The Imtrader Ed.3 – Alkyl Glycols in Suspension Concentrates & Crop Burn

 

Written by Neil McPhee (MBA MOHS BAppSc BSc.) – General Manager, Imtrade Australia

We regularly hear anecdotal evidence that crop burn may result from the over-the-top use of suspension concentrate pesticide formats, where other products of the same active ingredient, such as in water dispersible granular format, are without issue. These detrimental effects seem to have some basis in the inclusion of alkyl glycols as formulation ingredients in suspension concentrates.

Typically present as either ethylene glycol or propylene glycol, alkyl glycols are employed in suspension concentrates to act as humectants and as a means of depressing the freezing point in associated formulations. As such, they preserve the moisture content of formulations counteracting any evaporation of water content and thereby preventing surface skinning and flaking of suspension concentrate products. They also reduce the possibility of freezing of suspension concentrates and subsequent physical/structural destruction of this formulation type (which, after such an event, would result in separation/stratification into layers as the product falls apart). As such they are key components of suspension concentrates and not easily removed or substituted if such a formulation is to maintain its integrity.

The benefit that alkyl glycols impart to suspension concentrates comes with a downside however. Where conditions and product recipe specifics collectively conspire they may result in significant crop damage and ultimately decreased efficacy of the associated pesticide active ingredient and/or lower crop yields.

Suspension concentrate fungicides are at particular risk of eliciting alkyl glycol induced crop burn where applied post-emergent. These are highly likely to be present in the suspension concentrate form, are often applied to targets either under stress, or likely to come under stress through fungicidal pathogens and are often applied multiple times over a season. Consequently, exposure of the biota is often significant in terms of extent and frequency.

Adverse results from alkyl glycol excipients in pesticide formulations are not universally experienced. Nevertheless, when collective detrimental conditions combine (e.g. moisture stress, climate conditions, timing, recurrence of applications, high pathogen concentrations, high pesticide application rates per units area and/or per unit spray solution), alkyl glycol may elicit more than just superficial damage to crops.

Below are photographs of alkyl glycol application in water with wetting agent to grass and broadleaf weeds.

 

Alkyl glycol treatment of grass + broadleaf weed at 7 days

Plots (Front to Back): Propylene glycol, Untreated, Ethylene glycol.

The treatment application was made at 60mg of alkyl glycol in 200mL of water with 1%w/w non-ionic wetter added.

Assessment and photographs taken 7 days post-application.

Yellowing was apparent on the alkyl glycol exposed flora as early as the day after the treatment application, with effects enduring past 7 days.

 

Alkyl glycol treatment of grass + broadleaf weed at 14 days

Plots (Front to Back): Propylene glycol, Untreated, Ethylene glycol.

Assessment and photograph taken 14 days post-application.

Propylene glycol seems slightly less damaging in comparison with ethylene glycol, but recovery is minimal.

Both alkyl glycol treated plots remain significantly affected with enduring damage.

 

[N.B. Alkyl glycol-borne damage initiated by a broad range of agricultural chemicals presented as suspension concentrates is possible across a spectrum of application scenarios and crops  – not just fungicides, but extending to herbicides, insecticides and plant growth regulators.]

 

To address the problems inherent in the nature and makeup of suspension concentrates, Imtrade Australia has over the past five years developed and continues to develop a range of pesticides presented as water dispersible granules. These offer excellent performance in many aspects, including but not limited to:

  • Long term physical stability and integrity (homogeneous over time, none of the suspension concentrate issues of formation of lumps/masses, no issues of segregation into phases, no issues of pour-ability or retention of valuable active ingredient content in containers)
  • Long term chemical stability and integrity (no water content posing issues of hydrolytic degradation of the active ingredient; high purity with exclusion of the use of preservatives, stabilisers, humectants, anti-foams, viscosity modifiers and other excipients that are mandatory components of suspension concentrates)
  • Ease of storage, handling and container disposal as a result of their high active ingredient content and bag/box containment in preference to rigid plastic containers

While water dispersible granules are not the best available option in every single situation, the case for their preferred use is compelling in most circumstances when their advantages are viewed holistically.

For those of our actives presented as suspension concentrates, we tend to favour longer chain glycols as our humectant/anti-freeze component option and are also investigating non-glycol alternatives for future registrations.

Further investigations in this area are warranted, though the initial evidence described above is hard to ignore.