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THE farmers' handbook. 



them. Before bagging, the tops and roots should be trimmed off, leaving 

 about an inch of the top on the bulb; sheep shears are very suitable for the 

 purpose. Great care should be taken not to bruise any of the bulbs, for 

 decay sets in quickly. Storage is best effected in cases in a well-ventilated 

 shed. 



Under fair conditions a yield of 4 to 6 tons per acre can be expected. 



Insect Pests and Diseases. 



The worst insect pest is the onion maggot (Phorbia ceparum). The mag- 

 gots come from the egg deposited on the plant, and require about a week to 

 hatch; the larvae burrow into the bulbs and remain there about two weeks, 

 then emerge and pupate in the ground. The first indication of their pre- 

 sence is the tops turning yellow in colour, then withering, and finally dry- 

 ing before the bulbs have matured. It is difficult to suggest a remedy, but 

 liming the soil is found to be beneficial. If the infestation is very severe, 

 rotation of crops should be tried. 



Downy Mild or BHyht. — This is one of 

 the most important diseases of the onion. The 

 cause is a fungus ( Peronospora schleideniana, 

 Whetzel). The disease is best diagnosed by 

 the presence of more or less oval yellow spots 

 with a purplish border. On these spots the 

 fungus is produced, giving the surface a downy, 

 violet appearance. Owing to the breaking 

 down of the tissues, due to invasion by the 

 fungus, the leaves fall over or collapse. 



The spores of the fungus germinate and r ut 

 forth a tube which penetrates a stoma (breath- 

 ing pore) of the leaves and thereby causes 

 infection. Distribution of the spores can be 

 brought about by wind and cultivation. 

 Another type of spore, a thick-walled resting 

 spore (oospore) is produced in the tissue of the 

 onion leaf. This spore is much more resistant 

 than the summer spore and enables the fungus 

 to live over from season to season upon dead 

 leaves. Wet weather and humid atmosphere 

 favour the disease, whereas a dry spell v/ill 

 check its progress. 



Good results have been obtained by spraying 

 with Bordeaux mixture (6 —4 — 50). The 

 number of applications necessary to control the 

 disease will vary with the climatic conditions. 

 If the weather is moist and the atmosphere 

 humid, repeated sprayings may be necessaiy. 



Should a dry spell be experienced, a halt in 

 the operations can safely be made. As far as 

 possible all diseased material should be collected 

 and burnt. 



Onion Plant affected by 

 Downy Mildew. 



