Gardening: Surviving insect pest invasions

Is this the year of the aphid? Are leafhoppers and flea beetles devouring the garden? Can’t keep up with the thrips, slugs or squash bugs? How much are we able to tolerate before applying insecticides in our landscapes?

By Charleen Barr
Colorado State University Extension Master Gardener in Larimer County

There are many buzz words for garden pest control these days, chief among them is Integrated Pest Management, or IPM. IPM is a common-sense approach to managing problems in our landscape. If we can keep our garden in balance, we will have fewer problems in the long run. Using a combination of environmental, cultural and low-toxic solutions will allow “good” insect populations to survive. Beneficial insects control pest insects and pollinate our plants. IPM also keeps the soil healthy and fertile, and keeps our gardens safer for children and pets.

The first management step is setting personal thresholds of tolerance. If a handful of aphids are “bugging” you, consider if they are an aesthetic landscape (cosmetic) nuisance or if they an economic threat to vegetables or trees. Examine and monitor all the factors and their interrelationships. For example, how many lady beetles, spiders, green lacewings or parasitic wasps are hanging around those aphids? Organic controls include beneficial insects. They frequently eliminate the need for a gardener to resort to other controls. Each lady beetle larvae may eat up to 5,000 aphids in its lifetime.

Prevention of problems in the landscape alleviates plant stress. Ongoing problems are often a sign that the landscape is not getting what it needs to stay healthy. Many disease and insect problems attack plants under stress. Stress can be caused by a number of factors including weather, soil, water, fertilizing, over-crowding and other cultural practices. Prevention begins early in the gardening season. Choose the right plants for the location and soil conditions. Examine plants carefully before buying so new insects or diseases are not introduced. Cleaning the yard in the fall is a preventive way to control insects and disease for next season.

A soil analysis will evaluate soil type and fertility. Take care not to over fertilize and burn roots. Purchase disease resistant varieties of plants. Native plants provide diversity in the landscape in addition to thriving in their natural location and being more resistant to insect attacks.

Incorporate a wide variety of plants. Many insects and diseases are plant specific and by providing a diverse landscape with a variety of habitats we will attract a variety of beneficial insects. Vegetable crop rotation disrupts the life cycle of pests and disease. Annuals need to be rotated for the same reason. Watering is necessary, but many diseases thrive when conditions are overly moist. Be sure to keep water off of plant foliage.
Mechanical controls include physically removing pests by picking them off and hand weeding. Insects may be trapped with using yellow sticky tape or purchasing wasp and/or fly traps. Slugs are attracted to yeast and love a dish of beer or melon rinds. Pruning insect-infested woody plants eliminates threatening problems. Using mulch provides a barrier to reduce weeds and conserve moisture. Companion planting helps by using plants that have natural properties that repel insects.

Biological and organic controls mean paying attention to predators, parasites, pathogens, and organic chemicals. Beneficial insects include predators: praying mantids, spiders, “Hover” flies, paper wasps, lady beetles and minute pirate bugs. These carnivores hunt down leafhoppers, aphids, caterpillars, carrot weevils, spider mites and insect eggs. Insect parasites are tachinid flies, braconid and ichneumonid wasps. They lay eggs on various caterpillars, beetles and grubs, usually near the head. The eggs hatch almost immediately and the young maggots tunnel in to their host feeding internally. Pathogens such as Bacillus thuringiensis, or Bt, are a naturally occurring bacterial disease of insects. Bt is considered safe to people and non-target species, such as wildlife.

“Organic chemicals” include horticultural oils that kill insects by blocking the insect’s breathing holes causing suffocation. To work effectively, insects must be thoroughly coated with the oil. Insecticidal soaps and detergents are easy to use and the safety and selective action of soaps appeal to many people. Limitations of soaps include the need to wet the insect under leaves. Diatomaceous earth used as a dust or in a water spray works by scratching their exoskeletons and dehydrating the insect. However, moisture reduces the effect of these treatments.

It is a mistake to assume that naturally occurring chemicals are non-toxic. Many organic or home remedy sprays that kill harmful insects will also kill beneficial insects. One example is the use of capsaicin products.

Finally IPM includes synthetic chemical insecticides. These remedies are broad-spectrum controls and should be used with the understanding that they are not only harmful and toxic to pests and diseases we want to eliminate, but they can be toxic to beneficial insects, birds and soil microorganisms that are part of a healthy garden.

As with all chemicals (organic or synthetic), read the label carefully and follow the directions exactly. The label is the law—so using the pesticide in a manner that is not indicated is a violation of federal law.
Integrated Pest Management forces us to consider our landscape as part of the larger urban community ecosystem that we need to help manage responsibly. Besides impacting our family and pets, our gardening methods often have consequences that extend far beyond our property. Being a good steward of the environment is a benefit to everyone.

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