Fruit trees grown in Washington state are frequently exposed to environmental stresses that impact their health and production. During the summer, solar radiation levels are extremely high, and often exceed levels that can be utilized by the trees. When coupled with high air temperatures, which also raise the fruit temperature, sunburn browning and other skin disorders can result making fruit unmarketable. For young trees that do not yet have an adequate canopy established, sunburn can also occur to the unprotected bark of south facing tree trunks.
In May of 2015, a drought emergency was declared by Gov. Jay Inslee for the state of Washington. A WSU drought alert website has been established. At sites where access to irrigation water is restricted or cut off, drought stress could not only impact cropping but also tree survival.
Cold temperatures can also result in damage – whether it is before the trees become completely dormant in the fall, during winter dormancy, or during early growth and flowering in the spring. Hail can cause cosmetic damage to fruit making it unmarketable and also cause physical damage to leaves, shoots, spurs and bark. The latter may produce wounds that could lead to disease infection and insect invasion.
Site selection to minimize temperature extremes is important. There are two important questions to ask: has the site had fruit grown successfully on it before? and, is the site known for consistent cropping year after year or not? Ideal sites are on gently sloping land with good air drainage, so that cold air can move down slope and not accumulate in a low spot or “frost pocket” causing bloom damage in the spring and subsequent crop loss. At sites that are known to be windy, planting wind-breaks can be helpful to reduce wind damage to fruit but still allow cold air to flow out of a tree fruit block. Overhead netting can be installed over trees to protect from hail and reduce sunburn. By placing protective covers over cherry trees, rain-induced cracking can be reduced.
The proper choice of scion cultivar and rootstock for your particular location is an important factor affecting the ultimate tree performance and fruit quality. The particular scion/rootstock combination will affect tree hardiness, bloom date, stress and disease tolerance.
The WSU apple breeding program led by Dr. Kate Evans, for example, is developing new cultivars that were bred for and selected in the stressful climate of central Washington. See video: Cosmic CrispTM WA 38 Field Days. Performance of these new cultivars may be superior to those introduced from other parts of the world where the climatic conditions under which the cultivar was selected were quite different (e.g., Honeycrisp cultivar was selected in Minnesota).
Current research at the WSU-TFREC Tree Fruit Physiology lab in Wenatchee involves investigating changes in the physiology of apples under photo-selective anti-hail netting. The focus of their lab “has been understanding the complex physiological interactions between environment, genetics and horticultural management.” See Dr. Kalcsits’ website here.Stresses Relating to Sun and Heat Drought and Water Stress Management Practices to Protect Against Environmental Stresses Caused by Heat and Light Rain and Cherry Cracking Wind Stress Low Temperature Stress Hail Air Pollution Stress Resources for Environmental Stress of Tree Fruit