62 STATE HORTICULTURAL SOCIETY. 



CERTAIN KNOWN FEATURES OF THE CASE. 



Since the discovery of the cause of the scab, the following points have 

 been proven to be true. These points should be kept in mind by those 

 that hope to successfully combat the disease: 



1. The disease is of fungoid growth. 



2. The planting of scabby potatoes will cause the product to be scabby. 



3. The germs remain in the ground in a vital condition for several 

 years. 



4. Potatoes free from scab germs, planted on free ground, will raise a 

 clear product. 



5. Tops from affected potatoes, or litter from the potato pits, will carry 

 the germs. 



Knowing these facts, the grower will be chary about growing potatoes 

 on the same land without several years of intervening crops. He should 

 be careful to keep the tops in the field that grew the crop, and he should 

 seek to plant seed that is free from the disease. 



GERMS ON SEED MAY BE KILLED. 



There is as yet no known way of treating the grown potato to prevent 

 scab, but the germs can be killed on the seed potato, which, when planted 

 on ground free from the germs, rnust raise a product unmarked by scab. 

 When the cause of the disease was discovered, the different fungicides 

 were tried, to find which was the specific for this disease. Up to the pres- 

 ent, corrosive sublimate seems to give the best result, although Bordeaux 

 mixture, in the hands of some experimenters, has made a good showing. 

 From the results of the past two years we have advised the following 

 treatment: For one half of a barrel of water, dissolve two ounces of cor- 

 rosive sublimate in hot water, using two quarts or more; then dilute to the 

 one half of a barrel. If the potatoes are dirty, wash them, and then 

 immerse them in the solution for one and one half hours. They then 

 may be cut and planted. The time of soaking is immaterial. It may be 

 done weeks before planting, if desirable. The corrosive sublimate solu- 

 tion must be kept in glass, earthen, or wooden vessels, as it will corrode 

 tin or iron. 



It is not known how many bushels the one half barrel of the solution 

 will treat. The corrosive sublimate is absorbed by the potato, and in my 

 opinion it will become too weak before the quantity becomes too small 

 for use. This point can be settled in the experiment station by the aid of 

 the chemist. 



The poison will act on the germ of the potato, also, but if the solution 

 is made the proper strength and the potatoes immersed the proper time, the 

 germination is affected only by being slightly retarded. By treating and 

 growing many pieces in the college forcing-house, I found that the time 

 of vegetation of the treated pieces, as compared with the untreated was 

 twenty hours later. This was the average of a large number of pieces. 

 In the experiment where the solution was double the normal strength, the 

 seed that was soaked one and one half hours was four and one half days 

 later in vegetating than the untreated seed. In a triple-strength solution, 

 the difference was nine days. In no case did the seed fail, in time, to 

 germinate. 



This year the field experiments on potato scab comprise 120 plots, and 



