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‘ Liberty , ’ ‘ Redfree , ’ and ‘ William ’ s Pride ’ are all scab resistant . Now select 4 or 5 scaffold branches from those that remain , pruning out any “ duplicate ” branches that are growing just above or just below scaffolds . The classical model for erosion supposes that the erosion rate is dependent on average elevation with a denudation rate of 0.1 every million years ( 0.1 / My ) . Keep the chips away from the trunk of the tree . In order to develop this framework , the first pruning task is to select or develop what we call " scaffold branches . ' And yet , high quality , hardy pears are moderately easy to grow in the southern half of Minnesota — easier in some ways than apples . The term itself means ' swelling ' , which describes its initial stages . Dwarfing and Standard Rootstocks When purchasing an apple or pear tree , one is actually selecting a plant made up of two genetically different individuals grafted together , the " scion " and the " rootstock ” ( Figure 1 ) . Avoid pulling or yanking the fruit ; such an action may well remove the small woody " spur " to which the stem of the fruit is attached , taking with it next year 's flower buds . In addition , heavy crops can cause a phenomenon known as “ biennial bearing ” in which a heavy crop is followed the next year by little or no crop . Perhaps this is due to the pear tree 's reputation for becoming very large , for its history of susceptibility to fire blight disease , or the fact that varieties hardy to our region do not include the well-known and popular ' Bartlett ' or ' Bosc . Among Minnesota apple varieties , only ‘ Northwestern Greening ’ is truly green at harvest . With over 5000 fatalities and damage estimates exceeding $ 100 billion , it may rank as the most costly earthquake in modern history . 2.3 and 2.4 ) or bad topographic data ( Fig. 2.2 ) , all of which may yield quasiregular areas of " pseudo-deformation " crudely analogous to expected volcanic deformation patterns . This support includes installation of an ERS-1 ground receiving station in Hawaii and selected other locations , improvements in real-time navigation and control for the NASA DC-8 to extend the capability of the TOPSAR instrument to perform repeat-pass interferometry , and support for the required improvements in image processing . The scion is the aboveground part of the tree that produces the type of fruit desired ( for example , ‘ Keepsake ’ or ' Summercrisp ' ) . Oedema , often spelled ' edema ' , is a physiological disorder that develops when a plant absorbs water faster than it can be lost normally from leaf surfaces . In other words , fruit trees cannot be reproduced " true " to the original cultivar from seed . " These 4 to 5 scaffold branches should begin about 30 inches from the ground ( 40 inches if turf will be located beneath the branches and need to be mowed ) , should be spaced as equally around the trunk as possible and should be spaced vertically at least 6 inches from one another . Although there is more than one way to prune a fruit tree , home gardeners in Minnesota commonly prune and train using a " central leader " system , where a single central trunk runs the entire height of the tree and supports the fruiting branches .