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Both species ( Heterorhabditis and Steinernema ) have been shown to attack iris borer . Prevention through proper site selection , cultural management and good sanitation is by far the most important step in reducing the incidence and spread of disease . While geodetic methods may indicate that a region is deforming , detailed geomorphic studies help to determine which fault is active and point to promising sites for paleoseismic studies , a critical technique for determining recurrence intervals . Although pear trees are generally susceptible to a number of disease and insect problems , the fact that they are relatively uncommon in the Minnesota landscape often prevents these problems from becoming severe for home gardeners . To manage fourlined plant bugs , spray a labeled insecticide , such as acephate ( Orthene ) , diazinon , chlorpyrifos , carbaryl ( Sevin ) or malathion as soon as you see damage in May or June .