I have the opportunity to spray raw whey in the orchard this year (i.e. not a spray made from powdered whey).
In The Holistic Orchard, Michael P. references experiments done in S. America where whey was sprayed at a 2% concentration with good results. How could whey be beneficial? Michael touches on the possibilities:
1. general nutritional booster (proteins, vitamins, minerals)
2. contributes to leaf nutrition and aboreal mycology
3. "Calcium has been shown to inhibit fungal spore germination"
4. "A protein in whey produces an oxygen radical when exposed to UV light that is directly toxic to fungal conidia".
Some thoughts:
1. Might whey have enough calcium to help varities that have calcium deficiency issues (i.e bitterpit, honeycrisp zonal chlorosis, etc).
2. I think whey has a pH of approx. 6, a bit acid. Just a sulfur shifts the pH on the leaf, maybe whey could do this also - but at what concentration?? Seems like the concentration is the critical issue here - why was 2% (referenced above) used by these growers??
At the end of his whey section, Michael says fruits sprayed with a 2% concentration of whey (with some other things like kelp, fish, etc) "turned out impeccable...free of blemishes and infestations alike". Well, I don't know about that, seems just a little bit too good to be true?? I'm not thinking of this as a silver bullet, to be sure, but the possibilities are tantalizing.