Insecticides and Fungicides. 237 



Being so small and light, the spores are readily carried long distancef? by 

 the wind, are washed about by the rains, and are also carried by birds and in- 

 sects and probably by other agencies. These agencies are thus largely responsible 

 for the spread of fungous diseases from leaf to leaf, plant to plant, or orchard to 

 orchard. Over greater distances the spores may be carried on shipments of in- 

 fested nursery stock, fresh fruits, vegetables, seeds, etc. 



Should a spore fall upon suitable soil, such as the surface of leaf or fruit, 

 and the conditions of heat and moisture be favorable, it will germinate — push our 

 a delicate, slender germ-tube. In the case of most parasitic fungi this germ- 

 tube soon penetrates the apidermis of the leaf or fruit and the mycelium de- 

 velops in the underlying tissues entirely beyond the reach of fungicides. In some 

 cases, however, the mycelium spreads over the surface of the plant. In other 

 words, fungi, like insects, may be divided into two groups, as follows : 



Group I — Internal Fungi. — This includes those fungi in which the germ-tube 

 penetrates the skin of leaf, fruit, branch or root and the mycelium develops 

 entirely within the tissues of the host plant. Apple-tree anthracnose, brown- 

 rot, the grain-smuts and rusts, the downy-mildews, for all practical purposes 

 apple-scab, and many others may be included in this group. The philosophy of 

 spraying for this group of fungus diseases is based upon the fact that they 

 cannot be cured, but can be prevented. The germ-tube must be destroyed be- 

 fore it penetrates the epidermis and to do this the surface of the host must be 

 thoroughly protected by the fungicide during the entire time the spores are 

 germinating. 



Group II — External Ftivgi. — This includes those fungi in which the mycelium 

 spreads over the surface of the host. This group includes but comparatively few 

 serious pests. Perhaps the one that has attracted most attention in this State 

 is the powdery-mildew of gooseberries. The powdery-mildews of the grape and 

 of the rose also belong to this group. These diseases may be prevented by 

 proper fungicidal treatment the same as diseases of group I and in addition they 

 may also be cured by such treatment. The mycelium being exposed upon the 

 surface of the host may be reached and killed by the proper fungicides. 



INSECTICIDES. 

 GROUP I — FOOD POISONS. 



1. PARIS GREEN. 



This is used more extensively than any other poison. It has largely sup- 

 planted London purple but is, in turn, being supplanted by various other com- 

 pounds of arsenic. Pure, it is among the mose reliable of insecticides, but has 

 the disadvantage that it is a rather coarse crystalline substance which settles 

 rapidly to the bottom of the spray-tank unless the contents are kept thoroughly 

 stirred. For codling moth, bud moth, tent caterpillars and many other insects 

 of group I it is generally used as a spray in the following proportions : 



Paris green 1 pound 



Quick lime 2 pounds 



Water 160-200 gallons 



Slake the lime, stir the poison into a thin paste with a little water, then 

 strain the mixture through a sieve into a tank containing the required amount 

 of water. If it is desired to spray for both fungi and insects, Bordeaux mixture 

 (22 or 2.3) may be used in place of the water in the above formula. For peach 

 or other tender foliage 300 gallons of water or Bordeaux should be used. It is 

 necessary to keep this mixture well stirred while spraijiini. 



Owing to the excessive cost of Paris green and the difficulty of keeping it in 

 suspension in the liquid, various other compounds of white arsenc — arsenious 

 acid — are now extensively used in its place. In solution, arsenic is extremely 

 injurious to foliage. It is, therefore, necessary that it be combined with other 



