70l' thk farmers' handbook. 



The fungus causing the disease is Alternaria (or Macrosporium) solani. 

 Abundance of spores are produced on the dead spots, and they frequently 

 spread the disease from tne centre where infection started. The fungus 

 passes from one season to another on old diseased parts of the host plant. 



In the control of this disease the destruction by burning of all parts of 

 old plauts is the first consideration. Very often after a crop the refuse of 

 old plants is turned under, and in this way a resting place is afforded for 

 the fungus. Spraying with Bordeaux of a strength of 6 — 4 — 100 should be 

 regularly carried out to prevent infection..* If the disease is serious in any 

 year a rotation should be practised, but potatoes should not follow nor 

 precede the tomatoes. 



Late (or Irish) Blight. — This disease is caused by Phytophthora infestans 

 (Mont.), De Bary, the same as that on potato. 



It affects all parts of the plant above ground, making them look as if 

 killed by frost. Small blackened areas appear on the leaves, branches, and 

 stalks, and under favourable conditions rapidly grow in size and number 

 until the whole plant blackens and dies. Dark spots appear on the fruit, 

 which rapidly decays. Fruit in all stages of ripening may be attacked, and 

 diseased spots continue to develop after picking. .Young plants even about 

 3 inches high may be attacked. Tomatoes and potatoes are often grown 

 in the same area, and thus the fungus finds a living host throughout the 

 whole year. Bordeaux mixture (6 — 4 — 100) is the best spray to use to 

 prevent infection. 



Bacterial Blight. — This is a disease of the vegetative parts rather than 

 of the fruit, and is due to Bacterium solanacearum, the same as the Bacterial 

 Brown Rot of potatoes (page 504). On tomato plants it causes an early de- 

 velopment of a great number of incipient roots in the form of small nodules, 

 which appear on the shoots. Infection may take place through the leaf, by 

 biting and sucking insects or through the soil in contaminated areas. To 

 avoid its spread the sprays used must be those to keep the various biting 

 and sucking insects in check, and thus prevent infection. Once the plants 

 are infected, spraying with ordinary fungicides will have no effect. Avoid 

 a succession of tomatoes on the same land. Avoid soil known to be infected 

 from the last crop. 



Leaf Blight is caused by a fungus, Septoria lycopersici (Speg.), which 

 attacks the stem, fruit, a ad calyx, but more especially the leaves. It pro- 

 •duces small circular brown spots on the lower leaves first, and if these are 

 seriously affected they turn yellow and die. If weather conditions favour 

 the fungus, the attack progresses upwards, and in severe affections little of 

 the plant may remain but bare stems and small stunted fruit. The wither- 

 ing of the leaves makes the attack look like " blight," but the spots on the 

 leaves distinguish it from other diseases. Affected leaves have a tendency 

 to curl dorsally throughout their length, and may hang loosely on the stem. 

 With severe attacks, old leaves may be killed faster than new ones are 

 produced, and the plant is finally checked to such an extent that little fruit 

 is produced, or what has been produced may be ripened prematurely. . 



The fungus produces its spores in pycnidia, developed on the spots on 

 the upper surface of the leaves, and lives through the winter in old fallen 

 leaves and other parts of the plant. Thus in controlling the disease all 

 such refuse should be collected and burnt. 



* The method of making Bordeaux mixture is described in some detail in connection 

 ^vith potatoes on page 498. 



