Horticulture

Pest Control: Biological vs. Chemical

Resistance is inevitable!

There are some considerations to take into account when choosing which pest control method(s) to use. IPM (Integrated Pest Management) has been in practice for many years and uses an integrated approach to pest control. Growers use a variety of methods to reduce pest populations to or below a predetermined economic threshold level. IPM includes using environmental, cultural, mechanical, biological and, as a last resort, chemical control. Monitoring or scouting and recording must also be done; not only to estimate pest populations, species and locations, but also to evaluate pest control measures used to determine their efficacy.

In a greenhouse environment where temperature, light, air movement and humidity are usually controlled by a computer system, biological controls, when applied early and at proper rates, function much better than in a field environment. Often, greenhouses mandate the use of pesticides to prevent residues being left behind, and bio controls are employed. Greenhouse vegetables are typically picked every 2–3 days, so growers have a limited number of pesticides to use that have a Pre-harvest Interval (PHI) to match the picking frequency.

Out in the field, biological control is not as effective as chemical controls under most situations. The main reason is the wide open spaces. Also, some of the pests invading the outside crops are never an issue in a controlled environment, so the biological suppliers don’t waste their money trying to rear something that isn’t going to be in high demand. Insects such as Lygus and cutworm may have natural enemies, but no evidence has been found that they are produced commercially.

Because there are not many overlapping generations of insects out in the field (with the exception of spider mites, aphids and perhaps a few others), chemical sprays are usually the most effective method of dealing with a pest problem. Chemical sprays can be applied at the most susceptible stage of the pest’s life-cycle; so, generally, one or two sprays are all that are required for control. Almost all of the pesticides that are applied to food crops will have a PHI so the application timing coincides with the target life-stage of the pest. The big drawback to using chemicals outside is the effect they have on the native populations of natural enemies that may have moved in for a feast. And now, with (mainly) the neonicotinoids becoming a concern for honeybees, it is never recommended to spray any type of insecticide on a crop while bees are foraging.

By neglecting to alternate pesticides of different groups, the risk of pesticide resistance is likely within two or three applications. There is no resistance to biological controls. Chemical residues and/or vapours also repel most biological controls.

Even non-food crops are affected by residues left by some pesticides. If it is a foliage crop (such as ornamentals) the residues are an unwanted distraction. As well, pest damage is neither acceptable nor tolerated.

Both biological and chemical controls have their place; it is up to the grower to decide which is most suitable, feasible, responsible and economical to use in any given situation.

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