Will neem oil kill caterpillars?

Caterpillars are butterfly larvae that come in many different shapes, colors and sizes, but the damage they do is always the same.

They ingest plant leaves and pine needles as they feed, and thereby wreck often irreparable damage in the garden and in the vegetable patch.

Read also:

  • Recently, boxwood is a shrub often destroyed by boxwood tree moth
  • Maybe you shouldn’t kill caterpillars – pesticides endanger butterflies far too much!

Contents

What are the effective organic caterpillar treatments?

Many chemical synthetic products have been developed that are quite effective in destroying the pests.

But, alas, the products themselves are often toxic for the environment and their use must be foregone because, today, many organic treatment have appeared that are very effective.

Here are several organic caterpillar control options that aren’t a problem for the environment at all:

  • 1 – BT products – predator pest control of the microscopic sort
  • 2 – Caterpillar predator animals – insects & animals that eat caterpillar eggs or disrupt their life cycle
  • 3 – Manual picking – cleanest possible option. Requires daily follow-up.
  • 4 – Prevention – nets & traps against adult egg-layers and caterpillars
  • 5 – Horticultural oils – oils that smother eggs and caterpillars
  • 6 – Decoy plants and decoy objects – also the cleanest option. Attract caterpillars away from target plants
  • 7 – Companion planting and crop rotation – make it hard for pests to spread, maximize companion planting

Each of the above is summarized in the sections below (numbers are simply there to help you navigate the page easily. There isn’t any “better or worse” strategy, and you’ll likely end up using a combination of most).

Also, if you’re only dealing with the occasional caterpillar, perhaps it’s all right to let it feast and grow. It may turn into a wonderful butterfly. Try looking up what type of caterpillar it is.

1 – BT sprays, use microbes against caterpillars

Products based on Bacillus Thurengiensi are authorized for use in organic growing and only have a very reduced negative impact on our planet.

  • Generally, they can be found in horticulture stores under the label “Organic caterpillar killer“.
  • Usually they must be dissolved in water and sprayed.
  • These products must be ingested by the target insects and must thus be sprayed on the entire plant.
  • Anti-caterpillar treatments must be applied as soon as the first butterflies fly.
  • Treat during dry weather, with no wind and no risk of rain.
  • Repeat every three days until caterpillar populations are under control.

BT spares most beneficial insects. It breaks down within a couple days due to ultraviolet rays and water.

BT works by blocking digestion in the caterpillars, which can’t eat anymore. It can take two or three days for caterpillars to consume their reserves, after which they die without turning into moths.

2 – Caterpillar predator animals

There are a host of insects and animals that will either eat caterpillars outright or parasite them. These predator animals are a great option because target pests cannot develop resistance to them, as they would to chemical treatments.

Ladybugs against caterpillars

We’re all familiar with how ladybugs help against aphids, but these little Our Lady’s Bugs also eat caterpillar eggs when they come across them. Young, newly hatched caterpillars are a choicy snack, too.

  • Learn more about ladybugs in the garden

Birds against caterpillars

Birds love eating caterpillars. Even those ugly, hairy, colorful ones are often gobbled up in hungry beaks.

  • Attract birds to your garden with berry shrubs, insect hotels, and bird feeders

Parasitic wasps

Trichogramma is a genus of wasps that lays eggs inside caterpillars. After hatching, they eat the pest out from the inside and keep it from turning into a butterfly.

Not all parasitic wasps are beneficial, though. For example, the citrus wasp is a type of gall wasp that attacks plants directly, not other insects.

  • Citrus wasp and Gall wasp can also be controlled with many of the methods listed here for caterpillars.

Trichogramma are bought in massive amounts. For example, between 50,000 and 200,000 individual wasps are recommended to treat one acre of infected gardens. Ideally repeated weekly.

Chickens and caterpillars

Chickens love eating many kinds of caterpillars. Sometimes they have to be “taught” to like them though. Chickens which have been fed grain and housewaste aren’t always adventurous when it comes to “new” food. Not all caterpillar types are healthy, though.

  • To teach them to broaden their diet, give them time to “free range” around the garden.
  • Add the caterpillars to their feed daily for a couple weeks. Chop them in half first (the caterpillars, of course).
  • Dry the caterpillars out before feeding them to the chickens.

Once they’re familiar with that particular caterpillar type, you can release them in your vegetable patch for a short while.

  • Chickens always go around the garden in laps. First lap is always for bugs, snails, slugs. Second lap is when they start going for leaves and shoots. After that, they start scratching around for more grubs.
  • Best is to release them about twenty minutes before roosting time. They’ll have time for the first lap and eat the caterpillars, but will turn home to sleep before digging into your veggies.

Learn how to set up a chicken coop

Note: this also works with ducks

Other insects and animals

There are quite a few more animals and insects that have caterpillars on their daily menu.

Hedgehog is one of them. They also help get rid of slugs and snails, too. Green lacewing is an insect that is a great help because it eats all manners of eggs, caterpillars, larvae as it grows. Adults pollinate plants, too. Not to forget are frogs, toads, different types of rodents, several varieties of spiders…

  • Attract animals to the garden

3 – Picking caterpillars manually

This is of course the cleanest way of removing caterpillars from your plants.

It’s fairly time-intensive when caterpillar populations explode. However, if you make it part of a daily or weekly routine, you can quickly pick most caterpillars off before they do any real damage.

Simply going around your garden every couple days will let you avoid any serious contamination.

How to pick caterpillars by hand

  • Hand-pick caterpillars with gloves. Thin gloves work better than thick thorn-resistant ones.
  • Alternatively, you can hold a jar under the caterpillar and nudge it with a twig or popsicle stick, it will fall right in.
  • Some caterpillars gather in nests (at night, or at certain stages in their development). Be sure to detach and destroy these!
  • Best time to pick caterpillars is early evening or dusk. Next best time is early morning, while there’s still dew everywhere.

What can you do with caterpillars?

  • some caterpillars might be of a rare or endangered species, like monarch butterflies for instance. Try to keep these and feed them until they reach cocoon stage.
  • feed them to your garden chickens
  • drown them in a bucket of water (toss the water in the compost pit when they’re dead to recycle their nutrients)
  • dry them out in the sun in a jar closed with the lid. These dried caterpillars are great for feeding birds and chickens. They’ll keep until winter if well dried and stored.
  • Chop them up or squash them underfoot.

4 – Physical prevention against caterpillars

Caterpillars hatch from moth and butterfly eggs. You can protect against mothers laying these eggs on your plants in different manners.

Fence out moths and butterflies

  • Set up fine mesh netting around your plants. Horticultural fleece or mosquito net material is often enough. It may also go under the name “insect barrier“. Note, however, that you’re also blocking out beneficial pollinators. So if you’re hoping for fruit from plants that must cross-pollinate, you’re going to have to remove the netting during flowering.
  • Grow your most vulnerable plants in a greenhouse. You can release pollinators in the greenhouse and keep moths and butterflies out.
  • A simpler in-field option is to sow plants under cover.

Landscaping obstacles to hinder insect flight

Insects often have trouble navigating around obstacles. Additionally, they serve as windbreakers which means insects aren’t carried around as far.

  • Plant a hedge around plants you wish to protect. A hedge along the perimeter of the garden will reduce the distance an insect can fly.
  • Low-lying hedges are useful, too. Some insects only average a flight height lower than two feet. To them, a low hedge is a wall they must circumnavigate.
  • Fences, walls, and treillis in a vertical garden are effective, too.
  • A raised garden is easier to control. Insects usually hover at target height for leaves of shrubs they infect. A raised bed disturbs that. Additionally, leaves are easier to inspect.

Moth trap, trapping butterflies

It’s possible to find moth traps and butterfly traps that won’t release the insects.

  • Some use a light source (like a bulb) to attract them. This is especially effective for night moths.
  • Others use pheromones, which replicate mating calls and lure male insects to the trap. That way, they can’t find the females, which have a harder time getting fertilized.
  • Another tip is to always have a butterfly net at hand. With a little practice, it’s easy to swoop down on moths and butterflies. Every one you catch is that many eggs that won’t hatch into caterpillars. Bug zappers work too, but they’re battery-powered.

Traps to catch caterpillars

An alternative to hand-picking them is to lure them all together, which makes catching them easier. In short, you want to replicate conditions that will attract a nest.

  • Like slugs, caterpillars love cool, moist places during the day. Lay a slab of old wood down on the ground. When you turn it over the next day, scrape and collect all the slugs and caterpillars off the underside. They thought it would be a cool, safe spot for them to spend the warmest hours of the day.
  • A rag or cloth wrapped around the stem of the shrub or trunk will also attract caterpillars in the same manner. Visit the trap daily.
  • It’s also possible to ring stems and trunks with a glue trap that will catch any caterpillars trying to cross up and down it.

Against the devastation of oak processionary or spruce processionary worms, it’s possible to create a trap that will collect the thousands of caterpillars as they march down from infected trees, preventing their spread to others!

5 – Oils and soaps against caterpillars

It’s difficult to find sprays that will only target caterpillars. Usually, the following will get rid of pests like caterpillars, aphids and red spider mite. However, they’ll often remove beneficial insects, too.

  • These are to be sprayed on the topside and underside of leaves, and along stems, too.
  • Spraying on the ground up to a foot (25 cm) around the stem will protect the tree or plant from caterpillars that wish to climb up it.
  • Never spray during warm and sunny hours. Prefer dawn or dusk. Water drops would burn the leaves like a magnifying glass.

Neem oil to kill caterpillars

  • Neem oil (oil pressed from neem fruit) is a potent insecticide and insect repellent.
  • Dilute 2 ounces (3 centiliters) of neem oil in a gallon of lukewarm water (4 liters).
  • Spray in the evening.
  • Neem oil will suffocate the caterpillars and they will die off within hours.

Note: Neem oil will kill bees, so only spray it at dusk, when bees have returned to the hive.

Soap spray

  • Mixing spray prepared from lukewarm water and mild dish soap (two tablespoons to a gallon) will interfere with the caterpillar’s breathing.

Plant extracts to repel caterpillars

For one liter (one quart) of natural caterpillar repellent, add a combination of the following:

  • 1 teaspoon mild dish soap
  • 1 tablespoon of any of the these (chopped): garlic cloves, a whole onion, red pepper, ground chili

To extract the active compounds, you can either:

  • blend the mixture and let it sit for 24 hours, then filter it (keep the juice, discard the pulp).
  • or, boil the chopped plants for 30 minutes, let it sit and cool down. After that, strain out the spent plant materials, keeping the liquid preparation.

A specific variant of this is the garlic decoction. To a certain point, several fermented tea recipes can help against caterpillars, too, especially rhubarb fermented tea.

6 – Decoy techniques against caterpillars & moths

Moths and butterflies can also be tricked! Optical illusions will make them think a certain spot is taken. Let’s take a look at some of the tricks that would certainly trick us as well, if we were moths!

Decoy crops (also called trap crops)

Some crops can be protected if sacrificial crops are nearby. Typically, nasturtium is a favorite of many moths and butterflies. Having this climbing plant growing from an barrel nearby will attract egg-laying moths to it. Your own crops will be protected!

Some great decoy crops that lure caterpillars away:

  • nasturtium – climbing vine, very easy to care for. Also attracts aphids.
  • hollyhock – wonderful flowers
  • passion flower – uncommon radiant flowers, produces passion fruits in warmer areas
  • All the shrubs and plants that attract butterflies
  • Herbs like dill and fennel are great caterpillar food, too.

Best is to check on these decoy plants first and remove caterpillars from them as soon as you see them.

Decoy objects

You can trick moths and butterflies into laying their eggs further off!

  • Sometimes printing out drawings that are similar to those of the female moth and attaching those life-size images near the target plant is effective.
  • Indeed, moths naturally try to space out their offspring and will pass their way if they notice too many “competitors” on a given plant.

A traditional practice is to hang half-eggshells upside down at leaf height in vegetable patches and fields. Supposedly, moths lay their eggs in the underside which naturally forms a sheltered dry and wind-free spot. Only thing left to do is to check the undersides and remove any that have eggs under them!

  • However fun this eggshell hanging sounds, I have yet to see that this effective. It’s a traditional practice, but no proof has ever been provided that it works!

7 – Crop rotation and companion planting

Caterpillar larvae hatch after spending the winter in the ground or in secluded areas. Certain plants are also known to repel insects, and moths or butterflies in particular. Let’s see how using plants around the garden can help protect target plants, in addition to decoy plants that were described just above.

Crop rotation against caterpillars

Many of the most problematic caterpillars have a simple life cycle:

  • They hatch on the plant and eat from it
  • They descend from the plant and directly tunnel into the ground
  • Underground, they turn to pupae and finally hatch again

If crop rotation is practiced, fresh pupae hatch from their cocoon but can’t easily find new host plants when they emerge.

Additionally, crop rotation helps plants grow healthier. Healthy plants can resist caterpillars better.

Greater biodiversity

Having a high amount of different plants will have several beneficial consequences against caterpillars, too:

  • A mixed hedge naturally includes appealing traits for caterpillar-eating animals, as seen above: food, shelter, nesting, and more. This attracts caterpillar predators. A protective hedge will do just as well.
  • Target host plants are further apart, sometimes even too far to reach for the moth or butterfly.
  • Greater chance of the insect laying eggs on a non-ideal host. Eggs hatch but caterpillars can’t reach maturity.

Plants that repel caterpillars

Aside from decoy plants that attract caterpillars, there are also a set of plants known to repel most types of caterpillar insects.

  • strong-scented herbs such as rosemary, basil, thyme (including wild thyme), chamomile, mint, aniseed and peppermint
  • flowers such as French marigold, lavender
  • certain veggies such as tomato and all allium plants (leek, ornamental onion, etc)
  • other shrubs and garden plants like santolina, for instance.

Smart tip about caterpillars

Some caterpillars are definitely pests, while others will grow into beautiful butterflies.

Get to know those that are most common in your area!

Some may also be endangered species, which you can protect instead of killing them.

Read also

  • Fighting aphids
  • Hedges, great barriers against diseases and parasites
  • Recent boxwood caterpillar infestation: boxwood tree moth

Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Two caterpillars on nasturtium by Katja Schulz under © CC BY 2.0
Bird natural caterpillar control by kansasphoto under © CC BY 2.0
Hand-pickable caterpillar by Robert Stok under © CC BY-SA 2.0
Caterpillar nest by Steve Jurvetson under © CC BY 2.0
Caterpillar on dill by Adolfo Martinez under license
Young caterpillar on leaf by Timo Newton-Syms under © CC BY-SA 2.0
Monarch caterpillar by Mary under © CC BY-SA 2.0

Worm Free Cabbage Crops? Check out Neem Oil

Cabbage

I’ve done battle with the caterpillars of the small white and yellow cabbage butterflies for as long as I’ve gardened. The most destructive caterpillar, known as the Imported Cabbage Worm, is from a white butterfly native to Europe called the Cabbage White Butterfly (Pieris rapae). These insects have only been in North America since the 1860’s, but they like it a lot on this side of the ocean and are a truly destructive pest.

The small green caterpillars of this butterfly will decimate unprotected cole crops. Their presence is very easy to see. They eat huge holes in the leaves of the brasiccas, they like to burrow into the center core of cabbages, and they leave trails and piles of frass wherever they occur.

A lot of gardeners use BT (Bacillus thuringiensis) as an organic control. BT is widely used but I’ve left it alone mainly because of issues relating to its use in genetic engineering and several other possible problems, an overview of which you can read about here:

My best success has been using floating row covers of agricultural fabric. The row covers have some problems, however. The fabric tears easily and the moths find their way into and under the covers through the holes and any edges that might not be secured closely to the ground. The covers are a pain to maintain and keep in place. And it gets quite a bit hotter and more humid under the row covers than in the open air. Brassicas prefer it cooler and drier.

Neem Oil

Then we found neem. I’d heard about neem oil over the years. Three years ago at a Garden Writers Conference in Oklahoma City, Geoff and I attended a presentation where the origins and insecticidal properties of this natural product were explained in depth. And two years ago, at the MOSES Organic Farming Conference in La Crosse, Wisconsin, Geoff met Usha Rao of The Ahimsa Alternative, and we obtained a supply of neem oil to test in our own gardens.

Neem oil is a vegetable oil pressed out of the fruit and seeds of the neem tree, Azadirachta indica, a fast growing tree of the mahogany family that is farmed in India, Pakistan, and Bangladesh, as well as throughout a lot of Africa. All parts of the tree have useful properties and many people in India regard the tree as sacred. Within the oil is an active ingredient Azadirachtin, which disrupts the digestive and molting processes of insects that feed on leaves where the oil is present and they eventually die after ingesting the neem.

I’m using a mixture of one tablespoon neem oil, 3/4 tablespoon of liquid horticultural soap, and one tablespoon of seaweed extract in a gallon of water. The seaweed is there to help the neem mix better with the water and stick better to the plant leaves. And it also has its own beneficial properties in the foliar feeding of plants. After the initial spray, I spray after rains or after I have to water the plants. I’m presuming rains and watering may wash away the neem’s effectiveness. The solution needs be thoroughly mixed. Concentrated neem oil can burn plant leaves, and the neem oil will coagulate in colder water.

Also, while generally the neem is safe in use around beneficial insects, you should not spray it directly on them, so avoid spraying it when insects are pollinating squash flowers, for example.

Broccoli

I am happy to report that the results appear to be excellent. I’ve got uncovered brassicas of all types almost totally free of insect damage and I’m pretty sure I’ll get to harvest all without any major insect losses. It’s interesting, because the butterflies are present, they lay their eggs, the eggs hatch, but then the life cycle ends soon after the caterpillars start feeding.

Neem is supposed to be an all-around useful insecticide, but I haven’t figured out how to make it truly work well on all my cucurbits. It appears to be quite effective against squash bugs, but I lost several plants to vine borers, which I can understand, as the vine borer caterpillar is protected inside the stem of the plant. The neem spray seemed to do nothing to protect against early damage from cucumber beetles, which destroyed several melon and squash plants almost as soon as I transplanted the seedlings into the beds.

Neem seems to be a very useful approach to a lot of garden pests, however, and the upside is that it is very low in toxicity and potential environmental concerns. I’m going to keep working with it. If it only gave me good, worm-free cole crops, it would be well worth its cost.

Posted by: Noel

Neem Oil

  • What is neem oil?
  • What are some products that contain neem oil?
  • How does neem oil work?
  • How might I be exposed to neem oil?
  • What are some signs and symptoms from a brief exposure to neem oil?
  • What happens to neem oil when it enters the body?
  • Is neem oil likely to contribute to the development of cancer?
  • Has anyone studied non-cancer effects from long-term exposure to neem oil?
  • Are children more sensitive to neem oil than adults?
  • What happens to neem oil in the environment?
  • Can neem oil affect birds, fish, and other wildlife?

What is neem oil?

Neem oil is a naturally occurring pesticide found in seeds from the neem tree. It is yellow to brown, has a bitter taste, and a garlic/sulfur smell. It has been used for hundreds of years to control pests and diseases. Components of neem oil can be found in many products today. These include toothpaste, cosmetics, soaps, and pet shampoos. Neem oil is a mixture of components. Azadirachtin is the most active component for repelling and killing pests and can be extracted from neem oil. The portion left over is called clarified hydrophobic neem oil.

What are some products that contain neem oil?

Neem oil and some of its purified components are used in over 100 pesticide products. They are applied to a wide variety of crops and ornamental plants for insect control. Neem oil can be formulated into granules, dust, wettable powders or emulsifiable concentrates.

Always follow label instructions and take steps to avoid exposure. If any exposures occur, be sure to follow the First Aid instructions on the product label carefully. For additional treatment advice, contact the Poison Control Center at 1-800-222-1222. If you wish to discuss a pesticide problem, please call 1-800-858-7378.

How does neem oil work?

Neem oil is made of many components. Azadirachtin is the most active. It reduces insect feeding and acts as a repellent. It also interferes with insect hormone systems, making it harder for insects to grow and lay eggs. Azadirachtin can also repel and reduce the feeding of nematodes. Other components of neem oil kill insects by hindering their ability to feed. However, the exact role of every component is not known.

How might I be exposed to neem oil?

People can be exposed to chemicals by eating them, breathing them in, through skin contact and eye contact. Since neem oil is used on a variety of crops, people are mainly exposed to neem oil in their diet. People who apply neem oil may also be exposed if they inhale the mist or dust, let the product touch their skin, or fail to wash their hands before eating or smoking. However, the label includes directions for keeping exposure low. For example the label might require applicators to wear protective clothing.

What are some signs and symptoms from a brief exposure to neem oil?

Neem oil can be slightly irritating to the eyes and skin. Azadirachtin, a component of neem oil, can be very irritating to the skin and stomach. The remaining portion of neem oil is made of fatty acids, essential oils and other substances that are commonly eaten in a normal diet. These substances are generally recognized as safe (GRAS) by the United States Food and Drug Administration.

In other countries, neem oil has been used on cats for flea control. Some adverse reactions have been reported. Symptoms include feeling sluggish, excessive salivation, impaired movement, trembling, twitching, and convulsions. Some of the cats died. However, most of them recovered within 1 to 5 days.

What happens to neem oil when it enters the body?

Clarified hydrophobic neem oil (without azadirachtin) is made of fatty acids and glycerides. These substances are commonly found in food. When they enter the body, they are broken down, used for energy, and incorporated into cells.

In one study, scientists injected insects with azadirachtin. They found 90% of the dose in the insects’ feces within 7 hours. The remaining portion lingered in the insects’ bodies for 24 days after the injection.

Is neem oil likely to contribute to the development of cancer?

No. People have been exposed to neem oil in many ways for hundreds of years. During this time no association with increased cancer risk has been found. Studies showed that neem oil did not alter or damage genes. In laboratory tests, animals were fed neem oil for 90 days. They did not have increased cancer rates.

Further, one study found that certain components of neem oil caused cancer cells in hamsters to stop growing or die. Another study looked at prostate cancer cells from humans. Researchers found that neem leaf extract was able to slow their growth.

Has anyone studied non-cancer effects from long-term exposure to neem oil?

In rat studies, no effects were reported when the rats were fed either azadirachtin or clarified hydrophobic neem oil throughout their lives.

Are children more sensitive to neem oil than adults?

In general, children may be especially sensitive to pesticides compared to adults. When rats were fed neem oil in one study, their pregnancies ended. In another study, rats were fed azadirachtin in their diet throughout their lives. No effects to their offspring were found. Additionally, neem oil is used in toothpaste, cosmetics, soaps and traditional medicines around the world. Therefore, people of all ages are commonly exposed to neem oil. No data were found to show that children are more sensitive than adults to neem oil.

What happens to neem oil in the environment?

Azadirachtin, a major component of neem oil, is rapidly broken down. Microbes and light break down the pesticide in soil, water and on plants. The half-life of azadirachtin in soil ranges from 3 – 44 days. In water, the half-life ranges from 48 minutes to 4 days. It also rapidly breaks down on plant leaves; the half-life if 1 – 2.5 days. The remaining components of neem oil are broken down by microbes in most soil and water environments.

Can neem oil affect birds, fish, or other wildlife?

Neem oil is practically non-toxic to birds, mammals, bees and plants. Neem oil is slightly toxic to fish and other aquatic organisms. Azadirachtin, a component of neem oil, is moderately toxic to fish and other aquatic animals. It is important to remember that insects must eat the treated plant to be killed. Therefore, bees and other pollinators are not likely to be harmed.

Assistance for the Home Gardener from the Contra Costa Master Gardeners Help Desk
Client’s Request I’d like to consider myself an organic gardener. I’m having trouble with some pests on a blooming shrub even after some hand-picking and blasting with a hose. I’d like to spray with Neem Oil as I understand it is a natural pesticide and is considered safe for home gardeners. Can you provide me with some specific guidance on the use of Neem Oil sprays in the garden, especially with reference to bees?
CCMG Help Desk Response: Thank you for contacting the Contra Costa County Master Gardeners. It’s always a good idea to check the toxicity of a pesticide before using it! Neem oil is a naturally occurring pesticide found in seeds from the Neem tree (Azadirachta indica). While Neem Oil has a very low acute toxicity rating for people and other mammals, it can be toxic to bees if not properly applied.
The University of California considers Neem Oil as moderately toxic to bees and recommends application only during late evening, night, or early morning and when plants are not blooming, i.e., when bees are not typically out foraging.
The following UC IPM (Integrative Pest Management) website provides additional information on Neem Oil (http://www.ipm.ucdavis.edu/TOOLS/PNAI/pnaishow.php?id=53). When applying any pesticide it is very important to follow the label directions precisely, take all necessary precautions, wear appropriate safety equipment, and only apply the pesticide where appropriate and necessary for a specific pest. The following UC website provides guidelines on the safe and effective use of pesticides http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74126.html.

If you are interested in reading more about pesticides and bees, UC recommends the article “How to Reduce Bee Poisoning from Pesticides” by Oregon State University on the web at
Please feel free to contact us if you have any additional questions.

Contra Costa Master Gardeners Help Desk

Note: The Contra Costa Master Gardener Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we’re open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: ccm[email protected], or on the web at http://ccmg.ucanr.edu/Ask_Us/

A Home Gardener’s Guide To Safe, Bee-Friendly Pesticides

Looking for a way to fight pests or weeds in your garden? Many popular insecticides and weed killers are labeled as nontoxic and “biodegradable,” but recent science has shown otherwise.

Monsanto’s popular glyphosate-based herbicide, Roundup, for instance, has been proven to suffocate human cells, and has been linked to an array of health problems like cancer, autism, heart disease, and depression.

Not only do these toxic chemicals affect human health, but they have also been proven to be a major cause of Colony Collapse Disorder, the phenomenon that occurs when honeybees die off at record rates.

Studies have shown that when a bee lands on a flower treated with many popular and much-advertised pesticides, they attack the bee’s central nervous system, disorienting it, and damaging its thinking and memory. Bees poisoned by pesticides will struggle and often fail to find their way back to the hive, and thus the colony collapses.

Given that bees are our main pollinator, it doesn’t make sense to use pesticides that have been proven to kill them, especially when there are alternatives that are safe, easy to use, and cost effective. Chances are you’ve already got some of these tucked away in your pantry.

Andreana Bitsis

Derived from the Azadirachta indica evergreen tree native to the Indian subcontinent, neem has been hailed as the organic gardener’s best friend. While highly effective at repelling a variety of pests such as mites and aphids, as well as certain fungal diseases like powdery mildew, organic neem oil, when used at correct doses, will pose no threat to people or pollinators.

Unlike chemical pesticides, neem is biodegradable, breaks down quickly, and leaves no lasting residue. Neem oil is powerful, so be sure that your homemade solution is properly diluted- it should include no more than 3% oil.

Vinegar

Due to their acidic nature, both white wine vinegar and apple cider vinegar can be used as effective weed killers. Fill up a watering can or spray bottle and apply it directly to the difficult weeds you’d like to nix. You can also mix up a little cocktail of one gallon vinegar, with one cup Epsom Salt, and a tablespoon of castile soap.

Epsom Salt

An ideal component of any organic garden, Epsom salt is completely safe, non-toxic, and bee-friendly. In addition to being a magnesium-rich fertilizer for tomato and pepper plants, Epsom salts are also an effective way of keeping slimy critters like slugs and snails off your plants. Simply sprinkle salt around the base of affected plants, or apply a half-water, half-salt saline spray to the leaves of plants affected by other pests, like beetles.

Chrysanthemum

Naturally containing a pest-repelling compound called “pyrethrin,” Chrysanthemums can be planted in a garden to repel pests, or made into tea that can be sprayed onto the leaves of plants (after it’s cooled down, of course.)

Pepper, Garlic, and Onion

Just as pepper spray is harsh for human skin, at milder concentrations, it works similarly on the bodies of insects. A handful of chili or habanero peppers, garlic, or onions can be pulverized in a blender with a few cups or water, boiled over the stove, then cooled and transferred to a gallon container. Add extra water to make sure you don’t burn your plants, and be sure to wear gloves and protect your eyes when making this mixture.

Castile Soap

Given its much-lauded gentleness and non-toxicity, it might come as a surprise that castile liquid soap is a potent pesticide. Its effectiveness stems from the fatty acids present in the olive oil-based soap, so be sure to use the real deal; dish soaps and detergents will be both ineffective and harmful here.

Mix up a solution with only about 2% soap, and feel free to add a little cooking oil, vinegar, neem oil, or pepper to the mix.

Aluminum Foil

Don’t want to throw out the aluminum foil left over from that dinner you made last night? You can re-use it in the garden to repel aphids. Cut the foil into strips and wrap them around the base of plants affected, or tear it up and mix it in with the mulch around your plants. The light reflections will confuse pests and drive them away.

Essential Oils

An important component of many natural insect repellents intended for bodily use, eucalyptus oil is also an effective method of keeping harmful bugs away from your garden.

Strong, pungent smells are what works here. Other essential oils to use include orange, peppermint, and rosemary. Sprinkle a few drops around the area, or add them to a spray bottle full of water, and apply directly to the endangered plants.

Garden Snails And SlugsOrganic Snail Control With Neem?

Does neem oil work for garden snails and slugs?
An effective but natural snail killer would be nice, wouldn’t it?

Neem repels all kinds of biting, chewing and sucking garden pests, so wouldn’t it work for organic snail control, too?

After all the snails in the garden also chew and munch on green leaves, right?

Well, snails are a strange one. Neem oil certainly does not repel them as it repels other garden pests that feed on plants.

There has been one research study on land snails, and it wasn’t your typical garden snail, it was an edible snail. That snail was unaffected by neem oil but was killed when ingesting enough neem leaf or neem bark extract:

Molluscicidal effects of neem (Azadirachta indica) extracts on edible tropical land snails.

That means spraying neem oil would do nothing to control snails in the garden, but theoretically it should be possible to make an organic snail killer with neem leaf and/or bark extract. As far as I know nobody has done this yet.

Aquatic snails on the other hand are very susceptible to any form of neem, like many aquatic organisms. Neem should not be sprayed in large amounts around still bodies of water.

But garden slugs or snails… Science does not have an answer here and no natural snail control with neem is available yet, so I can only report from my own garden:

In my experience neem oil does not make any difference whatsoever to the little slimy bastards. But don’t despair, there is hope. Even without neem oil, snails and slugs can be dealt with naturally.

My preferred method of organic snail control is to use traps:

The good old beer slug trap is hard to beat. Pour some stale beer into a little bowl. (It doesn’t have to be stale, but why waste fresh beer?)

Snails and slugs find beer irresistible and can smell it from miles. (Or at least from a long way.) They start drinking, and drink and drink and drink, until they are so drunk that they fall in and drown.

It’s the best garden snail killer I know of.

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Plants are amazing things. Tethered to the spot, unable to run or hide from environmental threats, they have instead developed an arsenal of chemical weapons to help shield themselves from the everyday onslaught of the outside world. With a few tips and tricks you can hijack these defence compounds and put them to use with the other plants in your plot to help them withstand almost everything the summer might throw at them. Here are my top four favourites.

I have yet to meet a gardener who has not bemoaned the night-time raids of slugs and snails. Fortunately, nature has a simple solution. Allicin is a defence compound created by garlic bulbs which both repels and kills slugs and snails. To harness this, simply put a bulb of garlic in a litre of water and blitz it in a food processor. Leave to stand for 10 minutes for the chemical reaction that creates allicin to complete, then strain off the solids and pour the liquid into a spray bottle. OK, as you might have guessed, this stuff does have rather a strong salad dressing smell, but has proven incredibly effective for me – much more so than turning my garden blue with slug pellets. All you need to do is spray it liberally over the plants you find most susceptible just as night begins to fall.

In the steamy rainforests of south-east Asia, fungal and bacterial diseases thrive like nowhere else. This means the plants that live there have had to create a range of powerful antimicrobials to fend off crippling infections. Cinnamon is one of hundreds of examples, packing fragrant, antimicrobials into its bark. In fact, the same compounds that give cinnamon its flavour are also the active defence compounds. Traditionally, in Asia, it is sprinkled on to the soil of new seedlings and cuttings to prevent mould and mildew. I find it useful, as well, as part of the treatment for larger plants that might, for example, be experiencing root rot from overwatering.

There are, of course, several plants from closer to home that have adopted similar strategies, and chamomile is one example. A cold infusion of chamomile tea makes an excellent solution for watering young seedlings that are at risk of damping off.

For some plants, their key threats come in an altogether furrier form. For this reason, species like chillies and black pepper have evolved the ability to produce pungent, spicy chemicals to deter mammalian predators. Paradoxically, humans get a kick out of what to many other mammals is an instant, but harmless, natural deterrent. In my experience, the best way to harness it is by purchasing large containers of powdered black pepper or chilli from Asian supermarkets and sprinkling it generously around affected plants. I have found them effective in everything from protecting newly planted bulbs from mice to shielding sweetcorn (somewhat) from urban badgers.

OK, as soon as it rains this protection is lost. But, as with everything above, they are cheap, easy to apply and as natural as they come.

Email James at [email protected] or follow him on Twitter @Botanygeek

Using Neem Oil

It can be hard to find an organic pesticide that actually works on your garden invaders. When it comes to dealing with harmful pests, you’ll want to turn to neem oil.

What is Neem Oil?

The Azadirachta indica, more commonly referred to as the Indian lilac, margosa, or neem tree, produces seeds that contain neem oil. After pressing these seeds, people will typically use the extracted oil as either an organic pesticide or medicine. Unlike some more popular pesticides, neem oil does not kill insects on contact. Instead, it disrupts the bugs’ hormones and causes them to stop following some of their normal biological processes. For instance, some bugs that are exposed to neem lose the will to eat and experience disrupted fertility. Neem oil also prevents larval development, meaning you won’t have to worry about new generations of pests springing up anytime soon after using it. Plus, neem oil’s antifungal properties will prevent unwanted spores from germinating. Nearly all of neem oil’s beneficial properties can be attributed to nimbin and azadirachtin, two compounds in its chemical composition.

What to Look For in Your Neem Oil

You may have seen neem oil listed as an ingredient in some of the pesticides at your favorite gardening store. Unfortunately, most of these formulas use clarified hydrophobic extract of neem oil, a cheaper variant with a questionable chemical makeup that might not give you the best results. When selecting your neem oil, you’ll want to invest in one that’s cold-pressed and pure. Cold-pressed oils are extracted without the use of heat, an especially important quality considering that high temperatures can break most of neem’s beneficial compounds down. Purity is a little more self-explanatory. You wouldn’t want any chemicals cut into what is supposed to be an organic solution.

What Pests Can You Use Neem Oil On?

Neem oil works on a wide variety of problematic garden pests, including over 200 different kinds of insects. These include aphids, fungus gnats, beetles, snails, slugs, ants, leafminers, mosquitoes, locusts, and houseflies.

Make Your Own Neem Oil Spray

You’ll only need a few items to create your very own organic garden spray. The best part is, you won’t be using a lot of neem oil per application, so you’ll be able to spread a single batch out over a long period of time. You’ll want to invest in a pump sprayer that can hold at least 32 ounces of liquid. You’ll also need to get your hands on some cold-pressed neem oil, water, and dish soap.

Mix a teaspoon of neem oil and a ¼ teaspoon of dish soap into 32 ounces of water. If you’d like, you can just pour each of the ingredients into the sprayer and gently shake it up to mix them together. Upon first putting them into the sprayer, you’ll notice that the liquids separate into distinct layers. When you can longer see any of these layers, you’ll know you’ve shaken the bottle enough.

Using Your Spray

Remember that your neem oil spray won’t just target bothersome insects—it will target them all. To avoid harming any beneficial bugs, you’ll want to spray your garden either early in the morning before they show up or later on at night after they’ve left. Spraying at these times will also help you avoid any potential scorching problems.

Purchasing a sprayer with a “fine mist” setting can also help you in taming your neem oil application. Ideally, you’ll want to cover your plants in mist without going overboard and soaking them. Usually, neem oil takes full effect after about three days. Even after that time, you may find yourself having to deal with some leftover pests. In this case, you’ll want to spray your plants again as soon as the first three-day waiting period has ended.

When it comes to eliminating pests from your garden, neem oil is the way to go. It’s organic, can be easily mixed into a spray, and will usually last you a very long time. Use neem oil, and it won’t be long before those pesky bugs plaguing your garden start to disappear. Who needs man-made chemicals?

Effects of Neem Oil onHoney Bees and Beneficial Insects

Does neem oil hurt honey bees and other beneficial insects?

Insecticides kill insects. That’s why they are called insecticides. Usually pesticides make no difference beween pests and beneficial insects.

But neem oil is different.

As explained on the page about neem insecticide, neem oil is not really a knock down, kill-on-contact insecticide like the chemical poisons. Neem must be ingested (eaten by the bugs) to be effective.

If bugs don’t eat leaves they don’t get hurt. Simple.

In reality it is a little bit more complicated than that, but the fact remains that neem oil is impressive: it really does hurt bad bugs while sparing the good bugs.

Researchers have looked at it and found that neem oil is non toxic for spiders, butterflies and to insects that pollinate plants.

Scientists looked especially at how neem oil affects honey bees, since bees do eat plant matter, the pollen.

That’s why reaseachers studied what happens if flowers get sprayed with neem oil.

And what they found is very reassuring. To see any effect the scientists had to use very high concentrations of neem. They used a lot more than you would ever use for pest control.

Only if they constantly hit the flowers with a very concentrated neem oil spray did they see an effect, and only in some small hives (medium sized and larger hives were still unaffected.)

What happens is that the bees carry contaminated pollen back to the hive and feed it to the brood. In the small hives some of the new bees could not emerge from their cells (Schmutterer and Holst, 1987).

Weekly use of a neem oil spray at a normal concentration (0.5% – 2%) will not hurt honey bees at all.

You can also rest assured that while neem hurts aphids, whiteflys and the like, it does not harm ladybugs and other predators that eat the aphids, or the tiny wasps that are parasites on many pests.

In one field trial researchers collected and counted aphids and their parasites and predators from fields. In the neem treated field there was the same amount of predator activity as in the untreated fields, and the aphids carried even higher numbers of parasites!

As I already mentioned above, the reason is that the beneficial insects don’t eat the leaves and so never consume enough neem to be affected.

But you still need to be careful when you spray neem oil in your garden.

Any oil spray can smother and suffocate insects, and in that respect neem oil makes no difference between good and bad bugs.

So when you spray neem oil, please do it first thing in the morning or late in the evening, when the good bugs are least active. That way you won’t hit any bees or other beneficial insects directly. The neem oil spray will dry before they land on the plants, and only the insects trying to eat your plants will die.

More information about controlling pests with neem oil.

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Went and spayed 125 tomato plants with it tonight. It says on the label that it is harm full to bees when sprayed directly on to a bee. I found this info online-
Neem Oil Uses & Benefits
Effects of Neem Oil on
Honey Bees and Beneficial Insects
Does neem oil hurt honey bees and other beneficial insects?
Insecticides kill insects. That’s why they are called insecticides.
Usually pesticides make no difference beween pests and beneficial insects.
But neem oil is different.
As explained on the page about neem insecticide, neem oil is not really a knock down, kill-on-contact insecticide like the chemical poisons. Neem must be ingested (eaten by the bugs) to be effective.
If bugs don’t eat leaves they don’t get hurt. Simple.
In reality it is a little bit more complicated than that, but the fact remains that neem oil is impressive: it really does hurt bad bugs while sparing the good bugs.
Researchers have looked at it and found that neem oil is non toxic for example to spiders, butterflies and to insects that pollinate plants.
Scientists looked especially at how neem oil affects honey bees, since bees do eat plant matter, the pollen.
That’s why reaseachers studied what happens if flowers get sprayed with neem oil.
And what they found is very reassuring. To see any effect the scientists had to use very high concentrations of neem. They used a lot more than you would ever use for pest control.
Only if they constantly hit the flowers with a very concentrated neem oil spray did they see an effect, and only in some small hives (medium sized and larger hives were still unaffected.)
What happens is that the bees carry contaminated pollen back to the hive and feed it to the brood. In the small hives some of the new bees could not emerge from their cells (Schmutterer and Holst, 1987).
Weekly use of a neem oil spray at a normal concentration (0.5% – 2%) will not hurt honey bees at all.
You can also rest assured that while neem hurts aphids, whiteflys and the like, it does not harm ladybugs and other predators that eat the aphids, or the tiny wasps that are parasites on many pests.
In one field trial researchers collected and counted aphids and their parasites and predators from fields. In the neem treated field there was the same amount of predator activity as in the untreated fields, and the aphids carried even higher numbers of parasites!
As I already mentioned above, the reason is that the beneficial insects don’t eat the leaves and so never consume enough neem to be affected.
But you still need to be careful when you spray neem oil in your garden.
Any oil spray can smother and suffocate insects, and in that respect neem oil makes no difference between good and bad bugs.
So when you spray neem oil, please do it first thing in the morning or late in the evening, when the good bugs are least active. That way you won’t hit any bees or other beneficial insects directly. The neem oil spray will dry before they land on the plants, and only the insects trying to eat your plants will die.
I hope I do not have issues. I still have my doubts even though I was “assured” in this article that it isn’t a issue. Hope it doesnt affect my nucs etc. Wasn’t my decision to use this to begin with. Anyone else used this?
Thanks
Kingfisher

Journal of Apicultural Research

Abstract

The objective of this study was to determine the effect of neem (Azadirachta indica) oil on mortality and development of honey bee worker brood, queen oviposition, colony performance, and Varroa destructor mortality. As a hypothesis it was indicated that adequate concentrations of neem oil may control V. destructor without affecting bee colonies. Neem oil at concentrations of 0.33–21.1%, with 7.26–464.64 mg l−1 azadirachtin, was sprayed on bee (Apis mellifera) combs. Their effects on mortality and developmental time of the brood, worker bee response on feeding and capping the larvae, and number of eggs laid by the queen were quantified. A 21.1% oil concentration resulted in 100% egg mortality, but lower concentrations resulted in minimal egg mortality. Larvae that reached the fifth instar were capped and survived the presence of the oil, but when 21.1% was applied, their development was delayed one to two days. With concentrations of 5.3 and 10.6% (116.2 and 232.3 mg l−1 of azadirachtin, respectively), queen oviposition was not significantly different from the control, but 10.6% slightly decreased oviposition. The highest V. destructor mortality (85%) was proportional to the concentration and number of spray applications. When neem oil was applied to hives, none of the concentrations used decreased bee population, capped worker larvae or the reserves of honey and pollen. However, two queens died after one application of 5.3% and three applications of 10.6%.

El objetivo del estudio fue determinar el efecto de aceite de neem (Azadirachta indica) expresado en mortalidad y desarrollo de la cría de abejas obreras, postura de la abeja reina, desempeño de las colonias de abejas y mortalidad de Varroa destructor. Como hipótesis se indicó que concentraciones adecuadas de aceite de neem pueden controlar la presencia de V. destructor sin alterar las colonias de abejas. Se asperjó aceite de neem sobre panales de abejas (Apis mellifera), en concentraciones de 0.33 a 21.1%, con 7.26 a 464.64 mg l−1 de azadiractina. Sus efectos se cuantificaron en la mortalidad y tiempo de desarrollo de las crías, en la respuesta de las abejas obreras para alimentar y opercular a las larvas, y en el número de huevos puestos por la abeja reina. La concentración de 21.1% resultó en 100% de mortalidad de huevos, mientras que concentraciones menores resultaron en una mortalidad mínima de huevos. Las larvas que alcanzaron el quinto ínstar fueron operculadas y sobrevivieron a la presencia del aceite de neem, pero cuando se aplicó a 21.1%, su desarrollo se atrasó uno a dos días. Con concentraciones de 5.3 y 10.6% (116.2 y 232.3 mg l−1 de azadiractina, respectivamente), el número de huevos puestos por las reinas no fue significativamente diferente respecto al testigo, pero el aceite a 10.6% disminuyó ligeramente el número de huevos. La mortalidad máxima (85%) de V. destructor fue proporcional a la concentración y al número de aspersiones. Cuando se aplicó aceite de neem a colmenas, ninguna de las concentraciones disminuyó la población de abejas, la cría operculada de obreras o las reservas de miel y polen. Sin embargo, se perdieron dos abejas reinas luego de una aplicación de 5.3% y tres aplicaciones de 10.6%.

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