Crop Oil Concentrate is a petroleum based adjuvant while Methylated Seed Oil is vegetable or seed based. Both increase speed and volume herbicide adsorption by breaking down the cuticle (wax coating on leaf surface). MSO is more effective at breaking down the cuticle; this is advantageous in in arid conditions where weeds develop a thicker cuticle; and when weeds are herbicide tolerant or larger than the label recommends. Be advised, crop damage can result in high temperatures. MSO is also significantly more expensive than COC.

They are interchangeable in that they are compatible with and enhance the efficacy of most post emergent herbicides. Oils are antagonistic towards glyphosate; high surfacant oil concentrates were developed for use with glyphosate. As stated, MSO is more effective with nearly all herbicides, but you must decide if the higher cost and risk of crop injury is acceptable in your given situation.

Most post emergent labels recommend a rate of 1% v/v, so at 20 gpa, 1.6 pints/ac is the proper rate. Be sure to read the label as some will require at mimimum of 2 pints/ac. Generally, 1.25 pints/ac is the minimum; bear this in mind if you are applying at low volumes.