480 THE MONTHLY BULLETIN. 



COUNTY COMMISSIONERS' DEPARTMENT. 



Fall Treatment for Apple Aphis. 



By O. E. Bremner. 



A consideration of the life history and habits of an insect is the first 

 and most important step in effecting a method of control. A fall spray 

 campaign against the aphids we are discussing may not be found suc- 

 cessful in other localities and under other conditions, but Avherever the 

 climatic conditions are similar to those of this coast section we predict 

 the same results attending this treatment. 



Three years ago we commenced a careful study in the apple section 

 of Sonoma County, of aphids affecting apple trees in particular, and 

 have also made some observations on forms affecting cherries, hops, 

 prunes and other trees. 



The subject is a hard one owing to the very complex life of the insects 

 and at the present time we feel that we have practically mastered one. 

 the purple apple aphis. Aphis sorhi, which is without question the most 

 destructive in this county from an economic standpoint. The same 

 treatment will partially control the woolly aphis, Erisoma lanigera 

 and give good results on the green apple aphis, Aplus pomi. 



The purple aphis hatches early in the spring, in fact just with the 

 opening blossom cluster buds. It is a peculiar and noteworthy fact that 

 this hatching period absolutely follows the condition of the individual 

 tree so that on the same variety in the same row one tree may put out 

 leaves and contain young aphids several days ahead of the other trees, or 

 be equally as late. The same thing is more strikingly observed in dif- 

 ferent varieties. As an instance of this we found aphids hatching and 

 attacking the opening buds of the Gravensteins, Ehode Island Greenings, 

 and Red Astrachans on March 10th, but on Rome Beauties growing side 

 l)y side with these trees the aphids made their appearance April 1st. It 

 is thus seen at a glance that the spring treatment is a difficult but not 

 altogether satisfactory matter. Tbis is better understood when you 

 consider that if the aphid is not killed within less than a week from 

 hatching the damage to the crop is practically accomplished. The newly 

 liatched aphid attacks the developing leaves and also pushes down into 

 the cluster buds attacking the embryo apple even before it blooms. The 

 toxic effect of this attack causes the leaves to curl tightly so that the 

 insects within are perfectly protected against future doses of spray 

 material, and the apples to be stunted, ripen prematurely, have a rough, 

 pimply surface, and develop no flavor. In fact an attacked apple is fit 

 for nothing except vinegar and very little good for that, a^ it never 

 drops and is a tedious thing to pick. These stem mothers give rise to 

 several generations of parthenogenetic females and during the warm 

 weather in June winged females appear and migrate to some inter- 

 mediate host. No aphids can be found on the trees from this time until 

 about the middle of October, when winged viviparous females appear. 

 As to the intermediate host we have been so far unable to locate it, but 

 have found the aphids on careless weed {Amarantns retroflexits) at the 



