As with the first stage, practice moderate irrigation here. During the third stage, which lasts up to two months and involves tuber enlargement, the plant needs the most water. Water requirements are quite high during the first part of this stage and lower during the last part as the plants reach maturity. Too little water slows tuber development and sharply reduces yields. Uneven watering leads to growth cracking, knob formation or second growth, and to scab infections.
Excess water can result in late season hollow heart.
Irrigation should be uniform and related to evapotranspiration rates and rainfall amounts. Keep you eye on the soil. Don't get it sopping wet, but don't let it dry out and crack either. The fourth and final stage involves tuber maturation. The vines begin to die at this time.