Archive for Miticides

Alternatives to Toxic Insecticides

Alternatives to Toxic Insecticides

By George Giltner, Adv. Master Gardener, MS Biology

A third study now validates results of earlier research of associations between autism and prenatal exposure to agriculture chemicals (www.ehp.niehs.nih.gov/1307044/).  “Women who are pregnant should take care to avoid contact with agricultural chemicals whenever possible” says author, Janie F. Shelton who is now a consultant with the U.N.

Three groups of common pesticides were studied that included organophosphates (chlorpyrifos, acephate, diazinon, and others), pyrethroids (esfenvalerate, lambda-cypermethrin, taufluvalinate, and others), and carbamates (methomyl, carbaryl, and others). The organophosphates were associated with an elevated risk of autism spectrum disorder, especially chlorpyrifos applications in the second trimester. Pyrethroids had a moderate association with autism spectrum disorder immediately prior to conception and in the third trimester. Carbamates were associated with developmental delays.

The present rate of autism is now at 1:68 births according to estimates from the CDC.  Also about 1 in 6 children in the United States had a developmental disability in 2006-2008. In the birth year of 1992, the prevalence of Autism Spectrum Disorder was 1 in 150, which has steadily increased to 1 in 68 in the 2002 birth year.

Therefore as gardeners, we should always use the least toxic chemicals, read labels, follow all safety precautions, and keep up with the latest research concerning pest control.

The good news is that more and more information is available on less toxic pesticides.  Clemson Cooperative Extension has an outstanding article on “Less Toxic Insecticides” which conscientious gardeners should print out (www.clemson.edu/extension/hgic).  “Most essential oils used as pesticides work by disrupting an insect neurotransmitter that is not present in people, pets, or other vertebrates.” The EPA no longer requires approval for use as pesticides due to minimum risk to uses of these essential oils (cedar, cinnamon, citronella, citrus, clove, garlic, mints, rosemary and others).

Microbial insecticides include Bt (Bacillus thuringiensis) for caterpillar control.  Milky Spore (Bacillus papillae and lentimorbus) is used against June bug larvae – grub worms. Spinosad, Saccharopolyspora spinosa is a treatment for fire ants, caterpillars, thrips, whiteflies, aphids, and even borers of fruit trees. Beneficial nematodes are the good nematodes that control clearwing borers, cutworms, sod webworms, mole crickets, and grub worms.  However nematodes are difficult to get started due to humidity, moisture, shipping, and temperature issues.

Bacillus subtilis and pumilus combat downy and powdery mildews, rust, bacterial spot, blight, botrytis and multiple other mildews on veggies, fruits, ornamentals, trees, and shrubs.

Minerals like boric acid acts as a stomach poison which causes the insects to die from starvation.  Diatomaceous Earth controls slugs, millipedes, ants, cockroaches, and soft-bodied insects like aphids. However use the “natural grade”, not the swimming pool filtering-agent that poses an inhalation hazard.  Sodium Fluoaluminate has sharp edges which punctures insect (caterpillars, sawflies, beetles, etc.) gut cells from consuming leafy material, however beneficial insects are not affected since they are not leaf eaters.  Iron phosphate is used as an organic slug and snail bate.  It is not poisonous to cats and dogs.

“Organic Farm and Garden” 2013, Vol.1, 2nd Ed., lists Biological Control Options which incorporates predator and prey functions in every ecosystem.  Plant nectar sources attract beneficial insects, and allow them to lay eggs near this food source.  Plant small flower favorites like dill, parsley, fennel oregano, cilantro, and thyme.  Also include annuals like sunflowers, cosmos, amaranth, alyssum and statice.  Perennials like yarrow, tansy, daises and angelica can be inter-planted within your garden.  Your beautiful garden will buzz with beneficial insects, and will have an ecological balance of predator and prey bugs.

“Louisiana Gardener”, Feb. 2015, has a super article, “What’s Bugging You?” by Cindy Shapton.  She puts emphasis on learning good bugs and bad bugs. Numerous recipes for repellants to easy to make sticky-traps are highlighted.

“The Naturally Bug-free Garden”, 2012, by Anna Hess is now available at Amazon.  It focuses on the worst garden pests that we have here and in Texas, and gives organic control measures.  Good bugs and good animals are reviewed and used to make your garden a living balance of natural defenses.  Resistant varieties, row covers, companion planting, and plant nutrition are tools for helping plants resist insects.  This is a good book to assist the beginner and young gardeners in learning about organic gardening.  It is a treasure!

So this year, learn, read, and experiment with organic chemical-free gardening to avoid potentially dangerous chemicals that are used in commercial agriculture.

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Battle of the Bugs: Spider Mites of Summer

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Spider Mites of Summer

By George Giltner, Adv. Master Gardener, MS Biology

In the hot and humid Summer months, a common pest problem is spider mites which infect tomatoes, snap beans, roses, lantana, maple, redbud, blackberries, strawberries, blueberries, squash, cucumber, and about 200 other species of plants.  The most common spider mite throughout the U.S. is the two spotted spider mite, Tetranychus urticas . 

spider mites

Spider mites at various life stages. Photo by LSU AgCenter.

Symptoms appear similar to a graying of the leaves which is caused by destruction of chlorophyll containing cells by the piercing mouth parts of the mites.  One may think that the plant is undergoing some type of heat stress or fungal disease, but close observation of the leaves reveals small webs that all spider mites produce.  A magnifying lens with 10x power will reveal the presence of a minute (1/50th inch) spider mite with 8 legs.

The best chance of control is early in the infestation. Miticides are available in garden stores, however most are not effective on eggs.  Therefore plan on multiple applications. After continuous use, most acaricides  become ineffective as the spider mites built resistance to chemical sprays.  If no control measures are taken, populations can spread rapidly to completely defoliate the leaves or to impair plant flowering and fruiting.

Insecticidal soaps, commercially available natural predators, and oils are options that are friendly to nature and less toxic to humans.  Note that oils and soaps may burn plants, especially at higher rates.  Natural predators can be purchased from internet sites, but they are delicate forms of life that can be destroyed during shipping, especially in summer.

Important natural predators include lady bugs, predatory mites (Metaseiulus, Amblyseius, and Phytoseiulus), minute pirate bugs, lacewing larvae, big eyed bugs, and thrips (Leptothrips).  Therefore use of broad spectrum insectides can destroy these predators, making your problems much worse.

Spider mites are difficult to control.  For home gardeners persistence of treatment is the most important aspect of control.  If the infection becomes too difficult, consider eliminating affected plants by bagging and burning during calm periods of the day.  Spider mites are like spiders.  They use their webs to spread in the wind.

The entire life cycle (eggs to larva to two nymphal stages to adult) can be completed within five days, but can be extended with lower temperatures to 20 days.  Adult females can live 4 weeks while producing several hundred progeny. Continuous generations are produced though summer.

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