Abstract
The arctic bramble is native in Estonia. It is a rare species and has been under protection since 1958 already. The cultivation experiments were started in 1995. It appeared that losses due to the infection of fruits by downy mildew may cause significant decrease of the crop. Our preliminary observations indicate that the extent of the infection is correlated with the stress caused by low temperatures and water deficiency. The arctic bramble starts rapid growth with the first warm days in April, and the following night frosts in May often damage the young aerial shoots. This problem does not occur in natural habitats where arctic bramble grows under the bush layer and starts growing and flowering considerably later than in open plantations.
The climate conditions of North Europe are suitable for the lowbush and half-highbush blueberry cultivation (Paasisalo et al., 1994). In Estonia the soils suitable for blueberry growing are in the southern part where the climate conditions are also favourable.
In 1999 the effect of winter straw cover on the beginning of the growth of aerial shoots of arctic bramble was tested. The goal of a half-highbush blueberry experiment was to observe how different cultivation methods affect winter hardiness of blueberry plants in the Estonian climate.
Material and methods
The experiments were carried out in Tartu County, South Estonia. The experimental plot of arctic bramble was covered with plastic in autumn, 1996.Micro propagated plants were planted at intervals of at least 33 cm. The combinations of cultivars of Finnish origin and the native clone in the experiment were as follows: `Marika'+'Pima', Estonian clone (E)+'Pima', `Pima'+'Mespi', Estonian clone+'Marika', Estonian clone+'Pima'+'Marika'. Straw cover was laid in December and removed on the 20th of May, after the critical night frost period had passed.
The half-highbush blueberry cultivars ‘Northblue’ and ‘Northcoutry’ were used in the experiment. A plantation was founded in June 1997 with one-year-old in vitro plants. The gap between the plants was 0.7 m and the space between two rows was 1.5 m. In the trial different cultivation combinations were:
1. mineral soil without mulch (control);
2. mineral soil with sawdust mulch;
3. mineral soil with peat mulch;
4. mineral soil with plastic mulch;
5. soil mixture (mineral soil + peat) with peat mulch;
6. soil mixture (mineral soil + peat) with plastic mulch.
Each plant received 10 l peat into the growing substrate before planting (the variants 5 and 6). Mulch treatments were applied at a 70-cm-wide band centred on the plant row immediately after planting. The ground was covered with a 5-cm layer of peat and sawdust mulch. In the spring of 1999, winter hardiness was estimated using a nine-point scale (1 point - very low winter hardiness, all branches damaged; 9 points - very high winter hardiness, branches not damaged).
Data were analysed by ANOVA table. Error bars represent the standard deviation. Significant (p< 0.05) differences from the control are marked by an asterisk (*) in figure.
Results and discussion
Arctic bramble experiment
In 1999 unusually low temperatures followed the warm April days in May. We have registered -15 °C at the ground level for several times, which significantly affected the aerial shoots of the plants that had started their growth already. The plants that were still buried under the straw cover had not started to grow and did not suffer at all. The frost-affected plants recovered after some period, but the crop was always smaller.
The cultivars and straw cover had a significant influence on the berry production and on the number of drupes in fruit (Fig.1, 2). Arctic bramble is self-sterile and thus it is essential to grow together two or more productive cultivars and the number of drupes in a fruit affects the success of pollination. It is common in Finland to grow together `Pima' and `Mespi' (Kokko et. al., 1998). The average crop of different new cultivars is 421 g/ 10m² (Kokko et. al., 1993). In our experiment the combination had the lowest yield, 72...164 g/ 10m². The highest yield in our experiments were 337…474 g/ 10m².
The first berries ripened on the 8th of July and were picked four times before the 1th of August. In our former trials harvesting began on the 4th ofJuly and lasted until the 10th of September and berries were picked in total of ten occasions (Karp et. al., 1997). In 1999 the flowering period lasted only until the end of June because of the unusually warm and dry weather. Our former experience show that 63% of the crop is picked during August. Therefore we can conclude that a great part of the yield was not obtained because of the extremely dry and warm summer in 1999.
The results of the experiment showed:
- Straw cover turned out to be effective in delaying the growth and thus reducing the possibility of the aerial shoots to be affected by spring night frosts.
- The cultivars and straw cover had a significant influence on the yield.
Half-highbush blueberry experiment
Winter hardiness was estimated in the early spring. The hardiness rate of the cultivar ‘Northblue’ was 5.5…7.2 points (Fig. 3). The bushes of the cultivation combinations 3 and 6 hibernated worse than the control (p<0.05). The average winter hardiness was 5.5…6.0 points without any significant differences.
The winter hardiness of ‘Northcountry’ was 5.7…6.8 points (Fig. 3). The bushes had more damages in the cultivation combinations 4 and 6.
Our results showed that the winter damage was not very large, no plants died. In the case of plastic mulch, winter hardiness of both cultivar decreased. One-year-old shoots did not finish growing on schedule, they were herbaceous, not ligneous, and the first frost damaged the shoots in late autumn already.
The results of the experiment showed:
- The half-highbush blueberry grows well but the problem of the cultivation is that the plants do not stop growing in autumn and the herbaceous shoots are damaged when the first frosts start.
- Plastic mulch decreased winter hardiness of half-highbush blueberry.
References
Figure 1. Influence of straw cover and cultivar on total yield of arctic bramble in 1999 (mean, STDEV)
Figure 2. Influence of straw
cower and cultivar on number of drupes in the fruit of arctic bramble in
1999 (mean, STDEV)
Figure 3. Winter hardiness of
blueberry cultivar ‘Northblue’ and ‘Northcounrty’ in 1999 (points)
