Pesticide Formulations, Adjuvants, and Compatibility
Formulation determines behavior
A formulation is the active ingredient plus carriers, solvents, emulsifiers, and other inerts that make the product usable. Standard types: EC (emulsifiable concentrate - solvent-based, good coverage, higher risk of phytotoxicity and damage to sensitive surfaces, tends to increase penetration); SL (soluble liquid - true solution, minimal agitation); WP/SP (wettable/soluble powders - suspensions that need constant agitation and can abrade nozzles); WDG/DF (water-dispersible granules/dry flowables - low dust, good suspension); SC/flowable (suspended solids in liquid); microencapsulated (slow release - extended residual but greater risk to pollinators); granules (low dermal/inhalation risk for the handler but prone to off-site movement and water contamination); dusts, baits, fumigants, and ULV products.
Adjuvants
Adjuvants are added to the spray tank, not the jug. Key classes: surfactants (nonionic, organosilicone) reduce surface tension; crop oil concentrates improve penetration and are often the label-specified adjuvant; stickers/spreaders improve retention or coverage; penetrants; drift control agents increase droplet size; defoamers; buffers/pH adjusters; water conditioners for hard water; compatibility agents. Adjuvants are product- and site-specific: the wrong one causes crop injury, and more is not better - exceeding the label adjuvant rate can burn foliage.
Compatibility
The classic jar test: use the same water and the same proportions as the tank, add a compatibility agent if needed, and follow this order - fill with water, add compatibility agent, add dry formulations (WP, WDG, SP), then liquid flowables, then ECs/solutions, then surfactants and other adjuvants. Watch for heat, separation, flakes, or sludge. In the field, incompatibility often appears as curdling or a layer at the top of the tank.
Traps
Don't pick granules for a question about maximizing coverage; don't pick EC when the label warns about sensitive foliage. Questions about "why did my tank plug" usually point to order of addition or hard water.
Rule of thumb: dry before liquid, liquids before adjuvants, and always jar-test a new mix.