Practical Implications of Early- and Mid-Summer Water Stress
Mike Basedow, Tree Fruit Specialist
Eastern New York Commercial Horticulture
The sunnier weather we experienced in June 2022 should have been good for photosynthesis and resulted in greater production of carbohydrates to support fruit growth compared to other years, unless the hotter temperatures and lack of rainfall in late June/early July 2022 in portions of Eastern New York have induced water stress in the plant. This is the kind of situation where even with irrigation apples don't always size that well. We think it is because the high temps and high evaporative demands with the rather high hydraulic resistance of apple roots, we get some significant stresses even with wet soil. The following Figure 1, modified from Mark O'Connell and Ian Goodwin in Australia, shows that increased afternoon vapor pressure deficit (VPD) creates greater stress in the plant. In a study we did with fruit growth monitors we found the fruit started to expand about 2 pm each day but with afternoon VPD's of 3 kPa even with irrigation the trees still experience stress and fruit growth is reduced.
Practical Implications of Early- and Mid-Summer Water Stress (pdf; 279KB)
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