24 



CIRCULAR 270, U.S. DEPARTMENT OF AGRICULTURE 



limited to exposed roots. In the coast sections, particularly in heavy 

 soil that may crack, the aphids penetrate to the roots, causing swel- 

 lings and deformities (fig. 28) that may result in severely hindering the 

 growth of the tree. The colonies of aphids appear as bluish-white, 

 woolly patches, which are composed of the reddish insects covered 

 with woolly masses of wax. When the aphids are numerous this waxy 

 material, which contains some honey dew excreted by the insects, 

 hangs in festoons, smears the fruit, and makes picking a disagreeable 

 job. The aerial form also apparently prevents healing of cankers 

 caused by the perennial canker, in districts where that disease occurs. 

 The woolly aphid is found in practically all apple-growing districts, 



and it occurs on elm trees, and 

 occasionally on quince, pear, haw- 

 thorn, and mountain-ash, as well 

 as on apple. 



LIFE HISTORY 



The life history of the woolly 

 apple aphid is somewhat compli- 

 cated. Wintering eggs are laid on 

 elm trees, and the young hatching 

 from these feed on the elm leaves, 

 curling them severely. Later 

 winged forms appear and migrate 

 to the apple. Many wingless 

 forms also hibernate on the roots 

 of the apple trees, and many of 

 those on the upper portions of the 

 trees survive mild winters. Infes- 

 tations aboveground may thus 

 come from three sources — winter- 

 ing forms already present, mi- 

 grants from the roots, or migrants 

 from nearby elm trees. Heavy 

 infestations are likely to follow 

 mild winters. The aphids mul- 

 tiply rapidly, and winged forms 

 occur at times; these fly to other 

 apple trees and establish new colonies, or migrate to the elm in the fall. 



Figure 27.— Aerial colony of the woolly apple aphid. 



PREVENTION AND CONTROL 



Sprays applied during the delay ed-dormant period, as recom- 

 mended for the other apple aphids, are of relatively little value in 

 controlling the woolly aphid, since colonies from the roots or from elm 

 trees are established later in the season. No control is necessary for 

 light infestations, but if the aphids become numerous on the twigs and 

 branches, a contact spray, such as nicotine sulphate (40 percent nico- 

 tine) in the proportion of three fourths of a pint to 100 gallons of 

 water, added to an oil emulsion, or used with soap or casein spreader, 

 is effective. If used with an oil emulsion, this spray may replace one 

 of the lead arsenate sprays in the schedule for controlling the codling 

 moth. On account of the protection afforded the insects by their 

 woolly covering, the spray must be applied very thoroughly and with 

 adequate pressure. The oil emulsion alone is not effective. 



