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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