142 Bulb or Onion Crops 



one pint of commercial formaldehyde to sixteen gallons of 

 water should be applied in the furrow with the seed at the 

 time of sowing at the rate of two hundred gallons to the 

 acre. The application may be made in the open furrow just 

 ahead of the coverers by means of a watering device attached 

 to the drill. About a five-sixteenth inch flow of liquid from 

 the tank should accomplish the full application. A properly 

 equipped drill should discharge, when stationary, one gallon 

 of the solution every fifty seconds. 



Onion mildew (Peronospora schleideniana) . — The disease 

 may be recognized by the furry fungus coating on the outer 

 surface of affected leaves. As the fungus develops, the plants 

 yellow and finally die. The disease usually becomes evident 

 at a few points in a field and rapidly spreads under favorable 

 conditions of moisture. Partial recovery may occur in a dry 

 period by the growth of new leaves, but under favorable con- 

 ditions the disease will develop anew. Control: Burning of 

 dead tops to prevent the over-wintering of the fungus in them 

 and crop rotation to reduce infection from spores over-winter- 

 ing in the field, are desirable. Tillage may aid the plants to 

 outgrow the fungus. Spraying with bordeaux mixture to 

 which has been added resin-fish oil soap is sometimes recom- 

 mended ; applications should begin before the disease has 

 become established and will perhaps need to be repeated sev- 

 eral times. 



Onion thrips {Thrips tabaci). — Minute elongate yellowish 

 insects, 1/25 inch long when mature, that attack the leaves, 

 especially under the sheath at the base, causing them to turn 

 whitish and giving the plants a dirty yellowish appearance. 

 The tender leaves at the center become thickened, curled and 

 deformed. Badly injured plants fall over on the ground. 

 Most injurious in seasons of drought. Control: Spray early 

 before the leaves turn down with " Black Leaf 40 " tobacco 

 extract, 1 pint in 100 gals, water in which 5 or 6 lbs. soap 

 have been dissolved. Use the material liberally and direct the 

 spray downward into the base of the leaves. Make three or 

 four applications at intervals of four or five days. 



