spraying Issues and Confusion
Many questions and issues circle around this process. Gaylon Morgan, Texas A&M Extension Cotton Specialist, spoke on the issues surrounding current damage.
Applicator confusion about spray buffers is a likely cause of the 2,4-D damage in Texas, Morgan said. “If there is susceptible crop downwind from your field, you cannot spray when the wind is blowing in that direction — there are no buffers that allow you to spray,” he said. “I think that is the single biggest misunderstanding out there.”
Furthermore, heavy rain in a lot of areas has caused many spraying issues for growers. They have had very short windows of time to get in the fields and spray. There really has been no good time to do so. However, Morgan warns keeping dicamba and 2,4-D in your field is more critical than ever as postemergence spraying picks up in Xtend soybeans and continues in Enlist cotton in the weeks ahead.
“With this technology, whether Enlist or Xtend, there is a learning curve with how to keep things on target,” he said. “Individuals who have done it are learning that you have to follow every single step on that label to keep it on target.”
If you suspect 2,4-D or dicamba injury in your field, what should you do?
Steps to Identify and Handle Herbicide Injury
Experts offer advice on how to identify and deal with injury in your fields.
First, know the symptoms. Soybeans are extremely sensitive to dicamba and cotton is extremely sensitive to 2,4-D.
For the most sensitive crops, it only takes tiny amounts of the herbicide to cause visible injury. For example, just 10 to 16 drops from an eyedropper of dicamba, dispersed over an acre, could cause visible injury symptoms on crops such as soybeans and grapes, according to research from the University of Georgia.
A young soybean plant with dicamba injury will have very distinct signs. Leaves will be cupped and curled. Later in reproductive stages, soybeans tend to show damage with curled or aborted pods, and dead flowers.
Cotton plants exposed to 2,4-D will show “strapping”. This is where the leaves become long and narrow, and the leaf veins run parallel to each other.
“It is in the new growth that the symptoms become very pronounced,” he explained. “How long the symptoms are observed depends on the rate of herbicide. If it is a very, very low rate, the symptoms may be present for a couple of nodes … then normal-shaped leaves begin to appear. If the rate is higher, the symptoms may continue to be observed season-long on the new growth.”
Next, identify the source and report it. Suspected cases of injury go unreported far too often. It is important to first identify the source where it came from and then report it. Don’t forget to include yourself in the list of culprits either. Common mistakes this time of year include tank contamination, applicators in the wrong field, and more.
If you suspect a neighbor, inform them immediately so they can correct the issue. Young soybean and cotton plants can outgrow early season herbicide injury without yield loss, a second drift incident can do much more serious damage.
Finally, document the problem. University of Tennessee Extension weed scientist, Larry Steckel, advised the following.
Take detailed, time-stamped pictures of the damaged crop and record everything you know about the incident, such as the weather conditions, location and acreage affected. Keep in mind that dicamba injury takes anywhere from seven to 21 days to show up; 2,4-D injury is usually visible in seven to 10 days.
Be sure to document injury over time as well. Morgan said, “Injury from low rates of 2,4-D will grow out in two weeks, but injury from higher rates, the ones more likely to cause yield loss, could last three to four weeks.”
You can take samples yourself and send them for chemical analysis. You can have a state investigator do it as well.
Essentially, the only way to determine economic loss is measuring yields at the end of the season.
Image courtesy of AgFax
In a related piece Ag Nook explored the reported dicamba injuries so far in 2018.