Pesticide resistance

In 2016, 25 states report head lice that have mutated a resistance to all known chemical treatments. In gardens and farms, there are an estimated 500 - 1,000 varieties of pest that have developed a resistance to pesticides. This is due to several factors: 

• High reproductive rates - every pest that is not killed off by pesticides carries resistant genetic information which is passed on to its offspring
• Exposure to plant toxins - pests have already evolved to become resistant to plant toxins; from their perspective, our pesticides are just another chemical to get used to
• Exposure to residual pesticides - pesticides that remain in the soil provide the stimulus to pests to develop resistance. Glyphosate has been found in lettuce and carrots a year after the chemical was applied! (This is the same reason why it is critical to take all of an antibiotic prescription, rather than stopping as soon as you feel better. That interruption in treatment is what causes resistant strains of human diseases.) 
• Vulnerability of predators - Predatory insect populations are smaller and have not evolved to deal with toxins, so pesticides are more likely to kill off beneficial insects

Using chemical pesticides too freely can actually strengthen the pests we are trying to eliminate!


According to the World Health Organization (WHO), U.S. pesticide use doubled from 1960 to 1980. Levels have remained stable or been reduced since that time. However, pesticide use in third world countries for export crops has increased to the point that they represent 99% of the human deaths by pesticides. 


There are several different types of chemical pesticides on the market today.

Organophosphate pesticides (Malathion, Naled) According to the Centers for Disease Control (CDC), organophosphates are the most commonly used pesticide. Initially developed as a biological weapon in WWII, organophosphates can cause paralysis, decreased mental function, and there may be links to ADD/ADHD and leukemia.

Organochlorine insecticides (DDT, Chlodane, Toxaphene) Organochlorine pesticides disrupt the peripheral nervous system. Most of these pesticides have been banned, globally, but stockpiles are still being used in some third world countries.    Toxaphene has a half-life of 12 years.

Carbamate pesticides (Sevin, Temik, Furadan) Carbamate pesticides work by inhibiting an enzyme that controls nerve messages and they are banned in Canada and the European Union. One carbamate product, aldicarb, poisoned nearly 2,000 people in 1985. Twenty years later, it was officially phased out of use in an “agreement” between the FDA and Bayer, the manufacturer. This case makes me feel a little nervous about using any pesticide.

Pyrethriod pesticides (Raid, Ambush, Anvil) Pyrethroids are organic compounds from the Chrysanthemum family. Synthetic versions of naturally occurring pyrethroids are currently the most common ingredient in over-the-counter insecticides. Unlike their natural cousins, synthetic pyrethroids are more toxic to humans and they stay in the environment longer. Pyrethroids were developed in response to the damage caused by DDT. Pyrethroids work by overexciting nerve cells to the point of paralysis or cell death. Unfortunately, pyrethroids are highly toxic to the bees, dragonflies, gadflies, mayflies, and invertebrates that make up many food webs. They are also highly toxic to cats. Human exposure to pyrethroids may result in neurological and behavioral changes similar to ADD/ADHD. Anaphylaxis has also been reported.

Sulfonylurea herbicides (Glean, Accent, Harmony) Sulfonylurea pesticides halt an enzyme that helps create certain protein cells. This particular pesticide has a tendency to linger in alkaline soils, such as we have, and they move through the soil to groundwater. Sulfonylurea can adversely affect nearby plants that you are trying to protect. 


Now, don’t let all these highfalutin’ words put you off. In fact, I challenge you to Google all of the ingredients in any product you use in the garden. Let’s see what we’re really up against when it comes to pesticides.
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Pesticide alternatives

Rather than risking the uncertainties of political negotiations, accidental overuse, and the inevitable pesticide resistance, there are alternatives to pesticide use. First, be sure to identify the pests causing problems. If you are dealing with bagrada bugs, don't bother spraying. They will simply fly away until the toxins have dissipated.


Next, decide your tolerance level. I have two broccoli plants that are covered with aphids. I planted them at the wrong time of year (spring) and they never formed heads. Instead, I have a running supply of green leaves and protein-rich aphids for my chickens. The aphids seem to be perfectly content to stay on the broccoli plants and the abundant food supply is attracting other beneficial insects. Remember, many pesticides can kill beneficial insects, such as ladybugs, lacewings and parasitic wasps.


After identifying the pest and deciding how much you can tolerate, other methods can be used to combat pests on a small scale. As for my aphids, I could simply spray the plants each evening with a heavy stream of water from the hose. Rather than applying fungicides to my roses to prevent rust and brown spot, I place a large fan at the end of the row each damp morning to reduce moisture levels.


Pests need specific habitat and environmental conditions to become a serious threat to the garden. Interrupting just one aspect can minimize the damage, without adding toxins to your food supply and landscape. One effective method is the use of diatomaceous earth. Diatomaceous earth (DE) can be used as an insecticide against flea beetles, slugs and snails, mites, aphids, earwigs and thrips, without harming anything else. In fact, my hens love to take dust baths in the stuff and it is a common ingredient in toothpaste!


Do yourself and your garden a favor and take the time to learn about the ingredients in any pesticide or fertilizer you have on hand. If you decide not to use what you already have, please be sure to contact your local Hazardous Household Waste service for disposal instructions. These chemicals should never be thrown away in the trash.

Mites prefer soil that is high in organic content with plenty of moisture. Unfortunately, that describes nearly all of our container plants and many of the microclimates found in Bay Area gardens. A highly adaptable critter, there are over 42,000 species of mites worldwide. Aside from nest mites, dust mites, varroa mites, and many others that attack birds, animals, and bees, respectively, common garden mites include gall mites, spider mites, and thread-footed mites.

Mite damage

How could something so small be a threat to plant health? Well, normal leaf behavior includes water regulation. This is done by opening and closing small valves (stoma) on the underside of leaves. If there is too much water, the plant will drown. Not enough water, and critical life functions cannot occur. It’s an elegant balancing act until spider mites enter the scene. Using piercing mouthparts to puncture the leaf surface to feed, a mite-infested leaf will have thousands of tiny holes poked in it, allowing too much water to escape. A plant can go from healthy to near death in just a few days. Mites can significantly reduce citrus, berry, almond, and annual vegetable crops. They are a serious threat in our hot, dry climate.


Gall mites

Galls are areas of abnormal plant growth, similar to warts or benign tumors on animals and people. Gall mites get their name because, as they feed, deformations appear. Fuchsias are especially susceptible to gall mites.


Spider mites

Spider mites get their name because they build protective webs around eggs and feeding areas.  Three common spider mites are the two-spotted spider mite, the strawberry spider mite and the Pacific spider mite. They are often found on the underside of leaves, where they pierce plant cells to feed. These mites are very small, usually less than 1 mm (0.04”) long, so they are all too easy to overlook until the damage becomes significant. It doesn’t take long for a population to develop, either. A single female can lay 20 eggs a day and live for up to 4 weeks. Since each offspring hatches within 3 days and becomes sexually active in only 5 days, a single, fertilized female and her offspring can produce millions of spider mites in a single season!


An interesting note: female spider mites have two sets of chromosomes, like we do, but males only have one. If an egg is fertilized, it will hatch female. If it is not fertilized, it will hatch as a male. Also, female spider mites are able to “decide” whether to lay male or female eggs, depending upon environmental conditions. To control spider mites, insecticidal soap is your best bet. Neem oil can also help. If chemical pesticides are used, repeated applications will be necessary (and progressively ineffective, as mites can develop resistance).


Thread-footed mites

Most thread-footed mites, also known as white mites, feed on fungi and algae, a few varieties have evolved to attack leaves. Specifically, the cyclamen mite and the broad mite are able to inject toxins that thin the cell walls of mature leaves. Damaged leaves display puckering, twisting and stunting. 


Mite control

The only known effective chemical pesticides against mite infestations are endosulfan, dicol, and ethyl bromide fumigation. Endosulfan was globally banned due to its toxicity to humans and its ability to accumulate in an environment, Dicol is considered a “moderately hazardous” pesticide, closely related to DDT, and ethyl bromide is classified as carcinogenic and a reproductive toxin - not anything you want to be spraying on food plants.


​Broad spectrum pesticides do more harm than good because they also kill beneficial insects that feed on mites. You can buy predatory mites that help control mite infestations. If an infestation is discovered, sprays of water can be used to displace mites and make life harder for them. Garlic extract and oil of clove, rosemary, cinnamon, mint and others can also be effective. These natural treatments can be dangerous to plants, however, so use them carefully. The same goes for sulfur, especially on cucurbits. Observation and prevention are far easier than eradication.


Mite prevention

One of the easiest ways to avoid mite infestations is to create a quarantine area for new plants.  This protects established plants from new infestations and gives you the time needed to see if a new plant is carrying any pests or diseases. Also, proper irrigation reduces water stress in established plants, making them better able to protect themselves. Mites prefer dusty conditions, so keeping garden paths, trees, shrubs and other areas clean can significantly discourage mites. Encouraging beneficial insects, such as lady beetles, lacewing, and pirate bugs, by providing water and habitat, can significantly reduce mite populations without the use of pesticides or sprays.