Personally I wouldn't spray any weed killer near an edible root crop, but that's just a personal opinion. Perhaps someone here knows of a safe product. In any case, it should be weeded as garlic & onions hate weeds.

You could cover the weeds with a heavy mulch to smother them, but that may be more work than hand weeding.

TomNJ

I think there is something that's selective, it's really expensive though, I'll let you know more at a later date when I have results, but it acts as both a pre-emergent and a post-emergent and selectively kills a multitude of weeds without bothering the real crops.

Another item similar is Poast, which kills various grass type weeds and not the crop.

horster, what is the exact length of your row? Have you the space, energy, materials to establish an allium bed or two? Since I converted most of my veg garden to raised beds, am able to raise intensively, mulch and weed easier amd produce more than ever. Currently, garlic is in a 5' wide bed (rows are 5' crosswise),a bit over 20' long. Most onions (3 bunches Dixondale) are in a 4' wide bed. These beds are 6-12" deep and happen to have recycled rough cut white oak sides, held in place by metal stakes. Corners are purposely not fitted and allow wonderful drainage. Slightly mounded soil mix is mainly top soil with straw, some old strawy chicken manure and buried kitchen scraps. Mulch after planting is weed free wheat straw. It is easy to reach between plants and rows with an old 1.5" blade hoe or even hand weed weekly. Pulled weeds are left to dry on top of the mulch. Any grass is pulled or dug out ASAP.

Bought some corn gluten pellets from the farm store and plan to sprinkle between the alliums to reduce germinating weed seeds. Have been practicing 'no till' in my beds and notice fewer weeds each year-despite the winds carrying seeds from adjacent properties.

The first year I planted alliums (on the 'flat') on this property, I mulched with 12" wide strips of cardboard, leaving a 6" space for allium growth. This reduced the space for non-food plant growth, and labor. Crop was very good-but more labor intensive to keep the cardboard in place.

Am an organic farmer, but do use weed killer at pastures' edges/fence rows for Poison Hemlock that is the bane of this area. Will use vinegar for weeds in the blueberry paths.

Onion sets, multiplying onions, shallots and garlic all have sufficient shoot power to punch through a couple inches of loose mulch (as opposed to cardboard and large leaves). A mix of lawn clippings and shredded leaves is perfect, just lay it on after planting and you won't have much trouble with weeds.

Onion and leek transplants will require a bit more hands-on mulching, but the transplants are generally about 6" tall, so they can be mulched as they are planted.

Allium from seed (and garlic from bulblets) are more problematic because they are easily smothered by mulch. This is part of why they are often transplanted mid-season from seed-beds to final beds.