Last winter, 1932-33 was especially hard on filberts, in fact, much more winter injury was experienced than at any time since the Station orchard was set in 1925. It was a good season to separate the hardy and tender sorts. Throughout the winter the weather was exceptionally mild and favorable for that type of winter injury due to early growth activity. In a normally cold winter catkin killing as a rule is not very serious, except on a few tender varieties. Although catkin killing was so serious at Geneva, S. H. Graham of Ithaca, who is growing a number of varieties on an exposed location where winters are more severe than at Geneva, reports that his trees suffered less catkin injury than at any time since he has been growing them. Catkin killing does not seem to be due to extreme cold during the winter and rarely are the catkins injured before late February or early March. Injury may be severe even though the temperatures are not lower than the catkins are thought to endure when in bloom. Apparently the injury may be due to the cumulative effect of dessication throughout the winter months, this effect becoming apparent shortly before the catkins bloom. Catkins forced into bloom prior to late February bloom normally and without apparent injury.
The data on winter injury of catkins is being accumulated for two purposes. First, it is being used as a basis for recommending varieties as pollinators; and second, it is being used in selecting parents for breeding hardy varieties.
The amount of winter killed catkins is determined by observation during the blooming season in late March. All catkins that fail to open, or open weakly and shed no pollen, are considered winter killed and the proportion that are killed is expressed in per cent.
Based on the amount of winter injury of catkins during the winter 1932-33, I am making four groups. First, those varieties in which all, or practically all the catkins were killed. In the varieties suffering such severe catkin injuries, much of the wood was killed, but this will be treated separately.
The varieties in this group are Nottingham, Early Prolific, Garibaldi, Kentish filbert, Pearson's Prolific, Princess Royal, the Shah, Webb's Prize Cobb, Bandnuss, Barr's Zellernuss, Berger's Zellernuss, Grosse Kugelnuss, Heynicks Zellernuss, Lange von Downton, Multiflora, Sickler's Zellernuss, and a Corylus rostrata brought into cultivation from a glen a few miles away. The planting of varieties in this list is not recommended.
The second group includes those sorts in which 50 to 90 per cent of the catkins were killed. The varieties are Barcelona, Daviana, Fertile de Coutard, Montebello, Cannon Ball, Duke of Edinburgh, Duchess of Edinboro, Prolific Closehead, Red Skinned, Kadetten Zellernuss, Kaiserin Eugenie, Kunzemuller's Zellernuss, Liegel's Zellernuss, Prolifique a coque serree, Romische Nuss, Schlesierin, Truchsess Zellernuss, Voile Zellernuss, Kruse, and Littlepage, a variety of Corylus americana from Indiana. Some wood killing occurred among the varieties in this group. None of these varieties should be depended upon for pollination purposes.
The third group includes those varieties experiencing 20 to 50 per cent winter injury. The varieties are Kentish Cob, Italian Red, Bollwiller, Red Aveline, White Aveline, and Vollkugel. These varieties may be planted with caution if too much dependence is not placed upon them as pollinators.
In the fourth group are those with less than 20 per cent of catkin injury. These are Clackamas, Cosford, Minna, Early Globe, English Cluster, Medium Long, Oregon, Purple Aveline, Red Lambert, White Lambert, D'Alger, Althaldensleber, Ludolph's Zellernuss, Luisen's Zellernuss, Neue Riesennuss, Eickige Barcelonaer, and Winkler and Rush, the latter two being varieties of Corylus americana. Varieties from this group and the third group should be used as pollinators and as parents in breeding work to develop catkin hardy varieties.
Winter killing of the wood has not been as extensive nor as serious as catkin killing. It is usually slight and confined to a few varieties but during the past winter 1932-33, many varieties killed back severely.
The varieties are grouped according to the amount of winter injury of wood. Varieties in which more than 50 per cent of the wood was killed are Nottingham, Early Prolific, Garibaldi, Princess Royal, Webb's Prize Cob, Bandnuss, Grosse Kugelnuss, Jeeves Samling, Kaiserin Eugenie, Multiflora, Kurzhullige Zellernuss, Lange von Downton, and the Corylus rostrata previously mentioned.