What Is a Systemic Insecticide?

Whether you’re just starting out in gardening or have already been a gardener for many years, you’ve probably come across the term systemic insecticide. This is quite a common way to describe insecticides, so it’s important to understand exactly what it means.

Insecticides usually are classified into two groups: contact or systemic. Contact insecticides have no residual activity while systemic insecticides have residual or long-term activity.

How Systemic Insecticides Work

The easiest way how to explain what systemic insecticides do is to understand how they work. Contact insecticides kill insects on contact, hence the name. As soon as you spray the plant with this insecticide, any pests that come in contact with the poison will die.

Systemic insecticides, on the other hand, work a bit slower but are also very efficient. These insecticides usually become assimilated into the plant as a whole, generally in a protein form that is not toxic to humans or animals. When the targeted insects feed on this plant, they ingest the insecticide and die.

Because it stays on the surface of plants, a contact insecticide will wear off with the wind or rain while a systemic insecticide will stay within the plant and will work for quite some time.

The Downside of Systemic Insecticides

As we said, plants can absorb the systemic insecticide into their cells. This is because these insecticides consist of substances that are highly soluble in water. So, the plants can soak up the insecticide just like they would do with water.

The downside to this is that if you apply the insecticide just before it starts to rain, there is a good chance that the rain will wash the insecticide away. Along the same lines, if you apply the insecticide incorrectly, it can flow from the plant down into the ground. If it’s not raining and you apply the insecticide correctly, however, then the plants will easily absorb the insecticide.

You must apply systemic insecticides to the soil instead of the plants. These aren’t the best option because by applying the insecticide to the soil, there’s a greater chance that more than just your target insects will die. These insecticides can harm beneficial insects and even birds.

Systemic Insecticide Efficiency

The efficiency of these insecticides is usually determined by the application method. For example, a fogger will generally achieve much better results. Foggers produce very small insecticide droplets that will thoroughly cover the targeted area. A sprayer, on the other hand, distributes the solution in large droplets. In this case, the insecticide you are using might not coat all of your target plants.


Systemic insecticides are one type of insecticide that you should really consider if you have a pest problem. This is especially true if you need to target places that are near other objects that you don’t want to contaminate with the insecticide. For example, if you want to spray the flowers that are near a pool with an insecticide, you can’t use a contact insecticide because that can contaminate the pool. By using a systemic insecticide, you can safely enjoy your pool without having to worry about insects damaging your flowers.


Dan Dysinger

We are plagued with gypsy moth. I estimate we are in a down cycle currently with a year or two to go before they subside. I live with oak trees and am cultivating and encouraging locust variety due to shade benefit. I use “Isotox” to kill gypsy moth. This has been discontinued by Ortho, but it is a very effective system chemical. I treat the lower 4 ft. of tree trunks and it works.

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