I had some corn earlier in this season that had interveinal chlorosis. It seemed like it was on the new leaves so I thought at first could be an Iron or Manganese deficiency.  I checked the soil test and we had the desired levels of Iron and Manganese but our pH was 7.2.  At pH 7.5 Iron and Manganese are hard for plant to access. Someone else looked into this and pointed out that it was probably Sulfur since there was only 5ppm (missed that one!).  I had applied Sulfur in the spring to remedy that but perhaps since it was the granulated form it wasn't very plant available by the time the corn needed it.

So in order to test the hypothesis that it was indeed sulfur that was deficient I applied a foliar solution to the leaves of certain plants.  If sulfur was the deficient nutrient than the interveinal chlorosis would improve after some time.  Unfortunately elemental sulfur is hydrophobic and I didn't have any wettable sulfur so I used Iron sulfate, Zinc sulfate and Manganese sulfate, thinking that if all three worked it would be clear that sulfur was deficient, and if only one resolved the chlorosis then that would be the deficient nutrient.

I would say in general all the corn looks better, but the corn I treated with Iron sulfate didn't show as much dramatic change and I think this might be because it was quite chunky and hard to break up into a powder to get a good solution.  The Manganese sulfate and Zinc sulfate treated corn had a much clearer change.  You can see the two plants where I applied Manganese sulfate in the pictures. Interestingly the old leaves didn't seem to recover that well compared to the new leaves which might point again to the nutrient deficiency being Sulfur since S can be mobile when there is sufficient N.

Corn with Manganese sulfate applied foliarly at 10g/L at Day 1, Day 8 and Day 15