286 Appendix. 



the infection was tlius spread pretty generally through the yards. By the time 

 the hops began to form the aphids were very numerous and. where no remedial 

 work was undertaken, the damage done by them was very considerable. 



CHARACTER OF IX.TUKY. 



The injury wrought by the aphids upon the pistillate plants (female hops) 

 is twofold. At first the attack is confined to the leaves and tender growing tips 

 of the shoots, and the size of the leaves of the plants when the lice are numerous 

 iipon them is greatly reduced. So severe, indeed, was the effect upon the plants 

 under observation that by the first of July attacked vines in the yards could be 

 easily distinguished from the plants that were not attacked, because of the small- 

 ness of the leaves and their yellow, dry appearance. The crop upon these 

 affected plants is of .small size and light weight and greatly reduced in value. A 

 more serious injury, however, is that to the hop cones themselves, because of the 

 direct attack of the aphids on the heads. The insects seem to find the young, 

 newly-forming cones very much to their taste and gather in great numbers in 

 them, generally at the base of the bracts. When the hops are gathered and sent 

 to the kiln for drying, these aphids remain in place, and the result is that the 

 finished product is of poor quality and aroma because of the dried bodies of the 

 insects in them. This reduces not alone the value of the individually affected 

 bops, but also of the whole lot in which they may occur. The total injury de- 

 termined by comparing yards that were similar in every respect of soil, climate, 

 and exposure, was such that the crop of the yards where no control work was 

 attempted and where the aphids were allowed to take their full course, returned 

 to the owners not more than one-half as much per acre as did those yards where 

 control work was done. 



EXPERIMENTS WITH REMEDIES. 



While the hop aphids appeared in the Pajaro Valley yards very early in 

 May, 1903, (first observed May 2d), they did not become numerous enough to 

 constitute a serious menace to the crop until the middle of .lune. At this time 

 they had become quite well distributed from the points of beginning, and were 

 even occasionally to be found in the newly-forming hops ; and a brisk campaign 

 was organized against them. Through the co-operation and assistance of certain 

 growers of hops in the region we were enabled to carry out a series of experi- 

 ments in spraying on two hop yards. This work resulted in a complete control 

 of the aphids, and very greatly increased the value of the yield in these yards 

 over that of the adjacent yards that were not treated. 



KEROSENK EMULSION AND TOBACCO. 



One yard, comprising some forty acres, is situated near the town of Wat- 

 sonville, in the Pajaro Valley. During the third week in June the attack of the 

 aphids in this yard became so serious that it seemed as though a large proportion 

 of the crop would be ruined by them. The male vines in certain portions of 

 the yard were very much infested with the aphids, and they could also be found 

 in goodly numbers on the female vines and even in the young hops. After some 

 minor experimenting to decide the killing power of the material and its effect on 

 the hop foliage, we decided to treat this yard with a spray made up of tobacco 

 decoction and kerosene emulsion in combination. The tobacco decoction was made 

 by steeping tobacco stems and refuse from cigar factories for from two to three 

 hours in water that was kept heated to just below the boiling point. One pound 

 of tobacco refuse was used to each two gallons of water, and by this steeping 

 process a quite strong tobacco juice resulted. The kerosene emulsion was made 

 by dissolving seven and one-half pounds of ordinary laundry soap in fifteen gal- 

 lons of hot water, and to this adding five gallons of kerosene oil. The soapy 

 water and the oil were thoroughly churned together for from fifteen to twenty 

 minutes. This was best done by pumping back the material on itself through 

 the spray nozzle. The result was a fairly stable emulsion of a creamy con- 



