Crown-Gall of Apple and Peach 13 



In subsequent years many of the trees made excellent growth, as is shown 

 in table 2, but each winter the temperature was low enough to kill fruit 

 buds or else the buds were forced by a period of warm weather in late 

 winter and then killed by frost. 



The larvae of a borer (Sanninoidea exitiosa) gained entrance to a number 

 of the trees in the late summer of 1913. As they were not noted until the 

 following year, the number of trees showing effects of borer injury in 1914 

 is relatively large. The foliage of affected trees was slightly yellow 

 (off color), was often somewhat rolled upward, and in some cases showed 

 a marked tinge of red on the margins. Some of the borer channels extended 

 far into the roots, and practically all of the trees removed on September 1, 

 1915, were injured primarily by borers. In some cases frost cankers were 

 present, but these probably followed as a result of poor growth or immature 

 wood consequent to borer injury. 



Results of the peach experiment 



From time to time the trees that were crowding, and especially those 

 that were in poor condition, were removed. It was thus determined that 

 borers were chiefly blamable for the poor appearance of certain trees, 

 and that for the most part the galls had disappeared entirely. In many 

 cases the position of the original gall could be determined only with 

 difficulty or not at all. Usually the position could be determined by the 

 occurrence on the stock of an area having the appearance of a healed 

 wound (Plate II). 



No crop of fruit was obtained during the course of the experiment, and 

 so the onl}^ record is on the general appearance of the trees and the 

 condition of the roots at digging time. The condition of the trees from 

 year to year is shown in table 2. The same general reservations mentioned 

 for the apples (page 7) apply in the case of the peaches, although the 

 exact reason for the reservation is not the same in every instance. 



The trees still living in the spring of 1918 were pulled. Unfortunately 

 they were removed without warning and were not left in their regular 

 order. An attempt was made to compare the leafless trees with previous 

 growth records, but there was so much uncertainty about this that it was 

 abandoned. Examinations of the pulled trees bore out the condition 

 indicated in the table, namely, that most of the galls had disappeared. 



The most interesting outcome of the experiment is that no peach trees 

 died from the effects of crown-gall, and, so far as can be determined, 

 the disease did not affect the growth of the trees to any appreciable extent. 

 Tor the most part, galls either disappeared or were relatively small and 

 insignificant. In a few cases the whole stock of the_ tree seems to have 

 been enlarged, but even in such cases there was no indication, from the 

 general appearance and growth of the tree, that any injury had been 

 done. 



I 



