Nursery, Greenhouse, and Landscape News

Put Biological Control to the Test By Looking at Spring Vigor

Conservation of natural enemies can be a viable option in the landscape for many pests especially those with a rich natural enemy complex such as aphids, scales, and spider mites. Unfortunately, to successfully use this tactic, homeowners must be able to tolerate low levels of pests. This can be especially difficult when pests happen to be on a favored plant in a highly visible site.

Homeowners need to know that plants can withstand some injury without serious harm to their health. Spring can be a great time to show homeowners that their plants are vigorous and can sustain some plant injury. Plants that are having problems will often leaf out somewhat later and less fully than their neighbors. Just a quick scan of plantings and hedges in the newly foliating landscape should convince homeowners that most of their plants are doing just fine. Assessing plant vigor each spring could also help instill their confidence in using pest control tactics they tried in the previous year. Demonstrating sustained plant health is critical for widespread acceptance of any new pest management tactic. This is especially the case when trying to implement biological control through conservation of natural enemies. This approach represents a radical shift in philosophy from pest control tactics familiar to most homeowners that are designed to rapidly kill large numbers of pests. Homeowners and landscape managers trying to "eliminate" a problem are accustomed to using materials that leave large numbers of carcasses, providing a convenient alibi in cases where the plants died despite pesticide treatment.

In contrast, conservation of natural enemies often leaves fewer carcasses, and alibis can be more difficult to find. Unlike pesticide use this tactic involves creating a favorable environment for natural enemies and giving the beneficial insects the time they need to reverse a chronic pest problem. This can include introducing plants that provide pollen, nectar and shade for natural enemies. Alternatively, it can rely on use of pesticides with minimal impact on natural enemies as has been discussed for scale insects. Like other pest management tactics, conservation of natural enemies does not guarantee plants will be free of pest damage. Getting homeowners in the practice of evaluating plant vigor each spring could help instill their confidence in conservation of natural enemies when they find the pattern of foliation shows that plants are still vigorous despite minor injury in previous years.

- Cliff Sadof, Purdue University

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