Illinois Corn, Soybeans: Late-Season Herbicide Applications

Nearly all herbicide labels (soil-applied or postemergence) have rotational crop intervals that specify the amount of time that must elapse between herbicide application and planting a rotational crop.  This becomes particularly important with late-season herbicide applications.  These intervals are established to reduce the likelihood that herbicide residues will persist in sufficient quantities to adversely affect the rotational crop. 



Some herbicide rotational restrictions are based solely on time, while other factors, such as soil pH and the amount of precipitation received after herbicide application, can influence the length of the crop rotational intervals.

Soil moisture is often the most critical factor governing the efficacy and persistence of soil-residual herbicides.  Many herbicides are degraded in soil by the activity of soil microorganisms, and populations of these microorganisms can be greatly depressed when soil moisture is limited. 

Additionally, dry soils can enhance herbicide adsorption to soil colloids, thus rendering the herbicide unavailable for plant uptake and degradation by soil microbial populations.  Some herbicide rotational intervals are increased if a specified amount of precipitation is not received by a certain calendar date.

Please keep in mind that the labels of almost all postemergence soybean herbicides indicate a preharvest interval or a soybean developmental stage beyond which applications cannot be made.  Labels of some products may indicate both a developmental stage (before soybean bloom, for example) and a preharvest interval.  Preharvest intervals indicate the amount of time that must elapse between the herbicide application and crop harvest. 

Failure to observe the preharvest interval may result in herbicide residue levels in the harvested portion of the crop in excess of established limits.  Also, livestock grazing or foraging treated soybean is not allowed on the labels of many postemergence soybean herbicides.  Table 1 contains information regarding preharvest intervals and grazing restrictions for a number of postemergence soybean herbicides.

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

Herbicide Preharvest Interval Forage or Grazing
Assure II 80 days No
Basagran None listed on label Yes, after 30 days
Cadet 60 days No
Classic 60 days Yes, after 14 days
Cobra or Phoenix 45 days No
Engenia 45 days after planting or R1 Yes, after 7 days
Enlist One/Enlist Duo 30 days No
FirstRate 70 days Yes, after 25 days
Flexstar/Flexstar GT 45 days No
Fusilade DX 60 days No information on label
Fusion Prebloom No
Liberty/Interline/Cheetah 70 days No
Roundup PowerMax1

Broadcast: through R2

Harvest aid: 14 days

Yes

Yes, after 14 days

Harmony SG 60 days Yes, after 7 days
Marvel 60 days No
Poast or Poast Plus 75 days Hay
Prefix 90 days No
Pursuit 85 days No
Raptor Prebloom No information on label
Resource 60 days No
Select or SelectMax 60 days No
Sequence 90 days No
Storm 50 days No
Synchrony XP 60 days Yes, after 14 days
Tavium 90 days No
Ultra Blazer 50 days No
Warrant Before R2 No
Warrant Ultra 45 days No
XtendiMax/FeXapan 45 days after planting or R1 Yes

1Data, 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 information on forage and grazing restrictions.

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