Planting Site Affects Biological Controls
Jean Ferdinandsen, Commercial Horticulture Agent for Waukesha County

From the perspective of biological control, disturbed habitats are those where environmental factors separate a pest from local populations of its natural enemies. Poor soil nutrition, soil moisture, excessive or inadequate light or heat can contribute to insect outbreaks in landscapes. Natural enemies can be kept from finding their associated pests when infested trees are physically separated by long distances of turf or pavement.

Effects of physical separation of these trees can be more severe when a general lack of flowering plants reduces the amount of pollen and nectar that could be used to sustain natural enemies that are searching for new hosts. Natural enemies can also be mechanically separated from their pests by excessive road dust, or chemically separated by insecticide residues associated with mosquito abatement programs. Although these environmental conditions may interfere with the effectiveness of a wide variety of pests and their natural enemies, the impact on a given pest is likely to be influenced by the biology of both actual pests and natural enemies involved.