Beck's Blog

From Our Family Farm to Yours

Agronomy Update

E. Indiana and Ohio: Giant Ragweed and Marestail, Brittle Snap of Corn and Yellow Soybeans

Published on Friday, July 4, 2014

Giant Ragweed and Marestail
With all the rain we have received in certain areas there have been several farmers who have not had the opportunity to apply their post emerge herbicides. Many fields have giant ragweed (picture left) and marestail (picture right) escapes. Let’s talk about options for each.



For glyphosate resistant giant ragweed in glyphosate tolerant soybeans there are still a few chemicals that can be used to control it including Firstrate®, Classic®, Cobra®, Flexstar®, and Reflex®. If the giant ragweed is cross-resistant to both glyphosate and ALS chemistry (which many fields are) then options become limited to Flexstar®, Reflex®, and Cobra®. Mark Loux wrote a good article in this week’s CORN Newsletter which I would suggest reading at

Glyphosate resistant marestail in glyphosate tolerant soybeans is even more difficult to control post-emerge. Depending if there is cross-resistance to ALS-type chemistry, Classic®, Synchrony®, and Firstrate® are all ALS-type chemistries that may or may not work on glyphosate resistant marestail. You really have no other options but to try to get control with a tank mix partner.

Using Liberty® on Liberty Link® soybeans offers the best and most consistent option for control of marestail and giant ragweed. In fact, Liberty® is the only post emerge option for control of marestail that is resistant to glyphosate and ALS chemistry.
Here are some general rules regarding spraying Liberty® or Roundup® herbicides:

--- Spray when weeds are actively growing. If the weeds are stressed then the chemicals will have a more difficult time controlling them.

--- Spray between the hours of 9 a.m.- 6 p.m. Spraying earlier or later than these times will often result in less than ideal weed control. Weeds do shut down at night.
--- Don’t forget the AMS. Weed control is enhanced when you use AMS.

--- Coverage is important for Liberty® since it is a contact herbicide. If your weeds are pushing the label size for control, be sure to use more water (>20 gallons) and the right nozzle size to get as thorough of coverage as possible.

--- If your soybeans are flowering when Liberty® or glyphosate tolerant herbicides are applied, you may abort some of the flowers at the node in which it is applied (according to the Liberty® label you need to apply before bloom).

--- Insects such as stalk borers and corn borers like giant ragweed and marestail and can reduce the efficacy of the herbicide. If the plant is not killed, don’t just automatically assume it is resistant. The pictures below show beans that were sprayed- one giant ragweed plant was killed and one plant was not. When the giant ragweed not killed was split open there was insect tunneling. The insect stopped the translocation of the herbicide, not that the weed itself was resistant to the herbicide.

--- Be sure to follow label directions!



Just a few escaped weeds can provide enough seeds for many years to come. Marestail plants can produce up to 200,000 seeds/plant, whereas giant ragweed can produce 5,500 seeds/plant when growing with soybeans. Therefore, it is important to get as good of control as possible – using both preplant and post emerge chemicals.

Brittle Snap of Corn
With the recent storms we have received there have been some heavy winds which caused some brittle snap of corn (also known as green snap). Brittle snap happens every year, but is usually more of an issue the further west you go. Here are a few known facts regarding brittle snap:

---Corn is most susceptible to brittle snap when it is actively growing and prior to flowering - usually from V12-tassel. It can happen earlier (V5-V8), but it is rare.

--- Unfortunately, anything that promotes fast growth will enhance brittle snap potential - higher nitrogen rates, higher plant populations (plants are competing with each other and growing taller), good fertility, higher organic matter soils, etc.

--- All genetics are susceptible, although some genetics are more tolerant than others. Growth stage of the plant coupled with the the time of the wind will determine how much damage happens and to which genetics.

--- Once a plant snaps, it will not recover. Yield loss will depend on the number of plants that snap, but it is not a direct correlation. In other words five percent snapped plants does not equal five percent yield loss. Plants beside the snapped plants will compensate somewhat by pollinating better and having greater kernel depth. Yield loss will be a little less than the number of snapped plants.

--- Growth regulator herbicides, especially applied late, make plants more susceptible to brittle snap.




Yellow Soybeans
There are many areas where soybeans are still yellow, the question is why. In most cases the soybeans are yellow due to a lack of nitrogen caused by a lack of nodulation. The lack of nodulation is caused by the continuous rain which is causing anaerobic conditions. I saw the same thing happen in 2013 when we received too much rain in June. Nodulation stopped and our soybeans turned yellow. The bacteria require oxygen to breathe and continuous saturated soils will cause nodules to die off. Once we start to dry out nodulation should resume.

I have heard a few reports that soybeans after soybeans look better and greener than soybeans after corn and this is due to C:N ratio. In other words the soybean residue is breaking down quicker than corn residue and releasing nitrogen (which is the same reason we take a nitrogen credit with corn after soybeans). Soybeans take the easiest form of nitrogen available, so it will take the nitrogen released from the soybean residue instead of trying to produce nodules.

There will be a difference between soybean genetics and yellowing. Some soybean varieties will handle “wet feet” better than other soybean varieties. Unfortunately, it is difficult to determine which varieties handle the wet feet early until you get wet years - like 2014.






Firstrate® herbicide is a registered trademark of The Dow Chemical Company or an affiliated company of Dow.

Classic® herbicide is a registered trademark of E.I. du Pont de Nemours and Company or its affiliates.

Cobra® herbicide is a registered trademark of Valent U.S.A Corporation.

Flexstar® herbicide is a registered trademark of Syngenta Group Company.

Reflex® is a registered trademark of Syngenta Group Company.

Synchrony® herbicide is a registered trademark of E.I du Pont de Nemours and Company or its affiliates.

Liberty® and LibertyLink® are registered trademarks of Bayer. Liberty is not registered in all states.



Comments (1)Number of views (46250)
Mark Apelt

Mark Apelt

Other posts by Mark Apelt
Contact author

1 comments on article "Agronomy Update"

Tim Holsinger

8/5/2014 10:30 PM

I would like your opinion on what is causing the yellowing and stunting of the Liberty Link beans after Liberty was applied. I applied 23 to 29 oz. depending upon weed size. The rate did not seem to matter and the problem did not occur in every field. From my observation it is occurring in my neighbor's fields regardless of the seed brand and regardless of whether Liberty was applied by a private applicator or custom. Thank you.

Leave a comment

Add comment