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Conversion of Dry to Wet Metribuzin (05/21/15)

Question: I was wondering if you could help me clarify some questions that we have been getting from crop consultants and retailers lately. There is a trend of growers wanting to use liquid metribuzin instead of dry formulations due to ease of handling and sprayer cleanout issues. I have seen a lot of confusion in the field about what the conversion of dry formulations to the liquid equivalent is.

Conversion of Dry to Wet Metribuzin

Question: I was wondering if you could help me clarify some questions that we have been getting from crop consultants and retailers lately.  There is a trend of growers wanting to use liquid metribuzin instead of dry formulations due to ease of handling and sprayer cleanout issues.  I have seen a lot of confusion in the field about what the conversion of dry formulations to the liquid equivalent is. 

We contacted one of the technical service representatives for the manufactures of liquid metribuzin and were told to multiply the ounces of desired dry metribuzin by 1.58 to yield the ounces of liquid desired. Can you confirm that this conversion is accurate, it would help us let retailers and growers make an informed buying decision.

Answer: Thanks for sending. This would be an excellent problem for our undergraduates to use in their weed science courses. I think everyone is right if calculations are done correctly. It is most important to compare apples to apples and use active ingredient (ai) rates for both DF and 4L metribuzin formulations. 

                4 oz 75DF = 0.25 lb 75DF = 0.188 lb ai = 3 oz ai. 

                I was not aware the liquid formulations are 3.8 instead of 4 lb/gal. If so then:

                3 oz ai of a 3.8 lb ai/gal metribuzin = 6.32 fl oz Metribuzin 4L

                The conversion factor of 1.58 will work only when using oz of product not lbs. the calculation below is correct:

                4 oz 75DF x 1.58 = 6.32 DL 

In the weed guide we show metribuzin rates as lb 75DF/A. If incorrectly using 0.25 lb 75DF then the calculation will yield an incorrect number: 

                0.25 lb 75DF x 1.58 = ~0.4 fl oz 4L

Rich Zollinger

Extension Weed Specialist

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