Help building steam weed killer

I have a strange request. My goal is to build a weed killer using only steam and foam on our farm. I have the northstar 3000 psi 4gpm hot water pressure washer.

My plan is to use a water broom inside a hood roughly 30” wide to distribute and hold the heat. It will be run off the back of a tractor.

My main issue is I need to slow the water down to heat it more. I also don’t need this amount of pressure. I will remotely pull the wand trigger with a 12v actuator. It will run for about 4-5 minutes and then it will turn off while I turn the tractor around to go down the next row.

Water will be fairly cold right now 50-60*. Later on it could be 80-90* in the tank.

Can I just turn down the unloader valve or will I damage it too quickly? Is there a steam valve I could add to slow the flow down?

I will also use an organic “foam party” foam to hold the heat in longer. This process is used in other countries but my application is too specific for their pre built units.

You could always buy a steam jenny or an equivalent unit. The steam units aren’t just like PW, they have lower pressure and lower GPH. Maybe find one a small one used.

I use a propane torch for weeds. Works instantly.

Yes a torch works great. Unfortunately it won’t work for my application around existing grape vines. Too much bark, etc to also catch on fire. Plus we usually have a good amount of wind here.