490 



STATE BOARD OF AGRICULTURE. 



How the 

 snore attacks 

 the tomato 

 leaf. 



In 13 days 

 one spore 

 produces 

 thousands of 

 similar spores. 



Either the 

 upper or 

 lower surface 

 may be ♦.he 

 point of 

 entry. 



The fungus 

 lives over on 

 old trash 

 from last 

 year's 

 diseased 

 plants. 



The weather 

 does not 

 cause the leaf 

 spot disease. 



If a spore is put under proper conditions it will begin io 

 sprout in about twenty-foui' hours. The sprouts are threads 

 which push out from the needle-like spore. In a few hours 

 after sprouting the thi*ead-like tube enters the breathing pore 

 of the leaf. Then the fungus grows in the tissues of the 

 plant, twining among the cells. In about six days after the 

 spore reaches the leaf, the first watery discoloration produced 

 by the fungus can be seen. In less than ten days the spot 

 is definite and the killing of the invaded leaf tissue is com- 

 pleted. The fung-us fruits in about 13 days and produces 

 several black spore cases. Hence, one spore gives rise to 

 countless thousands of other spores, each capable of repeat- 

 ing this story. 



If the lower surface is the point of entry the spots are 

 large and may involve one-half or the whole of a leaflet. If 

 the upper surface is the point of entry the spots may be no 

 larger than the head of a pin. Usually the upper leaves show 

 this latter type of infection, evidently from dust as a source. 

 The lower leaves are infected from beneath, doubtless by 

 splashings from the ground or from the older leaves. 



The fungus lives over winter on the trash from a preced- 

 ing tomato crop. It lives over in the greenhouses or cold 

 frame in the trash from seedlings left in the soil. The spores 

 have not been found on tomato seed. Hundreds of plants 

 from all the common varieties have been grown in clean soil 

 without one case of leaf-spot appearing spontaneously. 



The spores of the fungus are released from the spore case 

 only when the leaf is wet. Heavy dews give conditions 

 which allow an oozing of spores. By far the greatest factor 

 in spreading the fungus is a washing, splashing rain. There- 

 fore, the disease is most serious in a rainy season such as that 

 of 1915. Many growers make the mistake in thinking that 

 the tomato disease is caused by the weather, while the truth 

 is that the disease is caused by a parasite whose spread is 

 favored by the wet conditions. 



Growers must adopt measures which will insure a crop in 

 spite of the weather. 



