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Assessing and documenting yield loss due to dicamba injury in soybean

by Jeff Gunsolus, Extension weed scientist

Photo 1. Leaf cupping symptoms of dicamba
injury in soybean. Photo Bruce Potter
As we enter August, the big unknown in fields presenting dicamba injury symptoms will be dicamba’s impact on soybean yield. Unfortunately, due to the sensitivity of non-Xtend soybeans to dicamba, injury symptoms are not reliable indicators of yield loss. The level of yield loss depends on exposure at vegetative or reproductive stage of growth, persistence of injury symptoms, and growing conditions post-exposure.

Relationship of injury symptomology to yield

Dicamba injury symptoms range from cupping and strapping of newly emerged leaves to height reduction and injury to growing points. Symptoms will reflect the level of exposure to dicamba. A publication written by Rodrigo Werle, Richard Proost and Chris Boerboom contains color photos of dicamba injury symptoms, mimics and assessment of yield loss:

Soybean injury from dicamba

Photo 2. Xtend soybeans (left) planted next to a
non-dicamba-tolerant soybean (right) that is
showing injury symptoms. Photo: Liz Stahl
Due to the challenges of associating dicamba injury symptoms to yield loss, the only equitable way that I can think of to assess impact of dicamba on yield is to determine the most accurate in-field assessment based on the criteria presented above and have all affected parties agree to accept the yield comparison results at harvest.

How much of the soybean injury is due to dicamba volatility?

The short answer is that I have no idea, at least at this time. The Proost and Boerboom publication addresses the three primary causes of dicamba injury to soybean: 1) Spray drift; 2) Contaminated spray; and 3) Dicamba vapor.

Currently, the greatest number of questions that I have received are about volatilization. This is likely due, in part, to the great efforts by the agrichemical industry to reduce the volatilization potential of the dicamba molecule and assurance that this route of injury had been addressed.

Data presented to the EPA has indicated a significant reduction in the volatility of dicamba; however, non-Xtend soybeans are extremely sensitive to dicamba and reduced volatility does not mean no volatility. Environment may have also played a role in enhancing volatility. Proost and Boerboom note that the potential for dicamba vapor movement is greatest under hot, dry conditions during and after application.

Documentation of dicamba injury to the Minnesota Department of Agriculture (MDA)

As I stated in my July 26, 2017 Crop News, in order to determine next steps for this technology, it is important to have good data regarding the conditions under which the off-target events occurred. This would include suspected particle drift, tank contamination and volatility.

Contacting the MDA to document this issue will help determine the scope of the problem. Reporting to the MDA provides the agency with valuable information that will aid in future discussions as the MDA engages with the dicamba registrants and inquiries about actions the registrants are taking to address these concerns. The MDA will also report their findings to the EPA.

Reporting to the Dicamba Damage Survey
does not equate to litigation. It is up to the caller to determine if they want to also pursue a field investigation and litigation/enforcement action.

News Release from the MDA regarding reporting dicamba injury:

The Minnesota Department of Agriculture (MDA) is concerned about the reports of damage from dicamba use. To assess the scope of the issue, the MDA is collecting information from various sources. Traditionally, drift complaints are caused by a pesticide not being used in compliance with the label. However, with the new formulations of dicamba that are approved for dicamba-tolerant soybean varieties, there are significant concerns about the incidence of dicamba injury to non-target crops when the label is being followed. If you suspect damage has been caused by the off-target (drift or volatilization) movement of dicamba, complete the Dicamba Damage Survey. This survey is meant to address the concerns that about half of the dicamba complainants have had, where they do not wish to initiate pesticide misuse complaint and the ensuing investigation.

If you believe dicamba was used in violation of the label or law, and you wish to request an MDA investigation, you will also need to complete the pesticide misuse complaint form or call the Pesticide Misuse Complaint line at 651-201-6333.

If you have already contacted the MDA, you do not need to report again. If you would like to report, please do so now rather than wait until harvest, because a lot of valuable information will be lost by that time.
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