White Cloud in the Tank: Hard Water and Glyphosate
You are filling a 500-gallon tank to treat 80 acres of field corn at 15 gal/A (1,200 gallons total, so two loads). The mix is glyphosate potassium salt (4.5 lb ae/gal), a chlorantraniliprole SC insecticide, ammonium sulfate, and a nonionic surfactant at 0.25% v/v. Your water comes from a farm well: 420 ppm hardness as CaCO3, pH 8.3. Your first jar test, with the four ingredients added in the order glyphosate, then the SC, then AMS, then surfactant, produces a white cloudy precipitate that settles overnight. The grower says, 'Just add more surfactant - it'll clear right up.'
1. Diagnose the precipitate. What is actually happening in the jar, and why won't extra surfactant fix it?
Read the worked answer
The glyphosate is being tied up by hardness cations - not by a surfactant shortage.
- At 420 ppm as CaCO3, the well water carries substantial calcium and magnesium. Glyphosate is an acid that forms insoluble calcium/magnesium salts. When the glyphosate went into untreated hard water first, those salts formed immediately; the white floc that settles overnight is the complex coming out of suspension.
- Adding AMS after the glyphosate is the critical error. Ammonium sulfate works by preferentially binding Ca and Mg (the sulfate is in vast excess), keeping the cations away from glyphosate. It must be dissolved in the water before the glyphosate is added; once the calcium-glyphosate salt has formed, AMS will not redissolve it efficiently.
- Surfactants wet and spread spray droplets; they do not chelate calcium. More surfactant would put a dispersant on top of a precipitate that has already formed, and the tank would still be delivering less active ingredient than the label rate. It also risks exceeding the label's adjuvant maximum.
A jar test with clear water and AMS added first should be run to confirm the diagnosis before anything goes to the field.
2. Give the corrected order of addition and the changed procedure for the two 500-gallon loads. What do you do if the precipitate persists?
Read the worked answer
Correct sequence (fill tank about half full first, keep agitation running):
- Water (half the total volume).
- Ammonium sulfate - 8.5 to 17 lb per 100 gallons; add as the dry product, let it dissolve fully. At 500 gallons that is roughly 42 to 85 lb per load.
- Dry formulations (WG/WP/DF) slurried first - none in this mix.
- Suspension concentrates (the chlorantraniliprole SC).
- Solutions (the glyphosate SL).
- Emulsifiable concentrates - none here.
- Surfactants/adjuvants last, at the labeled rate.
Practical changes: mix one 500-gal load and jar-test it at field strength before committing the second; check pH (glyphosate is fine at 8.3, but confirm no alkaline hydrolysis concern on the SC label); do not let a mixed load sit overnight; keep agitation on until the tank is empty.
If the precipitate persists after AMS: stop. Do not spray a tank with visible floc - it plugs screens and nozzles and delivers an unknown dose. Options are a different water source, a compatibility agent recommended on the label, or splitting into separate applications. Never 'fix' it by dumping in more surfactant; never dispose of the bad load on the ground or into a ditch.