The injury resulting from the cold weather of the past winter was much more severe than that of the previous winter. Whereas filberts were the only nut trees injured in 1948-1949, they escaped with relatively little damage in 1949-1950 in comparison with Persian walnuts.
On February 11, 1950, ten days after the really severe week, several walnut growers of long experience held grave fears for the entire industry. Peach and apple trees, which seem to exhibit winter injury more quickly than walnuts, showed so much damage then that walnut growers thought the injury to the Persian walnut would be even worse.
From February 11, 1950, to the present date (July 30) I have been making observations from time to time in different locations with special attention to walnuts and with some to filberts. It is thought that certain of these observations might be of interest to nut growers in other areas, even though there is nothing particularly new or startling about them. They do, however, tend to show how surprisingly well the Persian walnut trees can withstand severe cold if it occurs after they have once gone into dormancy.
Generally speaking, the winter injury to walnuts has been spotty. No areas of great size have been either free of injury or severely injured. Usually, where a difference in severity of damage is found between areas close together, some reason for the difference can be found, but it is not always evident on the surface.
Injury to Walnuts
With the possible exception of southern Oregon, it is safe to say that 100 percent of the walnut trees in Oregon and Washington suffered some twig injury as a result of last winter's cold. In many cases the subsequent dieback of the twigs may extend only a few inches, but sometimes the injury involves not only the past season's growth but that of three or even four years back.
As might well be expected, this twig injury of necessity has meant the loss of many terminal and lateral buds which bear the female flowers; so for that reason, if for no other, this twig injury has assumed serious aspects.
In many cases the catkins were severely injured even where there was little or no twig injury. The catkins of the Persian walnut seem to be extremely sensitive to cold. Many Persian walnut trees in Oregon this year failed to produce any catkins at all. Some produced very few normal catkins, but some half-developed and deformed catkins. An examination of these partially injured catkins, however, revealed the fact that they did produce some pollen. It will always remain a mystery to me how as many walnuts were pollinated and set as there were, with the scant crop of catkins.
In practically every orchard examined, where the temperature got as low as minus 10 degrees F., the pith cells were blackened. This is not uncommon in other tree crops following severe winter injury. Fairly good peach crops have been borne in Georgia on trees that had the pith cells completely blackened.
In the case of walnuts this year, many growers were considerably worried by the fact that even the wood tissue outside the pith region was black and watersoaked. However, to date (July 30, 1950) this condition has not proven serious; as long as the cambium cells were not injured no real trouble has developed. In some cases under observation, even where some injury to the cambium cells was known to have existed, enough live ones have been left to effect recovery. Compared to peach, holly, and even apple trees the Persian walnut has put up a marvelous fight to recover from the injury sustained.