52 



CIRCULAR 2 7 0, U. S. DEPARTMENT OF AGRICULTURE 



Aphids 



Four or five species of aphids occur on prunes and plums in the 

 Pacific Northwest. All have similar habits and may be controlled 

 in a similar manner. One of the commonest species is the hop aphid 



(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 pos- 

 sible. This aphid, which is green, 

 often covers the under surface of the 

 leaves of prune trees early in the 

 season. The mealy plum aphid 

 (Hyalopterus arundinis (F.)) 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 {Anur aphis cardui (L.)), the 

 leaf curl plum aphid (A helichrysi 

 Kalt.), and the green peach aphid 

 (Myzus persicae (Sulz.)) also occur on 

 prune and plum trees, and occasion- 

 ally 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 within 

 the opening buds and on the leaves. 

 After several generations have devel- 

 oped on the prune trees, winged forms develop and fly to the summer 

 host plants, and later generations 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 cattails, the thistle aphid on thistles, 

 chrysanthemums, and other plants, and the other two species on a 

 large variety of wild and cultivated plants. 



Figure 60. — Meal} 7 plum aphid on 

 plum foliage. 



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-sulfur is used, nicotine sulfate (40 percent nico- 

 tine) 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, 



