FORTY-SECOND ANNUAL REPORT. 81 



nothing else. The spray to which we have referred should go on 

 when the petals fall and should he put on under comparatively high 

 pressure. About 200 pounds is all right. A coarse nozzle of the 

 bordeaux type will carry the poison in between the calyx bars much 

 better than can be done with a fine nozzle especially if the spray is 

 directed downward from above. Of course the work must be done 

 thoroughly. One can always check up on his work by going back over 

 the sprayed part of the orchard and cutting open some of the little 

 fruit sets. If one finds a drop of poison in each little set, then he 

 knows that the work has been thoroughly done. 



The second spraying in the first week of August is aimed at the 

 second generation of larvae. As most of the eggs are laid on the 

 leaves and as the young feed where they hatch out before going into 

 the apple, a mist spray which deposits a thin layer evenly all over the 

 foliage is best. 



Now, about plant lice. For two years we have found numbers of 

 plant louse eggs on apple trees in early spring and late in the winter. 

 Some of you will remember finding large numbers of these eggs a year 

 ago last winter and again last winter, — little black shiny eggs on 

 the branches. Two years ago they were more plentiful than last year 

 but when the season came on two years ago it was warm and dry 

 and the plant lice hatched out all right but disappeared about blossom- 

 ing time. Last summer the season was wet and cold and they started 

 just the same as the year before only they did not stop at blossoming 

 time, rather getting worse as the season advanced. Now, we can see 

 the effect on the apples. Many apples in the middle part of the tree 

 are hard and undersized. 



Now, for the explanation. There are three kinds of plant lice that 

 work on apple trees. First the common green apple louse, the rosy 

 louse, and a third one. I do not know that the third one has any 

 common name. The common green louse lives on apple trees early 

 in the spring. About the time the blossoms open it goes to orchard 

 grass and stays there all summer to come back about the time that 

 apples are gathered. The other green louse leaves about the same time 

 and goes somewhere that we lose track of it, its offspring returning 

 also in the fall. The rosy louse stays on the apple all the year around. 



When the rosy louse multiplies and keeps its numbers up all sum- 

 mer, then is the time we have trouble. This happens in seasons when 

 we have a backward spring, a cold wet spring extending into the 

 summer and the reason is because cold Aveather does not agree with 

 the parasite which keeps the rosy louse in subjection. This parasite is 

 a little wasp-like creature which thrusts its eggs through the skin into 

 the bodies of the plant lice. There the young grubs from these eggs 

 feed ; each one on the tissues of a living host, to come out later as an 

 adult and repeat the egg-laying process. Now, it happens that the 

 parasites are more sensative to temperature than are the plant lice 

 themselves. The parasite will stop growing during cold spring days 

 at a time when plant lice will thrive and multiply. For this reason 

 cold, wet springs hold back the parasites for a long time giving the lice 

 a chance to get such a start that the parasites do not catch up with 

 them all summer. 

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