May. 1922 



BETTER FRUIT 



Pagel 



Effects of Miscible Oil Sprays 



By C. C. Vincent, 



Hortiridtinist University of Idaho, Moscow 



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I Probably no article Better Fruit \ 



I has ■published in several months at- | 



I tracted more comment and attention | 



I than that in the March number by J | 



I R. Parker, summarizing a series of | 



I tests in Montana ivith various tnis' | 



I cible oil sprays. Because it throws ad- \ 



I ditional light on the subject this | 



I paper by Professor Vincent is pre- | 



I sented at this time. It is hardly to \ 



I be denied that certain elements of \ 



I danger attend the application of these \ 



I sprays. The sooner orchardists learn | 



I the what and when of those da?!gers | 



I the better it zcill be for both the | 



I makers and users. The practical z'alue I 



I of the oil sprays has been -widely es- | 



I tablished. There is no deprecation of i 



I this value in presenting the dangers % 



I the Idaho horticulturist seems here | 



= 10 have disclosed. I 



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EVER since introduction of the San 

 Jose Scale into the United States it 

 has been one of the most formidable 

 insects that the fruit grower has ever en- 

 countered. 



Control of the scale is still a serious 

 problem. Its introduction in our state, 

 however, has taught the fruit growers many 

 valuable lessons. The most progressive 

 growers soon learned the value of spray- 

 ing and they were ever on the alert for 

 better spray mixtures, better machinery and 

 more effective methods of control. 



The lime-sulfur solution therefore be- 

 came the standard spray for the control 

 of the scale and it was not long until prac- 

 tically all of the growers were using either 

 the commercial solutions or home-made 

 concentrates. In 1 91 9, however, for some 

 unknown reason these solutions failed sat- 

 isfactorily to control the scale, the growers 

 in many cases sustaining a loss of from 2? 

 to 50 per cent of their fruit. 



Various reasons were assigned for the 

 tremendous loss, the principal one advanced 

 by the grower-; being the poor quailt^■ of 

 the lime-sulfur. Professor A. L. Melander, 

 entomologist of the Washington State 

 College, believes that certain strains of the 

 insect have developed more or less resist- 

 .ince to the action of lime-sulfur. He has 

 also found that oil sprays are more de- 

 -iructive than lime-sulfur and recommends 

 them in those districts where the lime- 

 Hilfur failed to give satisfaction. 



In our own experiments, which were 

 conducted in the Lewiston valley, covering 

 a period of three years, we found that the 

 miscible oil sprays give slightly better 

 results than the lime-sulfur, the efficiency 



ranging from 94 to 99 per cent. These 

 applications were made in early spring, just 

 as the buds were beginning to swell. 



What are Miscible Oil Sprays? — 

 Miscible oils may be defined as emulsions 

 or preparation of oils readily mixing with 

 water. According to a recent government 

 bulletin, "they are composed chiefly of a 

 mineral oil emulsified with a soap usually 

 made from a vegetable oil and an alkali. 

 In a miscible oil the mineral oil is sub- 

 divided into many minute globules and, 

 when mixed with water, the oil is evenly 

 distributed throughout the water. The 

 safe use of the miscible oils is thought to 

 be largely dependent upon the relative 

 fineness of these particles." 



To prevent recurrence of the 1919 loss, 

 the growers decided to use a miscible oil 

 spray as a clean-up spray in their orchards. 

 The general plan was to make the applica- 

 tion in the fall, followed by the regular 

 lime-sulfur solution in the spring. This 

 plan was generally accepted in view of the 

 fact that experiment station men have from 

 time to time recommended two applications, 

 one in the fall after the leaves had fallen, 

 and the other in the spring as the buds were 

 swelling. However, owing to the rush of 

 work the majority of the growers failed 

 to make the full application. 



Experiment Conducted — One grower, 

 however, started two spraying crews on 

 November 25, 1919, in a block of Bald- 

 win trees using the insecticide at the rate of 



one gallon of the oil to fifteen gallons of 

 water. This block of trees had been 

 planted during the late winter of 1910-1 1, 

 directly along the bank of the Clearwater 

 river, on rather poorer soil than most of 

 the balance of the orchard. 



The trees, however, had made a good 

 growth each year, and at the time of spray- 

 ing were in a good physical condition. 

 This block of Baldwin trees were selected 

 for the experiment in view of the fact that 

 .1 heavier infestation of scale was noticed 

 on the fruit at harvesting time, than in 

 other parts of the orchard. 



The man.ager of the orchard had in- 

 structed his foreman to spray in eight or 

 ten rows from the river, and in order to 

 do so, the river curving outward, he jogged 

 in and out from row to row in a very 

 clearly defined pattern. Therefore the 

 area covered was very easily distinguished 

 by the appearance of the trees after spray- 

 ing. The two outfits worked the entire 

 day, spraying in all, over 600 Baldwin 

 trees. 



CLIMATIC Conditions — The weather 

 bureau reported for the day a maxi- 

 mum temperature of 40 degrees and a min- 

 imum temperature during the night of 29 

 degrees. The weather turned cold the next 

 day so spraying operations were discon- 

 tinued. This was followed by a heavy 

 snow storm. 



(('>fi//hiiu\i uii pJ^f 27) 



Northern Idaho orchard where late fall application of miscible oil spray, followed by severe 

 cold weather, oroduced much damape. IJnsnraved trees are shown in background. 



