Soft Rot

Mole Gopher Slug Soft Rot Leaf Spot Borer Other

From an experience I had in Kansas:

A friend from work asked if I would teach her how to take care of her iris by thinning and transplanting them. Although these were "orphan" iris, they wer prized by her because were originally grown by her grandmother. We grabbed up our shovels and headed to her back yard. This iris foliage looked relatively good, except for some brown leaves. With the first lifting of a clump, we noticed the pungent odor associated with bacterial soft rot. I suggested the treatments listed in this article. Other photos from this infected clump are below. I don't remember if we were able to save any of her rhizomes because the rot was extensive in the whole bed.

soft rot 01 soft rot 02 soft rot 03 soft rot 05
Notice the foliage does not look extremely damaged. There are some older leaves that should have been cleared about, but no serious looking damage. Notice the mushy tissue in the rhizome. This is extensive damage.

Bacterial Soft Rot is a very smelly, soft, mushy bacterial -- Erwinia carotovora -- rot which affects the rhizome and the base of the fan. It causes a leaf in the fan to tip over and can usually be detected by the foul smell. Whenever we see an iris leaf that looks sickly (leaves might be falling over even in an otherwise healthy looking clump.) We remove this leaf and notice a distinctive foul odor. If it does smell foul, we immediately treat this plant with a solution of Agri-Strep. Agri-Strep can be purchased at any good farm store or nursery. It is an anti-bacterial agent. Prepare the solution at a rate of one teaspoonful per gallon of water. Put this into a one quart spray bottle available at a hardware store. LABEL and STORE PROPERLY !!

This really is important information, so please bear with me if I repeat some of this information. The Agri-Strep information is not known by all irisarians, but is an excellent cure.

The Erwinia bacteria which causes the bacterial soft rot is present in most soils and enters the iris through an injury such as snail, earwig, or borer damage, injury from careless cultivation and other openings. Soft rot occurs most often in warm moist conditions.

Overwatering and over fertilizing are potential causes of this foul-smelling problem. It often appears first at the base of the leaves where they join the rhizome, and is manifested by a yellowing of the fans. Keep a sharp eye out for such signs during wet weather. The sooner the problem is detected, the more successful your treatment will be. The soft mushy tissue must be removed.

There are a number of ways to deal with rot. All are most effective if you detect the signs early and scrape away the mushy parts. Then you can:

1) Drench with bleach
2) Dust with granular cleanser like Comet
3) Dust with garden sulfur
4) Drench with aspirin solution
5) Resort to chemicals -- such as Agri-Strep

When this disease is present, the rhizome should be dug, the infected tissue scraped away with spoons or wooden scoops, and the rhizome allowed to dry in the sun and replanted in another location. The rhizome may be soaked in a 1 in 10 solution of household bleach before replanting. It is absolutely essential to rinse the bleach solution off the rhizome after soaking. If the rhizome cannot be dug, clear away the soil, scrape out the infected tissue, and allow the rhizome to dry for several days before covering with soil. There may be loss of the mother rhizome, but a good chance of saving the increase. Disinfect all tools after usage too. Remove all infected material from the garden.

Some gardeners dust with a household cleanser that contains chlorine-based bleach. This works three ways: it helps to dry the wound, the bleach is fatal to bacteria, and the cleanser produces a strong alkaline environment in which any surviving bacteria cannot grow.

Dipping Siberians in Clorox solution is not a good choice. Better to go with Agri-Strep or Benlate works. Also soil sulfur is a slow acting soil acidifier, it would seem appropriate for use with Siberians.

Remember -- keep watch to spot softness at the base of the leaf fan and fans that have separated from the rhizome. We press on the top of the rhizome to make sure it is hard and firm. If it is soft and mushy to the touch, action needs to taken to preserve the plant. Bacterial soft rot can destroy an entire clump in a few days.

Bacterial soft rot can be prevented by avoiding poorly drained sites and mulches and by replanting before serious crowding takes place. Do not add too much nitrogen, which can produce soft growth, inviting Erwinia bacteria to grow and multiply. Remember, the disease thrives in wet weather and is most problematic in the spriing and the late fall.