Part 23 (1/2)

JOHN H. PAINTER

Horticulturist, United States Department of Agriculture, Agricultural Research Administration, Bureau of Plant Industry, Soils, and Agricultural Engineering, Oregon State College, Corvallis, Oregon

In western Oregon and Was.h.i.+ngton, where the j.a.pan Current is supposed to keep the winter temperatures moderate, something happens every now and then and we get really severe winters. We can't blame it on the ”A” bomb because we had severe winter injury in 1919 and 1935 long before the ”A”

bomb.

The last two winters have been exceptionally cold, but this past winter of 1949-1950 was much more severe than the previous one.

In 1948-1949, the cold came rather suddenly in the latter part of December. In the past winter, 1949-1950, the real cold came on January 30, with temperatures ranging from 10 to 30 degrees below zero F. Most official temperatures were higher; but at Corvallis the official temperatures were taken at least 60 feet above the ground level, on the roof of the Agricultural Building, which is over a steam-heated building and is old enough to be not very well insulated. This cold continued in somewhat modified form for a week.

During the previous winter the lowest temperature recorded in the nut growing areas was about 10 to 11 degrees above zero F., and the severe cold lasted for only a couple of days.

In both winters the ground was fairly well covered with snow, but with considerably more snow this past winter than the previous winter.

No apparent damage to Persian walnuts was observed as a result of the cold in the 1948-1949 winter, but in certain low-lying areas catkins of Barcelona and Daviana filberts were killed, especially those of the latter. Considerable dieback of filberts occurred; but during the following growing season recovery was effected and at the end of the summer very little evidence of winter injury was visible.

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 Was.h.i.+ngton 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 a.s.sumed 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.

Factors Accentuating Winter Injury in Walnuts

After the several months of observation, certain factors appear invariably to account for excessive damage to walnut orchards. Elevation seems to be a princ.i.p.al factor. The hillside orchards or those on upland sites (soils) were far less injured than the river-bottom or valley-floor orchards, even though the latter may be on a better soil as far as fertility is concerned. My early prediction of 50 percent of a crop in the hillside orchards seems now to have been about 10 percent short, unless other factors become involved. On the other hand, my early prediction of 25 percent of a crop in the valley-floor orchards has been close to correct. Of course, certain valley-floor orchards with a combination of adverse factors won't have even a 5 percent crop.

Older orchards were more severely hurt than younger orchards with otherwise similar conditions. This is possibly due to the lack of vigor and of reserve material, resulting from crowding and compet.i.tion for elements of nutrition.

The size of the crop the preceeding year seems invariably to have had an effect upon amount of damage done. The matter of reserves is again involved. Two orchards that bore a reduced crop last year because of spring frost injury have come through much better than some other similar orchards, at practically the same elevation and age, that bore a crop last year.

Two adjacent hillside orchards show considerable difference in degree of winter injury and crop prospects for this year. It is believed that this difference was due to the fact that in one orchard 35 percent of the crop was destroyed by blight last year, in comparison with a 1 percent loss in the other. The owners and I estimate that there is at least 20 percent larger crop this year in the orchard which had the heavy loss from blight last year.