THE MONTHLY BULLETIN. 561 



PRODUCTIVE SEED POTATOES ARE NOT DISEASED POTATOES. 



Seed potatoes should be free from diseases, or affected only with such 

 diseases as can be killed or removed by treatment before planting. We 

 mention some of the more common ones, which are causing potato 

 growers immense losses every year. 



Perhaps the most common potato disease in California, or even in 

 the United States, is what we know as Rhizoctonia. This is found on 

 the tubers in the form of small dark brown patches or specks, which 

 are usually not di.stinguished from soil particles, and hence are con- 

 sidered of little importance. This disease, however, causes an annual 

 loss to the potato growers of California which runs into more than a 

 million dollars. It is a fungus which attacks the stems of the plants 

 below ground and often cuts otf many or even all of the stolons which 

 should produce potatoes. 



Potato scab is another fungous disease which attacks the outside of 

 the potato. The scab can be fairly well controlled by treating seed 

 potatoes for one and one-half hours in a solution made by dissolving 

 four ounces of corrosive sublimate in thirty gallons of water. Rhizoc- 

 tonia may also be largely controlled in the same way, and it is best to 

 plant no potatoes without such treatment. This solution is poisonous 

 and should be handled with care, and used only in wooden ves.sels. 



Wilt diseases affect the inside of the tubers, beginning at the stem 

 end. The only way to get rid of this trouble with seed potatoes is 

 to cut off the stem ends and throw away the affected portions where 

 any considerable number are affected. 



Not only is the yield of potatoes greatly reduced when diseased seed 

 stock is planted, but the soil also becomes inoculated with the fungi 

 which cause these diseases. These fungi then live and multiply in the 

 soil under favorable conditions and future crops are affected even 

 when clean seed is planted. Since diseased seed potatoes have been and 

 still are causing enormous losses to the potato industry, the importance 

 of disease-free seed can hardly be too strongly impressed upon the 

 people Avho grow this crop, and the slogan "Clean seed in clean soil" 

 should be most strongly emphasized. 



Another characteristic of good seed potatoes is that they should be 

 true to name and free from mixture. There are perhaps not more 

 than two or three varieties of potatoes, at the most, that are likely to 

 succeed equally well in any given locality, and even those few are likely 

 to each be of the most value for a definite location and a definite pur- 

 pose ; that is. high or low ground, light or heavy soil ; or early, medium, 

 or late planting. To plant a late variety of potatoes under the name 

 of an early variety, or even an early variety with a 10 per cent mix- 

 ture of late ones, means a serious loss to the early potato grower. It 

 requires special care on the part of the potato grower, if he is growing 

 several varieties, to keep the varieties from becoming mixed ; and it is 

 almost impossible to obtain seed potatoes through the ordinary channels 

 of trade which are true to name and even practically free from mixture. 

 It is very difficult, however, to distinguish one variety from another. 



