Do Crushed Tomato Leaves Kill Aphids?

The meme pictured below suggests that crushed tomato leaves are a good way to get rid of aphids. Who knew?

This meme is making the rounds and based on comments, a lot of you will give it a try. Why? Why not just use Google and do a quick search to find the facts? That does not always work, but in this case the facts are readily available.

Check the Source

One of the first things I do when I see a new gardening meme is check the source because most gardening memes are wrong. This meme has the source right on it so it’s easy to check.

I searched the source website for this meme but could not find it – I did not see any memes but they do have gardening articles. Here are some things they suggest:

• 6 garden benefits of molasses – none of them are true!
• Use Epsom salts to kill aphids – not true
• Companion planting partners – these do not work.

I’ve debunked much of their advice on this site. That is not a good sign. This site will clearly publish any kind of nonsense to get you to click on its ads. But, maybe tomatine is one thing they got right and it does work on aphids?

What is Tomatine?

Wikipedia says, “tomatine (sometimes called tomatin or lycopersicin) is a glycoalkaloid, found in the stems and leaves of tomato plants, and in the fruits at much lower concentrations. It has fungicidal, antimicrobial, and insecticidal properties”.

That sounds promising, it is an insecticide.

Plants make thousands of natural insecticides – that is how they prevent being eaten by bugs. In fact, 99.9% of the insecticides you consume from fruits and vegetables are natural ones.

How Much Tomatine do Tomatoes Have?

A simple Google search will tell you this. Tomatoes have a high amount of tomatine at 0.04%, which is 400 ppm.

Why is this number important? The dose of any poison depends very much on the amount. Just because tomatoes contain an insecticide does not mean it exists in a dose that is high enough to do any harm when made into a spray.

How Much Tomatine is in the Spray?

The mixture is made up of 2 cups of chopped leaves and a quart of water (4 cups). Two cups of chopped leaves probably contains a lot of air, but let’s be generous and assume there is no air. In that case, the mixture results in a dilution of 1/3 (2 cups added in a total of 6 cups).

Since tomatoes contain 400 ppm, this mixture has a maximum concentration of 130 ppm tomatine.

But …. just a minute. How do you know all of the tomatine was extracted from the leaves? You don’t. Letting leaves sit overnight is a very poor way to extract any chemical.

How soluble is tomatine in water? It’s not!!!

Based on the suggested extraction method, there will be almost no tomatine in the spray.

What Does Science Say?

It is unlikely any scientist has measured the effect of crushed tomato leaves on aphids in which case there would be no scientific proof for the claim in the meme. Since we know tomatine is an insecticide the pure compound must have been tested and as it turns out it was.

Feeding by the potato aphid was not affected at 500 ppm, and mortality was only slightly affected.

Another study looked at aphids on okra plants and found the following numbers (# aphids/3 leaves):

• Control – 13
• Neem (3%) – 6.5
• Garlic extract – 5.2
• Tomatine (1,000 ppm) – 9.4

At 1,000 ppm tomatine reduced the number of aphids by 28%, but it was not nearly as effective as garlic or Neem. You can expect the effect to be much lower at 130 ppm.

It is important to understand that the species of aphid can make a difference, something gardeners tend to ignore. They assume a pest control method for aphids works on all species.

Do Aphids Attack Tomatoes?

From the University of Kentucky, “In the early spring, winged aphids migrate into tomato fields from wild hosts and begin to establish colonies on the plants. Two species of aphids are common on tomatoes, the potato and green peach aphids.”

If living tomato plants can’t control aphids, it is unlikely that mashed up, diluted leaves will do the job.

Do Crushed Tomato Leaves Kill Aphids?

The testing of tomatine to control aphids suggests that at the diluted ratios in the meme, it will not control aphids. It might control some species, but unless there is science to support that view we have to conclude it is unlikely to work.

Given the crude extraction method used and the fact that tomatine is not soluble in water, we can expect little to no tomatine in the recommended spray.

Even NEEM and garlic spray work better.

This myth is busted!