Canadian Forest Service Publications
Effets à moyen terme de la fertilisation par urée ou par potassium sur Pinus banksiana L. et le comportement de ses insectes dévastateurs : tel que Neodiprion swainei (Hymenoptera : Tenthredinidae) et Toumeyella numiscaticum (Homoptera : Coccidae) 1975. Smirnoff, W.A.; Valéro, J.R. Canadian Journal of Forest Research 5(2) : 236-244.
Available from: Laurentian Forestry Centre
Catalog ID: 16103
It was established in 1973 that fertilization with 400 kg of urea per hectare (1 ha = 1 x 104 m2) in 1969 and in 1970 was still influencing the level of chloride, the osmotic pressure and the activity of two enzymes, glutamic-oxaloacetic transaminase (GOT) and glutamic dehydrogenase (GLDH) contained in the foliage. In June 1974 in current and previous years' growth, the amount of chloride had decreased, respectively, to 81 and 50 p.p.m. (mg/kg) in fertilized trees, and the osmotic pressure increased by 37 and 49 mømol/kg. The activity of GOT and GLDH in the foliage of fertilized trees was 41 and 14 mU/g, respectively, compared with 163 and 21 mU/g, respectively, in the foliage of unfertilized trees.
It was found 3 years after fertilization that the mortality of N. swainei larvae was 50% higher and the damage they caused was 42% less in fertilized trees. Also, it was observed that urea fertilization, even at low dosage, favoured T. numismaticum, this infestation increasing 2, 7 and 9 times in plots fertilized with 100, 200 and 400 kg of urea nitrogen per hectare.
The studies revealed, however, that fertilization with potassium may reduce T. numismaticum. The infestation in the fertilized plot showed a reduction from 42 to 21%, and in the unfertilized plot there was an increase from 38 to 80%.