Hi Frank,
   I feel your pain as I am also dealing with horse tail in one of my raised beds which was introduced when I added new mulch. Controlling horsetail requires diligence over many years. I am currently checking my bed 3 times a week, snipping off the plant tops and throwing them in the trash. Eventually this will starve the rhizomes. You can also manipulate your soil to make it less hospitable to the weed. 
Horsetail prefers acidic, wet soils.  Apply lime to raise the pH and use drip irrigation or other watering methods to prevent overly wet soil conditions. Adding Nitrogen can help your desired plants compete with the horsetail.
When ordering mulch or soil, carefully examine it for horsetail and other weeds.
Don't till the soil as this will just spread rhizomatous pieces and make matters worse. 
Few herbicides have any effect on field horsetail.   In non crop areas Casoron (dichlobenil) may be helpful for homeowner use. Apply in mid-winter as a pre-emergent. Be sure to read and follow the instructions on the label and use only where specified.
Here is a link to more information on horsetail. This is a relatively new website being developed by OSU and is still a work in progress, but the horsetail section is robust. https://solvepestproblems.oregonstate.edu/weeds/horsetail
Good luck and keep at it!