Looks like a mustard - but its hard to tell which wild mustard it is. Wild Mustard is a brassica (like rapeseed). It is an annual, and is very intolerent to mowing once the flower blooms. You should mow your feild now before the seeds develop. Its not likely that you will have as many next year, or later this year. Its common in NY too, especially the first spring after plowing.
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good luck