174 ANNUAL REPORTS Or DEPARTMENT OF AGRICULTURE. 



TOMATO DISEASES. 



Particular attention has been devoted during the past season to 

 the control of early-blight, or nailhead spot, of tomatoes in Florida, 

 which causes serious losses in shipments to northern markets. Lab- 

 oratory and field studies have shoAvn that infection by this disease 

 can take place only on small immature fruit. After the fruit attains 

 a size approximately 2 inches in diameter, infection, even under the 

 most favorable conditions, is impossible. It follows, therefore, that 

 loss from this disease in transit can be avoided by packing only 

 sound and mature fruit and that control measures must be applied 

 in the field. Preliminary experiments have shown that spraying 

 with Bordeaux mixture is an effective means of control. 



THE MOTTLING DISEASE OF SUGAR CANE. 



There are several diseases of sugar cane that deserve special atten- 

 tion. Some of these, such as the root-rot and red-rot, have been 

 known in this country for several years, but exact control measures 

 have not been worked out. The malady most recenth' discovered in 

 the cane fields of the United States is the mosaic or mottling disease, 

 which has been known in Porto Rico for several years and has ap- 

 parently existed in Cuba, Java, and Hawaii for a longer period. Tha 

 cause is not known. It is propagated through the seed cane and 

 probably is carried from plant to plant by one or more species of 

 insects. The disease does not infect the soil and certain varieties of 

 cane are immiine to it. Of the susceptible varieties some are more 

 readily and seriously affected than others. A S3'stematic survey' has 

 been started in the cane States in order to determine the extent and 

 seriousness of the infestation. It is known to be present on all 

 susceptible varieties at Audubon Park and at Cairo. This disease, 

 thousli verv destructive, is not considered as serious as root-rot. 



POVv'DERY MILDEW OF THE APPLE. 



Apple powdery mildew has recently- been causing great alarm 

 among the apple growers in the irrigated sections of the Northwest. 

 Complete control is usually secured by the application of sulphur 

 sprays earl}' in the season. When late applications are necessary, 

 sulphur can not be used, as it is sure to cause injury. Various other 

 spray materials are being tested for use late in the season. 



SPRAY MIXTURES FOR CITRUS TREES. 



The special spraying requirements of citrus trees have necessitated 

 a comprehensive testing of combinations of spray materials. A 

 mctliod has been found for combining oil emulsion with lime-sulphur 

 sohition, and the resulting combined spray mixture gives promise 

 of reducing the number of spray applications necessary and in in- 

 creasing effectiveness in the routine treatment of citrus trees through- 

 out the year. 



NEMATODE INFESTATION OF CLOVER SEED. 



Early in the summer of 1919 attention was drawn to the fact that 

 a clover disease of considerable importance had visited southern 

 Idaho and other irrigated districts of the Northwest. It was a 



