Foliar applications do have some positive test results behind them. They have many more inconclusive test results when the tests are done correctly. Be wary of a 3-5 bushel increase claim as that is an increase that you cannot measure in the field without doing replications and subjecting the yield data to statistics to determine if any change is due to treatment or just natural variation. You see this every year in your yield data. Even a side by side can be deceiving as your yield can vary naturally from one row to the next.
The biggest hurdle to get a foliar to work is that the set of conditions needed for them to do what they need to do is diverse, ever changing and largely poorly understood. The one thing that is well understood is that if you decide to use a foliar, use it when the crop is at its best. None of the foliar products will remedy a deficiency or remediate any other type of stress on the plant.
I see this sell sheet recommends tissue sampling. They all do. Tissue samples are notorious for showing nutrient deficiencies, even in highly productive fields. Also, be wary of tissue samples taken last summer as weather conditions can influence test results. Also, how the sample was handled will make differences. A sample with soil particles on it will show higher levels of certain minerals since the soil particles will be ground up with the plant sample to analyze. Conversely, a sample that has been washed, in order to reflect more accurately the mineral nutrients, can influence the results of other nutrients. Hence the difficulty in using tissue sampling as a fertility guide.
Molybdenum is used in the plant for certain metabolic functions – primarily nitrogen metabolism. It is also more available to the plant in alkaline soils so a deficiency in our part of the world is less likely. The chart shows the relative availability of some nutrients as affected by pH.
If you decide to use a Mo foliar, I would be more interested seeing it on soybeans because of its role in N use and N fixation. You are not risking any injury to any crop by applying it unless the rate is extremely high. Just don’t expect anything to great or consistent.