Organic Pesticides

Organic pesticides can still be harmful

Bill Sevier: Ask a Master Gardener

Saturday, May 7, 2016

Q: Can organic insecticides be harmful? I always presumed they were not. R.D., Tulsa.

A: For the most part, all pesticides have the potential to be harmful. Organic pesticides are ones approved by the USDA’s National Organic Program, a division of the USDA. This agency evaluates and approves all aspects of organic food production.

Generally speaking, organic pesticides are those derived from plants and minerals “naturally” as opposed to those man-made (synthetic pesticides). However, there is overlap. Some organic pesticides are synthetic and some botanical and mineral products are not certified for organic use.

Organics are selected for reduced toxicity to other plant and animal life and also for a short duration in the environment. Organic farming principles also emphasizes improving soil health, use of pest-resistant plant varieties and improving overall growing conditions before using any pesticide.

The federal regulations concerning what is approved and what is not is an eye-crossing experience in an attempt to understand. However, the following are some of the organic pesticides (mainly insecticides) approved and commonly used by organic gardeners.

Bacillus thuringiensis (Bt) is a bacterium safe for animals, fish and beneficial insects. There are several varieties. “Kurstaki” is effective for most caterpillars. “Israelensis” is used in water to kill mosquito larvae and others are used for types of beetles. Bt is widely used on vegetables by homeowners and in agriculture.

Horticultural soap is another effective and safe pesticide. Not being found in nature, it is “synthetic” but is classified as organic. It is an excellent choice for many of the insects in vegetable and other gardens.

Horticultural oils are also effective for a wide range of insects. These oils come from either vegetable or petroleum sources. They smother insects and are safe to use in most garden areas.

Neem Oil is a horticultural oil but is a little different from the others. It comes from seeds of the Neem tree grown mainly in India, where it has been used for many years in medicines and cosmetics. The raw oily seed extract has a number of chemicals with pesticide properties. These are usually extracted, and the pure oil is sold in garden centers.

Azadirachtin is the main chemical extracted from the original neem oil. It is safe and effective for many insects. It has an effect of altering the feeding behavior and growth of insects.

Pyrethrin is an insecticide coming from certain varieties of chrysanthemums. It has a wide range of activity and deteriorates rapidly after sprayed.

Spinosad is an extremely useful insecticide derived from a type of soil bacteria. It can be toxic to bees but seems to be moderately safe if used when bees are not present. Do not use when plants are in flower.

There are many other approved organic pesticides not listed. As always, if you use any pesticide, the labeled directions must be followed. Any pesticide toxic to bees should only be used in the early morning or late in the day, when bees are back to their hives.

Garden tips

§  Prune and feed all of the spring-blooming shrubs, such as azaleas and forsythia immediately after blooming, if needed. Azaleas need less fertilizer than many shrubs and often a yearly addition of mulch, as it decays, it will add all the nutrients they need.

§  Cool-season lawns — tall fescue and bluegrass — can be fertilized again if you did not fertilize in March and April, do so now. Do not fertilize these grasses in summer.

§  Seeding and sodding of warm-season grasses such as bermudagrass, Buffalograss and zoysiagrass is best performed in mid-May through the end of June. The soil temperatures are warm enough for germination and growth. These grasses need a long summer growing season to promote winter hardiness.