Identifying Herbicide Injury on Soybean Leaves

“ Focus on the solution, not on the problem.” -Jim Rohn

Here are some thoughts on identifying herbicide injuries on soybeans that was inspired by a recent Beck's Hybrids July Croptalk Newsletter article by Austin Scott on this topic. The link for it is included in the references at the bottom of this page. Probably every farmer has driven by a soybean field and seen the field that looked off. Maybe it was the color, the shape of the leaves, or the shape of the plant that triggers the question: "What was that field hit with?" With choices of more herbicide platforms than ever before for soybeans we can see symptoms of injury that can cause confusion on what caused the problem. Also, insects and disease in soybeans can have a direct or indirect effect on soybean leaf injury to throw another diagnostic curve ball at us. Identifying the source however; can be important as the outlook on the soybeans recovery, and its possible cure is different depending on which product/disease/insect caused the injury. In the auxin family, for example; 2,4D and Dicamba exhibit different symptoms. This year with late corn and many crops in all stages of development, more spraying applications will be later in the season than in a typical year. Below is a guide with pictures of the symptoms to help identify antagonism.

Symptoms of Auxins (2,4D & Dicamba)

Symptoms of 10% field rate, dicamba on the left and 2,4D on the right. Photo: Purdue University

Similarities: At field application rate both 2,4D and dicamba will cause a conditoin know as epinasty, or in my simpler language seen as leaf drooping and stem twisting. At these higher rates there are only two practical ways to identify which chemical it was. Using sprayer records or find a spot where the where the exposure was very light. When there are low rates due to drift or volatility then there becomes a difference in the looks of the plants injury.

Photos: Purdue University Extension

Differences: When exposure is much lower, typically caused from drift or volatility; the symptoms of the plants carry small yet distinctive clues of the chemical family causing the problem. The simple clue is the leaves. The 2,4D will cause leaf strapping to non tolerant soybeans, and dicamba causes the leaves to cup. This is probably the most distinctive. Other symptoms might be shortened plant height which relates to dicamba, but twisted, calloused stems of the plant signals 2,4D injury. Below is a comparison chart of symptoms.

Symptoms of Group 15

This 15 family of long chain fatty acid inhibitors like Dual, Warrant, or Zidua can cause crinkled leaves and a condition called drawstringing. Sometimes the crinkled leaves can cup a little having a similar appearance to dicamba injury while driving by on the road as seen in the picture on the left.

Crinkled and drawstring leaves, effects of S-Metolachlor, Photos: Wendell Koehn

Symptoms of Group 14

The 14 family has some products that are a pre app only like Authority based herbicides or Sharpen. Sometimes, even if Authority is pre applied the chemical can splash on the emerging plants causing hypocotyl burn.

Photo Credits: University of Illinois

Other PPO Inhibitors of the same family are labeled for post applications, but will burn the soybeans' leaves. These products would be Cobra, Ultra Blazer, or Flexstar to name a few popular herbicides.

Bronzing and speckling on soybean leaves due to (a) lactofen (Cobra®), and (b) acifluorfen (Ultra Blazer®) application. Photo Credit: University of Nebraska

Symptoms of Other products like AMS or Herbicide Flash

Photo Credit: Ebelhar, S. A.; Varsa, E. C.; Hart, C. D. Soil pH and manganese effects on yield of Roundup Ready® soybeans. Illinois Fert. Conf. Proc. 2006, 54−65.

AMS burn after Liberty application. Photo Credit: Wendell Koehn

A list of some diseases that can be might be mistaken for herbicide injury:

Septoria Brown Spot

Typically does not affect soybean productivity if it stays on the lower leaves early.

Leaf spots caused by the fungus Septoria glycines. Photo credit: Brian Hudelson, UW Plant Disease Clinic University of Wisconsin-Madison

Bean Pod Mottling Virus

This virus is mainly transmitted by the bean leaf beetle. Since it is a virus the solution lies not in a cure, but a preventative. Insecticide!

Foliar symptoms of bean pod mottle. Image: Allison Robertson

Frogeye Leaf Spot

A critical disease as soybeans enter pod stage.

Figure 1. Frogeye leaf spot will show up as mostly circular lesions in the upper half of the canopy. (Photo in Stanton County, Tamra Jackson-Ziems)

References:

CROPTALK: COMMON HERBICIDE SYMPTOMOLOGY ON SOYBEANS

https://www.beckshybrids.com/Blog/ArtMID/841/ArticleID/2236/Croptalk-Common-Herbicide-Symptomology-on-Soybeans

Purdue University

University of Illinois

University of Nebraska

Illinois Fertility Conference

University of Wisconsin-Madison

Crop Protection Network

University of Nebraska-Lincoln

Southern Rust is almost here in corn, spraying maybe vital for yield protection.

This short report is on crops and watch outs in the near and very near future.

Corn:

Southern Rust was reported about a day ago in Labette County, KS east of Coffeyville. This means this disease is approaching and will be here to Bates and Vernon Counties, MO very soon. If you have been holding off on spraying to see if it will be needed, you may want this done soon. Southern Rust is one the biggest enemies in corn. This disease can knock of 20+ bushels of yield even if infected late in the season. Consider using a multi stack fungicide that will last you through later in the season. Some products to consider are Trivapro or Delaro. There are other great products as well, these are just a couple to get started.

Gray Leaf Spot (GLS) is a soil born disease and the risk for infection are every year. This is a fungus that is varies widely based upon soils, conditions, and hybrids. Some hybrids resist the disease, others yield through it, and still others simply crumble under it. Know your products and act accordingly. This year has been very conducive so far for this problem.

Northern Corn Leaf Blight or NCLB typically it does not affect us, but there are some disease present this year. Contrary to its name it blows in from the south, so you may find it in the upper canopy first. I think it will not be active from now on with the heat we have, but it is worth noting its presence this year.

Holcus Spot is bad this year but is generally not an issue related to yield problems.

Foliar feeding: might be worth looking up some research here with Beck's PFR for a product to try on your farm. With all the rain we have had and potential for the plant to be low on certain nutrients this might be a good thing. You can click the following link: 2018 PFR Fungicide Additive Study

Root Worm beetle tries to hide in a corn leaf

Insects: Insecticide may not be necessary for corn that has pollinated and is brown silk or beyond, with the exception of trying to control root worm beetles. For continuous corn growers or fields with a history of problems continue with the chemical for these pests.

Soybeans:

Insects, disease, and nutrition: Jap beetles are feeding pretty good in some areas that I have seen. For April planted beans be watching for R3, it is rapidly approaching. R2 full bloom to R3 beginning pod can happen in about 10 days. R3 to R4 full pod is as fast or faster. For soybeans the R3 timeframe is the best ROI according to Beck's research. But, scouting fields and applying product if needed will be better than blindly following a plant growth stage alone. Generally, the longer you can wait to hold your fire on disease and insects the better chance of getting killing insects and holding off disease for the last days of soybean pod fill. Scouting is critical here in the R2-R4 timeframes. We have found on our farm applying VersaMax AC a foliar feed to be a benefit for soybeans as well. Bear in mind for soybeans that are quite young, they are in the stages of Bradyrhizobia japonicum penetrating the roots to establish N fixation. This can make the them look a little ugly for a bit.

Soybean field in SW Missouri

Hopefully, soybean planting will be wrapping up in the next week for everyone and we can put #plant19 into the history books. What a year, eh? Call/text me with any questions or pictures of your crop, I can talk via phone or walk a field with you. I believe things will move and change very rapidly on our crops over the next few weeks. Good Luck!