How long does it take for insects to become resistant to an insecticide

[Steve333]

So I suspect this is a rather broad question with lots of potentially different answers, but I wanted to get a feel for how long can I continue using an insecticide which is working in my GH and garden, before I risk selecting for resistant bugs. Are there any general rules of thumbs about this; how often to swap insecticides or use two (or more) in combo?

What do folks think is a prudent approach on this?

[Richard]

It is insecticide dependent, with a gamut of results from “quickly” to “never”.

When a pesticide is susceptible to resistance, the EPA requires the label to state the maximum frequency of use and also pesticides to alternate with to avoid building superbugs.

What are you currently using?

[Steve333]

Thanks Richard. Right now I have settled on Spinosad primarily, with a bit of pyrethrum and some Botanigard.

I was under the belief that the max frequency of use was more due to human safety, did not know it related to resistance.

[Richard]

@Steve333

I was under the belief that the max frequency of use was more due to human safety

Both!
There are often limits on amount of product per year which is related to human and environmental safety. For commercial pesticides it is listed in quantity / acre / year.

Then there can be statements on the label regarding number of consecutive applications before switching to a pesticide with a different “Mode Of Action” (Group). This is where resistance comes in. For example, if one of your pesticides works by inhibiting respiration and another by neurotoxicity, usually a pest is toast because the successive generations can’t build a resistance to both at the same time.

Spinosad is fairly effective against weak pests, especially eggs. Some colonies of aphids have been known to develop a moderate resistance so I alternate.

Insects (e.g. White Fly) quickly develop resistance to Pyrethrin. It is ineffective here.

I’ve no experience with Botanigard.

Here are some links that include Groups …

Bacteri- and Fungi-cide usage in coastal influenced Vista, southern CA

This is not a spray schedule. Instead, it is what I have on hand and could use based on past experience and current observations. We are out among our fruiting plants almost every day and thus notice things as they occur. Note that for some plants there are multiple options. This is because I keep track of usage and rotate through different modes of action to reduce a build-up in pesticide resistance. This list is geared for our climate and soils and so the application of each line to other lo…

Pesticides for Insects, Bugs, and Spiders.xlsx (133.5 KB)

… and this link about adjuvants

Penetrants and Surfactants used in Vista, southern CA

Before using an adjuvant with a pesticide, check whether one is needed or would negate the main product. For example, Some insecticide products such as liquid BT and Spinosad are very good penetrants on their own and addition of a penetrant or surfactant can have poor results Other insecticide products such as Ortho Tree & Shrub *Fruit Tree Spray and Voliam Flexi have a surfactant built in so there is no need to add another Penetrant LI 700. Very good for enhancing herbicides. Otherwise I’v…