568 INSECTS AFFECTING VEGETATION 



shade, and several weeds of this family (Solanaceae) , are affected by 

 this bacterium. 



In some cases it is rather difficult to distinguish between plants 

 that are affected with the bacterial blight and those that are diseased 

 with the sclerotium blight. Typical cases of each form have many 

 points of similarity. As a general rule, a plant that is suffering from 

 the bacterial blight becomes infected through a leaf. This leaf shows 

 that it is infected by wilting. Next, that portion of the plant to 

 which the leaf is attached begins to wilt ; and finally the entire plant 

 will become involved. In the case of the sclerotium blight the whole 

 plant usually shows the distress at once, and does not, as a rule, die 

 off as quickly as a plant attacked by bacterial blight. In the case of 

 bacterial -blight a dark gummy substance is apt to be deposited in the 

 woody portion of the stems. Sometimes these dark streaks also grow 

 in the leaf stalks. In this respect the bacterial blight may be con- 

 fused with the fungous blight. It is not usual for this dark, gummy 

 substance to be deposited in the stems of the plant or in the leaf stalk 

 when the plant is attacked by the sclerotium blight. 



These three forms of blight may be easily diagnosed by the 

 plant pathologist with his microscope in the laboratory, but they 

 have so many points of similarity that it is very difficult to describe 

 them in such a way as to enable the tomato grower to distinguish 

 them beyond a question of doubt. The plant pathologist, however, 

 w r ho comes in contact with the three forms of blight regularly has no 

 difficulty in diagnosing them in the field. 



Dropping of Bloom Buds. During some years this trouble oc- 

 casions a greater loss to the tomato growers than any of the diseases 

 that are caused by micro-organisms. The plant puts out the bloom 

 hands or clusters, but after the blooms have opened they drop off, 

 leaving no fruit set. The plant continues to grow and produce new 

 blooms, but these in turn may be shed. There are a number of 

 causes which bring about this condition. 



First among the most general and widespread causes for the 

 dropping of bloom buds is the sudden occurrence of cold or cool 

 weather, coming at a time when the plants in the tomato field are 

 in active blooming condition. The temperature is too low to permit 

 the pollen to fertilize the ovaries, and consequently, the blooms drop 

 off. In cases of this kind we have no effective remedy, but have to 

 wait for favorable weather. This condition does not usually con- 

 tinue for more than a few days at a time. It, however, does occa- 

 sionally happen that we have a period of ten days or two weeks dur- 

 ing which we have continuous cold, raw winds. In addition to this 

 cold weather causing the bloom to drop off for want of fertilization, 

 the after effect of the cold is shown by the plants being debilitated to 

 such an extent that a considerable period follows during which the 

 tomato blooms do not set. 



Just the opposite condition may sometimes occur. Plants may 

 grow too rapidly, especially if the formula of the fertilizer used is 

 high in ammonia and the weather is favorable to the most rapid 

 growth. In this case the tomato plant grows very rapidly and grows 



