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A.2.0 INTRODUCTION The wild blueberry plant is native to North America. This plant belongs to the plant genus Vaccinium. There are 5 species of blueberries, which grow in the wild in Canada. The most important are:
In New Brunswick wild blueberry fields, we generally find the two most common species, that is, low sweet and sour-top. The wild blueberry is a plant which reproduces by cross pollination. Each seed gives rise to a plant with a different genetic make-up. This is why within each species, there can be significant differences in growth, colour, the size and shape of the leaves, resistance to diseases, maturity, flavour, productivity, size, firmness and shape of the fruit. SOIL AND CLIMATIC PREFERENCES The growth and development of wild blueberries is highly related to soil and climatic conditions:
Soil: The wild blueberry plant is considered an acid-loving plant, meaning that it prefers acid (or sour) soils. The pH scale is a measure of the acidity of soil, with the number 1 being very acid and the number 14 being very basic Most water has a pH of 7, which represents neutrality. Most plants prefer a pH around 6, while blueberries will grow in a soil pH of 4.0 to 5.5. Growth tends to be best at a pH of 4.6 to 5.2. Water: The wild blueberry requires less water than most cultivated plants, and is fairly well adapted to drought. Despite this adaptation, 2.5 cm (1 inch) of water per week is desirable for optimal plant growth. Water stress will cause an early reddening of the plant's leaves. Under prolonged water stress in a sprout field, new leaves are small and weak, floral bud formation is lower and the number of flowers in the floral bud is also lower. In the crop year, drought conditions can have a negative impact by causing young fruit to fall prematurely, and by significantly reducing fruit sizing. Wild blueberry plants do not tolerate poorly drained land very well, and drainage can be desirable to encourage the spread of the plant. Light: The wild blueberry plant enjoys full exposure to sunlight. Shady conditions yield plants with weak stems and few floral buds. In addition to light intensity, wild blueberry plants also respond to photoperiod (the number of daylight hours). Under long days, the plant grows vegetatively (that is, it produces green growth). It is during this period of time that the plant's height is determined. As the plant photoperiod shortens, vegetative growth stops and the formation of floral buds begins. Organic matter: The soil's organic matter content is a major factor in the growth of wild blueberry plants. Organic matter content plays a very important role in the soil's ability to retain water, and in the availability of nutrients to the plant. Some studies have even demonstrated that growth and yield are directly related to the soil's organic matter content. WILD BLUEBERRY PLANT DEVELOPMENT The wild blueberry plant begins its life as a seed. The plant which originates from the germination of this seed is the mother plant. The mother-plant gives rise to underground stems (called rhizomes) that allow the plant to spread throughout a field (Figure 1). With the passage of time, all the stems produced from the mother plant and the associated rhizomes form a large patch called a clone. Each clone is genetically distinct, and the presence of many clones in a field is necessary for effective pollination.
Stems (sprouts) originate from the mother-plant, or from buds that are present on the rhizome. The rhizomes develop under the soil surface in the organic matter layer. Roots develop along the length of the rhizomes and can be found primarily within the first few centimetres of soil. When a stand of wild blueberry plants is pruned by burning or mowing, buds situatedon the mother plant or the rhizomes come to life and begin to grow. This growth occurs from the beginning of spring until mid-summer. The plants stop growing in height and begin to set the next year's floral buds. The end of vegetative growth is evidenced by the presence of a black tip on the end of the stem (Figure 2). This tip is actually the remnants of the last leaf. Following this, the plant will begin developing buds until growth stops completely late in the autumn. The first year of growth is limited to vegetative (green) growth, and prepares the plant for fruit production in the second year of the cycle. In the autumn, after the plant has laid down the next year's structures, two types of buds can be distinguished. Leaf buds are small and narrow, and are located at the bottom end of the stem, to a height of about 2/3 of the stem. The floral buds are rounder and larger, and are located higher up the stem (Figure 3). Sprout length is very variable. This is due to differences in the genetic make-up of each clone, as well as to differences in growing conditions, including soil fertility, water supply, weed competition and predation by insects and disease. Generally, stems should be approximately 15 to 17 cm (6 to 7 inches) high. Floral bud numbers can vary for the same reasons as those listed above. These numbers are generally related to stem length. A 10 cm (4-inch) stem generally produces an average of 2.5 floral buds, while a 15 cm (6-inch) produces 4. In many New Brunswick fields, an average of 4 to 5 buds per stem would be considered good, though the number can be higher in some rich fields.
A dormant cold period is necessary before the plant begins to grow again. The wild blueberry plant is considered hardy, though very cold winters without snow have been known to cause serious damage to both aerial and underground plant parts. Recent studies by Paul Cappiello and Scott Durham of the University of Maine have demonstrated that the plant is most tolerant to cold around mid-winter in January and February. Floral buds are less tolerant to cold than leaf buds, which can tolerate winter temperatures as low as -30ºC. Strong and cold winter winds can cause serious damage to exposed fields, since the highest buds on the plant are the last to be formed in the fall, and they are the least resistant to cold temperatures. Under our winter conditions, any production technique which has an impact on reducing wind speed and/or increasing snow accumulation is desirable. Planting natural wind-breaks is one such technique (please refer to Fact sheet A.4.0). After the winter dormancy period, the plants begin to grow again. The floral buds begin to swell up, and full bloom generally occurs within 3 to 4 weeks. Each floral bud gives rise to a little stem of flowers. There are generally about 5 to 6 flowers in each floral bud. If pollinated, these flowers will give rise to fruits by summer's end. For more information on pollination, please refer to Fact sheet B.1.0. The wild blueberry fruit is a berry. Its development occurs from pollination to harvest. The size of the fruit varies according to the vigour of the clone, the degree of pollination and the supply of water. The largest fruits generally contain more live seeds. The fruit does most of its sizing during the 3 or 4 weeks prior to harvest. Under good growing conditions, fruit weight increases by 10 to 15% each week. The average weight of a berry is close to 0.3 grams. Several observations in north-eastern NB have shown a general distribution of fruit size to be 20% small (less than 6.5 mm), 60% medium (6.5-9.5mm), and 20% large (superior to 9.5mm). After developing their characteristic colours, the fruits no longer grow much, but do continue to develop improved flavour and sweetness. Productivity can vary, mostly because of factors like soil fertility, water and pollination. Fruit set is very important and is influenced by the availability of native or introduced pollinators, as well fine weather for these insects to work in. After harvest, the plants will continue to produce leaf and floral buds. Each year following the first harvest, the number of floral buds will decrease and the lateral branches will be shorter and less vigorous unless the crop is pruned. With the passage of time, the plant will become less productive, and pruning will need to be done again, in order to re-establish a productive stand.
Prepared by Gaétan Chiasson, P.Ag. Horticultural Specialist, and John Argall, P.Ag., Blueberry Specialist, N.B. Department of Agriculture & Rural Development Winter 1996 |
