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Such rootstocks may well prove to be hardy enough for our region . Seedling or standard rootstocks may cause the tree to grow 20 or more feet tall . Signs : To observe foliar nematodes , tear the suspected leaf in a dish with water . For example , pear trees produced by a local wholesaler are grafted to the semi-dwarfing rootstock OH X F 333 , one of the reportedly hardiest semi-dwarfing rootstocks . In general , these insects do not kill the plant , but may stunt or kill parts , affect flowering , or cause aesthetic damage . When the ground color begins to change from green to a greenish yellow color , the apple is starting to ripen . More people enjoy eating blueberries than growing them , yet blueberries are exceptionally handsome bushes worthy of planting in the home landscape . As more people add pears to their gardens , this situation may change . These nematodes are microscopic worms that seek out and kill the caterpillars by introducing a bacteria . Scab resistant varieties will not require fungicide sprays for this disease , an appealing factor for many people . Verticillium sp is a destructive fungus and nearly impossible to kill because it lives in the soil . M.7a would seem to be a good compromise between the standard and truly dwarfing rootstocks . Northern gardeners should be aware that the soil in our climate will not reach temperatures high enough to kill the fungus . If only a few plants are affected , handpick and kill the adults ( e.g ., drop them into a pail of soapy water ) . Varieties and Rootstocks : Apples Selecting Apple and Pear Varieties Apple flowers must receive pollen from another variety of apple to produce fruit . Since the deer may become desensitized to the soap over time , you may need to periodically change the brand of soap .