Liberty® and Hidden Group 2 Herbicide Residues: Why Clean Sprayers Can Still Damage Canola

By George A. Lewko, P.Ag. – Certificate in Forensic Agrology

One of the most frustrating crop damage investigations involves canola showing classic Group 2 (ALS inhibitor) herbicide injury, even though the sprayer operator insists that only Liberty® (glufosinate) was applied. The sprayer may have been rinsed, the herbicide records are accurate, and laboratory testing often finds nothing unusual.

So what happened?

In many cases, the answer is hidden herbicide residues inside the sprayer that were released by Liberty's surfactant package.

The Hidden Cause of Tank Contamination

Group 2 herbicides can remain inside a sprayer long after the original application. Small amounts may cling to:

• Tank walls
• Plumbing
• Filters and strainers
• Boom plumbing
• Boom end caps
• Areas coated with oily or waxy deposits from previous pesticide applications

These residues are often invisible and may survive ordinary water rinses.

When Liberty is added to the sprayer, its surfactant (adjuvant) package acts much like a powerful detergent. Rather than simply helping herbicide spread across plant leaves, it can also dissolve oily films and loosen herbicide residues that were previously trapped inside the sprayer.

Those tiny amounts of released Group 2 herbicide become mixed into the spray solution.

Because canola is extremely sensitive to Group 2 herbicides, even minute concentrations can produce obvious crop injury.

Why Laboratory Testing Often Doesn't Find the Problem

One of the challenges during a forensic investigation is that the amount of Group 2 herbicide responsible for crop injury is frequently below the detection limits of most laboratory herbicide analyses.

This means:

• Laboratory results may report "non-detect."
• The crop can still exhibit severe symptoms.
• Visual field observations become the most valuable evidence.

For this reason, proper documentation—including photographs, GPS locations, field history, sprayer records, and plant symptoms—is critical during any investigation.

Why Damage Often Appears in Later Tank Loads

Many operators report that the first load appears normal, while later loads produce injury.

This observation makes sense.

The cleaning action inside the sprayer takes time.

As Liberty circulates through the plumbing:

• residue slowly dissolves,
• agitation continues scrubbing the inside surfaces,
• herbicide trapped in filters and plumbing is released.

If the sprayer sits full while waiting for wind conditions—or especially overnight—the surfactants continue loosening residues.

Later loads may therefore contain higher concentrations of released Group 2 herbicide, increasing the likelihood of crop injury.

Recognizing Group 2 Injury in Liberty-Treated Canola

One of the easiest ways to separate Group 2 contamination from normal Liberty contact injury is to determine whether the symptoms are systemic or merely contact burn.

Liberty Contact Injury

Liberty only injures the tissue it directly contacts.

Typical symptoms include:

• tan leaf speckling,
• localized necrotic spots,
• injury limited to sprayed tissue,
• continued normal development of new growth.

Growing points generally remain healthy.

Group 2 Herbicide Injury

Group 2 herbicides move throughout the plant and attack the growing points.

Look for:

• bright yellow or pale green newest leaves (chlorosis) (growing points),
• purple or reddish leaves and stems from anthocyanin accumulation (growing points),
• stunted or bunched growing points,
• shortened internodes,
• delayed flowering,
• delayed crop maturity,
• bottle-necked, swollen, or clubbed roots,
• poor development of fine feeder roots.

One additional clue may be observed when contamination originates from the sprayer itself.

Tank contamination often produces white leaf speckling together with systemic Group 2 symptoms, while Group 2 herbicide carryover from previous years generally produces the systemic symptoms without the white speckling associated with Liberty contact injury.

Field Patterns That Suggest Sprayer Contamination

Field patterns often tell the story before laboratory results ever arrive.

Common indicators include:

The "V" Pattern

Damage is often most severe where spraying begins.

As contaminated solution is diluted during spraying, symptoms gradually become less severe, producing a characteristic V-shaped injury pattern into the field.

Boom-End Injury

The worst symptoms frequently occur beneath the outer boom sections.

Residues often accumulate in:

• boom end caps,
• plumbing dead ends,
• strainers,
• filters.

These locations may release concentrated herbicide early during spraying.

Preventing Future Problems

Proper sprayer cleanout is essential whenever changing to a sensitive crop.

Recommended practices include:

• Never assume a simple water rinse is sufficient.
• Use a quality tank cleaner designed to remove herbicide residues.
• Thoroughly clean the tank, plumbing, filters, screens, boom ends, and end caps.
• Remove and clean strainers separately.
• Avoid allowing spray mixtures to sit overnight or for long periods without agitation.
• Follow the sprayer manufacturer's cleanout procedures.

One product many applicators have had good success with is All Clear®, which combines detergents, a neutralizer, and foaming action to help remove residues from the entire spray system. The foaming action can be particularly useful because it increases contact with internal surfaces where residues often remain.

When Group 2 herbicides have previously been applied, cleaners containing ammonia are also commonly recommended because increasing the solution pH helps remove certain herbicide residues from sprayer components.

During a Forensic Investigation

When investigating suspected sprayer contamination, visual evidence is often more valuable than laboratory analysis.

A proper forensic investigation should include:

• detailed field history,
• complete spray records,
• product and tank-mix history,
• sprayer cleanout procedures,
• GPS-referenced photographs,
• field pattern mapping,
• plant symptom documentation,
• root examinations,
• independent laboratory testing where appropriate.

No single piece of evidence tells the entire story. Instead, investigators assemble multiple lines of evidence to determine the most probable cause of crop injury.

Final Thoughts

Sprayer contamination is one of the easiest crop damage problems to underestimate.

A sprayer can appear clean, pass a water rinse, and still contain enough hidden Group 2 herbicide residue to seriously injure canola. Because Liberty's surfactant system can release residues trapped deep within tanks and plumbing, damage may not occur until later tank loads and may not be detectable through standard laboratory testing.

Understanding how residues accumulate, how they are released, and how they appear in the field allows producers, agronomists, and investigators to distinguish between Liberty contact injury, Group 2 contamination, herbicide carryover, and other potential causes of crop damage.

For forensic investigations, careful observation remains one of the most powerful diagnostic tools available.