. . . you asked me how I would respond if a landowner asked what herbicide they should use to treat a large kudzu patch on their property.
My answer to a landowner concerning a large (1-20 acre) kudzu patch would be that they should not treat the site themselves. They should turn to a professional applicator with experience in difficult kudzu treatments. As we all know, large kudzu patches can be dangerous places, with draped ravines, ditches, and uneven ground. It can be dangerous to traverse the interior of a large kudzu patch, especially in the heat of summer when heat exhaustion and heat stroke make the job even more problematic. In my experience, when most private landowners try to treat a large kudzu patch with backpack sprayers or other low volume methods, they are not able to treat the site in a consistent manner. In many instances, they will either not put out enough volume of water to fully cover the vegetation, or they will over apply the product on the edges of the patch.
Because "Do It Yourself" landowner treatments on kudzu can be difficult to implement, it is common that the landowner ends up spending time and money trying to do the work themselves, but ends up contracting with a professional after a couple years of poor results. Remember that a kudzu vine can grow 60 feet a year, so if a treatment method does not adequately cover the infested area, the kudzu will readily regrow into the treated areas, and the progress is lost. An herbicide strategy with a large kudzu patch can include 3-4 sequential years of treatment for the desired control.
As a private landowner myself, I have learned this lesson the hard way. One of our family properties in Clarendon County has a kudzu patch, and even though I know a lot about herbicides, my attempt to control the patch with my backpack sprayer has been futile. The only way for me to eradicate this patch is going to involve a professional kudzu applicator who has the appropriate equipment to get the job done.