Current issue: 53(1)
An attempt was made in the study to determine the annual periods available for foliage spraying when cleaning Scots pine (Pinus sylvestris L.) dominated seedling stands. The study was made in nine experimental fields which were established in different parts of Finland. The spraying was applied throughout the growing season by DM, MCPA and Roundup. The results were inventoried one year after the treatments.
The results showed that there were big differences both in the destruction of hardwood sprouts and in the survival of pine seedlings due to the time period of the spraying. Threshold points were observed in the range of effect of DM and MCPA. By means of these it is possible to time the spraying treatments in such a way that there remains only slight damage to pine, but hardwood sprouts are destroyed totally. The results varied with Roundup so much, among other things due to rain, that such threshold points could not be determined. This preparation both had a milder effect on the hardwood seedlings and caused slighter damage to pine than the other preparations.
In Sodankylä in Northern Finland, the pines attained a good resistance to arboricides when the efficient temperature sum of the growing season was 550, but in Punkaharju in Central Finland only when it was 850. The seed provenance of the seedlings had an effect on the resistance. The threshold temperature sums of resistance in pine were on the average 70–74% from the long-term average number of degree days at the origin of the seed. The effect on the hardwood trees grew weaker as the long-term average was filled. Resistance of pine followed with a specific lag the lignification of the shoot and the ceasing of the growth of the needles.
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