Ferti-Lome Yield Booster RTU corrects calcium deficiency in plants such as tomatoes stopping blossom end rot. You can tell blossom end rot by the darker, sometimes black, sunken areas on the blossom and the bottom of tomatoes. Blossom rot can be very small or it can take up to half of the fruit itself decreasing your yield. Ferti-Lome Yield Booster RTU will increase your yield by stopping blossom end rot. This product is in a ready-to-use (RTU) bottle - no measuring, no mixing, easy to use.