In all wild blueberry fields, there are a large number of different "clones". A clone, as it is referred to in wild blueberries, is a distinct plant which originates from one seed. The various clones within a field may differ markedly in terms of vigour, rate of spread, yield potential, disease susceptibility and of course, physical appearance. It is this last characteristic which allows us to differentiate the clones within a field by colour.

The presence of many clones in a field is desirable for a number of reasons. The differences in relation to disease susceptibility and reaction to adverse weather conditions mean that there is a greater moderation of disastrous effects than if there was only one clone in the field. On the other hand, some clones are truly unproductive. Nevertheless, the presence of many clones in a field is an essential component for pollination. Fruit can not set if pollen is transferred from flower to flower within a clone. It is essential for good fruit set that pollen be transferred from one clone to another.

There are many components of productivity in blueberry fields which are beyond our immediate control. These include: winter damage, frost, drought and annual fluctuations in native bee populations. Other components such as weed control, proper pruning and the introduction of hives are entirely under our control. Another method to improve the productivity of our fields would be to fill the bare spots.

There are huge differences in the extent of coverage between blueberry fields. Some of these differences are due to the destruction caused by land clearing and levelling. Other sources of these differences can be the rate of spread of the clones within that field, the status of the soil at that site, and of course, the age of the field. Fields in production for 50 years or more may have nearly 100% cover, but younger fields generally have less than 50% cover. A survey conducted in Maine indicated that cover by blueberry plants in commercial fields is in the range of 40 to 70%.

Decades ago, scientists in the Atlantic region began looking for clones of blueberry which were vigorous and high yielding for eventual use in filling bare spots. Increasing the blueberry cover by the introduction of superior clones could greatly improve productivity. In addition, the practice would lead to a more efficient use of herbicides and pesticides, reductions in soil erosion and could even result in improvements in fruit set from cross-pollination by different clones. It has even been proposed that these superior clones might be transplanted into the centre of large clones for this purpose. These superior clones could also be used to replace clones of low productivity.

ESTABLISHING NEW PLANTINGS

Plant materials:

Two methods may be used to obtain plants for transplanting into existing blueberry fields.

• Blueberry sod may be dug from existing clones in the field. Superior plants can be marked off in the bearing year and sod can be dug out in the sprouting year. Sod will produce yields comparable to the mother plant and will re-establish well if it does not undergo stress after transplanting. A clump 15 cm in diameter can be dug with a shovel or a golf-hole cutter. A New Brunswick device called a Caron planter which was devised to move young tree seedlings has also been tried with some success.
• Plants may be produced from seeds of high-yielding blueberry clones, from stem cuttings of superior clones, or from tissue culture. This last method involves "mass production" of plants from superior clones in test tubes. Though more expensive, tissue-cultured plants will colonize the new area more quickly than cuttings and are less variable than the plants produced from seeds. One or all of these methods are used to produce blueberry plants from nurseries such as the Provincial Nursery in Hoyt. (see factsheet # A.11.0).

Site preparation:

Site preparation is extremely important and consists of sprout-year elimination of weeds which can inhibit establishment of the transplants. If the weeds can be controlled using Velpar, a normal spraying of the field should be used. This would be performed according to recommendations and prior to planting.

If the area consists only of shorter grasses, it may be best to transplant directly into the area without weed control, since the young plants appear to respond well to the buffering capacity of the undisturbed sod.

If the weeds in the field are Velpar-resistant, please consult your NBDARD agrologist for appropriate recommendations.

Planting:

Planting should be done as early in the spring of the prune year as possible, but after weed control and pruning. As with any planting operations, the important thing is to plant dormant plants with moist roots into moist ground. Get water to the newly transplanted seedlings if the soil is dry.

The plants produced from the Provincial Nursery are produced in plastic rolls which contain up to thirty-five plants. Christmas tree-planters may be used to set the plants to a depth of 5 to 7 cm below the crown (see Figure 1). Deep planting will encourage the production of rhizomes from the buried buds and will reduce frost heaving. When transplanting pieces of sod from existing clones in the field, plant the sod only slightly below the original depth. After planting, ensure good root-soil contact by compressing the soil around the roots with your heel.

If the plants are spaced approximately 60 cm apart in each direction, the area should take six or seven years to fill. An area of 6 by 9 metres will require 150 plants. Several different clones should be used in each planting, since these differences will lower the potential for disease susceptibility and improve cross pollination.

Fertilizer:

The use of fertilizer improves the rate of establishment of young blueberry plants. A study in Maine revealed that 1 kg per 12 square metres of slow-release fertilizers (like Peters Slow Release 14-7-7, Osmocote 18-6-12 or similar formulations) produced the greatest seedling growth and yields. A study in Northeastern New Brunswick demonstrated that urea-based nitrogen (46-0-0) applied at approximately 60 kg/hectare was very useful at rapidly increasing stand density during early crop establishment and this can be used the year after transplanting. Fertilizer recommendations in subsequent years should be based on soil and tissue analysis.

For the planting year, fertilizer should be applied to the soil prior to mulching and planting. For subsequent years, the fertilizer should be applied to the mulch surface.

Mulch:

The application of mulch for young seedling establishment is highly recommended. It will benefit the plants by:

• Protecting from frost heaving;
• Suppressing weed growth;
• Moderating soil temperatures;
• Reducing water loss;
• Reducing soil erosion
• Favouring rhizome growth.

Suitable mulches include sawdust, bark, wood chips and moist peat. Sawdust is the least stable of these; and if wood chips are used, they should not be too coarse. If a tree planter is used, the mulch may be laid prior to planting. Otherwise, mulch may be applied after the planting. Recommendations run from five to ten centimetres of mulch, but a PEI study found that the higher dose could discourage the growing plants. Use the lower rate if the site already has a significant organic layer of an inch or more. The mulch should be placed around and between plants. It is important to ensure that plants are not harmed during the application of mulch and the stems should remain exposed to light. For more information about mulching, consult the factsheet # A.8.0.

Maintaining transplanted areas:

Weeds, diseases and insects in the transplanted areas should be controlled in the same manner as the rest of the field. To encourage maximum rhizome growth, the area should be allowed to grow without pruning for four years. The transplanted area should not be burned until the sixth year. If the area is in the centre of the fields, it would be advisable to mow instead of burning. Quantities of fruit may be substantial by the third, fourth and fifth years, but care should be taken to ensure that the rhizomes are not pulled out by rakes.

The plant on the left is planted too shallow and the rhizome growth is poor. The plant on the right is planted 2 to 3 inches below the soil surface, resulting in good rhizome growth.

Prepared by Gaétan Chiasson, P.Ag. Horticulturlal Specialist , and John Argall, P.Ag., Blueberry Specialist, N.B. Department of Agriculture & Rural Development
Fall 1995