20 CIRCULAR 85 3, U. S. DEPARTMENT OF AGRICULTURE 



oak trees were cleared a few years previously or on areas where oak 

 scrub occurs in close proximity are very likely to be attacked at an 

 early age. In fact, many such plantings of Australian pines in various 

 parts of Florida have proved extremely short-lived and losses have 

 continued to occur over a period of several years. 



In clearing land precaution should be taken to get out all the roots. 

 While this is rarely possible, deep plowing prior to planting should 

 prove very helpful. Any infected roots left in the land may serve as 

 centers of infection to trees planted subsequently. Areas where oak 

 trees were prevalent prior to clearing or where dead oak trees or 

 stumps were left and interplanted often prove to be veritable hotbeds 

 of infection for root rot in subsequent years. Clusters of the mush- 

 rooms of the fungus frequently develop around dead oak trees and 

 stumps following rainy periods and disseminate myriads of spores. 

 Unless such sources of infection are removed completely, it is usually 

 better not to plant trees that are particularly susceptible to Clitocybe 

 root rot. 



Remedial measures to be employed after the disease develops de- 

 pends largely upon the nature, kind, and extent of planting, and the 

 local circumstances. In an orchard or windbreak planting, the re- 

 moval of the first diseased tree or trees may prove helpful in curtail- 

 ing further development and spread, unless it starts from a number 

 of sources. A timely cutting away of lesions of diseased bark at the 

 bases of attacked trees and the removal of the soil to expose the root 

 crown and adjacent roots to aeration and drying frequently will 

 prove very effective in preventing the fungus from girdling the tree. 



"Where diseased trees are removed, a soil fumigant such as carbon 

 disulfide, which has been used successfully against Armillaria root rot 

 in California orchards, should prove effective against Clitocybe root 

 rot, although there is no record of it having been tried in Florida. 

 Soil fumigation, however, appears applicable only where diseased 

 trees are to be removed. 



In the early stages of Clitocybe root rot on ornamental or other 

 highly prized trees, careful surgical treatment may be effective. Un- 

 fortunately, however, the disease usually makes such extensive inroads 

 before marked symptoms of the diseased condition develop that by the 

 time the layman becomes aware of the trouble and learns the cause it is 

 often too late to save the trees. Investigation of the root crown and 

 root system often reveals that a large proportion of the root system is 

 infected and the basal portion of the trunk more or less completely 

 girdled, especially in young trees or shrubs. 



Surgical treatment is tedious and painstaking and must be done by 

 skilled workers. The extent to which the disease has attacked the root 

 system can be determined only by removal of the soil from around the 

 root crown and adjacent lateral roots to permit a thorough examina- 

 tion. Remove the soil within a radius of at least 2 to 3 feet around 

 the root crown, as shown in figure 10, working carefully to avoid injur- 

 ing living roots. If facilities for forcibly washing the soil away are 

 not available, use a trowel. Remove the soil first from around the base 

 of the tree and then around the lateral roots. Half of a post-hole 

 digger is an excellent implement for removing the soil from around 

 the root crown under the lateral roots when they lie too close together 

 to permit use of a shovel, 



