. Better fruit. Fruit-culture. ipll BETTER FRUIT Page 83 ortho or pyro or contain straight pyro. \ Notwithstanding this fact arsenate of lead is generally considered a safe spray, \ and very little complaint is heard regard- ing foliage injliry over most of the United States. These facts may cause people who are not acquainted with the conditions pre- vailing on the Pacific Coast, and espe- cially in the Pajaro Valley, to fail to appreciate the exact requirements of the case. Also, it is not stirprising that chemists and entomologists in general have been satisfied with a very incom- plete kno
. Better fruit. Fruit-culture. ipll BETTER FRUIT Page 83 ortho or pyro or contain straight pyro. \ Notwithstanding this fact arsenate of lead is generally considered a safe spray, \ and very little complaint is heard regard- ing foliage injliry over most of the United States. These facts may cause people who are not acquainted with the conditions pre- vailing on the Pacific Coast, and espe- cially in the Pajaro Valley, to fail to appreciate the exact requirements of the case. Also, it is not stirprising that chemists and entomologists in general have been satisfied with a very incom- plete knowledge of the chemistry of arsenate of lead. The local conditions in the Pajaro A'alley made it imperative to study this problem, v/ith the resulting important additions to our knowledge of spray materials. These climatic conditions which have been referred to consist in the great abundance of wet fogs and dews, which occur almost every night. The foliage becomes thoroughly wet, but does not always drip, and a great many of the leaves retain the water until it dries up during the day. This is just the ideal condition for the gradual solution and absorption of the arsenic. If the arsenical is soluble in water and affected by weathering, then the repeated and long continued action of small amounts of water would give the maximum effect. Any injuries in the surface of the leaf admits the fog water to the internal tissue. This water carries with it any substance which it may hold in solution. If the arsenic in the spray deposits is being dissolved the time soon arrives when enough is introduced into the leaves to cause injury. The tissue begins to die around the points where the fog water gains entrance to the leaves, and these spots gradually enlarge until they may cover the greater portion of the leaf. Before this time arrives many of the leaves turn yellow and fall. The falling of the leaves frequently occurs much in advance of the normal autumn shedding, and with bad cases of a
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