March, 1921. SCIENTIFIC AGRICULTURE. 



The Story of Spraying Mixtures 



W. LOCHHEAD, Professor of Entomology aud 

 Zoology, Macdouald College, P.Q. 



fPresidential address at the IHth Annual Meeting of the Quebec Society for the Protection of Plants.) 



113 



Prior to 1860 the methods of protection of plants 

 from insects and fungous diseases were extremely crude 

 and primitive. Practically nothing was known. about 

 tiic nature of fungous diseases, and although insects had 

 been studied for many years, no serious attempt had 

 been made to control the injurious forms with chem- 

 icals. The best insecticides in use were various forms 

 of soap, tobacco, quassia chips, carbolic acid and lielle- 

 boi-e. 



As we all know, spraying mixtures are of two kinds: — 

 I itsecticidfs and Fungicides, but some mixtures, like 

 lime-sulphur and soluble sulphur, belong to both groups. 

 Insecticides. 



In the development of insecticides, as of other phases 

 of economic entomology, the United States has taken 

 the lead over all other nations. Two outstanding factors 

 contributed to this wonderful progress: — 1. The losses 

 which certain portions of the countr\' suffered at var- 

 ious times from (a) the potato beetle; (b) the Rocky 

 Mountain locust; (c) the cotton caterpillar; (d) the 

 San Jose scale ; (e) the cotton-boll-weevil ; (f) the Gypsy 

 aud Brown Tail moths, brought public opinion to bear 

 strongly upon Congress so that measures were taken to 

 discover methods of control; 2. The establishment of 

 State Agricultural Colleges and Experiment Stations 

 which made it possible to train men for the investigation 

 of sucli problems. 



It is interesting to note that in the matter of insec- 

 ticides, methods of fumigation with hydrocyanic acid 

 gas, and spi-aying with lime-sulphur and resiny washes 

 were developed first on the Pacific Coast, while arsen- 

 ical sprays and mineral oil preparations were develo])ed 

 in the East. 



Paris' Green. — Paris Green was the first insecticide 

 of merit to be employed against biting insects. During 

 the sixties, it came into use against the Colorado beetle, 

 in the seventies it was successfull\- used against the cot- 

 ton caterpillar and against canker-worms and the cod- 

 ling moth in orchards, and in tiie eighties against the 

 plum curculio and other pests. By 1890 Paris Green 

 hail become the standard insecticide again.st biting in- 

 sects. However, this and other arsenite compounds, like 

 London Purple and the Kedzie mixture made from 

 white arsenic, were soon found to be unsatisfactoiy on 

 account of their liability to burn foliage unless great 

 cai'C were taken to neutralize the free acid present. 



Arsenate of Lead. — In 1892 Arsenate of Lead was 

 first employed against the Gypsy moth, and graduallj^ 

 gained favor as a substitute for Paris Green. It has 

 the advantage of being hai'mless to foliage, of remain- 

 hig well in suspension without constant stirring, and of 

 sticking to the foliage for a long time. It can, more- 

 over, be used with Bordeaux aud lime-sulphur as a 

 comliination spray. As the paste form deteriorates on 

 exjjosure, while the powder is quite stable, tlie latter 

 is recommended for general use. 



Sanders and Kelsall, of the Dominion Entomological 

 Laboratory, Annapolis, Nova Scotia, liave done some 

 admiralile work on the reactions that occur when ar- 

 senate of lead is mixed with othei- ciieiiiicals. For exam- 

 ple, they found that ajjiile foliaiir is lialilc to be in- 



.jured when more than 15 nigms. of As^O^ are in so- 

 lution per 1000 cc. of water. In the case of lead arse- 

 nate (PbH ASO4) it is seldom soluble to the extent of 

 4 mgms. of As^O- in 1000 cc, and on the average about 

 2 mgms. However, when the manufacturer adds a small 

 amount of MgO to make it float better in water, a chem- 

 ical reaction occurs wliich makes it dangerous to leaves. 

 Magnesium arsenate (Mg H AsO^) is formed, which 

 dissolves to .such an extent in water that 40 or 50 mgiiu^. 

 of AsoO,-, are to be found in 1000 cc. of water. 



Again, when a very small quantity of lime is added 

 to lead arsenate, a lime arsenate (Ca H AsOJ is form- 

 ed which is highly dangerous. But if the lime be pre- 

 sent in large quantities CajCAsO!,). is formed which is 

 not dangerous. 



Arsenate of Lime. — During the last two or three years 

 arsenate of lime has been employed b\' many growers 

 as a substitute for the lead arsenates, on the score of 

 reduced price and higlier poison content pound for 

 pound, it is, however, less stable, but with the addi- 

 tion of a stabilizer such as hydrate of lime, Bordeaux, 

 lime-sulphur, or soluble sulphur, when excess lime is 

 present, it is quite safe to foliage. 



For the coming year arsenate of lime is being widely 

 recommended as a cheap and effective substitute for 

 arsenate of lead. 



Lime-Sulphur. Perfnap,s tjie most outstanding achie- 

 vement in commercial spraying during the last forty 

 years has been the introduction aud improvement of 

 lime-sulphur. In the eighties the California fruit grow- 

 ers used it against both the scale and the peach leaf 

 curl. As an insecticide against scale and many sucking 

 insects, it has been employed ever since, but by the early 

 method of preparation it had to be appliefl warm for 

 crystals soou formed, which tended to clog both the 

 spray pump and the nozzles. Moreover, it could be used 

 only for the dormant or semi-dormant stage. 



About 1912, a new method of preparation was dis- 

 covered, which removed the objectionable features of 

 the old method. It consisted in making a concentrated 

 sfilution by boiling together 50 lbs. of fresh stone lime, 

 100 li)s. of suljihur and 40 to 50 gallons of water. The 

 solution when properly made can be kept for months, 

 and for use can be readily diluted to any strength re- 

 quired foi- dormant aud summer spraying. 



The discovery by Sanders and Kelsall of the cau.se of 

 the heavy droj) of the fruit after applications of lime- 

 .sulphur is wortli.y of note. They found that when lime- 

 sulphur (1 to 30) was applied only to the upper sur- 

 face of the leaf no injury followed, but when both sides, 

 ■ or only the lower surface, were sprayed injur}- was done. 

 When s])rayed leaves were examined microscopically, it 

 was observed that the chloroi)liy]l of the h'af-<^'ells had 

 been acted upon by an appreciable amoinit of lime-sal- 

 phur absorbed through the lower surface. They ob- 

 served, however, that no such injury followed applica- 

 tions of Bordeaux and soluble sulphur. 



The excessive dropping of the fruit, they maintain, 

 is due to the injury to the leaves whereby they fail to 

 function as carbohydrate manufacturers for tlu' fruit. 

 Tlie <»reatest drop occurs after the fourth ai)plication, 

 tiiat is. the one given two weeks after the petals fall, 



