Iris Fusarium: What Causes Fusarium On Iris and How To Control It

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Several diseases can affect your plants, and some plants are more susceptible to a given disease than others. Such is the case with bulbous irises compared to rhizomatous irises.

Not only are irises with bulbous roots susceptible to more forms of iris mosaic virus than their kin, but they’re also susceptible to a nasty fungal rot known as iris fusarium basal rot.

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As this can be a deadly infection, it’s essential to know just how it occurs and what you can do to stop it.

What Is Fusarium Basal Rot?

The fungus Fusarium oxysporum f. sp causes fusarium rot. Gladioli. The fungus may be spread through dirty tools, infestations, wind, or water and can survive for several years in the soil without a host.

Usually, the fungal spores infect roots, bypassing the basal plate to infect the bulb. However, the fungus can also attack a bulb directly when the latter is damaged.

As the name implies, this particular strain of Fusarium oxysporum affects gladiolus plants and infects bulbous irises. There is evidence that it’s more than one strain, as it seems easy to transmit from a gladiolus to an iris but not vice-versa.

What Damage Does Fusarium Basal Rot Cause?

Generally, the first sign of infection is stunting new growth, with leaves beginning to yellow. Yellowed leaves often have lesions at their base, which can help distinguish fusarium rot from other causes of yellow leaves. In some cases, new leaves will fail to emerge at all.

Below the soil, the fusarium destroys the iris’s roots as it works its way to the bulb. Fusarium can leave the iris loose enough to pull from the ground quickly. Once the infection enters a bulb, it causes the basal plate to shrink.

The bulb itself will turn a light to reddish-brown color where it’s infected, and there’s a clear delineation between the infected and healthy tissue. The surface may also cover the bulbs with white or pinkish fungal growth where the infection has taken hold.

As fusarium rot doesn’t claim the entire bulb at once, the visible portions of the plant may be entirely infected or show signs of infection on only part of the plant.

How To Control Fusarium Basal Rot

Prevention is the best medicine when it comes to fusarium rot. Always purchase bulbs from a reputable source, inspecting them for any signs of softness or discoloration if you are able.

When dividing iris plants, always discard infected bulbs. Likewise, if you discover one of your irises has contracted fusarium rot, it must be excavated immediately and disposed of. Because the soil around the plant is also infected, you will have to avoid planting new bulbs there for 4 to 5 years.

Some fungicidal products may be used to treat the infected soil, as well as several fungicidal treatments that require you to soak your iris bulbs before planting.

Sterilizing the soil is another option if you cannot avoid planting irises in that area for the amount of time needed for the fungus to die out.

When transplanting, always check for signs of damage to the bulbs, as this can create an entry point for fusarium rot.

When dividing a bearded iris bulb, for example, give it a good soak in a 10% percent bleach solution, then let it dry in the sun. Conversely, you may choose to use a fungicidal powder to dust the bulb.

As with most diseases, proper care can be an effective preventative. Always sterilize your tools between plants, and make sure to wash your hands thoroughly.

Try to avoid causing any damage to the bulb by digging at a slightly wider radius than the root system. Use neem oil, neem cakes, and/or other forms of organic pesticides to help prevent potential infestations.

Add a layer of mulch over the bulb to help insulate it, and try to constantly water in the morning.

Keep the area free of weeds or debris, which can encourage the spread of diseases.

Finally, avoid planting your irises too close together, as overcrowding can allow diseases to spread through the entire group of plants quickly.

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