I was going to suggest Crossbow. It's a mixture of 2,4-d and triclopyr. It's nasty stuff, but it kills like nothing else and harms the roots. It can kill 4 inch saplings through thin bark, but doesn't do much to grass.
It helps if you can cut down anything big and brushcut smaller stuff, then wait a couple weeks for new growth apicals to form before spraying. Once you spray the swath of death, wait until new shoots or seedlings emerge and spray again. It might take a third application, but not much survives the first two.
Thanks for the tip!
Have you tried cutting it back and blocking light to the stump? It worked with some vines on my property.
That can work if you have small enough areas. Be careful of erosion once you defoliate.
Check this out (pdf warning) https://nrcspad.sc.egov.usda.gov/distributionCenter/pdf.aspx?productID=109
Our extension office publishes this in nicer form with pictures. It should be required reading in high school. The USDA hired this guy to study why any area cultivated by humans turns to desert. Topsoil conservation is paramount to long term human survival.
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