Spray adjuvants are used to increase the activity and efficacy of chemicals such as herbicides, insecticides and fungicides. These adjuvants do not have activity on weeds, pest and diseases like chemical active ingredients do.
Adjuvants like pesticides are registered through the APVMA.
The relationship between chemicals and adjuvants is complex and not well understood. While a certain adjuvant may enhance a particular chemical in a certain situation on a certain target it may do nothing with a different chemical, target or conditions. The relationship is quite chemical, crop and target specific. You can find many different ways in which adjuvants have been classified.
I’m going to use the one described by the GRDC in their excellent “Adjuvants – oils, surfactants and other additives for farm chemicals” which can be obtained through their web-site.
Adjuvant classification can be based on their chemical grouping (oil, surfactant etc.) or function (spreader, buffer etc.). This publication uses the chemical grouping classification because some adjuvants can have more than one function.
Adjuvants work with chemicals in the application process at three different stages;
- Modifying how chemical components or products interact in the spray tank
- Modifying how a product interacts with the target surface
- Modifying how a product moves into the target
The major adjuvant groups are;
Surfactants – the largest group of adjuvants which act as spreading or wetting agents. The major role is acting on the spray droplet when it contacts the target surface. Non-ionic surfactants are the most common group and in turf generally recommended with sulphonyl urea herbicides.
Oils – the second largest group which can act on spray droplets before they reach the target (reducing evaporation), at the target surface (extend life of the spray) or movement into the target (enhance penetration). Oils can be petroleum or vegetable based.
Acidifiers and buffers – are used to modify the pH of the spray solution. pH can affect uptake and translocation as well as degradation of the active ingredient. In turf sulphonyl urea herbicides can rapidly degrade under acidic conditions, while for the fungicide iprodione this degradation can occur under alkaline pH.
Fertilizer adjuvants – ammonium sulphate is the most common fertilizer used to enhance the effectiveness of some herbicides.
Others – various water conditioners, drift retardants, dyes, foam markers, defoam products are included in this group.
Adjuvants are all not the same and when one is recommended on a chemical product label it is important to ensure the correct one is used. Other adjuvants can improve performance of chemicals when spray conditions are not ideal. The publication previously mentioned can be found on the internet by searching “adjuvant grdc” and will be a valuable resource for all involved in chemical application.