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 Washington, 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 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 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.

In several orchards where different levels of fertilization have been used by the grower, it appears that the more liberal the application of fertilizer, particularly nitrogen, the less severe was the winter damage sustained.

At the college orchard in Corvallis, the one tree that got no additional nitrogen last year and that bore the heaviest crop of nuts is outstandingly the most severely winter injured of the 17 trees involved.

Only two varieties of walnuts have been studied, Franquette and Mayette, and some Carpathian seedlings in one orchard. Here in Oregon the Mayette seems to have generally withstood the winter injury better than the Franquette. It is my belief that they are just naturally a little more vigorous than the Franquette. Yet they never seem to overproduce as the Franquette sometime does. Last year was the "on" year for Franquettes and that might easily account for the generally apparent better condition of the Mayettes this year.

Carpathians Resist Winter Best

Near Ontario, Oregon, I saw 7 seedling Carpathian walnut trees early this spring. They were leafed out and the catkins were elongated before any Franquettes, even in the Willamette Valley, had started breaking buds. No sign of winter injury was apparent on the Carpathian trees at that time, yet Franquettes at the Malheur Experiment Station, a mile away, were obviously killed to the groundline. The owner, Mr. Peter Countryman, says these trees are often damaged by spring frosts but they always produce some nuts.

A letter dated August 4, from Mr. Countryman, indicates that a hard frost on the morning of April 24 when the temperature dropped to 22 degrees, did considerable damage to the new growth and catkins on the lower half of the Carpathian walnut trees. He estimates not to exceed one-third of a crop on these Carpathian trees this year; but he says that since the freeze the trees have made good growth, the new terminals being about 18 inches in length and the nuts on them are very large.

To sum up the walnut situation, then, the encouraging thing is that no walnut orchards have been called to my attention that were completely killed. Several badly neglected orchards and two orchards where it is said that the temperature dropped lower than minus 25 degrees F. are so severely damaged that it is impractical to try to save them, but even these are not completely killed.

Injury to Filberts

From the less comprehensive observations made on filberts following the severe winter just past, it appears in general that when the filbert tree has gone into dormancy it is more tolerant of cold than the walnut.

The difference of one month in time of occurrence of the cold in the two winters seems to have had more bearing on the damage to filberts than the difference in temperature. In the Forest Grove, Oregon, area, and in Clark County, Washington, filbert trees, however did suffer severely from the cold last winter, but these two areas were the "cold spots" of the Northwest.

It seems as if the same factors that accentuate winter damage in walnuts work in a similar way on filberts, except that the elevation factor does not seem to be of so great importance. Age of tree, level of nutrition, and size of preceeding year"s crop seem to be more important than elevation. Young filbert orchards, on either hillside or valley-floor sites, seem to be much less severely hurt than older orchards on the same sites. It is the acreage of _young_ filbert trees that will make good the agricultural statistician"s estimate of 40 to 50 percent of a filbert crop this year.

I have seen one 32-acre orchard of 24-year-old filbert trees that was injured beyond repair, but they were crowded and unfertilized. At the very same location a 14-acre orchard of 15-year-old filberts with adequate s.p.a.cing was not seriously injured, even though the trees were not fertilized.

One other orchard in a poor location and on waterlogged soil, which has had little or no care, has likewise been lost. Filberts definitely were hurt in the two "cold spots" previously mentioned, but official reports of minus 18 degrees F. were common in that area.

There was a noticeable difference in damage to catkins between Daviana and DuChilly. Very few Daviana catkins produced pollen; but DuChilly seemed to be fairly normal.

Injury in filberts was confined mostly to the catkins and twigs.

Excessive sucker growth up and down the main trunk and branches has taken place in the filberts, as is the case in walnuts.

In neither walnuts nor filberts was there much splitting of the bark on the trunk. This was probably because there was no sudden fluctuation in temperatures and sunshine was not excessive during the critically cold days.

It has been previously stated that the filbert is possibly more tolerant of cold than the walnut. In spite of this there probably has been more extensive damage to filberts than to walnuts; but it must be remembered that filberts are the princ.i.p.al nut crop in those two "cold spots." Not many walnuts are grown there, but the ones that are were likewise injured.

Editor"s Note: Mr. Gellatly"s following papers were read by t.i.tle.

Effects of the Winter of 1949-50 on Nut Trees in British Columbia

J. U. GELLATLY

Box 19, Westbank, B. C.

(Orchard at Gellatly, B. C.)