384 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION. 



trees. The insect feeds by sucking the nutritive juices from the 

 foliage of the tree and when abundant it may injure the tree to no 

 little extent by so doing. In dry years, when the trees are already 

 somewhat weakened, the bad effects are increased. It is also probable 

 that the tree is injured more or less by being coated over with honeydew 

 and sooty mold. The insect multiplies most freely in seasons or places 

 of rather cool, moist, summer climate, and is largely suppressed by 

 continuous hot sunshine. Its effects are therefore worst in regions 

 near the coast. In addition to the direct injury to the tree caused by 

 the aphis and its honeydew, there is some possibility that these effects 

 are connected with perforation of the walnut and also shriveling or 

 poor development of the meat. In all events these troubles usually 

 occur together, and years when there is an abundant development of 

 aphis, there has also usually been more perforation and more poor 

 meats. This may be the effect of the insect or it may be that all these 

 troubles occur more abundantly under the same conditions, partic- 

 ularly in a season following a dry winter. Another well-established 

 effect of the aphis is connected with the spread of the walnut blight 

 organism. There is no question that these insects in crawling about 

 and puncturing the leaves spread the blight to a considerable extent. 

 All in all, therefore, we believe that the control of aphis is one of the 

 most important problems of the walnut grower if the insect continues 

 to develop as it has during the past two or three years. 



APHIS CONTROL. 



The only feasible means of controlling this insect appears to be by 

 spraying with the most effective substance at the most effective time. 

 No definite experiments have been made along this line, nor has the 

 insect ever been carefully studied so far as we are aware. 1 It appar- 

 ently winters over upon the walnut tree, probably in the egg form, 

 so that it may be possible by a winter spraying to exterminate the 

 insect during the dormant season. Various winter spraying of wal- 

 nuts has been done by different growers, using lime-sulphur and other 

 similar sprays. The results of such spraying as to aphis control seem 

 to be somewhat doubtful. Some have thought that much benefit was 

 obtained, the amount of aphis during the following summer being much 

 reduced, while others could see no such effect. Summer spraying is 

 effective against many other kinds of plant lice, and there is no reason 

 why the walnut aphis could not be controlled in the same way, except 

 that the trees are large and the spraying expensive. Mr. George 



'It is described and illustrated by E. O. Essig in The Monthly Bulletin, Cal. State 

 Com. of Hort., Vol. 1, No. 5, p. 190. 



