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IPM and pesticides

Posted 10/29/2015

Grasshopper

Is there a gardener anywhere who has not had to deal with pests of one sort or another? These may be weeds, diseases or bunnies, but more frequently, they are insects. Whatever the problem, it needs to be addressed and, with luck, solved. In recent decades, solutions have become more chemically based, and we have become dependent on insecticides and herbicides.

When used correctly, pesticides are not bad. Whether organic or conventional, they have become a major tool for horticulture and agriculture. Not only do they help keep landscapes looking pristine, they have helped increase food production in America and the world far above the levels we could reach otherwise.

There are few unmixed blessings, unfortunately, and we are seeing problems from excessive and incorrect pesticide use. One important problem is resistance, where the target of the chemical is no longer vulnerable to it. This is a much larger concern than we might have thought, since increasing numbers of the products that have been mainstays of landscape and crop maintenance are not killing insects or weeds.

Herbicides (weed killers) are the most commonly used pesticides, but quite a few weeds have become able to survive treatments with three, four or even more completely different types of formulations. The resistance champion is barnyard grass, which is no longer susceptible to products with nine (of the 15 possible) different modes of action! Gardening would be difficult for many of us if our only weed control choice went back to hand pulling on a large scale.

Recently, the decline in pollinators has garnered attention throughout the country. Honeybees and butterflies are in trouble for many reasons, but pesticides appear to be a significant cause of their disappearance. How many products can distinguish between good and bad insects?

We can take several steps to keep our gardens healthy and productive before we need to bring out the big pesticide guns. The set of tactics is grouped together under the title of “Integrated Pest Management” or IPM.

This is not necessarily organic practice, but it is compatible with both organic and conventional horticulture. It involves the usual first steps in garden pest prevention: removing last year’s plant debris, which may shelter unwelcome organisms; rotating annuals so that the population of their pests does not reach an intolerable point; selecting plants that have the best chance of surviving our difficult climate; and using good horticultural routines when planting and watering.

The heart of IPM is called “scouting.” Looking closely at the garden and its inhabitants is perhaps the critical part of managing problems. For many gardeners, observing the garden is a part of daily life. It is a pleasure to see the plants we enjoy thriving in our yards and landscapes.

Casual inspection is good, but scouting entails considerably more. It also needs to be done regularly, allowing one to catch the problem before an infestation becomes unbearable.

IPM works best when the intrepid Mojave gardener knows which pests are likely to attack the specific plants in the garden, and a little about their biology. Certain insects are exceptionally fond of members of particular families. Tobacco hornworms devour members of the tomato family — peppers, petunias, and eggplant. It is so well camouflaged that you can miss it unless you really examine plants thoroughly. Sometimes it is easier to look for the dark brown droppings that land on leaves. The dreaded squash bug will be a major threat in spring, but less so in other seasons. Knowing when to control can be as important as knowing how.

In scouting, it is not sufficient to look only at the surface of leaves, flowers or fruit. The worst pests may have taken up residence in the axils between leaf and stem, or on the underside of leaves. By the time signs appear on the leaf surface, the infestation is very difficult to manage.

Our other senses are important. If you crush a bug and it stinks, it may well be a stinkbug, a problem for several fruits and vegetables. If a leaf feels sticky, you probably will not need to look far before finding aphids. It is likely you will have seen busy ants on the plants at the same time.

Hornworms, squash bugs and aphids are destructive pests that need to be controlled as early as possible. Not all insects demand that kind of attention. Some, like lacewings, praying mantises and ladybugs are beneficials and should be encouraged. Wasps may be terrifying but they devour pests of our plants. I choose to stay clear and let them eat.

Finally, not every insect is really a pest. Ants turn over the soil, and unless they are fire ants, ultimately help. How much of any pest can a gardener tolerate? That is a personal and environmental question, one that will determine if and when to take control.

Email Angela O’Callaghan, Social Horticulture Specialist, or call at 702-257-5581.

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