DISEASES OF CULTIVATED PLANTS 557 



nate. Plants of equal age may range in height from two inches to 

 two feet. 



Seed treatment by immersion in liquid fungicides failed to 

 produce good results, as the fungus within the seed is less susceptible 

 than the pea germ. Heating the seed failed for a similar reason. 

 Rolling the seed in Bordeaux dust increased the per cent of germina- 

 tion slightly. Tying up the vines and spraying, while increasing the 

 crop only slightly, produced peas much freer from this and other 

 fungi and is of much value in growing healthy seed peas. Spraying 

 in this manner should prove a commercial success in growing seed 

 peas. Planting such healthy peas in soil free from the fungus is 

 recommended as the best means of reducing the loss from blight. 



This blight fungus is known to attack alfalfa, chick pea, 

 common bean and hairy vetch. All the varieties of the common pea 

 examined this year were affected ; but some varieties much more than 

 others. (Ohio E. S. B. 173.) 



Powdery Mildew of the Pea. The powdery mildew fungus 

 (Erysiphe communis) is exceedingly common on beans, clover, lu- 

 pines, peas and other members of the family to which the pea belongs, 

 as well as on very many other hosts. It is ordinarily recognized by 

 the whitish or grayish coating on all parts of the pea plant, especially 

 late in the season. The loss from this mildew during the past season 

 was quite large. 



The mildew fungus likewise lives over winter on the seed. On 

 account of its habits it is easily prevented by applications of Bor- 

 deaux mixture. Unlike the blight fungus, Ascochyta, the vegetative 

 part of the mildew fungus grows mostly on the exterior of the host 

 plant. Hence, the fungicide is not only a preventive, but actually 

 kills the fungus in great part, when sprayed upon it. On account of 

 this manner of growing, many of the powdery mildews are controlled 

 by the use of sulphur alone applications of which have but little if 

 any effect on most other parasitic fungi. The sprayed late crop of 

 1905 showed not a trace of mildew; while the unsprayed late crop 

 was entirely covered. So bad was the attack, that many plants failed 

 to mature good seed. This is, in part, responsible for the very low 

 per cent of germination of peas from the unsprayed vines. 



POTATO DISEASES. 



Blackleg or Black-Stem Disease of the Potato. This is a bac- 

 terial disease which attacks both the stem and tuber of the Irish 

 potato. Various investigators, mostly in Europe, have isolated from 

 the diseased plants and described under different names bacteria 

 which were again capable of causing very similar effects upon the 

 host upon inoculation. Hence so far as our present knowledge goes 

 blackleg, strictly speaking, is a general term applied to a type of bac- 

 terial disease which attacks and destroys the base of the potato stem, 

 producing a characteristic blackening of the diseased tissues, rather 

 than a term applied to a single disease caused by a specific organism. 

 However, the organisms are so near alike and are so nearly identical 

 in their effects upon the host that so far as the practical agricultural- 

 ist alone is concerned the distinctions made are, in the opinion of 



