Problem with Marestail

I have a problem with Marestail on my allotment plot and I know it is quite difficult to get rid of.All I have been doing is either using the hoe or getting down on my hand's and knees and pulling up as much as I can.Have tried weedkiller but nothing touches it.Another plot holder uses something called I believe Kurtail which does kill it he brushes it on and have seen the results the plant just goes black after a couple of day's but not much use if the weed in in amongst plant's like pea's and bean's etc.Any advice appreciated.

 

It's got a waxy coating which sheds weedkiller, you need to bruise a few stems and bend them over into a pot of neat roundup. Cover it to keep the rain out and let the plant absorb it.