TOMATO DISEASES 



1977 



Control 



The most satisfactory method of con- 

 trol is the maintenance of dry atmo- 

 sphere. The foliage should be sprinkled 

 only on very bright dry days. It is 

 claimed that sprinkling lime-sulphur on 

 the heating pipes has checked the fungus. 



Leaf Mold 



Alternana Solani (E. & M.) Jones & 

 Grout. 



The fungus causmg leaf mold is the 

 same as that giving rise to the early 

 blight of potatoes. It often occurs on 

 the leaves and fruit of field crops. The 

 leaves affected with this fungus present 

 at first minute spots, which gradually 

 enlarge and become marked with con- 

 centric lines. These spots are sometimes 

 associated with the injuries caused by 

 the flea beetle. 



The remedy advocated is similar to 

 those that are applied for the early blight 

 of potatoes, namely, spraying with some 

 good fungicide. 



Mildew. See Leaf MoU, this section. 



Mosaic Disease 



The so-called mosaic disease,* whch is 

 common to tomatoes, is characterized by 

 a peculiar yellow spotting of the upper 

 surface of the leaves. These yellow spots, 

 particularly when exposed to bright sun- 

 light, subsequently become purplish in 

 color, and the margins of the leaves curl 

 up. Many crops are affected with what is 

 termed "mosaic trouble," and in all cases 

 this is associated with too extensive 

 pruning. The more a tomato plant is 

 pruned the more likely it is to be affect- 

 ed with the mosaic disease, and topping 

 or pruning of the leader induces this 

 trouble more than other methods of 

 pruning. 



The mosaic disease is apparently a 

 functional trouble, and little is known 

 about it. Similar troubles are associated 

 with tobacco (calico) and are believed 

 to be infectious. The presence of this 

 disease on tobacco is thought by some to 

 be associated with certain methods of 



transplanting. The disease on tomatoes 

 does not destroy the foliage of the plant, 

 but the abnormal metabolic processes 

 which appear to be associated with this 

 disease apparently affect the yield. 



Nematodes. See Boot Knot, this sec- 

 tion. 



Oedema 



This peculiar trouble of greenhouse to- 

 matoes was first investigated by G. F. 

 Atkinson* of Cornell University, who 

 made an exhaustive study of it. He 

 diagnoses the disease as follows: 



"Oedema of the tomato is a swelling 

 of certain parts of the plant brought 

 about by an excess of water, which 

 stretches the cell walls, making them 

 very thin and the cells very large. The 

 excess of water may be so great that the 

 cell walls break down, and that part of 

 the plant dying, exerts an injurious in- 

 fluence in adjacent parts." 



The cause of Oedema is insufficient 

 light, too much water in the soil and too 

 high a moisture content of the air. It 

 is an abnormal disease of very rare oc- 

 currence, and should cause no trouble if 

 good judgment is exercised in growing 

 the plants. 



Oedema is easily produced by maintain- 

 ing too moist an atmosphere and too high 

 a soil temperature. 



Point Rot. See Blossom End Rot, this 

 section. 



Boot Knot 



Eel Worm, Nematodes 



Heterodera radicicola (Greef) Mull. 



One of the common troubles on indoor 

 tomatoes is caused by nematodes — small 

 worms which inhabit the soil. They 

 gain entrance to the young roots where 

 a part of their development takes place. 

 The presence of these minute worms in 

 the tissue of the roots causes a reaction 

 on the part of the cells, resulting in the 

 formation of galls. On tomato roots 

 many galls are formed which cut off 

 the water supply and cause more or less 

 injury to the crop. 



Eel worms are very susceptible to treat- 



* Bureau of Plant Industry, TJ S Depart- 

 ment of Agriculture, A F Woods, Bulletin 18. 



♦ Cornell Bulletin 53 1893 



