11 Aug., 1919.] Tomato Diseases. 499 



In a general attack all the lower leaves are affected ; they turn 

 yeHow, become spotted, wither and die. The disease works upwards, 

 affecting the entire foliage with the exception of that at the tips ol 

 the stems, leaving the fruit and stem bare. 



On plants which have reached this stage the fruit, usually small 

 and watery, is ex}:)osed tO' the direct rays of the sun, and is destroyed 

 by sun scald. 



How THE Disease is Spread. 



Seedlings are liable to be attacked while still in the frame, and 

 plants which have borne a full crop are not immune. As a rue, how- 

 ever, they show the effects of the disease at or about the time they 

 have set the firet hand of fruit. 



Seed bed infection is far more common than growers suppose, and 

 many thousands of seedling plants affected with the disease are sold 

 annually. It is, therefore, unfortunate that the custom of using the 

 same soil and frames year after year without the slightest effort to 

 sterilize either, is so common. A fertile source of infection is found in 

 the old trash from a diseased crop, which is, as a rule, either ploughed 

 in or thrown upon the rubbish heap, or even sometimes mixed with 

 the soil in the cool frames. 



So long as these slip-shod methods are continued we must expect 

 the disease to claim a large number of plants each season. Even when 

 diseased seedlings are transplanted vigorous growth may ihold the 

 disease in check until the plant feels the extra strain consequent on a 

 supply of food being diverted to the developing fruit. It is at this 

 period of growth that the grower as a rule observes the evidence of 

 disease. 



On badly affected leaves the spores are, in the presence of moisture, 

 exuded in sticky masses, and on drying are held firmly to the leaf 

 surface, and may be removed only with difficulty. In rainy weather 

 they float about the leaf surface, and numbers are carried to neighbour- 

 ing plants by rain drops and splashes, but by far the greater number 

 reach the soil by dro]3s falling from the leaf tips. It has been observed 

 that when there are a few diseased plants in a plot, the disease spreads 

 rapidly in the direction of the prevailing winds. 



When we consider that the spores adhere firmly when dry, either 

 in the spore case or on the leaf surface, it is difficult to account for 

 the spread of the disease over large areas in the absence of rain. It 

 can, however, be accounted for by the dust from the soil on which the 

 spores have been carried, by the drippings from diseased plants being 

 blown or carried by air currents to the lower leaves of the plants. An 

 analogous case is found in the "black spot" of tlie vine — Manginia 

 amjjelina, Vil. et Pt. The spores of this disease are without cloubt 

 carried by the spore-laden dust from the soil beneath the diseased 

 vines. 



A number of tomato plants were sprayed with water containiuij 

 spores of Septoria h/copersici (Speg.), and all develoned the disease, and 

 produced spores within twelve to fourteen days. On the other hand, 

 the check plants were clean. 



Control Measures. 

 The chief causes of infection have been noted viz., the old diseased 

 plants from last year's crop, soil containing fragments of. diseased 

 ]:>la)its, and hot-beds and cool frames. 



