October, '21] smith: prune aphid 423 



and most varieties of pliim are apparently entireh- dormant and those 

 of peach are only slightly swollen. The stem mothers which at firts 

 are dark green but become distinctly reddish with a brown band on the 

 dorsum of each body segment at maturity, feed at the bases of buds and 

 thru the bark of the last season's growth until the fruit buds begin to 

 open. The stem mothers begin reproducing about the time green tips 

 appear on the fruit buds of prune. Migrants occur chiefly in the third 

 and succeeding generations. The progeny of the stem mothers are 

 pale green w^ith the body integument sem.i-translucent ; only the distal 

 ■ends of the antennae and the tarsi show slightly dusky. In some instances 

 plum trees have remained heavily infested thruout the summer. 



Character of Injury. The aphid is strictly leaf-feeding on prune 

 and pliun but on red clover and other simimer host plants it feeds chiefly 

 on the more concealed parts of stems, petioles and blossoms. Infested 

 leaves of prune and plum curl tightly and develop numerous pocket-like 

 galls. New leaves at the tips of infested branches become curled as 

 soon as they start to develop. The new growth of such branches is 

 somewhat stunted and malformed and there appears to be a tendency 

 toward premature dropping of the fruit as a result of the infestation of the 

 foliage. Infestation is usually confined to one or a few branches on 

 m.oderately affected trees, the aphids not spreading readily from one 

 part of a tree to another. 



Host Plants. All varieties of prune and plum that have come under 

 our observation have been susceptible to attack though seedlings and 

 root sprouts appear to be favored. Occasional colonies have been found 

 on peach and apricot in early spring but these did not thrive in the same 

 vigorous m.anner as did colonies on Italian and Hungarian prunes, and 

 varieties of plum,. The most favored summer host plants in Idaho as 

 determined at present are Trifolium pratense L., garden varieties of 

 Aster sp., Chrysanthemum sp.. Dahlia sp., and Erigeron canadensis L. 

 The aphid has been observed in smaller numbers on Achillea milli folium L, 

 Solidago serotina Ait., Trifolium hybridum L., T.repens L., and Solidago 

 spp. 



Control Measures. Black Leaf 40 used at the rate of ^4 pint to 100 

 gallons of water with soap as a spreader or to 100 gallons of dilute lime- 

 sulfur solution, and applied just before the buds open on prune and plum 

 has given perfect control. Lime-sulfur at winter strength has not 

 been effective in destroying either the eggs or the young stem mothers. 

 Control of the pest in red clover fields is somewhat complicated and is 

 •discussed in detail in a bulletin on the Clover Aphis (Anuraphis bakeri 

 •Cowen) now in course of publication by the Idaho Experiment Station. 



