I don’t think it’s a maturity issue. Possibly stress from flooding plus the possible leaching of minerals, lime, etc. due to the flooding, so a combination of the perfect storm (sorry, couldn’t help it). I don’t think you should fertilize this close to harvest. Topping early, unless you are bagging for seed, may actually help as stated in this article in regards to calcium deficiency. “Topping early can stimulate root growth as much as 40%.”
“Corrective Measures
Once calcium deficiency is confirmed, additional foliar or soil applications containing calcium fertilizers have not shown to be of great benefit. In fact, research has shown that foliar applications of calcium may result in leaf phytotoxicy (burn). In addition, the use of calcium chloride foliar sprays should be avoid due to the potential of the chloride imparting off flavors to the tobacco.
Most often, it is the practice of early topping that prevents or reduces the effects of calcium deficiency. Early topping has been shown to stimulate root growth by as much as 40%, thus allowing for greater root exposure to various nutrients found within the soil profile. This practice will also divert the flow of nutrients and photosynthates to leaf growth instead of flower and seed development.”