4 TROUBLING STATEMENTS ABOUT DICAMBA DAMAGE

DATA IS LACKING WHEN IT COMES TO SUPPORTING THESE QUESTIONABLE STATEMENTS, SAYS AARON HAGER, UNIVERSITY OF ILLINOIS EXTENSION WEEDS SPECIALIST.

Gil Gullickson

(Successful Farming Staff) – Soybean injury from dicamba has occurred each year in Illinois since the product was first commercialized, writes Aaron Hager, University of Illinois (U of I) Extension weeds specialist, in this week’s issue of The Bulletin, a growing-season web newsletter from the U of I. (For the full column, go to http://bulletin.ipm.illinois.edu/?p=3942.)

“However, the response of some individuals from companies who market formulations approved for use in dicamba-resistant varieties has been unlike anything I’ve experienced during my 24-year tenure at the University of Illinois,” he writes. Some comments heard from the field, social media, and industry are, in my opinion, quite troubling.”

Reasons Hager writes in The Bulletin article include:

1. ONLY A NEGLIGIBLE PERCENTAGE OF SOYBEAN ACRES ARE AFFECTED.

I doubt anyone has completely accurate data on the actual number of soybean acres that have been impacted by dicamba. Even if those data support the aforementioned statement, I haven’t spoken with many farmers who consider themselves or their acres as “negligible.” Merely counting official reports filed with the Illinois Department of Agriculture does not accurately reflect the extent of acres impacted.

2. THOROUGHLY INVESTIGATE BEFORE DRAWING CONCLUSIONS.

This is excellent advice, especially when followed. Without question, there have been instances of symptom misidentification. However, it seems that other factors are repeatedly being mentioned as able to cause leaf cupping. Environmental conditions are frequently mentioned as inducing leaf cupping. Yet, I cannot find any peer-reviewed literature that specify or describe these conditions. If these conditions exist, one would speculate they could be replicated under controlled conditions to confirm their impact on symptom development. Also curious to me is that I have yet to see or have anyone report cupping of dicamba-resistant varieties. Are these varieties somehow immune to these environmental conditions?

3. THE INSTANCES OF VOLATILITY LIKELY ARE DUE TO APPLYING OLDER, NONAPPROVED FORMULATIONS.

Again, I ask, where are the data that indicate older formulations are being applied? If we should “thoroughly investigate before drawing conclusions,” it seems premature to me to conclude the instances of volatility are wholly attributable to older dicamba formulations. Much discussion has been made about the newer formulations that are purportedly lower volatility formulations.  (These include BASF’s Engenia, Dupont FeXapan Plus Vapor Grip Technology, and Monsanto’s Xtendimax with Vapor Grip Technology.) These statements will have to be taken at face value, as I am aware of only one university that has evaluated volatility of only one commercial formulation. Please keep in mind that low volatility is not the same as no volatility. The new formulations are still volatile, albeit less volatile than older formulations. Symptoms in many affected fields do NOT follow patterns associated with physical drift or contaminated application equipment, and exposure though volatility remains a very possible source of exposure.

4. IT IS UNLIKELY YIELD WILL BE REDUCED. YOU MIGHT EVEN SEE A YIELD INCREASE.

This is perhaps the most troubling statement I have heard. In my opinion, statements similar to these are unprofessional and unethical. These individuals do NOT have the necessary data to make such bold predictions, which include:

  • when the exposure occurred 
  • the dose of the exposure 
  • what the growing conditions will be like the remainder of the season 

When dicamba is applied in a state that grows soybean, the occurrence of off-target symptoms is not a question of if, but rather scale. Some suggest the solution is to plant all soybean acres to dicamba-resistant varieties. That might solve issues associated with soybeans, but it would likely increase the incidents of damage to other dicot species across the Illinois landscape.

POLLINATION STRESS IMPACTS YIELD

(Mycogen Seeds) – Pollination often takes place over a week’s time or longer, and corn plants are most vulnerable to pollination stressors during the two weeks of pollen shed. Extreme heat and drought stress lead the list of factors that hinder effective pollination.

This is especially true when daytime temperatures exceed 95 F with low relative humidity and plants are experiencing drought stress during the critical pollination period. The greater the number of days the plants experience the described conditions, the greater the potential yield impact. In addition, temperatures above 100 F can seriously hinder and even kill pollination.

Corn

Most weather-related pollinator stress is caused by hot temperatures combined with a lack of rainfall. However, damage resulting from hailstorms during the tasseling stage can be equally harmful, further reducing the pollen source.

“During pollen shed, without any cooling at night, farmers will see the most issues,” says Jason Welker, Mycogen commercial agronomist for western Nebraska. “Unfortunately, we can’t control Mother Nature, but understanding how conditions can impact pollination can help us to determine potential yield loss.”

While growers are powerless against the forces of Mother Nature, there are steps to take to mitigate the effects of both insect feeding damage and environmental conditions. For example, applying irrigation during drought stress can help.

Managing pest populations is one way corn growers can improve pollination potential. Feeding by corn rootworm beetles and Japanese beetles can damage cornsilks, potentially decreasing the silks available for pollination.

Drought or heat stress during pollination can also result in zipper ears, or ears with missing kernel rows. Ears affected by zippering have kernels that developed poorly or more slowly than other kernels or have ovules that aborted shortly after pollination. Also, scout for silk-feeding beetles during pollination, and treat when population thresholds are reached.

“Understanding how heat and other environmental factors impact yield can help growers plan,” Welker adds. “If you know you’re a in drought- or heat-stressed geography, consider lower populations, a full-flexed ear type and even a stress-tolerant hybrid.”

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