Plant Sickness – Why Do Pests Eat The Sick Plants?

Studying plant sickness is fascinating because we know pests only dine on sick plants.

What I have for you today is some info on why those plants invite pests when they’re sick, and how to avoid that.

Plant Sickness Transcript

Today I’m going to talk about plant sickness and specifically I’m going to be looking at a book that was written by a French guy named Francis Chaboussou – it’s called Healthy Crops and it’s really amazing.

What he did is he went and looked at a lot of different research about why plants get sick and why they get attacked by insects and I want to talk about that here.

So let’s say you have a plant. You have a plant and it’s getting attacked by insects and I’ve talked a lot before about how only sick plants get attacked by insects. A healthy plant doesn’t get attacked because it’s not food for insects – an insect cannot digest it.

But this research really got more interesting as to exactly what’s going on in the plant and what makes that happen, and he found out that if a plant has excess soluble nitrogen and I think also excess sugars then what’s gonna happen is insects are gonna wanna come and get those – especially nitrogen is my understanding.

As to what happens, there can be many reasons, but for some reason the plant is having a problem taking these things and producing proteins and carbohydrates. The synthesis of these things is stopping. Now this could just be a soil imbalance of minerals – you know, we have very imbalanced soil.

It could be a poor soil food web where we don’t have the beneficial microorganisms to help them out. It could be a water issue.

It could be that the plant got injured. It can be a number of things so on its own – it doesn’t really tell us that much but there are a couple of implications for us gardeners.


One is definitely that if we apply too much nitrogen, which is very common in the spring, especially soluble nitrogen if you use chemical fertilizers (pile them on the lawn in the spring to get that nice green up and even into the garden), what’s gonna happen is often you’ll see later in the summer the insects come to dine on the excess nitrogen.

So we don’t want to be applying too much nitrogen. It’s an important nutrient but we don’t want to apply too much.

Now if you’re applying compost, it’s more slow release so it’s not going to be as big of an issue, but you can apply too much compost and especially manure as well. My main point there is let’s not apply too much nitrogen at any one time cause that can cause a problem.

The other one interesting thing he found is that chemicals, especially pesticides, cause this to happen. They sort of stimulate this response where the plant can’t form protein or carbohydrates, so if we’re spraying an insecticide to kill insects we know that it hurts the plant. It causes this to happen to a plant.


So more research showing you how spraying any kind of pesticide, insecticide, fungicide – these things affect the plants too. They affect the whole soil food web.

So that’s the main thing to realize. I guess it’s really just more proof that only sick plants get attacked. If a plant is balanced and has the right amount of nitrogen and sugars and minerals to create protein and carbohydrates, it’s not gonna be food for the insects.

They simply won’t even find the plants. So that’s just what I wanted to talk about today about plant sickness. It’s a little more advanced and the details, the science of it, is not super crucial but some of the implications are: not applying too much nitrogen, not using pesticides and just making our plants healthy instead of fighting the pests.

Any questions?



Comments Are Down - Should Be Back By January 23