SEEDLING DISEASES AND INJURIES 3 



Symptoms. 



The critical period in the development of tree seedlings, so 

 far as damping-off is concerned, extends from the time of the 

 germination of the seed until the stem-tissues become woody, 

 — a period of one or two months. Usually the first indication 

 of damping-off is a water-soaked or brown area of decaying 

 tissue in the stem, near the surface of the ground. If the dis- 

 ease occurs very early in the development of the plants, the 

 stems may be killed before their tips emerge from the ground. 

 Often, also, the lesion originates just below the surface of the 

 soil after the plant has pushed out, and wilting of the plant is 

 the first sign of the trouble. Wherever the lesion may occur, 

 the diseased stem-tissue soon collapses and allows the plant to 

 fall over, while further disintegration of the tissue results in 

 the death of the seedling. Root-rot may accompany damping- 

 oflF and often is only another indication of the work of the same 

 fungus. In the case of deciduous trees, especially the beech, 

 the first lesions may show as cotyledon-spots. These lesions 

 soon enlarge, however, so that the stem is involved and damping- 

 off follows. Under conditions favorable for the development 

 of damping-o£P fungi, large circular areas of dead plants appear 

 and only a few days are sufficient for the spread of the patho- 

 gene from a few centers to all parts of the seed-bed. 



Cause of damping-off. 



Numerous species of fungi have been found to cause damp- 

 ing-off. In general these fungi have no restricted host-range, 

 and are so prevalent and omnivorous that seedling crops uni- 

 versally suffer. In this country most of the work on these 

 diseases has been done with conifers. Numerous species and 

 forms of fungi belonging to the genus Fusarium have been 

 found to be the most common cause. Pythium debaryanum 

 Hesse and species of Rhizoctonia have also been found to be 

 important damping-off pathogenes in certain cases. In Europe, 



