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SW Iowa | IMO, it completely depends on the size of the rye in question. If it's big enough none of the residual is going to reach the soil directly I'd probably just kill the rye and let the rye residue hold back weeds for a bit, then run residual in your first post pass if it's early enough and/or you have rain in the forecast to activate.
My strong preference is not to let rye get that big--I'd much rather plant with the rye 6-12" above ground and then spray with residual a couple days behind the planter. At that point more of the rye growth is underground; I think that gives me the best mix of erosion control while minimizing nutrient tie up or otherwise effect growth/yield of soybeans.
I believe if you look around there are some studies on amount of rye biomass needed to provide weed control, and it's quite a bit. If you have consistent stand across the field it will definitely suppress weeds fairly effectively without residual herbicide, though... I've gotten into that situation a couple times due to untimely rains preventing termination and avoided disaster (just not my preference). | |
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Soybean premerge in standing cover crops
