21 

 (Fungi).. 



Downy Mildew (Peronospora schleidenii) : This is a common dis- 

 ease of onions. The leaf first shows yellow patches, covered with a 

 greyish mould. Later, the patches increase in size and numbers, and the 

 leaf shrivels and dies. Two kinds of spores are produced, viz., thin- 

 walled summer spores, on the minute branched stalks forming the greyish 

 mould, and thick-walled winter spores (oospores), in the tissues of the 

 leaves killed by the fungus. The summer spores are scattered by the 

 wind during summer, and are the agents in the spread of the disease. 



Treatment : Rotation of crops is necessary, especially when winter 

 spores are in the infected soil ; removal and burning of diseased plants ; 

 spray with Bordeaux or potassium sulphide (i ounce to 2 gallons of 

 water); dusting the plants with powdered quicklime and sulphur (2 to 1). 



Tkuk Squash Bug. (Anasa tristis, De G.). a. mature female; b. side view of 

 head, showing beak ; c. abdominal segments of male ; d. same of female ;— a. twice 

 natural size ; b. , <: , d. , slightly more enlarged. After Chittenden, Div. of Entomology, 

 Dep. of Agriculture. 



Smut (Urocystis Cepulce) : This disease is often troublesome to con- 

 trol. Early in the season leaves of onions may show the black smut 

 masses arranged more or less in lines. The onions are only infected dur- 

 ing their seeding stage from the spores, either attached to the seed or 

 lying in the soil, hence the danger of planting onions in smut-infested 

 soil. 



Treatment : Destroy and burn diseased plants ; when soil is smut- 

 infested grow seedlings in smut-free soil, then transplant; in infested soil 

 "apply in the drills, per acre, one hundred pounds of sulphur thoroughly 

 mixed with fifty pounds of air-slaked lime; sprinkle seed with formalin 

 solution (1 pound to 30 gallons of water) to kill the attached spores." 



Black Mould (Macrosporium parasiticum) : This fungus is usually 

 found associated with the Downy Mildew, but it is supposed to be respon- 



