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Use of HSMOC Adjuvants with Herbicides (06/25/15)

I have been getting many questions about the use HSMOC adjuvants. These questions show the confusion about use and function of this adjuvant type.

Use of HSMOC Adjuvants with Herbicides

I have been gettingwdsci.zollinger.1.oil adjv rates chart many questions about the use HSMOC adjuvants. These questions show the confusion about use and function of this adjuvant type. Below I have rephrased the questions and provided answers to help folks understand conditions for which they are intended.

Background information: Acronym HSMOC = high surfactant methylated oil concentrate – see page 126 in the 2015 weed guide for various brand names.

Question #1: I was reading section A5 on page 74 of the weed control guide concerning oil adjuvants. You say we should use PO at 1 to 2 pts/A with 2 pts/A being optimum rather than going by %v/v (as in 1% v/v) because of the various gal/A used by farmers. Does PO mean petroleum oil?

Answer:  Yes, PO is the abbreviation for petroleum oil. PO is used instead of crop oil concentrate (COC) because the oil is petroleum based not crop based as one might infer with COC. Also, we recommend oil adjuvants be applied on an area basis to ensure the minimum amount of oil adjuvant regardless of spray water volume used. See the chart accompanying this article for the penalty of using oil adjuvants at a % v/v rate in low gpa. When applying PO or MSO adjuvants at 1% v/v at 10 gpa (9.4 gpa) the amount of oil applied per acre is only 0.75 pt which is far less than the minimum amount needed to enhance and fully optimize post herbicides = 1 to 2 pt/A.

Question #2:  Is that 2 pt/A rate for both MSO and PO (COC) adjuvants?

Answer: The golden rule of 2 pt/A was established first for PO adjuvants. PO at 2 pt/A was the rate used for decades since atrazine was introduced in the 1950s. The 2 pt/A rate has been eroded down to 1% v/v for reasons I have not been able to determine. MSO - When Dr John Nalewaja and the NDSU Weed Science group invented MSO adjuvants in the early 90s the research showed that 1.5 pt/A was the optimum rate. This 1.5 pt/A rate was used with Accent, Steadfast, Raptor, Pursuit, and other herbicides. That 1.5 pt/A rate has also been eroded to 1% v/v. Growers using MSO with very active herbicides (Raptor, Flexstar, others) on less tolerant crops (dry beans) adjust the rate based on temp and humidity to minimize crop injury. For example, in warm temps and average humidity growers may use 1.5 pt but in hot temps and high humidity they may use 1 pt/A or less or 1% v/v or less.

Question #3:  Would that also mean 0.5 pts to 1 pt/ac when using the HSMOC adjuvant formulations?

Answer: This is where there is much confusion. A new adjuvant class has been invented called HSMOC (high surfactant methylated oil concentrate). The function of this adjuvant class is for use with tank-mixtures of glyphosate + lipophilic (oil loving) herbicides. Oil antagonizes glyphosate but HSMOC adjuvants enhance the oil loving herbicide without antagonizing glyphosate. Glyphosate is the most water soluble herbicide and is enhanced by surfactant. Oil loving herbicides (Raptor, Flexstar, 2,4-D, Banvel, Laudis, Sharpen, and almost all POST herbicides) are enhanced most by oil based adjuvants. These HSMOC adjuvants have at least 25-50% emulsifier rather than the 17% in PO or the 10% in MSO. This HSMOC adjuvant class invention was needed for these water + oil soluble herbicide mixtures but then everything got discombobulated when adjuvant companies charged twice as much per gallon as compared to PO or MSO and recommending cutting the rate in half of whatever the oil concentrate adjuvant they were using. For example, recommendations were to use 0.5 pt of HSMOC instead of 1 pt of MSO or to use 0.5% v/v of HSMOC rather than 1% v/v of MSO. NDSU research clearly shows that 0.5 pt and 0.5% are not sufficient to enhance the lipophilic herbicides. HSMOC adjuvant cost per acre is high which decreases the likelihood of growers using them at the rates which provide the greatest herbicide activity – a minimum of 1 pt/A. Thus creates a dilemma for you in your cost analysis.

Question #4: I typically have sprayed my pinto beans using an HSMOC at 0.5 pts/A. However, now I am thinking I should be using HSMOC anywhere from 0.5 to 1 pt/ac to be in your optimum range for oil adjuvants. I'm considering using 0.8 pts/ac this year. Will this be okay?

Answer:There is no need for you to use an HSMOC adjuvant or incur the high cost from an HSMOC with your dry bean herbicide program because glyphosate is not part of the tank-mixture. HSMOC are for glyphosate + lipophilic (oil loving) herbicide mixtures and you are not using glyphosate in your dry beans. You only need a reputable MSO and adjust the rate from 0.75 to 1.5 pt/A depending on herbicides mixtures you use, and the temperature, humidity and vigor of the dry bean crop.

Rich Zollinger

Extension Weed Specialist


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