ANNUAL REPORT, 1943^4 63 



period shows that growth has been negatively correlated with severity of leaf 

 scorch which is a principal symptom of magnesium deficiency. 



Certain treatments designed to correct the deficiency were started in the fall 

 of 1942 and continued in 1943. Four early-season spray applications of 2 per- 

 cent magnesium sulfate (16 pounds of Epsom salts per 100 gallons of water) on 

 young trees of several varieties gave commercial control of foliage scorch in 

 1943. Applications were made at approximately the dates for the pink, calyx, 

 first cover, and second cover sprays. 



Soil applications of Epsom salts, magnesium oxide, and kieserite, made in 

 1942, benefited young mulched trees in 1943 but not older bearing trees growing 

 in sod. These materials were mostly broadcast on the soil under the affected 

 trees in quantities varying from 5 to 15 pounds per tree. Magnesium limestone 

 applied in amounts up to 50 pounds per tree was not eflfective. Other experi- 

 ments likewise indicate that benefits from surface-applied limestone will be com- 

 paratively slow. Nevertheless, an important aspect of the use of magnesium 

 limestone is its beneficial efTect in reducing soil acidity as well as its capacity to 

 prolong the effectiveness of the more soluble magnesium materials. A full report 

 of the experiments will be published in Volume 44 of the Proceedings of the Ameri- 

 can Society for Horticultural Science. 



Thinning Apples and Peaches with Caustic Sprays. (J. K. Shaw.) Experi- 

 ments in thinning with caustic sprays were started in the spring of 1944 on 

 Wealthy, Duchess, and Mcintosh, also on several varieties of peaches. Com- 

 parisons were made of concentrations of from 1 to 3 pints of Elgetol jn 100 gallons, 

 of one and two applications, and of time of application as related to the develop- 

 ment of the flowers. It is too early to draw final conclusions, but some prelim- 

 inary statements maj' be ventured. 



A spray of 2 pints to 100 gallons took off all or nearly all the fruits on moder- 

 ately vigorous Mcintosh. 



Duchess trees were sprayed once, 2 pints in 100 gallons, on May 9, May 11, 

 or May 12. All sprays were more or less successful. The spray on May 11, 

 when practically all spur flowers were open and a few petals were falling, gave 

 the best results. These trees need little or no further thinning. Wealthy trees, 

 treated similarly on the same dates, when the flowers were less advanced, show^ 

 no apparent results from the early spray and only partial thinning from the med- 

 ium and late sprays. 



Concentrations of from 1 to 3 pints in 100 gallons applied once (Ma)- 12) or 

 twice' (May 12 and 15) to Wealth}- in another orchard gave varied results. Only 

 the double spray, 2 pints in 100 gallons, seems to have thinned the fruits effec- 

 tively. The w^eaker and the single sprays seem to have had more or less eff'ect 

 on the weaker trees, which are somewhat lacking in nitrogen, but all these trees 

 require further thinning. Nearly all sprays were less effective on stronger trees 

 which have been heavily mulched. 



These preliminary observations suggest that Mcintosh is easily thinned w'hile 

 W^ealthy requires severe treatment, especially when the trees are vigorous and 

 high in nitrogen. Duchess takes an intermediate position. Perhaps strong or 

 double sprays should be used on trees known to have the habit of setting heavily, 

 and weaker sprays on trees known to set only moderately. 



Injury to the trees was less than expected. Measured by what is expected 

 from pesticide sprays, it was rather severe; but the trees now look all right and 

 perhaps the spray injury weakened the trees less than would the setting of an 

 excessive crop. All these trees (except the Mcintosh) have been distinctly bien- 

 nial. Whether any of them will set a crop next year remains to be seen. 



