Damage of Cone from Insects in Pine Seed Orchard and Preliminary Spray Application of Insecticides

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  • マツ採種園における球果の虫害と薬剤防除の試み
  • マツ サイシュエン ニ オケル キュウカ ノ チュウガイ ト ヤクザイ ボウジョ ノ ココロミ

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Abstract

In 1968, investigations on the damage of cone from insects and on the preliminary spray application of insecticides were conducted at the pine seed orchard of the Kanto Forest Tree Breeding Station, consisting of Pinus densiflora and Pinus thunbergii. Most of the damaged cones were infested by Evetria cristata and a few of them by Dioryctria splendidella. The ratio of them was 15:1.<br> E. cristata completes two generations in a year and mid-July is approximately the border between two attacking periods. By mid-July, 8.5 per cent of second year cones of P. densiftora and 25.9 per cent of those of P. thunbergii were injured. By the end of summer, the percentages increased to 23.1 per cent in P. densiflora and to 43.1 per cent in P. thunbergii. Tree height and the altitude of the orchard also seems to have influenced the damaged cone percentage. First year pine cones were killed due mainly to the death of new shoots caused by the attack of several kinds of pine shoot moths.<br> The extent of damage in the second year cones varied from ‘slight’ to ‘dead’. In the cones which escaped from death and contained normal seeds in them, the seed scales were hardly opened because of resin exudation from wounded portions of the cone. Death of cones was mainly caused by the attack of the first generations of E. cristata and D. splen. didella.<br> Emulsions of DDT (2g/1l water), Baycit (0, 0-dimethyl 0-(4-methylthio-m-tolyl) phosphorothioate; lg/1l water) and Ekatin (0, 0-dimethyl S-2-(ethylthio) ethyl phosphodithioate; 0.5g/1l water) were sprayed in mid-July with the intention of reducing the cone damage by the second generation of E. cristata. Average percentages of the injured cones after the spray treatment were 2.0, 4.7 and 11. 4, respectively, as compared with 20.5 in control. Analysis of variance and DUNCAN'S multiple-range test after aresin √percent transformation of injured cone percentage of each plot showed that DDT and Baycit treatments reduced the cone damage significantly.

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