The calcium is being drawn into the large fruit, sometimes at the expense of the smaller, younger fruit. Symptons first appear as small, light brown spots at the blossom end of the immature fruit, and then enlarge to form dark, sunken, leathery lesions. The first management step to avoid blossom-end rot is to maintain a good pH and high calcium levels. Lime is the cheapest, most effective way to achieve this. Foliar sprays can be of some benefit but are expensive.
Hollow heart is the void, or empty area in the internal center of the melon at harvest.
Often not notice until harvest and a melon is cut, hollow heart results from extremely high growth rates and expansion of the fruit. Over irrigating and over fertilizing with nitrogen are often associated with hollow heart. 150 to 175 pounds of nitrogen per acre is adequate to achieve excellent yields of watermelons. Irrigation scheduling becomes problematic and almost a moot point under the conditions we have experienced during the past week. The goal should be to replace and maintain the soil moisture that is lost through evapotranspiration.