MARKET DISEASES OF FRUITS AND VEGETABLES 53 



moderate growth even up to 80°. Information on either the growth 

 of the pathogen or the development of the disease at low tempera- 

 tures is meager. Observations suggest that celery apparently free 

 from the disease at the time of shipment may show it later on. In 

 one experiment, however, badly diseased celery stored at 31° for 

 10 weeks showed no appreciable increase in the amount of late blight 

 during the storage period. 



CONTROL MEASURES 



Several practices are involved in the successful Control of late 

 blight. Field sanitation is one of them. Trimmings from diseased 

 plants should not be left in the field nor allowed to accumulate 

 where they might later reach the field. The seedbed should receive 

 particular attention in this respect. 



The causal fungi of late blight can remain viable in infected seed 

 for 2 years. Seed that is not older than this may be treated with 

 hot water, calomel, formaldehyde, or corrosive sublimate to elim- 

 inate this source of infection. The value of seed treatment may, 

 however, be questioned in view of the wide infestation of celery 

 soils. 



Spraying with bordeaux mixture or dusting with copper-lime dust 

 is undoubtedly the most important control measure. Here again, 

 special attention should be given to the seedbed, with as early and 

 as frequent applications of the fungicide as appear necessary. The 

 spraying or dusting program should be continued in the field through- 

 out the season. 



Transportation, storage, and market losses can be reduced by the 

 control of the disease in the field. However, if infected celery is 

 marketed it is important to keep it at as low a temperature as is 

 practicable and to move it through the channels of trade as rapidly as 

 possible. 



(See 161, 164, 183, 194, 204, 205, 207, 223.) 



MOSAICS AND OTHER VIRUS DISEASES 



There are several mosaic diseases of celery. Although differing 

 in other respects all produce a mottling of the affected leaves. These 

 mosaics are caused by various plant viruses, which for the most 

 part are spread from plant to plant by sucking insects. 



One form of celery mosaic found in the Northeastern and North 

 Central States is characterized by a stiffness and erect ness of the 

 affected plants. The leaves are distorted by uneven puckering and 

 become filiform in shape. The disease appears to be caused by the 

 common cucumber mosaic virus. Ordinarily the losses from this type 

 of mosaic are not great, and the disease is of no importance on the 

 market. 



Another type is that known as southern celery mosaic. Plants 

 affected with this disease appear stunted and the leaves are con- 

 spicuously yellowed and mottled. As growth continues, however, the 

 new shoots are more erect and the mottling is often faint and not 

 readily noted after blanching. The leafstalks often show brownish 

 or buff-colored, sunken, translucent spots and such stalks eventually 



