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 principal 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 competition 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.