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THE MONTHLY BULLETIN. 



THE CONTROL OF WALNUT APHIS 



( Chromaphis juglandicola). 



By A. A. Brock, County Horticultural Commissioner, Santa Paula, Cal. 



Iu recent years this aphid has evoked considerable comment and much experimental 

 work has been done by investigators, with reference to possible injuries to trees and 

 mils from their attack. These iujuries have caused great anxiety, and a desire for 



an effective and economical control measure. It 

 would require considerable space to enumerate all 

 of the deleterious effects theoretically attributed to 

 this insect ; however, it is an established fact that 

 the physiological functions of trees are greatly- 

 impaired by the sticky excretions of this and other 

 hemiptera. 



In this county the infestations usually alternate, a 

 heavy infestation being followed by a light one. In 

 the summer and fall of 1913 the groves were severely 

 attacked, all parts of the trees being covered with 

 sooty mold fungus (Eliola camelliw.) The loss 

 accruing from this created a demand for an effective 

 means of control. Before this time the pest had been 

 considered of little importance by the walnut growers. 

 Early in the spring of 1914 we sprayed a number of 

 groves in an experimental way with a dormant spray 

 of commercial lime-sulfur and quicklime, the latter 

 being used as a marker. A few rows in several 

 orchards wen? treated, leaving the remainder for a 

 check. In a grove 31 years old we sprayed 33 trees 

 with a 5 per cent solution of commercial lime-sulfur, 25 pounds of lime being added to 

 each. 200-gallon tank. It required a day and a half to thoroughly spray these trees, 

 using M. A. C. uozzles, and the cost to the grower was $1.37 per tree. The following 

 summer the infestation was very light throughout the walnut-growing section. A 

 close watch was kept of the sprayed groves, but little difference could be noted in the 

 sprayed and unsprayed trees, although the former were practically free from erinose, 

 which is normally very abundant, though of little importance. In 1915 the infestation 

 was quite serious again, while in 191G it was severe only in a few scattered groves. 

 No control measures were attempted during these years. In 1917 the infestations 

 promised to be very severe early in the summer, creating alarm. We had kept close 

 watch, and were prepared to start spraying as soon as conditions warranted treatment. 

 Our first attempt was with nicotine sulfate and whale-oil soap at the rate of 1* pints 

 of tobacco extract and six pounds of whale-oil soap to two hundred gallons of water. 

 The aphids were found to be dead very shortly after the application of this insecti- 

 cide, it being almost impossible to find a live aphid on the sprayed trees. The 

 grower for whom the work was done was so pleased with the results that he decided 

 to spray thirty acres which were heavily infested. There were six hundred and thirty 

 trees in this orchard, requiring six days to spray, at a cost of 34 cents per tree. 

 After approximately half of the grove had been sprayed with li-6-200 formula, the 

 strength was reduced to 1-4-200. No difference in results being noted, it was again 

 reduced, this time to J-4-200. The only difference observed was that the aphids 

 were not killed as quickly as with the stronger solutions, though the final results 

 were identical. Had the minimum strength been worked out before starting this 

 spraying the cost of the work would have been reduced from 34 cents to 17 cents per 

 tree. Other groves were sprayed with like results. Arrangements had been made 

 to spray several other orchards, but the hot weather of June 14 to 17, inclusive, so 

 destroyed the aphids that it was unnecessary. The heat also destroyed about 25 

 per cent of the walnut crop, the districts inland being damaged the most, some 

 properties losing as much as 50 per cent of the crop. Another spray of nicotine 

 sulfate and lime-sulfur has been tried out, but its use is not recommended because 

 of the danger of severe burning if hot weather follows its application. 



An attempt to control has been made here and elsewhere by applying tobacco dust 

 and lime or sulfur as a carrier, with a large power dusting machine. This promises 

 to be an effective and economic method of controlling the pest. Professor Ralph E. 

 Smith, of the University of California, has had charge of this experimental work. 



