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Simply rake or comb out the dead foliage next spring to remove older growth and leaves . The symptoms of foliar nematode damage are due to the nematodes ' feeding on the foliage , stems and buds . The most common above-ground symptom of crown and root rot is a rapid yellowing of foliage and dropping of flower buds . The University of Minnesota has long advised gardeners to plant pear varieties grafted only to hardy seedling pear rootstocks to ensure survival in Minnesota . 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 . Although there are nematicides labeled for nursery use , these products are EXTREMELY toxic , especially to fish and wildlife , and are not available to the homeowner . If you plant a pollen-sterile variety , you may need to plant a third variety in order to get fruit on all three pear trees . The cause of aster yellows is a microscopic organism called a phytoplasma ( formerly called a mycoplasma-like organism or MLO ) . Some indoor plants often affected are geranium ( especially the ivy-leaved types ) , clivia or Kaffir lily , peperomia , jade plant , members of the Ficus family , schefflera , epiphyllum ( orchid cactus ) , English-ivy , and begonia . At the end of the growing season , cut back and remove infected foliage to prevent fungal spores from surviving winter in plant debris . A cleft graft , bottom right , covered with asphalt grafting compound is used for topworking established apples and pear trees . It will also feed on the foliage of trees and shrubs . Misapplication of these pesticides has been linked to death of hundreds of songbirds , fish and wildlife .