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Barley Injury following Pursuit and Raptor (06/25/15)

Question: In this area of the state soil pH is 5.4-6.0 and organic matter is 3.2-3.5%. Some growers are planting barley on sunflower stalks treated the prior year with Beyond herbicide at 4 fl oz/A.

Barley Injury following Pursuit and Raptor

Question:  In this area of the state soil pH is 5.4-6.0 and organic matter is 3.2-3.5%. Some growers are planting barley on sunflower stalks treated the prior year with Beyond herbicide at 4 fl oz/A. We see injury early in barley with the yellow flash and we even see more injury on soybean land treated the previous year with Extreme at 1.75-2 pts/A or Pursuit at 1.5-1.75 fl oz/A. If Beyond was applied to sunflower in the 2 to 4-leaf sunflower stage at 2.5 fl oz/A instead of 4 fl oz/A, will there be less carryover and less barley injury the following year? What factors influence breakdown of Imi herbicides?

Answer:  This topic was partially covered earlier this year in Crop and Pest Report #1, May 7, 2015. Imi herbicides, in fact most all ALS herbicides do not show a significant rate response in activity. In other words, they can work as well at reduced rates as at full rates on susceptible weeds. Weeds with some tolerance will require full herbicide rates. Before the Roundup Ready crop era we did a significant amount of research with Accent and Steadfast (grass control in corn). These herbicides applied with effective adjuvants would control weeds whether used at reduced or at full rates. We also saw the same ‘no rate response’ from Pursuit and Raptor. Raptor at 2 fl oz/A + MSO produced the same weed control as Raptor at 4 fl oz/A + NIS. This is what we mean by very little rate response. For many susceptible weeds, the rate can be reduced and will still get equivalent weed control as the full rate ONLY if you use the most effective adjuvant = MSO at 1-1.5 pt/A, NOT 1% v/v! Research also shows that multiple applications of Pursuit and Raptor at low rates (1-2 fl oz/A) always gives better control than 1 application at the full rate. Remember though that reduced rates encourages herbicide resistance in weeds. That is why we recommend always using full label rates.

For breakdown and soil residues of Imi herbicide read paragraph Y2 on page 100 in the 2015 ND Weed Guide. Especially read #8 in that section: “Imi herbicides are strongly bound to organic matter at pH <6.5. Amount of Imi herbicide adsorbed to soil and organic matter changes little from 6.5 to 8. At soil pH <6.5, pH reduction as small as 0.2 pH units can DOUBLE the amount adsorbed. Large variation in pH can exist in the same field. In low pH, residues of Imi herbicides can injure sensitive plants for many years.” Imi herbicides are broken down by microbes and when Imi molecules are bound (adsorbed to soil) to soil particles at pH <6.5 then microbial degradation is slow. Soil pH and moisture are the two most important factors affecting microbial breakdown of Imi herbicides. Actually, I am surprised you do not see more barley injury with your low soil pH. As mentioned in that section (Y2) that the injury will be more pronounced on any soil with pH <6.5. Imi herbicides are so biologically active that even by cutting the rate I am not sure that will help to reduce your risk of barley injury. With the exception of increasing the soil pH, I am not sure there is good way to improve barley safety of barley planted the year after Raptor application.


Rich Zollinger

Extension Weed Specialist


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