Two-pass herbicide programs often refer to systems where a preemergence herbicide is applied near planting and is followed by a postemergence herbicide. In corn, the preemergence herbicide may target grass weeds or a mixture of grass and broadleaf weeds and the postemergence herbicide may be focused more on broadleaf weeds or perennial weeds. In soybean, it may be more beneficial to target broadleaf weeds with the preemergence herbicide because grass weeds are easily controlled postemergence with glyphosate. In general, the benefit of a two-pass program may be more frequent and of greater magnitude in corn than soybean, but two-pass programs in soybean still need to be considered.

Before asking if two-pass herbicide programs are viable, it’s more important to consider why two-pass programs are even needed. Reasons why two-pass programs fit in corn and soybean weed management systems include (1) improving controlling of problem weeds; (2) reducing the risk of yield loss from late postemergence applications; and (3) increasing herbicide diversity to reduce the risks of herbicide resistant weeds.