Symptoms

Iris bulb rot is characterized by softening or rotting of the bulbs. Symptoms of bulb rot include appearance of orange, white or blue-green growth on the iris bulbs. Affected bulbs also release an unpleasant smell. As the disease spreads, it cause yellowing of iris leaves, slows down the plant’s growth, eventually causing it to die.

Preventive Measures

Prevention of iris bulb rot isn’t too hard. All it takes is a few simple steps. Poor drainage plays a major part in promoting bulb rot. Make sure the site for planting irises offers well drained soil. Irises growing in shade or crowded locations are more susceptible to diseases. Make sure to keep these factors in mind while picking the planting site. When planting bearded iris rhizomes, make sure they’re partially exposed to the surface. Store iris bulbs in a clean, dry location and check the bulbs carefully before planting. Bulbs that are only partially affected by rot can be saved by removing the affected part with a clean, sharp blade. Make sure to disinfect the blade before further use and dispose of the infected portion.

Treating Iris Bulb Rot

Immediate remedial action is the best way of preventing the spread of disease. Cut off all affected tissue with a clean, sharp blade and place the bulb in a sunny spot. Once the bulb dries, you can proceed to replanting it.

The fungi responsible for causing bulb rot can be present in the soil. In such a situation, it’s best not to plant irises in the soil for at least 3-4 years. Remove the infected bulbs and removed tissue and dispose of at a safe distance.

Bacterial Leaf Blight

The infection usually starts from the tips of iris leaves. It spreads gradually, engulfing the entire body of the leaves, thus, causing them to die. Presence of small, pale spots on the edges of the leaves is a clear indicator of the infection. The spots initially have a watery appearance and turn brown as they grow in size. The early symptoms of bacterial leaf blight aren’t unlike those of fungal leaf spot. Also, both diseases are prevalent in wet, foggy weather. This often leads to confusion and makes it hard to identify the exact cause of the infection. Fortunately, there are a couple of differences between these two maladies. The leaf spots in case of bacterial leaf blight are larger, more irregular than those that occur in case of fungal leaf spot. Bacterial leaf blight spreads primarily in mild weather conditions whereas fungal leaf spot can occur anytime except in the cold season, when the ground is frozen.

And now that you know what you’re up against, let’s take a look at some measures that can help you safeguard iris plants against this menace.

• Regular inspection of iris plants is the simplest, most effective way of checking against diseases as well as pests. Add it to your routine.
• Prune iris plants every fall, cutting off all dying, damaged foliage. Carefully dispose of the discard once you’re done pruning.
• Once you’ve detected the disease, don’t lose any time. Cut off and destroy all infected leaves.
• The infection spreads readily through the garden tools. Make sure to wash your hands and sterilize the tools after handling affected plants.

Fungal Crown Rot

Once you’ve detected the signs of infection, take immediate remedial action. If the infection is in its early stage and only the tips of the leaves are affected, cut off the leaves from the base and dispose of. Clean the plants with a fungicidal solution and check the soil for presence of fungal structures. In case of severe infections, immediately remove the affected plant from the site. Also, remove the soil surrounding the affected plant and dispose of at a safe distance.

The Disease

Iris leaf spot is caused by Mycosphaerella macrospore, a fungus that affects both bulbous and rhizomatous irises. The spores are released in spring and spread by means of water splashed on the plants either during irrigation or rainfall. Strong air currents, too, assist the spread of the spores. Spore germination can take place over a wide range of temperatures (from 50°F-77°F).

Prevention

Irises planted in shade, damp or waterlogged places are easy targets for fungal infection. Picking the right site for planting irises hence holds immense importance. Good drainage and air circulation are essential too. Addition of lime is an easy way of improving the soil’s drainage properties. In case of heavy or clay soil, you can incorporate gypsum to loosen the soil layer and improve drainage. When planting, make sure to provide a separation of at least 6-8 inches between adjacent plants. Irrigate iris plants early in the day, allowing ample time for the foliage to dry up. Clean the bed in spring and remove the old mulch and dead leaves which can serve as a safe haven for the fungal spores.

Treatment

Regular inspection is one of the most significant aspects of iris care. Early detection not only makes disease control easy but also helps prevent further infection. Cut off the infected foliage and apply standard fungicides. Remember to dispose of the removed foliage at a safe distance.

The very first thing you should do once you’ve decided to grow irises is check your garden for the right planting site. Irises tend to do best in locations that offer full sun. If you’re living in a region that’s subject to very hot climates, I’d recommend a partly shaded location. Next step, check your soil type. The ideal pH range for growing irises lies between 6.5-6.8.  Amending the soil isn’t too hard a task. If the soil is too acidic, incorporate lime to the soil. If, on the other hand, the soil is alkaline, addition of sulfur will do the job for you. Good drainage is another important factor. The simplest way of cultivating in soils with poor drainage is making raised beds or planting on slopes.

A good cleanup always serves well. A couple of weeks from planting, remove all the weeds and debris from the planting location. Dispose of all refuse at a safe distance. Add good amount of well rotted compost or well rotted manure to the soil. Alternately, you can also incorporate bone meal in order to add to the soil’s nutrient bank.

With that, your garden is all ready for iris plants. Go ahead and plant the irises!