A Technical Update
Carmen® trees have a round, compact and dense growth habit. The trees are precocious in bearing and a first flower and subsequent crop has been observed on top works of only 6 months of age. Further, in a commercial planting on Westfalia’s Goedgelegen Estate (Mooketsi) an excellent first crop of 9kg/tree was harvested from 27 month old trees (on Dusa® rootstock). The cultivar is a consistent producer with a less pronounced alternate bearing pattern when compared to Hass. The characteristic of Carmen® that offers the biggest advantage over Hass is its season of maturity. Carmen® typically matures earlier than Hass and can extend the Hass harvesting season with up to four weeks. The cultivar also regularly produces an out-of-season flower and subsequent out-of-season crop that is ready for picking from November to December. Data collected at Westfalia Estate showed this crop to be as big as 40% of the normal season crop. Carmen® fruit are of the same shape (ovate/egg-shaped) and size (190g-305g) as Hass. The cultivar can withstand an extended period of low temperature storage (28 days at 5.5°C) as is needed for export via sea freight with no compromise on fruit quality. Carmen® fruit are of excellent eating quality and it also has processing potential (guacamole, evaluated by Westfalia Fruit Products).
An 8 ha high density planting of Carmen® on Dusa® rootstock was established on Goedgelegen Estate in 2007. The trees were planted at a 3m x 3m spacing resulting in 1111 trees/ha. The first crop was harvested in February 2010, amounting to 10ton/ha. Trees were allowed to develop and grow without any interference until Jan. 2009 (14 months old). By then, some of the trees had reached the recommended height of 2.2m (±70% of row width) and were topped. In order to avoid an abundance of shoots developing from the immediate area below the cut, Naphthalene Acetic Acid (NAA) was applied as an experiment (in PVA tree paint) to the cut surface and to an area of about 1-2cm below the cut (Figure 2). NAA is an auxin, which influences plant growth in many ways, including being responsible for apical dominance (suppression of lateral growth from lateral buds due to the presence of the terminal bud) in plants. When the terminal bud (shoot) is removed, apical dominance is broken and the lateral shoots will develop. In this case, NAA applied to the cut surface, re-instates apical dominance by replacing the auxins that were produced in high numbers in the terminal shoot, thereby inhibiting lateral bud development.
The figure on the left indicate Naphthalene Acetic Acid (NAA) was applied (in PVA tree paint) to the cut surface and to an area of about 1-2cm below the cut in Carmen®; The figure on the right indicate no NAA was applied; note three new shoots growing from below the cut.
By September 2009 (22 months old), the between – row areas had grown shut and regular pruning became necessary to maintain tree width and allow sufficient penetration of sunlight. The width of the trees is restricted to 2m in diameter. A stick of 1m in length is simply held against the stem of the tree and any growth extending past the length of the stick is removed. The plant growth regulator uniconazole (Sunny®) was also used to aid with vegetative growth control.
The biggest challenge with this planting will be to maintain the size of the tree by pruning regularly but without compromising the expected yield. It remains to be seen whether this high density planting will be manageable in the long term.
