Iris leaves turning brown

The following is a response from a fellow Master Gardener that may address your issue. If this doesn’t help please feel free to respond with a photo of the problem. Iris leaf spot may be responsible for the symptoms on the iris foliage. Iris leaf spot is a common disease of bearded irises. The disease is caused by the fungus Mycosphaerella macrospora. The first symptom of iris leaf spot is the appearance of small yellow-brown spots on leaves that are surrounded by water-soaked borders. The spots eventually turn grayish brown, develop reddish-brown borders and grow in size. As the spots grow, several spots may coalesce and destroy entire leaves. Iris leaf spot is most severe when the weather in spring is cool and wet. Good cultural practices will reduce the severity of iris leaf spot. Remove all diseased leaves and flower stalks in fall or early spring. (The causal fungus survives the winter on infected plant parts.) Plant bearded irises in full sun, space plants adequately, control weeds, and avoid wetting plant foliage when watering. Fungicides will likely be necessary to control iris leaf spot on plants that were severely infected the previous year. The first application should be made when the leaves first appear in spring. Continue to spray as directed on the product label. Effective fungicide products include those that contain chlorothalonil and myclobutanil. Since bearded iris leaves are waxy, add a spreader-sticker to the fungicide to make sure the fungicide adheres to the iris foliage.

Iris Root Rot: Preventing Rotting Iris Roots And Bulbs

Garden irises are hardy perennials and live a long time. They delight gardeners by blooming when the garden needs flowers, after the spring bulb blossoms have had their moment in the sun. Irises are easy-to-grow, graceful flowers that form the backbone of many a garden in this country, but they not entirely without problems. Iris root rot is one of them. Read on for information on root rot in iris and how to treat iris rot.

Root Rot in Iris

Root root in iris is also known as soft rot, and if your irises have ever had it, you know why. The leaves become soft, and the rhizome root grows mushy.

Iris root rot is a caused by Erwinia carotovora, a bacterial phytopathogen. It usually gets inside the rhizome through an opening created by some kind of injury. Any pest could provide this entry, including borers, slugs, snails,

beetle larvae or even rough use of tools.

With iris root rot, you’ll first see yellowing at the center of the fan of leaves. In time, the center turns brown and collapses. Root rot in iris always produces a mushy, bad smelling rhizome. Often, you’ll also see decay in the plant’s leaves.

Preventing Rotting Iris Roots

Iris root rot is not easy to cure. However, many times you can avoid it by using good cultural practices in your garden.

First, make sure that your irises are planted in sunny sites. Good soil drainage is critical, so consider raising your beds if need be to ensure proper drainage. Adequate spacing between rhizomes is also important since overcrowded plants are more vulnerable to bacterial growth.

Don’t plant your rhizomes too deep in the soil, and keep dirt from the base of the fans. Never use fresh manure on your iris plants, especially if drainage is a problem. Instead, feed your plants with gentle fertilizers.

How to Treat Iris Rot

If you want to know how to treat root rot, it means your irises are already under attack. You’ll need to dig up each diseased rhizome and inspect it carefully. If the iris root rot is extensive, destroy the iris rhizome. Unfortunately, this is the only method of root rot control in iris if the rot has spread.

You can learn how to treat root rot that is not so extensive, however. For less seriously affected plants, cut out and dispose of all parts of the rhizome that are diseased. Use sterilized tools to do this, and sterilize them again after use to prevent spreading the bacteria.

This is the time of year that one question is asked about irises just about every time we pick up the phone or turn on the computer. The question is, when do we cut the leaves back on our irises? The answer is NEVER, except when you are transplanting your rhizomes. I wish I knew how that myth got started in the iris world. The leaves on your iris plants help in feeding the plant, so why would you want to cut part of it’s food supply? The next line I get is, some of my plants have brown tips on the leaves in the summer and I don’t like to look at that. OK, if you want to set there and cut one inch off of each leaf to make the clump look better, do it. The key is, I said one inch, not 6 inches. The more you cut off, the more you are cutting the food supply. One more tip, cut the bloom stalks out all the way to the top of the rhizomes, as soon as the last blossom fades away. This is very important, as the stalks left in place, can cause rot.
The next question is how much should I water my irises in the summer? The answer is, you don’t water your irises in the summer. If you are east of the Rockies, that rule will be great. West of the Rockies, I will leave it up to you, but it is never good to push irises to grow when they should be resting. Unless you have found it just absolutely kills your irises in the west if you don’t water in the summer time, I would not do so. If you do, I would do it sparingly, not on a regular basis.
I can hear the howling already. I know there will be a number of you that will say I water my irises all summer and I don’t have any problems. The key phrase will be, YET. You are asking the plant that wants to go dormant and take a rest to keep growing. In warm climates, like California and Arizona, and perhaps southern Texas, this may be fine. My thought is, in colder climates, this summer growth will wind up being tender for the winter and your plants may develop rot problems. There is a reason that almost every iris grower in the US ships their plants to their customers in mid summer to early fall. It is because the plants are dormant and it shocks the plants less to ship them at that time.
Now for the surprise, you must water your rebloomers in the summer or you won’t get rebloom in the fall. If you are reading between the lines here, a problem may have surfaced for some of you that grow both types of irises. How do I water my rebloomers and not my once blooming irises? You don’t. Plant your rebloomers in one area and the once bloomers in another area at least 3 feet apart. Now, water the rebloomers and not the once blooming irises. Remember, your reblooming irises will NOT REBLOOM without extra water. Have you ever noticed how much better your rebloomers bloom in a wet summer and fall season? I wish I had a dollar for every time I am asked why my rebloomers don’t rebloom and they tell me they never give them extra water in the summer. It is absolutely the key to rebloom. Also a little extra fertilizer 2 or three times a year will work miracles for rebloom. It must be a light nitrogen blend like, 6-24-24, 6-12-12, or 5-10-10. Apply in March, late June, and October for most zones. Colder climates may back the fall application up a month for the fall application and pass the summer application.
I don’t care what how many times I give culture tips to iris customers, there is always an exception to the rule. I share with you what I have learned from 31 years of growing and shipping irises to every state and several foreign countries. You should benefit from these suggestions for iris culture.
Thanks for listening until the next time.
God bless you and your gardens and our country.
Respectfully,
Jim Hedgecock
Comanche Acres Iris Gardens

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