50 



CIRCULAR 270, U.S. DEPARTMENT OF AGRICULTURE 



(Phorodon humuli Schr.), which is a serious pest of hops, but spends a 

 part of the year on prune trees. Planting hops near prune orchards 

 should therefore be avoided, if possible. This aphid, which is green, 

 often covers the under surface of the leaves of prime trees early in 

 the season. The mealy plum aphid {Hyalopterus arundinis Fab.) 

 may be recognized by its bluish-green color and its whitish, powdery 

 covering (fig. 60). It frequently becomes exceedingly abundant on 

 the under surface of the leaves. The thistle aphid (Anuraphis cardui 

 L.), the leaf curl plum aphid (A helichrysi Kalt.), and the green peach 

 aphid (Myzus persicae Sulzer) also occur on prune and plum trees, and 



occasionally become abundant. 



These are green or reddish, and 



they curl the leaves considerably. 



All of these species are of European 



origin. 



LIFE HISTORY 



The life histories of these aphids 

 are similar. Wintering eggs are laid 

 on the trees and hatch early in the 

 spring before the buds have swelled 

 appreciably, the young feeding with- 

 in the opening buds and on the 

 leaves. After several generations 

 have developed on the prune trees, 

 winged forms develop and fly to the 

 summer host plants, and later gen- 

 erations return to the trees in the 

 fall. During the summer the hop 

 aphid is found on hops, the mealy 

 plum aphid on reed grasses and cat- 

 tails, the thistle aphid on thistles, 

 chrysanthemums, and other plants, 

 and the other two species on a large 

 variety of wild and cultivated plants. 



CONTROL 



A dormant-season application of 

 oil emulsion, containing 4 percent of 

 oil, is ordinarily fairly effective in 

 controlling aphids on prune and 

 plum trees. If lime-sulphur is used, 

 nicotine sulphate (40 percent nicotine) should be added to it in the 

 proportion of three fourths of a pint to 100 gallons of water. If the 

 dormant spray has not been applied, and the infestation becomes 

 serious, a special application of nicotine sulphate may be made at any 

 time it is needed, adding to it 2 or 3 pounds of soap in solution or 1 

 pound of casein spreader to 100 gallons. 



RED SPIDERS 



Prune and plum trees are often seriously affected by red spiders. 

 The foliage is bronzed and defoliation may occur in nonirrigated 

 orchards, frequently accompanied by the dropping of some of the 



Figure 60.— Mealy plum aphid on plum foliage. 



