370 THE MONTHLY BULLETIN. 



However, in spite of the freedom from insect and fungous pests 

 which I have mentioned, it would be a unique condition indeed if any 

 crop should have been grown as long as potatoes have been grown in 

 the delta, and on such an extensive scale within a limited area, and the 

 crop still remain entirely free from insect or fungous diseases. What 

 has happened in other parts of the world has taken place in the delta 

 except that it has, perhaps, not become so aggravated, and has been 

 brought about by slightly different causes. It has been a matter of 

 common knowledge for a long time that the potato yields on a given 

 tract gradually decline the longer the tract is kept under cultivation 

 and the oftener it is planted to potatoes. There are quite a number 

 of factors which work together and cause this decrease in yield. One 

 of the most direct and important factors is a fungous disease which is 

 very widespread over the United States. This fungus is known as 

 Rhizoctonia. It does but little injury to the tubers, but can be found 

 on most of the potatoes in the markets. It is introduced into the soil 

 on the seed potatoes, where it develops rapidly and attacks the young 

 shoots below the surface of the soil, seriously injuring the productive 

 power of the plants. A conservative estimate of the damage produced 

 by this disease in the delta in 1913 would be placed at 20 to 25 per cent 

 of the total crop. This means that it cost the potato growers of the 

 delta at least a million dollars the past season. 



Potato scab is a fungous disease which is familiar to practically 

 every one who has had anything to do with potatoes. All the growers 

 recognize it and usually try in some measure to control it. It is common 

 throughout the United States. It is introduced into the soil on infected 

 seed and then infects the tubers grown from these seed pieces. 



The so-called "leak" of the tubers during the warm part of the 

 harvesting season is another fungous disease which sometimes causes 

 serious loss, especially where the tubers are injured in digging. This 

 disease causes a rapid watery decay of the potatoes, and while not 

 common in some other sections of the country, is of such a nature as 

 not to make it a menace to potato growing in other localities where 

 delta potatoes are likely to be shipped. 



The potato "wilt" is another fungous disease which is common 

 throughout the United States and M^hich injures both vine and tubers. 

 This disease is serious in the delta because it is the original cause of 

 injury to the plant and tubers affected, and also because it forms a 

 means of entrance for other diseases of the tubers such as dry rot, 

 "jelly end," and perhaps "leak." This disease also finds entrance to 

 the soil through infected seed tubers. 



The eelworm is a real M^orm and not a form of insect life. It is quite 

 widely distributed through the southern and western portions of the 

 United States and lives upon many other plants besides the potato. 

 Thus far it has not become distributed throughout the delta, and a 

 determined effort is being made to control it. This pest is also intro- 

 duced into the soil through infested seed stock and will remain living 

 in the soil for a long time after the potatoes are harvested. 



Another potato pest which has not as yet become generally distributed 

 throughout the Pacific coast is the tuber moth. This is an insect which 

 lays its eggs on the potato vines or tubers and the young larvae when 

 hatched burrow into the tubers, rendering them unfit for domestic use. 



