DISEASES OF CROPS 957 



CUCUMBER 



Downy Mildew {Pseudoperonospora cubensis, B. and C. Rost.). — 

 This disease causes yellow, angular spots on the older leaves and eventually 

 causes the entire leaf to turn pale and die. Considerable quantity of white 

 growth appears on the under surface. 



Treatment. — Spray with Bordeaux mixture. 



Anthracnose. — See Melon. 



Leaf Blight and Fruit Spot (Cladosporium cucumerinum, Ell. and 

 Arth.). — This disease appears on the leaves as water spots and finally 

 causes the entire leaf to wilt and rot. On the fruit it appears as minute 

 gray, sunken, velvety spots which frequently unite and finally become black. 



Treatment. — Prompt spraying with Bordeaux mixture. 



Wilt.— See Melon. 



CELERY 



Leaf Spots (Cerospora apii, Fr., and Septoria petroselini, Desm., var. 

 apii) . — There are two leaf spot diseases which can be controlled by spraying 

 with Bordeaux mixture. The first treatment should be while the plants 

 are in the seed-bed and should be given whether the plants do or do not 

 show the disease. Other sprayings should be at intervals of two weeks 

 and with a high pressure sprayer. If necessary to spray late in the season, 

 the last treatment should be with ammoniacal copper carbonate solution. 



ONION 



Smut (Urocystise cepulce, Frost.). — This very destructive disease 

 attacks the young plants, causing dark opaque spots on the leaves. The 

 leaves finally die and dry up and the spots burst and permit the escape of 

 masses of spores. The mature bulbs show black masses of spores in the 

 outer and sometimes in the inner leaves, and when badly infected dry and 

 rot. Sets and young onions when well started are practically immune 

 from the disease. The spores persist in the soil for many years. 



Treatment. — Prevent the introduction by using clean sets. Use lime 

 and long crop rotations for infected soil. In small plantings disinfect the 

 soil with formaldehyde. 



Downy Mildew or Blight (Peronospora schleideni, Ung.). — Diseased 

 plants have a tendency to develop a violet tint by which they can be 

 recognized at a distance. As the disease advances, they become covered 

 with a mouldy coating and finally collapse. Slightly affected plants may 

 recover under suitable weather conditions. The disease spreads rapidly 

 in damp, warm weather and on wet land. 



Treatment. — See that lands are well drained. Rotate crops. Spray 

 with Bordeaux mixture. 



CARROT 

 Soft Rot (Bacillus carotovorus, Jones). — This is a bacterial disease 

 which causes a soft rotting of the roots. It also attacks turnips, radishes, 



