If there are clear tracks, they should be easy to identify.

DH put in 3 raised beds for me 3 years ago. This is our third year and only minimal Bermuda grass coming through. Here is what he did. 1. Scalp the ground with the weed wacker down to dirt. 2. Lay down two layers of 10 year black weed blocker paper (water permeable). The bottom layer north to south and top layer east to west -and- he extended the paper about 3 inches outside the wood box. 3. Fill the beds (all 4x4) with potting mix and peat moss and all the old growing medium from our EarthBoxes. 4. During the summer and fall he regularly weed-wacks all around the raised beds to keep down any weeds in the area. The Bermuda grass has only rarely grown up thru the 10 inches of 'dirt' and I have no mulch around my okra, beans and squash. I plant collard greens in these same beds in fall and they stay until spring - still very, very few weeds. I credit the scalping DH does with weed-wacker for keeping the weeds from growing wild around the beds. I credit the weed-block paper for keeping the weeds almost completely out of the beds. DL

A little more info is needed: How much sun do they get? All day? Only in the morning? Or only in the afternoon? How deep are they (front to back)? What kind of soil is in them? Native desert dirt? Potting soil? Sand? Kinda in between? It's hard to make suggestions without the specs. : )

Good advice in all the previous posts. I second that. If you get a soil test and find nothing major wrong with it in terms of nutrients, and the appearance/texture of the soil is basically the same, and nothing else in the conditions or location explains it, it may indeed be an herbicide problem. You could remove and replace soil, or build a compost bed on top for a year. Or even dig some if it out and make a layered lasagna bed with compostables. A high level of microbial activity should degrade just about anything. Soil test should include NPK (you can skip N if it is priced separately, it's changeable and easily corrected anyway); micronutrients (Ca, Mg, Fe etc.), pH, organic matter. Tell the lab it's for flowers/vegetables. Hopefully NH has an Ag Extension service that offers soil testing reasonably.