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Arthropod Pests and Improper Horticultural Practices

May 19, 1999

Proper implementation of sound horticultural practices has the greatest impact in maintaining healthy plants in the landscape. Cultural practices such as watering, mulching, pruning, and fertilizing, when properly implemented, cause plants to grow and flower to their fullest potential. However, when these cultural practices are improperly performed, insect/mite problems can result.

Water. Underwatering or overwatering often leads to plant stress, and these plants are more susceptible to insects such as wood-boring beetles. Stressed plants emit volatile chemicals that attract these insects. The wood-boring beetles use these chemical cues to help them easily locate plants whose natural defenses have been compromised by improper watering practices. Underwatering plants may lead to higher populations of spider mites because there is less moisture in the air from ground and foliar evaporation, resulting in lower relative humidities and drier conditions. These conditions favor spider mite development.

Mulch. Proper mulching moderates soil temperatures, conserves moisture in the soil, reduces competition from other plants, reduces weed pressure, prevents soil compaction, and minimizes soil erosion. However, improper use of mulches can often lead to increased plant susceptibility to insects. For example, applying too much mulch or covering the plant crown prevents the bark from exchanging oxygen and the plant suffers from asphyxiation. This leads to plant stress and a higher probability of attack from wood-boring beetles. Thick mulches (6 to 8 inches) can provide a moist environment that is attractive to voles, who feed on the bark of these plants.

Pruning. Proper pruning performed during the dormant period and growing season generally involves removing dead, diseased branches and weakened growth to maintain plant health and vigor. However, excessive pruning during the growing season, such as removing large portions of the plant canopy, will result in spurts of succulent growth highly susceptible to insects. Suckers that are produced from heavy pruning are also susceptible to insects such as aphids because this succulent tissue does not possess a protective waxy covering. In addition, improper pruning cuts, such as stubs, emit volatile odors that attract insects and provide easy entry sites for wood-boring beetles.

Fertility. Overfertilizing and underfertilizing plants often leads to stress or the production of susceptible growth. An excessive application of highly soluble nitrate fertilizers (generally used for turf) generates lush, weak growth that is susceptible to attack by insects. In addition, excessive amounts of fertilizer cause plants to allocate more of their resources toward leaf production, and less is shunted toward defense, exposing plants to insect attack. Conversely, plants that are unable to obtain sufficient quantities of nutrients are also more prone to insect/mite attacks because their natural defense system has been compromised.

Proper implementation of sound horticultural practices such as watering, mulching, pruning, and fertilizing are important in maintaining plant health. However, when these same practices are improperly performed, problems with insect/mite pests, which may require applications of pesticides, can result. Therefore, maintaining sound cultural practices can often lead to less use of pesticides.

Author: Raymond A. Cloyd


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