The leaf activity requires water, which the roots cannot deliver. The plants stop evaporation and water will be unavailable for cooling the leaf surface on bright days, so the plant reduces active leaf area by leaf abscission. Partial or complete defoliation was never critical if the root ball was kept more on the dry side, but if it was too wet, a quick root decline developed even if Poncirus trifoliata was used as a root stock. But in recovering the whole canopy, often the trees used up much of their starch reserves in the stock, which did not fully refill during the short summer times. After some years, many trees suffered, growth was stopped and the trees died because all of the starch had been depleted.
Irrigation reduces the plant stress during cold winter time and is therefore recommended.
Keeping the trees in a room with high humidity seems also to slow down WLD but cannot prevent it. The plant functions are minimized, but water and nutrient uptake for leaf activity is high enough to support the breathing process and leaf surface cooling by water evaporation. Sometimes during the winter, fruits dry out on the tree and drop if the tree is stressed too much. So for fruit development and fruit maturity, higher temperatures and good leaf activity should be maintained. Irrigation with a nutrient solution should be done even in winter.