THE DOWNY MILDEWS 223 



The chief preventive measures are the planting on high 

 land of seed gathered from a field where the mildew was 

 not present, the rotation of the crop, the destruction of all 

 old bean vines, and spraying with Bordeaux mixture. 



The Downy Mildew of the Onion is a widely distributed 

 disease that causes serious loss in some parts of the 

 United States nearly every year. It attacks the leaves, 

 at first causing a yellowish discoloration that may later 

 show the white threads of the fruiting fungus. Vast 

 numbers of summer spores enable the disease to spread 

 rapidly during the growing season, and well protected 

 winter spores enable it to live through the winter in dead 

 leaves or in the soil. These winter spores appear to be 

 able to survive in the soil for two years. Consequently a 

 crop rotation in which onions are not grown on the same 

 land oftener than once in three years is desirable. Clean 

 culture, burning of diseased leaves, and spraying with 

 fungicides are also helpful. 



Another Downy Mildew is often destructive to cucum- 

 bers, melons, and squashes. It is likely to destroy the vines 

 in almost any region when warm damp weather favors its 

 rapid growth. It seems to do as much damage in the South 

 as in the North, or more, and it often appears as an active 

 epidemic quickly blighting the vines over great regions. 

 The white mildew that gives off millions of summer spores 

 shows on the under surfaces of the leaves. 



Clean culture, burning or deep burying of infested plants, 

 rotation of crops, and spraying with fungicides are the chief 

 remedial measures against this disease. 



Among the numerous parasitic enemies of the grape the 

 Downy Mildew or Brown Rot is at times one of the most 

 destructive. In its life history it does not differ essentially 

 from the other Downy Mildews. It reproduces in summer 



