No. 15 Article 3/July 15, 2011

Preharvest Intervals for Postemergence Soybean Herbicides

Across much of Illinois, "planned" postemergence herbicide applications in soybean already have been made. However, because performance in some cases--on waterhemp in particular--has been less than ideal, some fields will likely be resprayed in an attempt to control weeds that survived the initial postemergence herbicide and/or those that have emerged since.

An earlier article in the Bulletin ("Waterhemp Survival After Postemergence Herbicide Applications," issue 13, July 1) discussed potential causes for poor control of waterhemp after applications of glyphosate. We remind you here that retreating a glyphosate-resistant waterhemp population with glyphosate is unlikely to provide satisfactory control. Alternative herbicide active ingredients for control of glyphosate-resistant waterhemp in glyphosate-resistant soybean varieties include fomesafen, lactofen, and acifluorfen.

Be reminded that almost all postemergence soybean herbicide labels specify a preharvest interval or a soybean developmental stage (before soybean bloom, for example) beyond which applications cannot be made-and some products specify both. A preharvest interval is the amount of time that must elapse between herbicide application and crop harvest. Failure to observe the interval may result in herbicide residue levels in the crop in excess of established limits. Table 1 lists preharvest intervals and grazing restrictions for various postemergence soybean herbicides.

Table 1. Preharvest intervals and grazing restrictions for postemergence herbicides used in soybean.

Herbicide

Preharvest interval

Forage or grazing?

Aim EW

Broadcast: V10 soybean
Harvest aid: 3 days

No

Assure II/Targa

80 days

No

Basagran

30 days?

Yes, after 30 days

Cadet

60 days

No

Classic

60 days

No

Cobra or Phoenix

45 days

No

Extreme/Tackle

85 days

No

FirstRate

65 days

Yes, after 14 days

Flexstar/Rhythm

45 days

No

Flexstar GT

45 days

No

Fusilade DX

60 days

No information on label

Fusion

Prebloom

No

Ignite

70 days

No

Roundup PowerMaxa

Broadcast: through R2

Yes

Harvest aid: 14 days

Yes, after 14 days

Harmony SG/Unityb

60 days

Yes, after 7 days

Poast or Poast Plus

75 days

Hay

Prefix

90 days

No

Pursuit

85 days

No

Raptor

Prebloomc

No information on label

Resource

60 days

No

Scepter

90 days

No

Select or SelectMax

60 days

No

Sequence

90 days

No

Storm

50 days

No

Synchrony XP

60 days

No

Ultra Blazer

50 days

No

Warrant

R2

No

aData, taken from the Roundup PowerMax label, are for broadcast applications in glyphosate-resistant soybean varieties. Intervals change for applications (spot treatment and preharvest) made to nonglyphosate-resistant soybean varieties. Forage and grazing allowances can vary among glyphosate-containing products. Consult the respective glyphosate product label for specific forage and grazing restrictions.
bUnity does not allow treated areas to be grazed or fed as forage.
cThe Raptor label indicates there is no preharvest interval for any crop, but applications must be made before soybean bloom.

--Aaron Hager

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