Spinosad Spray: What It Is And Its Uses

One of the most potent organic insecticides out there, spinosad spray, comes from soil bacteria. But how should you use it? We explain!

Spinosad spray


One of the most frustrating aspects of gardening is dealing with insect pests, which may frustrate some home gardeners to the point of giving up. Before you throw in the trowel once and for all, you need to hear about spinosad spray if you aren’t already familiar with it. It’s an organic form of pest control that’s derived from a bacterium called Saccharopolyspora spinosa and doesn’t pose much of a threat to nature, except for some beneficial insects.

You may have heard of Bacillus thuringiensis, or BT, which is another godsend for organic gardeners. There are many pests BT can’t kill, and spinosad spray will kill most of those. When you use both of these together on your vegetables or other produce, your garden will remain almost completely pest-free. Spinosad is highly toxic to bees when it’s wet, so you’ll need to be strategic about the time of day you apply it. But, once dry, it can kill chewing pests for up to four weeks!

If you want to learn more about this magical spray called spinosad, we’ll tell you everything you need to know about it, including directions on how to use it.

What Is Spinosad?

Spinosad spray
Applying spinosad spray will reduce pest pressures in your garden. Source: Oregon State University

Spinosad is made of chemicals called spinosyn A and spinosyn D. While it may sound unnatural, these chemicals are derived from the fermentation juices of soil bacteria, which means the product is completely naturally derived. Spinosad is a relatively new insect killer, having been approved by the US Environmental Protection Agency (EPA) in 1997. In 2003, it was officially given organic status by the USDA National Organic Program (NOP). With these seals of approval, you can safely use them in vegetable gardens and on your ornamental plants.

Since spinosad is natural, it’s safe to apply on food crops, but you should keep the habit of washing off all your food after you harvest it just to be safe. You can spray it on leaves or fruits, or wherever you spot insect pests.

The most popular form of spinosad is a spray that can be applied directly to the plants and will dry within a few hours. It’s also available in the form of dust and granules. Dust may be easier to find than granules, and granules are typically sold as a fire ant killer. Ant killer usually has a bait in it, so the ants will pick up the granules and take them into the nest, so it may not be suitable for organic gardening. You may find other synthetic pest control products that list the active ingredient spinosad in them.

How Does Spinosad Kill Insects?

So, how does this wonder product work? Saccharopolyspora spinosa is toxic to pests and affects their nervous systems. Once spinosad is applied to the plant, insect larvae will feed on the substance and will die within a day or two. Spinosad will cause the insect’s muscles to flex uncontrollably, which leads to paralysis and eventually death. It’s most effective when the larvae eat it, but simply walking over it is usually enough to do some damage.

Spinosad can kill a wide variety of insects, including fire ants, fruit flies, leafminers, mites, mosquitoes, spider mites, and thrips. This relatively new insect killer is generally used on vegetables and fruit along with other garden species. Many organic gardeners use BT to take care of caterpillars and use spinosad spray for everything else.

Keep in mind that this garden insect spray can harm beneficial insects such as bees, but we’ll get into the details of that in a bit.

Benefits Of Using Spinosad

Structures of Spinosyn A and D
Diagrams of the chemical structures that make up spinosad.

There are more benefits to using spinosad than there are dangers, so you’ll probably want to keep this insect killer on hand if you don’t already.

An obvious benefit is that spinosad kills insects that BT doesn’t, such as thrips, flies, and fire ants. The best part is that it lasts much longer than BT. It can last up to four weeks unless it gets washed away by rain or the garden hose before then. When a liquid spray can stick around for that long, it’s hard to say no to it!

An important benefit is that because it’s a natural substance, it won’t negatively impact the environment, unlike synthetic pest control chemicals. The two chemicals that spinosad is made of come from the fermentation juices of bacteria, so you’re fighting nature with nature. It’s OMRI-listed as organic, meaning it’s deemed organic by the Organic Materials Review Institute.

Spinosad is rapidly broken down by sunlight and water and disperses in the soil, so you don’t have to worry about it polluting groundwater or the soil. Some chemical pesticides can stay in the environment for up to a year, causing them to build up in the soil and in groundwater. Fortunately, we don’t have to worry about this with spinosad. Remember that it originated in the soil, and so it’s just going back home!

Drawbacks Of Using Spinosad

The biggest drawback of spinosad that may deter home gardeners from using it is that it’s highly toxic to bees while the spray is wet. Timing is everything when it comes to spinosad. Bees are most active during the day, usually mid-morning to the late afternoon. Apply spinosad spray in the evening or very early morning to allow plenty of time to dry. The spray should take no more than three hours to dry completely.

Since spinosad spray is considered safe to use around bees once it’s dried, the dust and granules can be considered safe, as well. Still, you should wait until the bees aren’t active to take precautionary measures. Take the extra step and avoid applying spray, dust, or granules on flowers or anywhere else you see bees frequently land on.

Another concern is that spinosad is moderately toxic to earthworms. You can avoid harming worms by making sure only to apply it to plants as needed. Using granules for fire ant treatment will certainly pose risk to the worms, so try to avoid using it around your garden beds or other places where you’d like to keep the worms safe.

Finally, spinosad is slightly toxic to humans, animals, birds, and fish. This toxicity is incredibly low. If it comes into contact with your skin or eyes, the only problems you should experience are irritation and redness. Animals may have a similar reaction if they should come into contact with it.

When using spinosad, avoid letting it touch your skin. Wearing safety goggles while applying it, especially if you’re using it in dust form, will protect you and keep you safe from irritation. Be mindful of when and where you apply it so you can keep worms, bees, and other animals safe. As long as you follow these guidelines, you’ll see that spinosad isn’t that dangerous to work with.

How To Use Spinosad

Spinosad powder
Spinosad in powder or dust form is less common than spray but just as effective.

Spinosad liquid spray comes in two forms, ready-to-use (RTU) and concentrate, both of which you should be able to find in the gardening department of the home improvement store. An easily accessible brand is Monterey garden insect spray, but there are plenty of other options available on the market. 

RTU spinosad sprays are the easiest to use in home gardens because you can begin spraying it as soon as you open the bottle. It won’t require any mixing or measuring, but you should still read the label of your RTU product to make sure you use it correctly.

Spinosad concentrates are intended to be mixed with water before you apply them to plants. Mixing it with water will dilute it to a safe amount so you won’t end up harming the wrong insects or yourself. The label of the product will tell you the exact measurements. You’ll need to measure out the proper amount of liquid and mix it into water. It’s usually a few tablespoons per gallon, but this may change depending on the product. Once it’s properly proportioned, you can begin spraying it on your plants as directed.

For both kinds of spinosad liquid spray, you should apply it to the tops and bottoms of the leaves as well as on stems. You should spray it wherever you see pests and larvae. Remember, avoid spraying flowers to keep the bees safe, and avoid spraying the soil if you can. You can spray larvae directly, but it’s when they eat sprayed leaves that you’ll find it to be the most effective. If you see eggs on your plants, you’ll need to spray again in a few days after the eggs have hatched.

Spinosad dust will either come in a bag or in a squeezable container. If you have the container, you simply squeeze it so the dust comes out and apply it to the tops and bottoms of leaves just as you would with spray. You may find it to be a bit trickier to apply if it comes in a bag. Find a squeezable container you can clean and repurpose for spinosad application, or don some gloves and sprinkle it with your hands. To prevent skin irritation, you should wear gloves and cover your arms to reduce exposure when you’re handling dust, regardless of its packaging. It’s advisable to wear a mask as well to avoid inhaling the dust.

Spinosad granules are easy to apply since all you need to do is broadcast them evenly across the ground. Follow the directions on the label to find out how much to apply to a specific area. Since it’s often used to control ants, you’ll probably find the ratio for how much to apply per 1,000 square feet, so you may need to know the size of where you want to apply it and pull out a calculator. If you apply the granules by hand, be sure to wear gloves to avoid skin irritation.

Although dried spinosad is safer for beneficial insects than in wet form, you should wait for the evening or early morning to apply dust and granules as an extra safety precaution so you can lower their chance of exposure.

Frequently Asked Questions

Q: What insects will spinosad kill?

A: Spinosad will kill several kinds of pests, including caterpillars, fire ants, fleas, fruit flies, leafminers, lice, mites, mosquitoes, spider mites, and thrips. Be careful when you apply spinosad spray since it can be highly toxic to beneficial insects such as bees while it’s still wet.

Q: Is spinosad harmful to humans?

A: The active ingredient spinosad is only slightly toxic to humans. If it touches your skin or eyes, you may experience redness and irritation. The effects are rarely, if ever, worse than that. You’ll most likely only come into contact with low levels of it, which doesn’t have much cause for concern.

Q: When should I spray spinosad?

A: Since spinosad (saccharopolyspora spinosa) is highly toxic to bees, the best time of day to spray spinosad is in the evening or early morning when the bees aren’t active. It remains toxic for about three hours or until it dries completely, so it’s wise to learn when the bees come out so you can properly time when to spray.