Hi David,

That’s a bit hard to answer, according to me it depends on a few factors. Some elements are more toxic than others and have lower recommended rates. For instance with foliar Boron sprays (170 g/kg B) I never go higher than 0.75% but with some of the less hazardous elements I sometimes go higher.

The other thing to consider is the formulation. SC (Soluble concentration) burn less easily with higher rates than for instance SL (soluble liquids) or powders. The other thing is to consider is the salt index of the fertilizer for instance MAP is relatively low and Urea is higher. Also the quality of your water. If your spraying water has a naturally high EC, I would also add less fertiliser.

The best thing in my opinion would be to consult the label for max and min rates or to maybe speak to a agronomist from the fertiliser company you are going to buy from.

Sorry for the long-winded answer, hope it helps!