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With the lift in optimism present in the apple industry now there is again interest in new plantings among apple growers.
Some new plantings will be going into new land or be planted into land from which peaches or nectarines has been removed. In these situations apple trees will establish easily and grow well, provided drainage and Phytophthora root rot problems are addressed.
The great majority of plantings, however, are likely to go into old apple land and this means that replant problems will need to be properly addressed if the new orchard is to be successful.
The two most common problems to be addressed are:
- Specific Apple Replant Disease (SARD)
- Apple Leaf Curling Midge (ACLM)
In addition to the above we also need to carry out good orchard husbandry in regard to other pests and diseases, notably black spot and powdery mildew, weed control and irrigation in the first couple of years after planting if the project is to be successful.
SARD
This is the most damaging condition found in orchard re-development. When young apple trees are planted into land that has recently grown apples, the new trees often fail to grow well. It's a phenomenon that has been reported from most apple producing areas in the World. To date, the exact cause of SARD has not been fully identified. Usually affected sites will respond to fumigants such as steam sterilization, chloropicrin or fomalin, which gives control of a wide range of soil organisms. Where SARD problems are suspected, pre-planting soil fumigation treatment along the rows is carried out for its' control.
The level of SARD is very dependent on soil type, length of time since the previous apple crop was removed, and what apple root density was present in the previous apple crop. Some of the most severe SARD affects I have seen have been following a single two-year crop of apple trees in a nursery situation.
Presence of SARD can depress apple tree growth by up to 50% or more. In some instances growth can be almost a good as new soil, however even though there is little evidence of growth reduction fruit sizing can be depressed.
Apple Leaf Curling Midge (ALCM)
Replanting into old apple land immediately after grubbing of the previous apple orchard is inviting severe infestation of ALCM because the heavy population that built up last season will emerge in the spring and strip the foliage of the newly planted trees. Without leaves, they do not grow. Letting the land lie fallow or be planted in an alternative crop for a year will clean out the resident ALCM population so when the new apple orchard is planted you only have to deal with migrating ALCM from adjacent established apple orchards. Because ALCM is a fairly weak flier, it will take a little time to re-establish in the new orchard. Even so, you need to monitor for its' presence right from green tip of the newly planted trees and if detected apply insecticides for its' control.
Trees are Smaller in Replanted Orchards
As a general rule, even where fumigation is correctly carried out against SARD, tree growth and ultimate tree size is less in re-plant orchards.
The success of your re-planting project will be determined by the orchards' productivity and the length of time taken to bring it into production.
Orchard productivity is directly related to canopy area and will reach its' full potential once the trees fill their allotted space. Until the allotted space is filled, orchard production is directly related to the tree density. Individual tree production on the other hand, tends to be independent of tree spacing until the tree growth exceeds the allotted space and shading competition becomes an issue. In fact there is some evidence to show that in the initial years of production closely planted trees tend to produce better than those at wider spacing's because of the benefits of tree to tree shelter at the closer spacing.
One of the biggest and most common mistakes made in orchard re-development is to be too conservative with tree density and end up with a slow growing orchard that will never reach full potential because the trees are planted too far apart.
As a general rule, if you are replanting with a similar vigour rootstock to the previous planting, the tree density for the new orchard can be almost doubled. The established orchards we are replacing at present have been planted around 5 x 3 m or 667 trees per hectare.
Second time round we need to be thinking planting distances in the range of 4 to 4.5m by 2 to 2.5m for rootstocks of MM106 vigour levels which will give tree densities in the range of 889 to 1250 trees per hectare.
Now-days there is strong evidence to support going fully intensive on developing rootstocks in which case we need to be thinking 3 to 3.5 m between rows, and 1 to 1.5 m in the row ie tree density of 1900 to 3333 per hectare.
Trees on dwarf rootstocks tend to be slow growing so it's very important to obtain well grown trees from the nursery and look after them really well in their orchard establishment years.
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