Diskases 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. If 
