Non-Tolerant Seedling Study Guide

Non-tolerant Seedling Study Guide

This study guide contains descriptions of seedlings that are non-trait, that is, not tolerant to the herbicide in question.  The descriptions and images on the upper part of this page apply to seedlings from substrate imbibition tests or seed soak tests.  Seedlings from spray methods appear later.  Some of the images contain only non-tolerant seedlings, while other images are of both tolerant and non-tolerant seedlings. Click on the images to enlarge them.  Additional images will be added as they are available.  If you have additional images, please contact Mike Stahr  (   

Additional information may be found in publications such as the SCST Seed Technologist Training Manual, Chapter 14.  This  study guide is the work of the SCST Herbicide Bioassay Working Group.

Note: There are approved methods for conducting Clearfield® assays for winter wheat, canola, rice and sunflower.

  • Substrate Imbibition and Seed Soak Methods

Herbicide Trait

Seedling Type

Non-tolerant Description

Round up Ready®


Short, stiff primary root; shoot short and pale



Short primary root often “off-color”; primary leaves may be “crossed”
Canola– Stunted primary root.  Root is generally smooth with very little root hair, if any.  Short hypocotyls.  Hypocotyls and root have a thickened appearance.   

Liberty Link®


Short primary root;  necrotic mesocotyl (“halo” effect)



Short primary root, lesions
Canola- Short hypocotyls & primary root.  Generally, secondary roots are not present and there is little root hairs present.



Reduced primary root development



Reduced root development.


Dicot (soybean)

Roots unaffected; small, crossed primary leaves, reduced in size



Reduced root development;  lesions on hypocotyl


Crop Round Up Ready®  Liberty Link®


Others as marked
Corn  image002.gif  image004.jpg  image006.gif  NA
Soybean  image007.jpg    NA



Canola  image011.jpg  image013.jpg    NA
Cotton  image016.jpg  NA    
Rice        NA
Sunflower        NA
Wheat        NA
Sugar Beets        NA


Spray Methods

Round up Ready®
Corn:  Plants first appear stunted, twisted, and wilted, then turn reddish or brown with necrotic regions and die.
Soybeans:  Plants are severely stunted.  Stems and leaves turn reddish brown and necrotic.  Leaves curl under and the plant dies.

Soybeans:   Plants are stunted and pale green with dark red veination on underside of leaf.  Petioles also turn dark red.

Corn:  Water soaked, dark areas appear at leaf margins and tips, expanding to leaf base.  Plant is stunted, turns yellow, and dies.  
Note: if Liberty is applied (painted) onto a small portion of the leaf, only that portion of the leaf will die.  If sprayed to the point that Liberty runs off the leaf, or if sprayed over large areas of the plant, the plant will die.



Round up Ready® Soybean STS® Soybean  Round up Ready® Corn Liberty® Corn
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2017 Annual Meeting Seed Technology Journal