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Posted 15 May 2020. PMN Crop News.

Residual Soybean Herbicides Applied Postemergence

Source: University of Illinois Bulletin Article.

By Aaron Hager, University of Illinois Extension

Urbana, Illinois (May 7, 2020)--Soil-residual herbicides are important components of integrated weed management programs. Reducing the number of weeds exposed to foliar-applied herbicides helps reduce the selection intensity for weeds resistant to foliar-applied herbicides. Residual herbicides applied with postemergence soybean herbicides also can reduce the need for a second postemergence application. However, simply applying a soil-residual herbicide does not guarantee the product will provide the desired level or duration of weed control. Many edaphic and environmental factors influence the level of weed control achieved by soil-residual herbicides.


Soil-residual herbicides applied with postemergence herbicides require precipitation to move them into the soil solution where they are available for uptake. Herbicide effectiveness is reduced when a soil-residual herbicide is sprayed on a dry soil surface with no precipitation for several days following application. Residual herbicides generally require 0.5 to 1.0 inch of precipitation within 7 to10 days after application for optimal incorporation. Soil condition, soil moisture content, residue cover, and the chemical properties of the herbicide influence how much and how soon after application precipitation is needed for optimal activity.

Also, keep in mind the labels of soil-residual products that can be applied postemergence include a maximum soybean growth stage or time interval prior to harvest beyond which an application cannot be made. A sample of these growth stages and preharvest intervals is presented in Table 1. Many of the products included in Table 1 can be tankmixed with dicamba- or 2,4-D- containing products labeled for use in dicamba- or 2,4-D-resistant soybean varieties, but be sure to check the respective tankmix web pages prior to making the application.


Table 1. Maximum soybean growth stage for foliar application of soil-residual herbicides.


Aaron Hager