What Is Iris Leaf Spot and How To Control It?

It can be hard to imagine that the Iris (EYE-ris) genus is prone to illnesses.

These plants are beautiful, resilient, and hardy. Some species are accustomed to marshes, and others are cold-hardy into sub-zero temperatures.

iris leafPin

One of the first signs you may have that your iris is in trouble is the appearance of strange spots on the leaves.

Spotting can happen to any iris, although bearded species tend to be most susceptible.

These spots may be due to improper care or manifest a more severe leaf spot condition.

What Is Iris Leaf Spot?

Fungal leaf spot is a condition caused by multiple fungi that can happen to a wide range of plants.

The one that most often attacks bearded irises is Cladosporium iridis.

Meanwhile, Didymellina macrospora focuses on irises with rhizomes rather than bulbs.

Both have similar symptoms and treatments.

It’s most often caused by splashing the leaves while watering but may appear in humid weather.

Since this iris fungal disease can overwinter in host plants, it’s essential to deal with it when you see the signs.

What Damage Does Iris Leaf Spot Cause?

The initial signs of leaf spot are small oval lesions on the plant’s leaves, bearing a yellow or tan center and brown outer ring.

If left untreated, these spots will grow until they take over the leaf.

At this point, the leaf may appear grey with reddish-brown edges.

While the fungus is non-lethal, it can spread to the stems and buds, severely weakening the plant.

If weakened enough, the plant may be unable to sustain itself, and it will die, roots and all. Learn about root rot on iris plants.

How To Control Iris Leaf Spot?

There are many ways to treat leaf spots on your irises, although prevention is always the best medicine.

Chemical Options

Fungicides are often the go-to method, especially for those who don’t have time for non-chemical solutions.

The more severe the infection, it will need the more treatments.

Fungicidal solutions are usually not necessary to control this disease if you have the time to tackle it manually.

Additionally, the best fungicides to use for this condition tend to be contact fungicides, which have a habit of washing off when it rains.

Non-Chemical Options

Removing any leaves or stems that show signs of infection can often stop this disease in its tracks.

It is best to do this in the fall, as leaf spots can overwinter, but early spring is also a viable time to treat your plants.

In some cases, you can remove the infected leaf portions, but you often need to remove the entire leaf. Either way, use sterile shears.

While a seemingly simple remedy, this will often be enough to protect the rest of the plant.

Under extreme circumstances, you may need to resort to a chemical solution. If you act before the fungus has had a chance to spread to multiple leaves or stems, you can avoid this.

Prevention

When possible, be proactive and indulge in some preventative maintenance.

Because splashing from water can cause the disease, it may not always be possible to protect an outdoor iris from rain.

But you can keep it away from sprinklers and water the plant slowly at ground level.

You can also pick species known to be resistant to the disease, such as Iris cristata, Iris graminea, and Iris sibirica.

Finally, try to keep the humidity lower near the iris. Use a dehumidifier or avoid planting it in close groups outdoors.

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