Tree death or decline may be caused by several factors. For new trees, roots can dry out or freeze during shipping, or after shipment or purchase, they can become desiccated if not planted, healed-in, or watered immediately. In this case, trees generally fail to produce any new growth or develop only a few leaves and subsequently collapse. Lack of water after planting, usually greater in areas with higher soil temperatures during the growing season, will result in foliar wilting and/or eventual tree death. Trees with extensive root systems, such as MM.111, generally tolerate drought conditions better because they can absorb water deep within the soil profile. Under experimental conditions, trees on M.9 performed poorly at soil temperatures above 77°F, while M.7 is relatively resistant to high soil temperatures.
Low temperature exposure may also cause tree death or decline. Young trees are particularly susceptible to cold temperature injury during late fall or early winter. Rootstocks such as M.9 and M.27 are among the most sensitive rootstocks to winter low-temperature injury. When temperatures rapidly drop below freezing at this time, tissues near the soil surface can be injured. More information on winter hardiness of apple trees is available at Palmer et al. (2003) and Webster and Werteim (2003).
Using a fingernail or small knife to nick the bark of a young tree to see if there is a green layer just beneath the bark both above the soil line and slightly below may help in identifying why trees are weak or why they collapse. In many cases when trees collapse and die, the damage may have occurred months earlier. Being able to identify what portion of the tree was first or most seriously affected can be very beneficial in determining what happened to prevent future occurrences.
References
Jones, A.L. and H.S. Aldwinkle (eds.). 1990. Compendium of Apple and Pear Diseases. The American Phytopathological Society. 100 pp. <<Updated version in print>>
Palmer, J.W., J.P. Prive and D. Stryart Tustin. 2003. Temperature. In: Ferree, D.C. and I.J. Warrington (eds). Apple Botany Production and Uses. CABI Publishing. Cambridge, MA.
Webster, A.D. and S.J. Wertheim. 2003. Apple rootstocks, p. 91-124. In: Ferree, D.C. and I.J. Warrington (eds). Apple Botany Production and Uses. CABI Publishing. Cambridge, MA.
Ferree, D.C. and R.F. Carlson. 1987. Apple rootstocks, p. 107-143. In: R.C. Rom and R.F. Carlson (eds.). Rootstocks for Fruit Crops. John Wiley & Sons, New York.
Schaffer, B., P.C. Andersen, and R.C. Ploetz. 1992. Responses of fruit crops to flooding, p. 257-313. In: J. Janick (ed.) Horticultural Reviews, vol. 13. John Wiley & Sons, New York.
Dr. Michael Parker, North Carolina State University
Dr. Michele Warmund, University of Missouri