MINERAL NUTRITION OF APPLE TREE INFLUENCED BY HERBICIDE 



Mack Drake, John H. Baker, W.J. Lord and J.F. Anderson 

 Department of Plant and Soil Sciences 



A block of 20-year-old Delicious apple trees is being used in 

 a study of the effects of levels of nitrogen and potassium on fruit 

 yield, color, and storage quality. These trees are surrounded by 

 a vigorous sod cover consisting of orchardgrass, Kentucky bluegrass, 



Ladino and White clover. In 1967, the leaf 

 20, and 2.27%, and in 1968, 2.23, 2.29, and 

 for low, medium, and high nitrogen treatments 



timothy, witchgrass, 

 ni trogen was 2.16, 2 

 2.40%, respectively, 

 (Table 1). 



During the winter of 1967-68, dichlobenil (Casoron) was broad- 

 cast under the trees and extending a little beyond the drip line at 

 the recommended rate (100-150 lbs/A 4% granular). During the sum- 

 mer, all grasses and clovers appeared to make their usual vigorous 

 growth. The dichlobenil application was repeated during the winter 

 1968-69. A growth of grasses and clovers in the treated areas was 

 retarded during the summer of 1969 and some plants were killed. 

 There were no visual signs of leaf injury on the trees. During the 

 winter 1969-70, the dichlobenil application was repeated (the third 

 annual appl i cation ) . 



By mid-May 1970, both grasses and clovers were severely in- 

 jured or were killed except in the areas beyond the tree line where 

 dichlobenil had not been applied. Foliage was a deeper green and 

 growth was unusually vigorous even on the low nitrogen trees by mid- 

 July 1970. In late July, many of the leaves on terminal growth 

 showed marginal yellowing ("halo") which is the distinguishing symp- 

 tom of dichlobenil injury. Growth continued to be vigorous with 

 dense shoot growth ranging from 15 to 20 inches. 



Discussion: 



It appears that in this orchard the dichlobenil application 

 was ineffective in the first year and only partially effective in 

 the second. However, the third application in 1970 produced the 

 undesirable effect of apple leaf injury in addition to killing the 

 grass-clover sod. This injury to apple leaves and killing of the 

 sod may be the result of the accumulative effects of dichlobenil 

 applied 3 consecutive years 



