Stuck Nuts: Varietal Influences
Nuts can be hard to remove during harvest for a number of reasons. They include hull rot, boron toxicity, inconsistencies in ripening, and poor irrigation practices. Causes for each of these issues have strategies that can be implemented to reduce the problem and have been highlighted in previous posts.
When discussing challenges in nut removal, one major factor that is often overlooked is nut variety. Due to differing growth habits of each variety, good nut removal may be difficult to achieve at varying points of orchard establishment. For example, Aldrich, Independence, and Wood Colony can be difficult to shake during the establishment years, while Padre is a challenge at maturity. These differences are due to tree architecture and the location of the developing nut.
Tree architecture impacts nut removal because the process requires the transfer of energy from the shaker. Trees that are tall, upright, and tend to bear at the end of the limb have a lower amount of energy that is transferred during shaking. Due to the height and proximity of the limbs to the central axis, these trees often require different shake patterns or procedures to achieve the optimal removal of >99% of the nuts within the tree. Pruning to minimize height may reduce the problem for a year or two, but once the wood regrows, often redeveloping with a very vertical structure, the shaking difficulties will return and increase. It is best to try and develop these trees with a wider structure at orchard establishment. Cultivars that fall within this category include ‘Padre’ and ‘Aldrich.’
Positioning of the nut also impacts shake efficiency. Young trees that tend to bear a lot of nuts on the primary wood are very difficult to shake. This effect is two-fold: the closeness to the central access prevents energy transfer, while the rapid growth of the primaries or secondaries can grow around the nut’s spur position, effectively gluing it to the tree. This is quite common with ‘Wood Colony’ and ‘Independence’ as well as other precocious varieties. In these instances, it is best to realize that optimal nut removal might not be possible as shaking too hard or too long can lead to barking of the young tree. Try initiating harvest earlier as the greater moisture weight in the hull can help with removal (Note: a longer drying time on the orchard floor will be needed). If a clean shake isn’t possible, other methods should be considered to remove the stuck nuts. Typically, after the fourth year (i.e. second harvest) this problem tends to decrease as the bearing position moves away from the primary and secondary scaffold to the lateral fruitwood.
Difficulty in shaking should be considered when planting any variety. This is especially true when reviewing new varieties to plant. Recognizing the cause of the poor removal may provide guidance on what to expect at the initial and mature bearing ages.