Onions is a challenging crop in which to achieve good weed control. They are planted in high density configurations that preclude the effective use of cultivation. Cultural practices such as locating plantings in fields have low weed populations, as well as preirrigating up a flush of weeds followed by killing them with shallow cultivation can be effective in minimizing the population of weeds that emerge during the crop cycle. In general, excellent weed control for many of the common cool and warm season vegetables can be accomplished by a combination of the registered pre and post emergence herbicides. The weed control challenges in onions occurs with weeds that are not well controlled by currently registered herbicides. It is...

From the California Ag Today website on March 21, 2018
https://californiaagtoday.com/herbicide-limits-plantings-cilantro/

Caparol Label Change Sought To Reduce Plant-Back Restrictions Following Cilantro

By Patrick Cavanaugh, Editor, California Ag Today

Cilantro production is important in California and more growers are planting it. However,...

Spinach is susceptible to weed pressure because it is produced on high-density 80-inch wide beds with 18 to 42 seedlines. There is no opportunity to cultivate the bed top so all weed control is accomplished by managing weeds in prior rotations, cultural practices, chemical weed control or hand weeding. Clipped spinach is mechanically harvested and must be kept as weed free as possible to reduce hand weeding costs. In the recent UC publication, Sample costs to produce and harvest organic spinach (Tourte et al, 2015 http://coststudies.ucdavis.edu/current/ ) hand weeding costs averaged $440 per acre. However, weeding costs can easily exceed $1,000 per acre in weedy fields, and...

I've reposted (with permission) Stephen Flanagan's article from The IR-4 Project.  Check out the whole issue  "Volume 48 No.1 Winter 2017" for several interesting articles from a program that is incredibly important to pest management in specialty crop agriculture.