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Brookings, SD – Agronomists are called out to fields to observe a portion of the field that is not on par with the rest of the field.  Plants may be lacking in vigor, color, or size due to various issues ranging from soil health to fertility to pesticides.  With knowledge of past seasons, the agronomist may have a couple of ideas, but actions as far back as 20 years could still be affecting the plants in that area.  With farmers taking on more acres, they may not know all of the history of that particular field as they would a field they have worked for the past 15 years. 

So where does the agronomist start? 

A pesticide spill many years earlier could cause a dead spot in the field.  The pesticide continues to linger as the residue degrades over time, but the amount of pesticide may be sufficient that removal of soil may be the solution. 

Residue degradation may have been slowed in the soil due to cool conditions causing a carryover pesticide situation in a field that is hampering a sensitive crop.  Environmental conditions will most likely correct this situation over time, but alternative crops may need to be used for the current cropping season.  Carryover is best assessed in a soil sample.

Pesticide drift is the most prevalent cause of injury to growing crops.  These injuries may or may not be visually evident.  In a glyphosate drift study in Canada (Acker, 1999), visual injury symptoms in canola did not predict yield loss whereas visual symptoms of wheat and flax could be used to predict yield loss due to pesticide drift.  

In most cases, injury of the plant is evident and the determination of what herbicide has caused the injury is the mystery to be determined.  Assessing crops located near the field as well as location in relation to the injured area leads to probable types of herbicide.  Finding out what has been sprayed in the area may be difficult, but different classes of compounds cause a variety of symptoms, which can be used to indicate a starting point for testing. Drift is best determined using leaf tissue samples.

SGS tests for pesticide residues in soil, plant material and water.  Screens for plant growth regulators, neutral herbicides, sulfonylureas and imidazoles, are available, as well as individual analysis for glyphosate, glufosinate, flumioxazin, aminopyralid and clethodim.  Other pesticide tests may be available, so please inquire. 

Rose Neal, Pesticide Residue Scientist at the Brookings, SD laboratory, has over 20 years of experience in residue analysis and can assist clients in determining a testing plan for individual situations.  Standard turnaround time is 5-10 days, although during the busiest season of July through September turnaround time may increase.

SGS is the world’s leading inspection, verification, testing and certification company. SGS is recognized as the global benchmark for quality and integrity. With more than 70,000 employees, SGS operates a network of over 1,350 offices and laboratories around the world.