POTATO DISEASES. 205 



the edges, and later to develop mottled spots thereon ; also 

 to become stunted in growth. The disease may be con- 

 veyed by spores in the soil or floating spores in 'the air. 



Remedies.— Burn all diseased haulm and tubers. Avoid 

 planting sets containing red streaks in the flesh. Dress 

 the soil with ground lime in winter, and sprinkle Kainit 

 thinly along the drills at planting time. 



Leaf Spot. — A fungoid disease attacking the foliage 

 late in the season, caursing brown spots to form and these 

 eventually to become dry and fall out, thus producing 

 holes in the leaves. The effect is cessation of growth of 

 the tubers and a light crop. Tubers not affected. 



Eemedies. — Spray with Woburn Bordeaux Emulsion 

 (Fo]-mula 21), as advised for Potato Disease, and burn all 

 infected foliage. 



Potato Disease (Phytophthora infestans).— This is 

 the dreaded disease which commits so much havoc among 

 the potato crop in wet seasons. It first manifests itself 

 in the form of brown patches on the leaves, followed by 

 curling of the latter, and finally by their becoming black 

 and decayed. The disease is caused by a fungus, the 

 mycelium of which penetrates the tissues of the leaves 

 and destroys them. In due course the mycelium develops 

 what are technically known as conidiophores, or tiny stems 

 which appear in the form of a mould on the surface. On 

 the conidiophores are borne conidia, which give birth to 

 zoopores. These, coming in contact with globules of 

 water, emit germ tubes that penetrate the epidermis of 

 the leaf or tuber, and eventually form tlie mycelium which 

 does so much mischief to the tissues. The mycelium will 

 often lie dormant in the tubers all the winter, and start 

 into activity when new growth begins in the soil. The 

 disease is mostly prevalent in rainy seasons. The fungus 

 also attacks tomato plants grown in a moist, stagnant 

 atmosphere, the spores under such conditions easily ger- 

 minating, followed by the development of thread-like 



