64 THE EEPOET OF THE Xo. 36 



Soft Eot of Celery this year, for which the Tarnished Plant Bug is blamed. Efforts 

 for control of the disease have been directed towards destroying this insect. The 

 disease appears to winter over in the soil. 



Bacterial Wilt op Crucifers {Fscudomonas cmnpesiris). Jones and others 

 have shown that insects and slugs are important and common disseminators, though 

 there are also other agents. 



Other Bacterial Diseases. Very little is known as to the part ]»layed by 

 insects in the spread of the other common bacterial diseases. Bean Bacteriosis 

 [Pseudomonas campestri?) , Black Spot of Plums and Peaches {Bacterium pruni), 

 Crown Gall {Bacterium tumefaciens) or Potato Wilt {Bacillus solanisaprus) . We 

 know, however, that the bacteria of the first two of these may enter directly thnnigh 

 stomata witliout the aid of wounds. 



Insects as Disseminators oe Physiological Diseases o\\ Diseases oe 



Unknown Origin. 



There are already many well known physiological diseases, and the list is 

 being added to each year. A considerable proportion of our worst plant troubles 

 come under this category. Insects do not play a part in the distribution of all. 

 for instance they seem to have nothing to do with the spread of Peach Yellows 

 and Little Peach. In many cases, however, insects appear to be either the sole 

 agents in distribution or else very important agents. Prom the evidence available 

 it would appear that most of the insects concerned are of the sucking and piercing 

 types, though there seems no good reason why biting insects cannot also play a 

 part. The infectious principle or virus seems in most cases and probably in all 

 to be takeJi into the body of the insect and inoculation occurs through feeding. 



Examples of Physiological Diseases or Disease of Unknoavn Origin 

 Disseminated by Insects. 



Mosaic Disease of Saveet Peas... Most growers of sweet peas are probably 

 familiar with this easily recognized disease which weakens the plants and diminishes 

 the size and beauty of the blossoms. Taubenhaus has shown that it is readily 

 transmitted by aphids, but he says any biting or sucking insect may spread it. 

 Most of the spread will naturally be due to aphids, because they are the most 

 common sweet pea insects. 



Mosaic Disease of Tobacco. This is a very important disease of Tobacco 

 in the United States and may be identical with Mosaic Disease of Tomatoes, though 

 probably not with Potato Mosaic. Allard has shown that the Peach Aphis {Myzus 

 persicae), and also the Aphis {Macrosiphum tahaci), are very important spreaders 

 of the disease. White Flies and Eed Spiders he thinks do not distribute it. 



Mosaic Disease of Cucumbers. This disease causes an annual loss of 

 about $1,000,000 in the United States. I have not seen it in Ontario but believe 

 it has been found in a few localities. Doolittle and Jagger have proven that aphids 

 are carriers and are probably the chief agents in its spread. 



Curly Tor of Sugar Beets. This disease occurs in the South-western 

 States and some years is exceedingly destructive. The Beet Leaf-hopper {Eutettix 

 tenella) has time after time been proven to be the distriliuting agent and so far 

 as known the sole agent. 



Spinach Blight. This blight attacks both spring and fall crops of spinach 

 in Virginia, Ohio and parts of New York. Leaves of affected plants become 



