Garlic Mustard is classified as an invasive species and I wouldn't be surprised if you or your neighbor have some growing in your garden. Rather than using harmful chemicals to manage or eradicate populations, eat it!
In early spring, the leaves are so small, sweet and tender that we can only recommend using them in a salad, whatever type of salad that may be.
Later in the season as the leaves become larger they can be used to make an amazing pesto.
The seeds can easily be collected and ground into breads, used to make a mellow and garlicky mustard, or added into soups for added thickness and depth of flavor.
Garlic Mustard will produce leaves almost year-round, it is always one of the first to emerge after the snow.
Fresh Spring growth
Tiny leaves in Winter
Nutrition Scientists have analysed Garlic Mustard leaves and produced a set of nutritional values which demonstrates the nutritional potency of this leafy plant.
It has been found to contain, per 100g:
5.38 g Fiber 150 mg Omega 3 fatty acids 12350 mcg B-Carotene 261 mg Vitamin C 200 mg Calcium 3.2 mg Iron 0.91 mg Zinc 0.13 mg Copper 0.99 mg Manganese 
To put that into context:
Collards contain around 3.6 grams of fiber per 100 g Navel Oranges contain about 59.6 g of vitamin C per 100g Milk contains roughly 119 mg Calcium per 100g Beef typically contains 2.6 mg Iron per 100g 
Dried out stems with seeds in summer
Early Spring growth
*Please note this species is on the DEC invasive species list so one must have a permit to handle, transport, or sell.