Does Rain Wash Away Insecticide and Pesticide? 5 Useful Tips

rain flows down from a roof down

Whether you’re doing your own pest control treatment or hiring a company, knowing how long the treatment will be effective for could be useful information.

The length of the treatment depends on several factors – with the weather being one of them.

Outdoor pesticide and insecticide treatments will be diluted and less effective after it rains.

The amount that the insecticide and pesticide are diluted depends entirely on both the specific product and the amount of rainfall.

It’s challenging to sum every pest control treatment into one key point because every treatment is an entirely new situation.

While some applications are designed to work over a long period of time, other treatments are intended to work almost immediately, and today we’re going to talk all about it!

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Why It’s Difficult to Keep Insecticide and Pesticide on After Rainfall

Pesticide and insecticide sprays are just that – sprays.

Antique Tractor and orchard. An antique farm tractor sits amidst an orchard of blossoming apple trees

In high school and a little bit in college, I worked across several different apple orchards around my small town.

One thing that you learn VERY quick is that if farmers don’t utilize pesticide on their crops, then there is a 100% chance, they won’t have a harvest for fall.

From an economic standpoint, farmers have to use pesticides to yield a higher crop.

If pesticides weren’t used, we would see food prices dramatically increase while having less food available – it’s just the way it would work.

Regardless of the situation, pesticide and insecticide are useful for both farming and around the house.

Farmers spray pesticides by hooking a tank full of treatment up to the back of a tractor.

Typically, they spray at night or early morning on perfect weather days.

The Weather Needs To Have Ideal Conditions

Well, if it’s windy, half of the pesticide application will blow away when its sprayed.

If it’s raining, the rain will dilute the treatment and cause it to have to be reapplied much sooner.

With each continued rainfall, the pesticide or insecticide becomes less and less potent.

On the other side of my house is an apple orchard.

Soon after just about every other day of heavy rainfall, I hear the steady spray of a tractor covering the farm with pesticides during the night.

Note how I said “every other day” of heavy rainfall.

If you’ve ever seen them, the majority of pesticides on apples have a slight white coat on them.

After it rains, that cloudy, white coat turns into a splotchy covering that leaves parts of the fruit unprotected.

One day of rain won’t totally wipe out the treatment, but it does make the treatment the less effective.

The more rain that takes place, the faster both farmers or homeowners will have to reapply the pesticide.

Other Methods Of Pest Control

There are some pest control treatments like lawn granule pellets, that actually work better in the rain.

Lawn granule pellets are a form of pesticide that is placed onto your lawn and then activated by water to soak into the ground.

Most pest control sprays, however, will become very diluted after a few heavy rainfalls.

The good news is that most commonly used pest control, or insecticide sprays that are used outdoors are aimed at eliminating something rather than repelling it.

For instance, on the farm, you would spray to protect our crops from insects, whereas at home, you would spray to get rid of a pest.

Unless you’re dealing with something long-lasting and extremely difficult to deal with (like termites), you shouldn’t worry too much about the rain washing away your pest control treatment.

This is because many treatments work EXTREMELY fast.

The speed of treatment depends entirely on the insect or whatever you’re trying to eliminate.

More often than not – the problem will be mostly taken care of by the time the rain dilutes the pesticide.

Tips For Not Wasting The Product

If hiring a pest control company, ask questions about what will happen when it rains for that specific project.

Just go into the process expecting that you’ll likely need to reapply the treatment after some heavy rainfall.

If you’re doing DIY pest control, aim to apply your pesticide or insecticide treatment on a great weather week.

Check to see if the manufacturer put anything about rain on the product, and give them a call to ask about applying their product in the rain.

Here are a few tips to make sure that you make the most use out of your pest control treatment.

Check the Weather Forecast Before Using Pest Control Spray

This is the common theme here and the most straightforward practice you can do.

If you’re doing your own pest control, check the weather!

Unless it’s something extremely urgent, then you have the power to determine when the best time to spray is.

natural green grass. closeup background

If you can look up the weather and see a 7-day forecast of clear skies ahead, you would more than likely have little issues with your treatment, depending on what it is.

Contact the Manufacturer to See if the Pesticide or Insecticide is Rainproof

Whatever treatment that you’re using take a look at the back label.

Does it say that it’s rainproof anywhere? Or maybe it says how long it takes to settle in?

The key here is that we still want to apply the pest control treatment on a nice weather day with no days of rain in the forecast.

This way, regardless of the set-in time or rainproof resistance, the treatment will still be relatively effective.

The best course of action to make sure is to make a quick call to the manufacturer or supplier.

Better yet, if you purchased it at a physical location, the representatives there would be able to deliver some crucial insight.

You’ll either be able to find a number for manufacturer on the product itself or on their website.

To Avoid the Rain, Use a Pesticide That Takes Effect Quickly

You’ll want to use a quick-acting pesticide simply because the quicker it the treatment takes effect, the less you’ll have to worry about that rain diluting it.

A very common pesticide ingredient called permethrin takes place quickly and solves a variety of different pest problems.

This is a common ingredient across many different types of pesticide because it’s pretty useful for both DIY and commercial use.

Personally, I would opt for getting a treatment that takes effect ASAP to avoid having to apply re-treatment.

If Hiring a Pest Control Service, Try and Schedule on Good Weather Days

If it’s your first appointment, many pest control professionals will more often than not be able to get you in pretty quickly, and if you are looking for a professional please feel free to check out our pest control directory.

The good thing is that professionals make a living by making sure your home and property are pest-free.

Call your local pest control service to see how soon they can get out to your property and ask for quotes.

Check the weather, and depending on how long they say it might take for them to get to you, call around and ask different services for their estimate.

You are the primary source of income for these companies.

Your lifetime value (the amount you spend over your life with a company) can be pretty high if you need reoccurring services.

More than likely, one if not all of the services you call will see you rather quickly.

Try and time up your call with a weather forecast that looks like it’ll be pretty steady and clear for the next 14 days. You should be in decent shape for some pest control treatment.

Ask Your Pest Control Service About Treatment in The Rain

While making your initial call to a local pest control company, ask about what will happen to your treatment when it rains.

More than likely, they’ll say it won’t play a huge effect – and they’re right.

However, rainfall will dilute the pest control treatment and pesticide over time naturally. 

The longer we can hold off on it raining during the peak days of the application (right after applying) then the more effective the treatment will be.

When you’re calling to discuss your problem with the pest control company, ask them if you’ll end up needing to reapply treatment or not.

If you have to reapply treatment, you may have to do it much sooner if there is heavy rainfall.

If you have a single treatment and can manage to get a few good weather days after pesticide/insecticide treatment, then you’ll be in a really great spot – regardless of the weather.

Run-Off and Pollution Can be a Problem After Rainfall

Believe it or not, the main problem with pesticides and rain is leaching.

Sure, the pesticide treatment will be diluted after rainfall and make your treatment less effective over time, but the real problem is pesticide leaching.

Pesticide leaching is where any type of pesticide or insecticide gets washed away and “leaches” into the soil.

According to the Natural Research Conservation Service, leaching is a large scale, well-researched problem that shows pesticide leaching can significantly impact life.

Part of the controversy regarding pesticides is where the pesticide and insecticide treatments actually go when it rains.

Sure, pesticide and insecticide treatments may be rainproof – but the treatment that isn’t absorbed by the target is likely to run off into a stream or leach into the ground.

Downfalls Of Using Pesticide

When masses are worried about pest controls, its usually in part due to run off, leaching and contamination of previously healthy land.

While pesticides play an extremely vital part of our agricultural system, there are some downfalls of it what happens to pesticides and insecticides when it rains.

The runoff/leaching of pesticides usually happens more when there is a large amount of rainfall in a brief time period.

One of the most amazing, natural defendants of pesticide runoff is a riparian buffer.

riparian buffer is a natural blockade of vegetation consisting of tall trees, plants, and shrubs that help to repel and block outside contaminants.

riparian buffer protecting lake from pesticides

What the riparian buffer will do is act as a “sensor” to incoming pollutants which in turn, helps protect against flowing streams that could contaminate a precious freshwater source.

Here’s how it works:

When pesticide runoff occurs during heavy rainfall, the contaminants may flow downward towards a stream.

Luckily, the stream the pesticide runoff is flowing towards is covered by a riparian buffer.

As the contaminants get close to the riparian buffer that is surrounding the stream, they begin to get soaked up by the surrounding vegetation INSTEAD of going into the stream.

Essentially, nature is absolutely brilliant.

Let’s say that somehow, the freshwater stream became contaminated with something vicious.

The riparian buffer would reflect that conditions of the stream. You’d see plants start to turn brown and trees begin to wilt and look weak over time.

This would be natures all-natural way of saying “this isn’t good.”

While it isn’t ideal that the trees and soil get contaminated with pesticides, it’s much better to save the freshwater source instead of losing all three to the contaminants.

Preventing the use of commercial pesticides has become much more apparent over the years because of runoff. In part, it has helped to spark the organic industry tremendously.

For instance, individuals in the organic farming industry aren’t allowed to use any synthetic pest control methods which have been implicated in runoffs/leaching issues over the years.

While this last section speaks more to broad-scale pesticide and insecticide use – the ones that we all use at our homes can have the same effect on a much smaller scale.

That’s A Wrap!

If you use pesticide or insecticide at your home and have a body of water nearby, there may undoubtedly be some runoff flowing into that body of water – especially after a heavy rain.

The best thing you can do to combat runoff/leaching is to be aware and conscious of it.

Avoid it as much as possible, but sometimes the use of these pest control treatments are necessary and need to be done.

Try to be conscious and avoid spraying compounds that have a high tendency to create runoff/leaching problems as often as you can.


Fortunato, R. P., Degrande, P. E., & Fonseca, P. R. B. D. (2011). Simulate rain about action insecticide flonicamid in the control of the cotton aphid. Acta Scientiarum. Agronomy, 33(4), 603-606.

Alexander, A. C., Culp, J. M., Liber, K., & Cessna, A. J. (2007). Effects of insecticide exposure on feeding inhibition in mayflies and oligochaetes. Environmental Toxicology and Chemistry: An International Journal, 26(8), 1726-1732.

Wenger, S. (1999). A review of the scientific literature on riparian buffer width, extent and vegetation.

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