No. 8 Article 5/May 27, 2011

Can Soil-Residual Soybean Herbicides Be Applied After Soybean Emergence?

Last week's edition of the Bulletin described which soil-residual corn herbicides can be applied after corn emergence. This week brings an analogous discussion of soil-residual soybean herbicides. Soybean planting has recently proceeded at a rapid pace, and it's altogether likely that fields were planted before soil-residual herbicides were applied. If a certain number of days have elapsed since planting or if soybean plants have begun to emerge, proceeding with the planned application depends on the herbicide.

Only a few herbicides that are most frequently applied before soybean planting or emergence can be applied after soybean plants have begun to emerge. Several soybean herbicide active ingredients can cause severe injury if applied directly to the soybean plant or close to emergence. Labels often restrict application timing relative to soybean planting (for example, within 3 days of planting) and/or to visible signs of soybean emergence. Keep in mind that, in general, the potential for soybean injury increases as the interval between application and planting decreases. Crop genetics and environmental factors, such as timing of precipitation in relation to herbicide application and soybean planting or emergence, also influence the potential for soybean injury.

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

Herbicide

Maximum soybean growth stage for broadcast application

Authority Assist, First, MTZ or XL

Before soybean emergence

Boundary

Before soybean emergence

Canopy or Canopy EX

Before soybean emergence

Command

Before soybean emergence

Dual Magnum, Dual II Magnum

Through third trifoliolate

Enlite

Before soybean emergence

Envive

Before soybean emergence

Extremea

Before soybean bloom

FirstRate

Before the 50% flowering stage of soybean

Gangster

Before soybean emergence

IntRRo

Before soybean emergence

Lorox or Linex

Before soybean emergence

OpTill

Before soybean emergence

Outlook

Through hird trifoliolate

Prowl H2O

Before soybean emergence

Prefix

Through third trifoliolate

Pursuit

Before soybean bloom

Python

Before soybean emergenceb

Scepter

90 days before harvest

Sequencea

Through third trifoliolate

Sharpen

Before soybean emergence

Sonic

Before soybean emergence

Treflan/Trifluralin

Before soybean emergence

Tricor

Before soybean emergence

Valor or Valor XLT

Before soybean emergence

Warrantc

Before R2 stage

aApply postemergence only to glyphosate-resistant soybean varieties.
bA supplemental label allows for postemergence aerial applications of 0.125 ounce/acre to soybean up to the fifth trifoliolate stage for control of prickly sida.
cMust be applied after soybean emergence.

Not all soil-residual soybean herbicides that can be applied after soybean emergence will control emerged weeds, so additional management procedures (such as adding a herbicide with postemergence activity) may be needed if weeds also have emerged. Table 1 summarizes information about postemergence applications of the more traditional soil-applied soybean herbicides. Please consult product labels for additional information, such as the need for tank-mix partners or spray additives to improve control of existing weeds.--Aaron Hager

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