-15- 



Cultural Problems . 



Tree training difficulties were experienced particularly 

 with Empire because the central leader lost its dominance. 

 Leader leaning, which was corrected by staking, appears assoc- 

 iated with the growth characteristics of Empire on interstem 

 trees on M26 rootstock rather than due to cropping. None of 

 the trees needed staking because of poor anchorage. 



The burrknots on the M9 stempieces on trees particularly 

 at the (A) and (B) (the soil line at the mid-section of the stem- 

 piece) planting heights were the entry sites of apple bark borer 

 larvae in 1981. These were eradicated manually by probing for 

 the larvae with a knife as well as scraping with a wire brush. 

 Observations here, and at other locations have led us to conclude 

 that the problem is associated with the use of mouse guards made 

 of plastic which impede adequate coverage of pesticide sprays on 

 the tree trunks. 



Crovvfth and Yield 



Burying or partially burying the stempiece tended to decrease 

 the number of root suckers and increase the trunk cross- sectional 

 area (TCA) and yield efficiency, but did not affect tree height 

 and spread. Trees with the stempiece exposed had smaller trunks 

 than those with the stempiece buried, but trees with the stempiece 

 partially exposed did not differ in TCA from those at the other 

 planting depths. Trees with the stempiece exposed produced the 

 most root suckers regardless of the cultivar/inter stem/rootstock 

 combination. These findings support the claim of Carlson in Michi- 

 gan that deeper planting reduces the tendency of interstem trees 

 to produce root suckers. 



Since root suckering was most severe when the stempiece was 

 exposed, the question was posed whether the amount of suckering 

 affected tree growth. There was a negative correlation between 

 number of suckers and trunk circumference (r = -.15, p = .02). 

 Because tree size varied across rootstock and cultivars, each 

 rootstock and cultivar were evaluated separately. The number of 

 suckers correlated negatively with trunk circumference for M9/MM106 

 (r = -.23, p = .01) and the Macspur (r = -.33, p = .01) and Mcin- 

 tosh (r = -.48. p = .001). Ferree in Ohio reported a positive 

 correlation between number of root suckers and trunk circumference 

 on interstem trees with the lower union of the stempiece 5 cm above 

 the soil line. 



