DISEASES OF VARIOUS CROPS 



121 = 



943 - Trichoderma koeningi causing Root Rot of the Apple Tree, in Virginia. 



— Crabill C. H. ill P/!y/o/5fl//;r)/oA,'y, Vol. 6, No. ::, pp. i59-i6i,Fig. i, Baltimore, Md., 

 1916. 



In Virginia, rotting of the roots of the apple tree occurs chiefly in the 

 valley of Shenandoah and the district of Piedmont. It is responsible for 

 very heavy damage, and nothing has np to now been done to control it. 

 Trees from ten to fifteen years old are usually attacked. The pathological 

 process is rapid and fatal. The first visible symptom of the disease is a 

 stoppage of growth, followed by the partial falhng of the leaves and the 

 withering of the terminal buds. At the moment when these symptoms appear, 

 the root system is alread}' dead, the roots are cracked and fragile, and the 

 tissues invaded by an abundant growth of m.j'celium. Infection begins 

 with the deepest roots and progresses upwards. 



The following facts have been ascertained : i) the rot is more frequent 

 in land cultivated for the first time, especially if it contains some decom- 

 posing vegetable residue such as tree stumps; it is rarer in localities already 

 cultivated for some years ; 2) the rot is equally widespread in all types of 

 soil, both on steeply inclined slopes and in plains and depressions ; 3) in 

 orchards, several trees forming a group die at almo.st the same time, which 

 is a proof of the rapidity whith which the disease spreads ; 4) " York Im- 

 perial " is said to be the variety most liable to attack ; next follow : " Stay- 

 man Winesap ", " Ben Davis ", " Yellow Newton " (" Albemarle Pippin ") 

 and " Arkansas " (" Black Twig "). 



The writer obtained many cultures from infected material of different 

 origin, and in all cases obtained abundant growth and fructification of Tri- 

 choderma koeningi Oudemans. 



Trichoderma may be regarded as the specific cause of root rot. Other 

 fungi however may be associated with it, for instance Hydnum and a bac- 

 terial flora which is sometimes very abundant. 



