Honeydew, But Not the Melons: When Aphids Attack

By Jay White

Have you ever felt a light mist fall upon you as you stood under a tree on a summer day? The next time you feel this, stick your tongue out, and taste it. 

It is sweet. This sweet-tasting liquid falling from the sky isn’t manna, it is aphid poo! Well, not poo exactly, but it is excrement from the back side of an aphid. Honeydew! That’s right, honeydew is aphid poo! In this scenario, honeydew is a sticky, sugar-rich liquid that aphids secrete. 

Aphids have modified mouth parts that allow them to drill directly into the phloem and extract all of the rich carbohydrates and sugars that it needs. Once they “tap a vein” there is so much food available under so much pressure from the plant that the phloem just passes right through their little bodies and right out of their butts! 

Now that you are completely grossed out, stick your tongue back in your mouth and ask “What do honeydew and aphid anuses have to do with gardening?”  Well, a lot actually.

I first learned about this interesting little tidbit in “Applied Physiology of Horticultural Plants.” This fascinating course was taught by a true Master of Horticulture, Dr. Leo Lambardini.

Our class was discussing how to get a pure sample of the contents of the phloem for analysis. Since the phloem is a very tiny internal structure of a plant, it is basically impossible to mechanically “tap” into it and get a pure, unadulterated sample of plant juice.

So, a brilliant horticulturist solved this difficult problem by applying something he had observed in his study of aphids.

Since aphids attack a plant in the same way that a mosquito attacks you, this scientist decided to gas an infested plant with CO2 to kill the little aphids. Then, he snipped the bodies away from the mouth parts that were still in the plant. This gave him literally thousands of “straws” from which to gather samples. Brilliant! I love it when someone figures out how to make something useful out of something basically useless.  And … let’s face it, aphids are basically useless to us gardeners.

If you have spent much time in the garden, you are probably very familiar with aphids. These tiny little pests are quite common and quite annoying. They have the cutest little nickname: plant lice. 

Aphids do more damage to agricultural and horticultural plants than any other species of insect. Aphid infestation can cause decreased growth rates, mottled leaves, stunted growth and even death. 

In fact, one species of aphid almost entirely destroyed the wine industry in the 1870’s. They also contributed to the spread of the “Late Blight” fungus that caused the Irish potato famine. And, let’s not forget the honeydew. So not only can aphids harm your plants, they can harm you as well.

And what about that honeydew? Turns out, it is harmful too. Lots of various molds and fungi that attack plants grow very well in honeydew. Have you ever seen that black stuff covering your crepe myrtle’s leaves? Well, that is sooty mold and it is growing on the honeydew left behind by the aphids.

Luckily, aphids are easy to control. There are a lot of chemicals that you can spray, but spraying chemicals today is frowned on. Luckily, there are many ecologically friendly alternatives. 

The easiest is water. Once you start seeing signs of an infestation, get your water hose and spray the plant. If the impact doesn’t kill them, falling onto the ground usually will. 

There are also bio-friendly pesticides that have shown some promise. Neem and Lantana are two of the best. Also, don’t forget that lady bugs love aphids. So, go to your local nursery and buy a container of ladybugs and set them free in the area of the aphids. They are a natural predator of aphids and do a very good job ridding your plant of these pests. Besides, who doesn’t love ladybugs?

Aphids cause untold dollars worth of damage to agricultural crops each year.  They also cause problems for the gardener. With a little observation and a little effort the home gardener can control these pests. 

So the next time you find yourself getting “misted” under one of your trees, or all of the leaves on your crepe myrtle turn black, head for the hose or unleash the lady bugs!