11 



have been some reports of occasional marked increases in flesh 

 browning (considered to be COp injury) in some CA rooms in New 

 York State where a few CA operators have maintained temperatures 

 at 35-36 F. Apparently, there sre also a few people in Massachu- 

 setts who have been holding Mcintosh in their CA rooms at 35-36 F. 

 Although it is quite possible that fruit injury may not appear in 

 most years or only on occasional lots of fruit in a given room, ^q 

 do not believe the relatively minor improvement in fruit condition 

 warrants the risk of serious fruit injury once every 5 to 10 years, 



*************** 



COLLAR ROT 



Department 



Duane W . 

 of Plant 



Greene 

 and Soil 



Sci ences 



At a recent meeting, the problem of collar rot or crown rot 

 disease in apple orchards was discussed. The symptoms of this dis- 

 ease, caused by the fungus Phytophthora cactorum , are reduced tree 

 growth, sparse light-colored foliage and a premature reddish colora- 

 tion of leaves in the fall. Trees may show symptoms 2 or 3 years 

 after planting, but generally they are more pronounced when trees 

 start to bear. 



Initial stages of collar rot are often difficult to detect. 

 However, if infection is suspected, move all soil away from the 

 trunk down to the large roots. Early stages of infection may be 

 recognized by dark water-soaked areas in the bark. Advanced stages 

 are characterized by large dark irregularly shaped areas on the 

 trunk. Removal of some of the bark in these dark areas will reveal 

 a tan or reddish brown inner bark. The disease will continue to 

 spread until the tree is completely girdled. 



Collar rot is most prevalent where trees are grown on heavy 

 soils with poor drainage. On of the major avenues of entry into 

 the tree is through injured tissue at the crown caused by ice dam- 

 age. Infection generally occurs in the fall or spring when the 

 fungal spores are most numerous. 



Rootstocks differ in their resistance to this disease. Both 

 MM 104 and MM 106 are especially susceptible. In addition, MM 104 

 grows very poorly under wet soil conditions and should not be 

 planted in low, poorly drained areas. A low incidence of collar 

 rot has been reported in trees on EM VII and EM II. Mcintosh, 

 Wealthy and Melba have proved to be resistant stocks. 



Various measures may be taken to control this problem. In- 

 arching above the infected area with seedling trees or clonal root- 



