352 Journal of Agricultural Research voi. xv. No. 6 



decay the potatoes when the hyphge were inserted into wounds. Inocu- 

 lated potatoes held at laboratory temperature and confined in a moist 

 chamber would usually decay in from 3 to 6 weeks. A number of 

 potatoes were inoculated on December 5, 191 6, and 43 per cent were com- 

 pletely or nearly decayed by January 2, 1917. The causal organism was 

 recovered from a potato rotted in the above experiment and used to 

 inoculate another lot on January 22, 191 7. Seventy per cent of the 

 latter were from two-thirds to completely decayed by February 23. 



SCURF 



Scurf is a common field disease of sweet potatoes caused by Monilo- 

 chaetes infuscans Hals. It is very prevalent in California, the entire 

 South, and other sweet-potato growing sections of the country. Scurfy 

 potatoes sell for from 25 to 50 per cent less on the market than clean ones, 

 depending naturally on the severity of the infection. To this loss must 

 be added those scurfy potatoes which are so badly dried and shrunken 

 that they are not fit for food. The spotted discoloration of the skin is 

 well known to nearly everyone (Pi. 26, B). These spots may be small and 

 separate or they may coalesce so as to form a continuous discolored 

 covering over the end or even over the entire potato. The discolored 

 or infected areas are for the most part present in the field before the crop 

 is harvested, though they may enlarge slightly in storage, and possibly 

 a few new ones may be formed. 



Although Monilochaetes infuscans is superficial, the hyphas penetrat- 

 ing only through the cuticle {ig), it injures the epidermis so that water 

 escapes, thus resulting in a shrinkage of the potato. This shrinkage is 

 slow, but after one or two months in storage a considerable percentage 

 is unfit for the market. Naturally the shrinkage is greatest in houses 

 where the relative humidity is low and the temperature is high. Plate 

 26, C, shows a badly shrunken scurfy potato. The shrinkage is generally 

 worse at one end, usually the end that was attached to the stem. That 

 there is more shrinkage at the attached end is not surprising when one 

 remembers that scurf, like several other diseases of the sweet potato, 

 is largely carried to the field on the slips. Being a surface organism, it 

 readily grows from the slip on to the roots or is washed there by rains. 

 That many of the infections on the attached ends results from the 

 spores being washed down the stem on to the roots is evident from the 

 fact that the infections for the most part are in spots. 



There are no varieties of sweet potatoes immune to scurf, so far as the 

 writers know. Data collected over a period of six years show that the 

 following varieties of sweet potatoes are susceptible to scurf: Yellow 

 Jersey, Red Bermuda, Japan Brown, Red Brazilian, Florida, White 

 Gilke hybrid, Vineless pumpkin Yam, Pumpkin Yam, Eclipse Sugar 

 Yam, Porto Rico, Triumph, Yellow Yam, Yellow Strasburg, Early 

 Carolina, Creola, Georgia, Miles Yam, Pierson, White Yam, Key West 



