8 



CIRCULAR 8 53, U. S. DEPARTMENT OF AGRICULTURE 



require 2 or 3 years from the time the first symptoms become apparent, 

 new foliage branches may develop following the shedding of a large 

 proportion, but the new ones usually attain only about half the normal 

 length for the species. 



By the time a pronounced yellowing or defoliation or other decline 

 of the tops of attacked trees is apparent, the mycelial growth of the 

 fungus usually has progressed upward on the base sufficiently so that 

 its presence can be verified by making a cut in the bark down to the 

 wood ; though sometimes it may have developed only up one side of 

 the tree. The upward progress of the mycelium at the base of the 

 attacked tree frequently is indicated by a slightly sunken lesion. Such 



Figure 3. — Base of a large guava tree killed by Clitocybe root rot. Lesions extend 

 up the trunk divisions; dead bark cracked loose on one at right, and shed on 

 two at left. 



basal lesions are most conspicuous on trees and shrubs with thin 

 bark and do not show on thick-barked trees. They frequently develop 

 first on one side before encircling the trunk. By the time the crown 

 begins to become thin from defoliation, the cutting test of the bark 

 usually shows the base of the tree immediately above the ground to be 

 completely girdled. This girdling is often accompanied by longi- 

 tudinal cracking of the bark as it dies, and sometimes also by a pro- 

 nounced cracking, demarking the extent of the lesions (fig. 3). The 

 basal lesions usually extend upward from a few inches to about a foot 

 and rarely as high as 2 feet above the ground before the attacked tree 

 dies, the height frequently being greater on one side than on the other. 



