March, 1922 



BETTER FRUIT 



Page Seven 



Miscible Oils and Fruit -Tree Leaf Roller 



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Mniiiiiiiiiiii^ 



I Exfertmeiits -uith spay materials, | 



I u-hen srienlifiiiilly carried out by | 



i experts, are certain to add something \ 



i lo the sum total of existing knozv- | 



I ledge about them. The question of | 



I virtues and efficacy of fniscible oil | 



I sprays for this or that disease or pest | 



i IS still one of keen debate. Every | 



I n-ide^a-.L-ake horticulturist must be | 



I glad to learn anything he can from | 



I • the experiences of others. With this | 



I /// mind u-e print here the results | 



I obtained in combating leaf-roller on \ 



I a small scale in Montana, by Profes- | 



I snr Parker and associates. If his | 



i report provokes reply and elicits fur- = 



I ther discussion, so much the better | 



I for those studying the uses of mis- | 



I cible oils. \ 



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THE fruit-tree leaf roller (Archips 

 argyrospila) for the past two sea- 

 sons has been extremely injurious 

 in several of the largest apple orchards in 

 the Bitter Root Valley and during the same 

 time has also appeared in injurious numbers 

 in a number of localities in Washington 

 and Oregon. The enormous damage this 

 insect is capable of doing, the difficulty of 

 its control and its ability to increase and 

 spread very rapidly make it one of the most 

 dangerous orchard pests with which the 

 fruit growers of the Northwest have to con- 

 tend. Because of the general interest with 

 which the leaf-roller is now regarded, our 

 experience in Montana in attempting to 

 control this pest with miscible oils is here- 

 with presented. 



The spraying tests were conducted 

 jointly by R. K. Thompson, manager of 

 the University Heights Orchard Company, 

 the Division of Horticulture of the Mon- 

 t.'.na State Department of Agriculture, and 

 the Montana Experiment Station. The 

 general arrangement was for Mr. Thomp- 

 son to furnish the trees and spraying equip- 

 ment and for W. L. Shovel 1, now Chief 

 of the Division of Horticulture, and Mr. 

 Thompson to jointly supervise the actual 

 spraying operations. The writer aided in 

 planning the experiments and in checicing 

 up the results. 



Results of SprAying in 1920 — The 

 first appearance of the leaf-roller in Mon- 

 tana in injurious numbers was at University 

 Heights orchard, at Darby, in 1919. Dur- 

 ing that season damage was done over a 

 very small area, b t the moths appeared 

 in great numbers and laid eggs very heavily 

 over an area of about 400 acres, many of 

 the trees having from 200 to 300 egg- 

 masses. R. K. Thompson, manager of the 



By J. R. Parker 



Montana Experiment St-ation, Bozeman 



orchard, realizing that the great quantity 

 of eggs laid in 1919 meant trouble the 

 following year, immediately took steps to 

 find out the best known method of control. 



Entomologists n several states who had 

 had experience with the leaf-roller were 

 consulted and all agreed that spraying with 

 miscible oil had proved the most successful 

 of all the control methods that had been 

 tried. Mr. Thompson also wrote to the 

 Montana Experiment Station for aid, but 

 we had had no previous experience with 

 the leaf-roller and could only hand along 

 the recommendation of entomologists in 

 leaf-roller states which, .as Mr. Thompson 

 already knew, was miscible oil. 



Acting on these recommendations, the 

 University Heights Orchard Company 

 bought two car loads of miscible oil known 

 as Spra-Mulsion. Four hundred acres were 

 sprayed with this oil in the spring of 1920, 

 25 acres being sprayed early at the rate of 

 seven gallons of oil in 100 gallons of water 

 and 150 acres at the rate of 8 gallons of oil 

 in 100 gallons of water. 



The early spraying was done under un- 

 favorable conditions, the weather being 

 cold and cloudy and the spraying was in- 

 terrupted by storms. The later spraying was 

 done under ideal spraying conditions, the 

 weather being warm and clear. The first 

 spraying gave practically no results, while 

 the later spraying at the stronger strength 

 gave only 50 to 60 per cent control. As 

 a result the trees over approximately 300 

 acres were almost completely defoliated, 

 great numbers of moths matured and eggs 

 were laid over a much larger territory than 

 in 1919. 



^VT^INTER Spraying Experiments in 

 1920 — The costly and negative 

 results from the use of Spr.a-Emul- 

 sion in 1920, together with the enlarged 

 area of infestation presented a very dicour- 

 aging outlook for the following year. 

 Miscible oil is a highly expensive insecticide 

 and no one wanted to put money into it 



TABLE I- 



-RESULTS OF WINTER SPRAYING WITH MISCIBLE OILS TO CONTROL 

 LEAF-ROLLER 



TABLE II— RESULTS OF SPRING SPRAYING WITH MISCIBLE OIL TO CONTROL 



LEAF-ROLLER 



