We have a volunteer tomato plant that came up in some composted "horse manure/kitchen scrap" soil. The plant is the healthiest and most pest free tomato one could want. Early in its life, it bloomed profusely. Those flowers have remained unchanged all summer with no sign of tomatoes coming. Can this be an absence of a key nutrient? It would be hard to believe it is lack of pollenation, given that it is growing in the open full sun in full view of whatever pollenates tomatoes. Any thoughts?
Non-fruiting volunteer tomato
Do the flowers have stamens? If not it could be a sterile male mutation. Otherwise I'd say the extreme heat and humidity has caused pollen death or clumping which inhibits pollination.
Agreed. High nighttime temperatures and humidity seem the most likely culprit. It could be Potassium or Magnesium deficiency, but you'd be seeings signs in the foliage itself if that were the case, which it sounds like you're not.