Koo found that after freezes, non-irrigated trees showed more leaf and fruit loss than trees irrigated one to five weeks before freezes. He suggested that temporary leaf wilt at midday could be used as a guide for fall irrigation. With variable fall and winter rainfall, it is difficult to maintain cold hardiness, particularly if the winter daytime temperatures are above normal. As suggested above, over-irrigation in the winter can potentially reduce flower induction and decrease cold hardiness. Water restrictions are another reason for not applying too much water.
Excessive irrigation can promote greater weed growth and cause other problems.
In the example given above, the trees that received 100 inches of water had excessive weed growth, particularly when the trees were young. This could be managed with extra mowings, but the caretaking costs were higher. This excessive irrigation also caused dilution of the soluble solids in the fruit. Due to the greater fruit production, total pounds solids per acre were greater, but pounds solids per box declined with the high irrigation rate. Phytophthora propagule counts also increased to higher levels after several years of the high irrigation treatment.