Although they’re easy to grow, agapanthus is subject to a few problems, including pests, diseases and other issues, including very few or even no flowers and yellowing/brown leaves. Below, I discuss the main pests and diseases to watch out for and what to do about them. Although this guide mainly talks about pests and diseases which agapanthus can be prone to. However, I also have links to my other guides on yellowing leaves and flowering problems.

Agapanthus Pests

Mealybugs, get them early as there often resistant to pesticides

Mealybugs are insects that suck the sap from your agapanthus plant, among many other types of plants that I’ve discussed in detail on many a guide on this site. Sucking the sap out of the leaves and stems leaves the plant in a weakened state. Maintaining its existing foliage becomes too much work for the plant, and the leaves start to turn brown and die off.

What mealy bugs look like

If you see oval flat insects that look pinkish, they’re probably mealy bugs. As protection, they have a white wax coat. They’re not too small to see, but they hide away in parts of the plant that are difficult for you to get to. As they do hang out in groups, you can see them at times when they are in a mass.

A good clue that there are sap-sucking insects around is a clear sticky substance called honeydew on the leaves. These insects secrete this as they feed, and it remains on the leaves. As all honeydew looks alike, you can’t tell that it’s specifically from mealy bugs. But you do know you have an insect problem, and most can be treated in the same way.

What to do

Catch the mealy bugs as soon as you see them. Just a few of them quickly become a whole horde. Isolate the agapanthus in grown in pots, so the insects don’t spread. Then remove the infected parts using a sharp sterilised cutting tool. I usually pair a good pair of secateurs.

That’s all you can do. On rare occasions when your agapanthus is really infested in mealy bugs, you may have to destroy the whole plant for the sake of your garden or other potted plants. This is why it’s essential to catch them early, as you can, just remove some of the affected foliage if you need to. You can try spraying them with insecticides; however, from experience, I have found that it’s usually not effective as the waxy coat usually protects them.

Watch out for Red spider mites

Red spider mites are a common pest, both for outdoor plants and for house plants. You need a magnifying lens to see them, so be patient if you think your plant has an infestation. Spider mites are also a sap-sucking insects so they basically drink your plant to ill-health just like most insects, including aphids.

What red spider mites look like

You see spider mites if they’re grouped together. They may appear as a green or reddish-brown clump, or may even look translucent. But you’re more likely to come across the spider mites’ webbing across the leaves and onto the stems.

And look for the honeydew secretion left behind. This clear and sticky substance is everywhere the spider mites have set down to feast on your plant.

What to do

Use a jet of water to dislodge the spider mites. Be sure to direct the water stream away from any nearby plants or grass. Trim off the infected bits of the plant using a sharp and sterilised cutting tool (use alcohol wipes). And then spray the rest of the plant with neem oil or a natural insecticidal soap. Red spider mites are usually not detrimental to the plant but they are easier to treat than mealybugs

Snails and slugs

Snails and slugs, especially like agapanthus plants. They hang around young foliage and feed on that. It’s difficult to remove slugs and snails once they’ve moved in, so it’s best to prevent them in the first place rather than rely on treatment. Thats being said, slugs can at least be seen. I like to go out in the dark and remove them.

What to do

There’s a whole article devoted to the problem of slugs and snails. Head over to How to deter and get rid of slugs and snails for advice on what to do about your gastropod invasion. To quickly sum it up, clear debris that offers slugs protection and consider using slug trap or go out after dark when they appear to collect them. If you grow them in pots, you can also get sticky copper tape you can put around the edge of the pot, and slugs won’t cross it.

Agapanthus Diseases

Botrytis blight

Botrytis blight is a fungal disease more commonly known as grey mould. It likes cool and humid weather and a similar environment. Any agapanthus plants you have that are in the shade, over-watered or in water-logged soil are fair game for this disease.

What botrytis blight looks like

This disease starts off as a grey, fuzzy mould on the leaves, flowers, buds and flower stalks of the agapanthus plant. The fungus grows on top of the infected part of the leaves, which then become slimy. The infected parts of the plant eventually fall off.

What to do

First of all, search out and remove any infected parts of the plant. Burn the diseased parts if possible so the fungal spores won’t infect anything else in your garden. Spray the plant with a neem oil, an organic oil often used as a fungicide. Unfortunately, botrytis blight is well-known for quickly developing resistance to commercial fungicides that are developed to combat it.

Change the cool, wet environment to a warm one for your plant. Create better drainage and replace the wet soil. Place the plant (if possible) in an area with more sunlight, more the better. Space the plants out more for better air circulation. Water the plants from below so that no water remains on the leaves at all.

Root rot

Root rot starts in the agapanthus’ roots where it can’t be seen. By the time you notice the yellow leaves and the somewhat squishy stems, this fungal disease is well-established. Root rot is invited into your plant when its over-watered and is left in water-logged soil.

What to do

Root rot is such a common problem that I have a separate article just for it. Please read Phytophthora Root Rot – prevention and treatment for what you need to know to identify and treat this disease, and to restore your plant to good health. It all comes down to providing better-growing conditions with plenty of sun and good drainage.

Powdery mildew

Like root rot, powdery mildew is a commonplace disease found on many plants. It usually appears after a period of warm and wet weather. Poor air circulation also encourages its growth as does warmer weather and cooler nights. Patches of white powder on the agapanthus leaves are a give-away sign that your plant has been infected by this disease.

What to do

As it’s such a common problem, I devote an entire guide to the identification and treatment of powdery mildew. Please read Powdery Mildew – How to control and prevent. To sum it up, remove badly effetced leaves and spray with a fungicide labelled for to treat powder mildew.

Anthracnose

It’s difficult to diagnose anthracnose as this disease is a group of fungal diseases that looks different on different plants. But is usually creates dark discolouration on leaves along with blemishes. Unfortunately, it looks like several other diseases. But if you have very small brown dots on the underside of the leaves, that’s an indication of anthracnose.

What to do

Yet again, anthracnose is a problem that affects many plants. I wrote a whole guide on this fungal disease too, How to Identify and Control Anthracnose Disease. Please visit there for all the details.

Other problems

I’ve dealt with the most common problems in separate articles. Head over to Why is my agapanthus not flowering? and Why are my agapanthus leaves turning yellow and brown?

All of the above should common most issues you have with agapanthus. Most of them can be prevented with better-growing conditions including plenty of sun and well-drained soil. You can learn more about growing agapanthus here and how to grow them in pots here.