Diseases of Vegetables 1321 



limited by its high cost to use in greenhouses, plant beds and 

 similar places, where small areas bring large returns. 



Steaming is the most satisfactory means of sterilization. Three 

 methods are commonly used. A galvanized iron pan, five to ten 

 inches in depth and any convenient size, is inverted over the soil 

 and live steam passed into it. A drag-like arrangement with 

 many perforated perpendicular pieces which are jabbed down into 

 the soil is occasionally used. Many prefer to lay perforated iron 

 or galvanized pipes in the soil horizontally at a depth of two to 

 seven inches and a foot or more apart, covering the surface with 

 canvas or paper to hold the heat. A steam boiler giving at least 

 40 pounds pressure, and better 80 to 100, should be used. Steam 

 is usually applied for one to two hours. For the treatment to be 

 fully effective all parts of the soil to a somewhat greater depth 

 than worked must be heated to a temperature of around 200 

 degrees, Fahrenheit, and held at that temperature for a time. 



Drenching the soil with formaldehyde solution is sometimes 

 as effective as steaming, but can be recommended only for very 

 small areas. Use one pint of 40 per cent, formaldehyde to six or 

 seven gallons of water, and apply with a sprinkler at the rate 

 of one gallon per square foot. A weaker solution is often recom- 

 mended but can not be relied on to give satisfactory results. Crops 

 must not be started until two weeks after the application. 



Clean Seed and Seed Treatment. Several parasitic fungi and 

 bacteria are perpetuated in or on the seeds of the crops, and the 

 resulting diseases can be wholly or in part controlled by selecting 

 seed free from the parasite or by treating the seed to kill the 

 parasite. Where the parasite is within the seed, methods of killing 

 it have not been determined, and the selection of disease-free seed 

 must be practiced. Parasites on the surface can usually be killed 

 by a short soaking in a weak solution of formaldehyde or corrosive 

 sublimate. 



Resistant Varieties. One of the most promising methods of 

 controlling vegetable diseases is by the development and use of 

 disease resistant varieties and strains. There are very few strains 

 and varieties of vegetables which resist disease, but there are 

 sufficient to indicate great possibilities. Growers can accomplish 

 considerable in obtaining more resistant varieties and strains. Tf 



