54 MASS. EXPERIMENT STATION BULLETIN 398 



ammonium sulfamate at dosages of one-fourth and one-half pounds per gallon 

 of water. By August 1 the younger leaves were considerably browned and dried 

 out and the older leaves showed some injury. During the following week, most 

 of the ivy appeared to be dead. The carry-over value of the treatment remains 

 to be determined. Experience showed that care must be exercised not to get 

 this poison ivy eradicant on apple trees. 



Magnesium Deficiency in Massachusetts Apple Orchards. (L. Southwick.) 

 In September 1939, medium to severe intervenal leaf scorch was observed on 

 individual Mcintosh trees in two experiment station orchards. These trees also 

 showed excessive preharvest drop of truit. A test for potassium showed a high 

 level of this element in the leaves from afifected trees. In August 1941, the same 

 deficiency symptoms became prevalent in these and other orchards, particularly 

 in a young orchard set in May 1939. In 1942, the trouble was evident in many 

 commercial orchards. Other typical symptoms besides leaf scorch included 

 occasional yellow banding and mottling and usually abnormally early leaf fall 

 commencing near the bases of current shoot growths and progressing upwards. 

 The symptoms suggested magnesium deficiency and chemical analyses of leaves 

 in the late fall of 1941 tended to support this hypothesis. At that time, soil was 

 collected from the young orchard mentioned above and Mailing rootstocks were 

 set in 2 and 3 gallon crocks and forced into growth in the greenhouse in February. 

 Typical deficiency symptoms became evident in all pots where magnesium was 

 not added and the trouble was most severe in the potassium-fertilized pots. 

 Chemical analyses of the leaves showed low amounts of magnesium wherever 

 deficiency symptoms were prevalent and high amounts where symptoms were 

 not present. 



In August 1942, leaf samples were obtained from many apple trees. Chemical 

 analj'ses of unburned leaves from trees showing variable degrees of foliage scorch 

 and leaf fall showed that there was consistent correlation between symptom sev- 

 erity and the magnesium and potassium leaf contents. Magnesium was always 

 low and potassium always tended to be high in trees showing deficiency symptoms. 

 Most of the afifected orchards were on acid soils. 



Just why the trouble has been more prevalent and severe in the past two 

 years is not easy to explain although several factors may be significant. Increased 

 use of potassium in recent Aears may have caused a build-up to such a point as 

 to accentuate the need for magnesium. Increased use of mild sulfur sprays and 

 sulfur dusts has tended to increase soil acidity. Weather conditions, particularly 

 rainfall, may have influenced the amounts of magnesium available to trees. These 

 are surmises only. Of course, it is probably true that magnesium deficiency in 

 apple orchards is not new but that It had not been recognized as such. 



Magnesium deficiencies may be overcome either through the use of adequate 

 applications of high magnesium (dolomitic) limestone or, where quicker results 

 are desired, by applying some soluble magnesiuni compound such as magnesium 

 sulfate. 



Temperature of Orchard Soils. (J. S. Bailey.) Thermographs were placed in 

 the soil under two Mcintosh trees in the Clark Orchard, one under a mulched 

 tree, and the other under a tree growing in sod. The following observations were 

 made: 



1. The soil temperature under mulch was lower than that under sod from 

 March to August; from August to late January the temperature under 

 mulch was higher; from late January to March the soil temperature under 

 sod and mulch was about the same and nearly constant. 



2. Soil under sod warmed up faster In the spring and cooled of? faster in the 

 fall. 



