280 STATE BOARD OF AGRICULTURE. 



BLIGHT OF THE IRISH POTATO, TOMATO AND EGG PLANT. 



It has been shown* by Dr. E. F. Smith that a sin,c;le species of bacteriaf has 

 the power of producing blight in a number of plants of the potato family. Among 

 the cultivated ones may be mentioned the Irish potato, tomato, egg plant and 

 pepper. Several common weeds such as the horse nettle, jimson weed and ground 

 cherry are also susceptible to the disease. However, we are especially concerned 

 with the disease as it occurs in our common garden vegetables. 



The blight manifests itself in the vines by a sudden wilting either of a part 

 or the whole. The stems usually wither, turn yellow and finally black. Young 

 plants appear to contract the disease more readily than old ones. By cutting 

 across the affected stem one can see the characteristic brown or black woody 

 tissue in which the bacteria are at work. The tubers from sick plants show a 

 distinct ring of discolored tissue a short distance from the outside of the potato. 



Fungicides are of no value in treating the disease and prevention is the only 

 remedy. Do not use diseased tubers for planting and avoid planting on potato 

 sick land as well as on land which has had diseased tomatoes or egg plants. 



The symptoms of the blight in the tomato and egg plant are much the same 

 as those for the potato. The vines wilt as if suffering from too hot sun or lack 

 of water. Decay of the stems and branches soon sets in, resulting in the destruc- 

 tion of the plant. 



Here, too, spraying has been found useless, for the cause of the disease is 

 deep seated within the tissue and beyond the reach of any germicide. Insects, 

 undoubtedly, play some part in carrying the germs from plant to plant and thus 

 spread the trouble, but the soil seems to be the principal medium of infection. 

 What has been said in connection with the potato may be said about planting 

 tomatoes and egg plants on land that has had diseased specimens of the potato 

 family. 



If the disease is not too general, it is possible to control its spread by remov- 

 ing the dead vines with the roots from the field and burning them. It is of 

 utmost importance that the vines be destroyed and not thrown down carelessly 

 to start the disease in a healthy part of the field. Remember that you are deal- 

 ing with a contagious disease and it is your duty to keep it from spreading. One 

 sick vine in your field this year may mean the loss of half your plants next year. 

 Numerous cases have been reported where soil diseases have been carried from 

 farm to farm, up and down the road by the infected mud that adheres to the 

 wagon wheels. The greatest care should be exercised in plowing and cultivating 

 not to drag sick vines over healthy soil for by so doing the disease is spread 

 and what might have been a mild attack is aggravated to such a degree that a 

 general epidemic results. Tools should be thoroughly cleaned before going from 

 an infected field into one free from the disease and as a further precaution, 

 they should be disinfected by washing or dipping them into a 5% solution of 

 either carbolic acid or copper sulphate, commonly known as blue stone. It is 

 important that the gardener's shoes as well as those of his horse be free from 

 clumps of Infected soil before going into a new field. 



There is a common practice among some farmers of hauling the soil that has 

 washed down a hillside back up onto the shallow places of the farm. If this is 

 done, one should be very certain that the hillside from which this soil has 

 washed is free from all plant diseases, for the writer is familiar with several 

 instances where infection has been spread over healthy land in this way. 



Where no remedy can be given, it is clear that our only hope of controlling 

 a disease is by preventing its spread. By observing the foregoing suggestions, 

 it is believed that the most serious plant disturbances can be entirely prevented 

 or at least controlled. 



* Bulletin 12 Div. Vep. Path. U. S. Dept. of Agr. 

 t Bacillus solanacearum (Smith). 



