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Use residual herbicides properly for maximum effect

These considerations can impact how well your residual application controls weeds in your soybean field.

By Aaron Hager, University of Illinois

 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 7-10 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 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.

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

Herbicide

Maximum soybean growth stage for broadcast application

Anthem Maxx

Through the third trifoliate leaf stage

Dual Magnum/EverpreX

Do not apply within 90 days of harvest

Dual II Magnum

Through the third trifoliate leaf stage

FirstRate

Before soybean reach growth stage R2

Outlook

Fifth trifoliate

Prefix

Do not apply within 90 days of harvest

Sequencea

Do not apply within 90 days of harvest

Warrant/Warrant Ultra

Before soybean reach growth stage R2

Zidua

Third trifoliate stage

aApply postemergence only to glyphosate-resistant soybean varieties.

Originally posted by University of Illinois.

TAGS: Weeds Soybeans
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