Minnesota Plant Diseases. 323 



the bush are killed off. The fungus fruiting cushions at first 

 bear colorless spores, which are pinched off of threads on the 

 top of the cushion in great numbers. The spore sacs are 

 formed in the fall and arise in pear-shaped capsules. The latter 

 are formed as protuberances from the summit of the button and 

 have an apical opening, through which the spores are forced 

 out. The mycelium is perennial in the cane and can be trans- 

 ferred by cuttings. An infected bush may thus be a constant 

 source of infection. Cuttings from plants should therefore be 

 selected from bushes free from the disease. Infection from 

 spores probably takes place only through wounded canes. 

 Wounding of canes should therefore be avoided as far as possi- 

 ble. Diseased plants should be immediately and completely 

 rooted out and destroyed. 



Strawberry leaf-blight [Sphaerella fragariae (TuL) Sac'c.]. 

 This disease is a very common one in the state and attacks cer- 

 tain varieties more vigorously than others. It appears on the 

 leaves and the first indication is a spotting of the leaf. The 

 spots are circular and purple in color. As they increase in size 

 the center of each spot becomes whitish and the edge remains 

 purple. On the whitish area appear in early summer minute 

 tufts of fungus threads, which constrict off countless summer 

 spores of exceedingly small size. By means of these the fungus 

 disease may be carried to other plants. The spots are often so 

 numerous that they run together and cover such a considerable 

 portion of the leaf that the latter is rendered useless for starch- 

 making purposes. On the same white spot, later in the season 

 or in the fall after the leaf has fallen, the winter or sac spore is 

 formed. The sacs are produced in very minute, spherical cap- 

 sules which protrude from the spot as tiny black points. They 

 open to the exterior by means of small apertures through which 

 the spores escape. The release of the spores is delayed until 

 the following spring, so that infection by the sac-spore myce- 

 lium does not take place until that time. 



To check the spread of the fungus spraying with bordeaux 

 has proved beneficial and several applications should be made. 

 The plants should be sprayed just as the leaves unfold, again 

 after the petals fall, and once or twice after the fruit has been 

 picked. Where the disease is serious, a removal of the plants 



