1242 



Clover Stem- rot. 



[mar.». 



susceptible to the other, and, vice versa, hence the extreme 

 importance of correctly identifying the nature of the disease. 

 The present article deals solely with the fungus disease nowr 

 usually termed Clover Stem-rot and caused by the fungus 

 Sclerotinia trifoliorum. The Clover Eelworm Disease is dealt 

 with in Leaflet No. 46, issued by the Ministry. 



Description of Clover Stem-rot.— Stem-rot attacks the clover 

 plant in winter and spring, and causes a rotting of the leaves- 

 and shoots. If the attack is slight, the crowns may escape 

 damage and later develop healthy growth, but in bad cases the 

 fungus works down into the roots and completely kills the plants. 

 In damp weather the disease spreads rapidly and in a short time 

 destroys the foliage of whole fields ; if dry or frosty weather 

 prevails its progress is checked, but it is liable to renew its 

 activity with the recurrence of suitable weather- conditions in^ 

 spring or, indeed, at any time up to the cutting of the crop. 



Careful inspection shows that Stem-rot usually commences 

 in November. Spores of the fungus Sclerotinia are at that 

 season abundant in the air and give rise to the disease. Having, 

 once gained a footing, the fungus, which appears externally 

 as a sparse white mould, spreads readily over the foliage. The 

 affected leaves and shoots are quickly destroyed and turn a 

 characteristic olive-brown or yellowish- brown colour. Many 

 separate spore-infections usually occur in any given area, but 

 in addition to this, owing to the close proximity of the clover 

 plants, the fungus easily spreads from one plant to another. 



All the stems are not necessarily killed, and the shoots which 

 escape injury, together with new buds from the crown, develop 

 fresh growth in spring, though this is naturally rather weak. 

 In bad cases, however, the fungus invades the roots and kills 

 Ihe plants outright ; and when damp, muggy conditions 

 prevail, and the land is thoroughly infested, very serious loss 

 over an extensive area may occur. 



Contamination of the Land.— The fungus perpetuates itself 

 in the soil by means of resting bodies known as sclerotia. These 

 bodies, which are formed chiefly early in the year and in spring, 

 are hard, black in colour, and spherical or flattened in shape. 

 The sclerotia occur chiefly around the collar of the plants or on 

 the dead roots, and may be found 3 or 4 in. below the surface 

 of the soil (see Fig. i). They also occur in and on the stems, 

 in which position their development may readily be traced. 

 It will be seen that each arises as a dense, white, cushion- 

 like growth which soon turns grey and finally becomes firm 

 with a hard, black coat. Inside they are white and ol the 



