‘Tis the season for insect pests to be munching around in our gardens!

Looking for some ideas to help control the frustration that comes along with insect pests in your garden? Dr. David Krantz, UToledo Department of Environmental Sciences, has put together some great advice to keep your garden looking, and tasting, good all summer long!

In the UToledo Plant Greenhouse and Garden, we avoid using any synthetic chemical pesticides. Too many harmful effects, and many remain residual either on the plants or in the soil. That choice leaves out the huge majority of products that typically are available in big-box hardware stores.

Trying to find pesticides that are appropriately categorized as ‘organic’ is a bit of a challenge in local retail stores. Black Diamond and a few other landscaping/garden centers have some organic products, but you usually have to look carefully. That includes reading and interpreting the label on the product.

For plant operations either in the greenhouse or the garden, we generally start with the mildest pesticide and work up as necessary. That also means matching the applications to the pests. For example, aphids are easily controlled with insecticidal soap, but shield bugs with a hard outer shell need something stronger.

The following products are both relatively safe and effective.

Insecticidal soap – These soaps are potassium salts of fatty acids, and are most effective on soft-bodied insects and mites, such as aphids, mealy bugs and spider mites. Do NOT use synthetic detergents, such as typical dishwashing liquid or laundry detergent. Those products will damage the plants, especially young plants.

Pyrethrin, with piperonyl butoxide – Pyrethrin is extracted from a type of chrysanthemum, and is toxic to insects but has very low toxicity to mammals, birds and other vertebrates. Most formulations of pyrethrin as an insecticide include piperonyl butoxide, which is an adjuvant that increases its effectiveness. This is our primary insecticide for both the UToledo Greenhouse and Garden. Some formulations – especially for fruit trees – include neem oil, which helps penetrate the resistant carapace of scale insects.

Rotenone – Prior to about 20 years ago, rotenone was approved, and widely used, as an ‘organic’ insecticide. Rotenone is extracted from several different plants. It is toxic to insects, and very toxic to fish. Following evidence that long-term exposure to rotenone produces symptoms equivalent to Parkinson’s disease in mammals, including humans, rotenone has been banned for organic farming.

Neem oil – Neem oil is extracted from the seeds of a tropical plant native to India. It is used fairly widely in greenhouses and gardens mostly as a repellent of insect pests. The active chemicals in neem oil interfere with reproduction and feeding of insects. Although it is generally safe for humans, pregnant women and children should avoid exposure.

BtBacillus thuringiensis – This natural soil-dwelling bacterium infects and kills the larvae (caterpillars) of moths and butterflies. Gardeners use it most commonly to control invasive pests such as the cabbage butterfly and cabbage looper moth – both of which are damaging to brassica plants such as cabbage, kale and broccoli. A strong note of caution: Bt also kills the caterpillars of beneficial, native, butterflies. Be careful when applying Bt on plants that the spray does not drift to adjacent flowers.

Iron phosphate – slug bait – An infestation of slugs can be both devastating and difficult to control. Slugs are particularly damaging to vegetables such as Chinese cabbage, where they get into the leaves at the base of the plant. Iron phosphate is a good control, but this is where reading the product label carefully becomes important. The Slug & Snail Bait by Garden Safe is pellets with iron phosphate. Quite effective at killing slugs, and it simply dissolves into the soil with time. In contrast, other formulations include EDTA, such as sodium ferric EDTA. EDTA is a mild organic acid (‘organic’ in the chemical, not agricultural, sense) and chelator. EDTA is generally not recommended for use in organic farming, because it can be persistent in the soil, and it may mobilize other metal cations that could be contaminants.

Some final, philosophical, points. It’s nearly impossible to keep any garden completely free of pests. Further, many of the treatments used to control pest insects also will affect beneficial insects. The best advice from the organic-gardening community is to build up the fertility of the soil. Good soil leads to strong plants with healthy defensive systems. The gardener also should be a good observer, and identify potential outbreaks of pests before they become a large problem. For example, look carefully for eggs and newly hatched juveniles of insects such as squash bugs. Control the first generation, and reduce later, larger, outbreaks.

For many insect pests, careful observation and removal by hand is effective if caught early. Some organic gardeners carry a container of soapy water, and simply sweep pests into the container. Or you can squish the bugs – although this is definitely not suggested for any of the shield bugs – appropriately called ‘stink bugs.’

Whenever you are spraying, pay attention that you don’t also kill spiders and beneficial insects, such as praying mantises and lady beetles (ladybugs).

And finally, learn to accept some minimal insect-munching damage to the vegetables. They don’t have to be grocery-store perfect to be nutritious and good to eat!

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