Canopy Management and Orchard Thinning

Transcription

1 Avocado Growers Manual Canopy Management and Orchard Thinning Canopy Management and Orchard Thinning Main Points Initially planting at a tree spacings of 7m x 7m on the square or 5 to 6m x 7-10m hedgerows is ideal Tree thining is required to prevent loss of production over time Thin when 80 to 90% of the orchard floor is shaded Thin by removing alternative tree or alternative diagonal rows Excessively tall tress can be pruned using several systems Canopy management and orchard thinning are often causes of major management headaches for avocado growers. These headaches can be alleviated to some extent if the grower has the luxury of good planning prior to planting the orchard because the initial tree spacing and layout of each block sets the orchard down a pre-determined management track to some extent. For existing mature orchards, a new owner may have to adapt to a situation or adopt a make-do approach initially, to get back on track. Although a short section on planting distances appears in the chapter, Preparation and Planting, in this manual, it is probably useful to delve into this subject in more depth, to emphasise the importance of prior planning, if you happen to be starting from scratch. Tree Spacing Tree spacing can be a complex topic and there are not always easy answers, due often to a lack of local production data to support a given point of view. Although there are currently many different approaches to tree spacing and canopy management worldwide (these are reviewed briefly in this chapter), local growers are almost invariably faced with the unique situation, wherein bearing trees in New Zealand are almost always carrying fruit during every month of the year. This allows very little latitude for the use of plant growth regulators, which other systems elsewhere rely upon, because of the risk of fruit residues. This constant presence of fruit also has a significant psychological effect on many growers, inhibiting their desire to cut or remove trees while a crop is visibly hanging on their trees. Initial tree spacing should be done to maximise early production, allow for canopy modification and/or systematic tree removal later so as to optimize yield of mature trees and to provide for cross-pollination if deemed necessary. To determine optimum distances between trees a number of factors should be considered: Figure 1: Crop on Tree Copyright NZ Avocado Growers Association August 2001 Site, including aspect, climate, soil, contouring etc, all of which can affect tree vigour. Figure 2: Trees starting to crowd PG 1 of 8

2 Canopy Management and Orchard Thinning Avocado Growers Manual Figure 3: Trees growing together Figure 4: Tree cut down to stump The necessity of using mechanised picking machinery. Variety growth characteristics: Hass is a relatively upright grower, but not as upright as Reed, for example. Cultivar precocity. Rootstock effect. Unfortunately we are still some way off from having a good, proven dwarfing stock and clonal stocks are relatively untested locally, but we do know that the seedling stocks used in New Zealand can be very vigorous. Potential for tree size modification. As already mentioned, the potential for the use of plant growth regulators is not particularly rosy here at present because residues will always be an issue, so local growers have less hope of implementing technological advances in this field than their overseas cousins. The option of very high-density plantings therefore loses some of its attractiveness. Grower capability and philosophy. Some people are inherently conservative, while others are willing to accept risk and embrace technology. cropping begins. Significant vegetative growth and tree size increases can already have taken place in that time. Once the trees begin to crowd, thinning must be considered and production prior to this may not have adequately covered input expenses if the trees were initially spaced too closely. Observations in New Zealand over the past few years indicate that, when using current seedling rootstocks with good management inputs, Hass avocados can begin to bear 2 and a half to 3 years after planting, provided climatic conditions have been conducive to fruitset. However, it is usually only in their fifth year that heavy PG 2 of 8 Optimising bearing surface area means maximising the canopy area that is exposed to sunlight, while also remembering to cater for mechanised picking requirements as the trees grow larger. With this in mind, there are basically two planting options that can be considered for implementation under New Zealand conditions at present. Square planting so that free standing trees result, even after thinning. There is no doubt that this planting system results in the maximum potential bearing surface area possible at orchard maturity, but it also results in very large, tall trees over time, which are difficult to harvest. The best spacing for this system is 6m or 7m square, with most growers opting for the 7m by 7m option. Any spacing wider than this is considered an extensive type planting as opposed to an intermediate or intensive planting. A square planting results in the diagonals being of equal length, making it easier to thin trees out later. Many growers make the mistake of planting a rhombus instead August 2001 Copyright NZ Avocado Growers Association

3 Avocado Growers Manual Canopy Management and Orchard Thinning of a true square, with diagonals of unequal length resulting. This makes for headaches later at thinning time. Canopy Management and Tree Thinning Right It is important for any reader to know that a review of the literature reveals quite a lot of information about pruning techniques, but very little on the effect these techniques have on orchard production. In other words, it is easy to prune and cut but the end result is a bit hazy and most of the research is still in the experimental phase and growers must accept that cast iron recommendations cannot easily be made. Wrong Hedgerow planting: this is done so that the trees eventually form a solid hedgerow with larger gaps between rows for ease of management access. This system results in a somewhat lower bearing surface area than free-standing trees, but there is a strong feeling among some growers that production costs can be reduced due to easier orchard access for such operations as picking, mowing and spraying. Whether this is in fact the case will only be proven once someone manages to keep very detailed production, cost and income records. Typical spacings for a hedgerow planting would be 5 or 6 m in the rows and 7 to 10 m between rows. Whatever spacing is used, it is important to orientate the rows so they face north/south, in order that maximum canopy illumination can occur as the sun traverses the sky from east to west. Also, any grower initially deciding on a hedgerow spacing is advised to use in-row and between-row spacings that are wholly divisible by one another (e.g. 6m by 12m or 5m by 10m), so that if they change their minds they can revert to a square planting at the first thinning simply by thinning each alternate tree in each row. What do we do when our orchard gets crowded? This is one of the most commonly heard questions voiced by growers the world over. The fact that there are still so many crowded orchards is testament to the difficulty of answering this question. However, where canopy management or pruning is done in conjunction with the use of plant growth regulators, recent information suggests that orchard canopies can be managed without compromising productivity too severely. But it may be some time, if ever, before New Zealand growers can avail themselves of this technology. What is well known, is that carrying fruit has the effect of retarding vegetative growth on avocado trees, so it is in the grower s interests to optimise all other inputs aimed at setting and carrying fruit from early on. There are a number of different approaches to canopy management, starting from an early age. Initial Tree Shaping Growers who have visited orchards may have noticed that different nurseries sometimes produce trees of different shapes as a result of using different grafting heights and production systems in the nursery. While Figure 5: Stump grinder at work Copyright NZ Avocado Growers Association August 2001 Figure 6: Orchard now after thinning PG 3 of 8

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