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Scorch

There was a lot of iris damage in the Spring, 2000 from Dallas on northward through Kansas and Missouri. The diagnosis was varied from Scorch, to Crown Rot, to Bacterial Soft Rot, or just a reaction to "freeze/thaw" damage. There was much discussion everywhere. There was a lot of scorch present at the 2013 Dallas convention also.

A couple of reference:

1. Scorch -- Disease of Rhizomatous Iris

2. Scorch -- Evey's Blissful Garden

3. See also "Scorch Identified" by John Burton Hamilton Tall Talk, September 2000, p. 28.

4. See also "Scorch: Mystery Killer At Large" by Paul Black A.I.S. Bulletin 252,32

Scorch is a devastating condition and is characterized by the presence of brown leaves not easily pulled away from the clump, and no noticeable foul smell. Central leaves, beginning at leaf tips, wither and die back. Affected leaves may turn reddish brown, giving the disease its name. The rhizome remains firm, but the roots rot. If the rhizome were dug, there would be a healthy looking rhizome, but there would be no roots.

The scorch does not appear to be particularly contagious since it will occur only in scattered spot of large plantings. It has also been confirmed that scorch cannot bbe transmitted by soil, water, or direct contact between plants.

scorch Note: there is only one clump in this bed affected. All other clumps were clean and healthy.

Note: the leaf tips are affected first and are beginning to wither backwards.

When I dug this clump, there were no roots on the rhizome.

Studies were being conducted in California in 1970s, but there was not enough scorch in that state to warrant intensive information. What was seen under an electromicrosope was a double flagellated bacterium of Pseudomonas sp. But this was not the cause of scorch, only a suspected organism.

A research team from the Botany Department of the University of Iowa discovered that the diseased plants showing symptoms of scorch all contained particles of a mycoplasma-like organism (MLO).

The fact that MLOs cause scorch suggested that both antibiotics and heat could be used to cure scorch. The research team found that subjecting scorched rhizomes to temperature of 104 degrees F. for three to four days completely cured the treated rhizomes.

Suggested treatments: The temperature and time required to kill the MLO responsible for scorch can easily be obtained in an incubator or a food dehydrator. Placing tthe rhizome in a closed greenhouse or cold frame should also work in a sunny week.

Another suggested treatment: Dig up the rhizome and let it cure in the sun on asphalt paving for about a week. The heat does not kill the irises, but only the MLOs.

At present the suspected agents are aphids, so control of these insects could also limit the disease. Scorch also seems to happen during rapid growth in high temperatures following a very cold winter.

Another suggestion: Incorportate the fungicide Terrachlor (PCNB) into the soil.


Thrips

Adult thrips are very tiny, being no more than 1/25" in length, and are usually yellowish, black or brown in color. Nymphs look like smaller versions of the adults and are typically yellowish or pale green in coor.

In the beginning of spring, adults emerge from overwintering and lay eggs in the plants. After the eggs hatch, usually in a few days, the nymphs begin to eat. They continue eating for up to three weeks before beginning the molting process which will turn them into adults in another two weeks. Then the process begins again with another laying of eggs, hatching, and nymphs eating. Due to their fast reprocuction cycle, there can be up to as may as 15 generations of thrips in one growing season.

thrips I purposefully left these pictures as thumbnails so you can click on the images to open them and see how small the thrip really is.
To the right, is a close up of the thrip and to the left there are many on an iris fall.
thrips 03

The only way to control trips is to break their molting cycle and eliminate the thrips from turning into adults, killing them in the process. One product is called Safer Brand BioNEEM. Read more about this chemical on the internet.

bee pod Most everybody in the iris world know the photo to the left is a
bee pod. But, not everybody who grows iris know what a bee pod is. I've been asked what the little watermelon looking thing on their iris are and what they should do about them. I tell them to remove it by breaking it off of the stalk and throwing it away.

Now, I would not want an inexperienced iris grower coming into my yard and breaking off MY BEE PODS because we are now hybridizers and it might not be a bee cross, but human cross. Gotta take precautions sometimes.

pulling weeds mowing iris

I like these cartoons from Squiggles collection. The one on the left reminds us all that we need to weed our gardens, trying to keep it as clean as possible. I had few weeds in Kansas compared to what we tolerate in Oregon. It is an endless task to be weed free.

The cartoon on the right shows a disgruntled husband (or maybe just a neighbor) mowing the iris instead of just the grass. Not to worry. The iris will return if that is all that was damaged -- the foliage and not the rhizome and roots.