I would continue to fertilize as you have been doing before the sheath.
Sometimes there is a benefit to reducing fertilizer N (first fertilizer number) so that a plant is not focusing on vegetative growth, possibly at the expense of flower production. It is not necessary to boost phosphorus (second fertilizer number), because plants need much less P than either N or potassium (K, the third number).
Sheaths need energy too. Why would you not fertilize you plant just bec it has a sheath in it?. Sheaths don't make the flowers they protect the buds. Having sheaths doesn't mean you are going to have buds or flowers. Carry on as usual with the plants, sheath, no sheaths, buds or blooms. Still needs the same care and attention.