Friday, January 21, 2011

Check scionwood for winter injury

This winter has been a little colder than normal (whatever normal is in SE Kansas). Temperatures dropped to near 0 F on two consecutive nights in mid-January. As a general rule, we usually don't see serious cold injury until temperatures drop below -10 F even on our most cold tender cultivars. However,  the past season's crop load does influence cold hardiness. If a tree bears an excessive crop in the fall it becomes very prone to winter dieback. 
In the photo above, you can see two pecan twigs that have had the bark scraped off. The top twig was taken from a Maramec tree while the bottom twig came from a Kanza tree. Note take the interior bark and cambial area of the Kanza twig is clean and green with no indications of cold injury. In contrast, the Maramec twig  shows the signs of internal browning that are associated with cold injury. Last fall both these cultivars had a full crop load of nuts but only the cold sensitive Maramec  has been injured by the cold. Susceptibility to cold injury is one reason Maramec is not recommended for propagation in northern pecan states.
    In a month's time, you should start to collect scionwood in preparation for next spring's grafting season. When you do, slice into a twig and check for winter injury. Significant internal browning translates into scionwood that will not perform well in the field.