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Iris Borer

It is doubtful that the "worm" was an Iris Borer, this time.  The Iris borer, Macromoctua onusta, is native to North America, and it probably fed on native species such as Iris versicolor before the arrival of Europeans, who brought bearded irises with them to this country.  Originally thought to be limited to the eastern part of the United States and adjacent Canada, iris borers have been reported from as far south as Carolina and as far west as Iowa, Wisconsin, and Missouri; there have even been a few isolated reports from Texas, Nebraska, and the Pacific Coast.
Iris borers are serious pests that damage iris directly and also create entry points for bacterial soft rot disease. 
The photo to the left shows the damage caused by Iris borers.  Note the left margins are chewed.  Irregular tunnels appear near leaf bases, and pinholes dot foliage a few inches above the ground.  Leaves may have dark streaks and be wilted or rotten.  Plants may collapse.
Iris borers are caterpillars, the larvae of a medium sized, nondescript brownish moth.  The moth lay eggs on old iris leaves and debris near the iris plants in the autumn.   
The eggs survive the winter and hatch with the onset of warm weather in spring, when the foliage is 5 to 6 inches high. 
These tiny caterpillars begin attacking fresh iris leaves.  Early damage is not  noticeable.  But as these tiny caterpillars grow, the damage becomes quite visible as shown in the photo.  The leaves of the iris plant can be easily pulled away from the fan.  Full grown borers are up to 2 inches long, pinkish in appearance, and with dark brown heads.
In the later summer, the caterpillar leave the iris rhizomes and enter the soil near the plant where they then become pupae.  A pupa is a mummy-like dormant stage that allows the caterpillar to transform into a moth.  The pupae are about one inch long, dark brown, and somewhat spindle-shaped and may be seen in the soil during planting time.  In the autumn, they emerge as moths, mate, and lay the eggs that cause next year's infestation.  The photo on the right shows the moth stage of the iris borer.
Signs of Borer infection:  small pinholes in the iris leaves, notched leaves during early summer, small piles resembling sawdust around the base of the iris plant, and hollowed out rhizomes.

Click the "worm" above NOW!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Murphy's Oil Soap and Iris Borers
Taken from AIS Region 18 Bulletin -- Spring 2000
Michael Gullo
West Walworth, New York

(This article was recently on Iris-Talk and originally printed in the January 1998 AIS bulletin)

I first heard about the Murphy's Oil Soap method of borer control in the January 1998 AIS Bulletin.  The title of this article was "Sand and Soap" written by Marie Gebert.  In the article she presented the following advice: "use a mixture of one half cup of Murphy's Oil Soap to one gallon of water.  Spray on the iris leaves weekly (or after a rain) from early May to late July.  This should be used after any other sprays."
I use the soap that comes in the refill bottles not that which comes in the spray bottles which is already diluted.  I feel that a thorough garden cleanup (very later fall or very early spring) is also very important to make borer control even more effective.  I have been using this method of borer control for the past two seasons with great success.
I only find a very small number of borers that manage to survive the spraying, which I promptly squish.  One could probably combine the oil soap treatment and beneficial nematodes (alternate sprayings) and achieve even more complete protection.  With just two sprayings last season I only found a dozen or so borers.
Marie, in her article, mentions that she and others in her area (northeastern Connecticut) have been using it to great effort for five seasons (as of 1998).  I don't believe in using harsh chemical treatments to control pests or other problems, so Murphy's Oil Soap has been quite a help.  Your climate will dictate how early you need to start spraying.  Some years the first of May is early enough, but lately here I have needed to start even earlier, usually mid to late April.  If you wait till the borers hatch then it will be too late, at least to stop the early ones.
I won't use harsh chemicals, but for those who do I would suggest trying a test plot for the Murphy's to see if it is as effective as chemical treatments.  I know of a number of people who use chemicals like Cygon only out of desperation.

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Diseases will fall into the broad categories of:

  • Bacterial Diseases 

    • Bacterial Leaf Spot, aka Bacterial Leaf Blight (Xanthomonas tardicrescens)

    • Bacterial Soft Rot (Erwinia carotovora)

  • Fungal Diseases

    • Fungal Leaf Spot (Didymellina macrospora)

    • Fusarium Basal Wilt Rot (Fusarium oxysporum)

    • Sclerotium Root Rot 

      • Southern Blight

      • Crown Rot (Sclerotium rolfsii)

      • Mustard Seed Fungus

      • Botrytis Rhizome Rot (Scherotinia or [Botrytis] convoluta)

    • Rust (Puccinia iridis and/or Puccinia sessilis)

    • Miscellaneous Fungal Diseases

      • Blossom Blight (Botrytis cinerea, Glomerella cingulata, or Iris xiphium)

      • Bulb Rot (Fusarium oxysporum, Penicillium sp., Sclerotium rolfsii)

      • Root Rot (Rhizoctonia solani or Phytophtora sp.)

      • Oak Root Fungus (Armillaria mellea)

  • Viral Diseases

    • Iris Mosaic Virus (MIMV, SIMV, BIMV)

  • Diseases of Unknown Causes

    • Scorch 
      -- MLO - mycoplasm-like organism [a bacteria] proposed cause in 1990s 
      -- Pseudomonas sp. [a bacteria] proposed cause in 1970s

Pest listings often include: 

  • Aphid

  • Iris Borer (Macronoctua onusta)

  • Iris Weevil or Iris Snout Beetle (Momonychus vulpeculus)

  • Scale

  • Thrips (Bregmatothrips iridis)

  • Verbena Bud Moth (Endothenia hebesana)

  • Whiteflies (Aleyrodes spiraedides)

  • Leaf Miners

  • Other

    • Nematodes (Meloidogyn sp or Pratylenchus sp)

    • Slugs and Snails

    • Voles (Microtus sp.)

    • Animals

      • Rabbits

      • Squirrels

      • Deers

Other listings might include:

  • Pineappling

  • Bloom Out

 

Irises suffer less from diseases and pests than most other garden plants under normal conditions.  However, some diseases and pests do attack iris and they must either be prevented or destroyed to have a healthy garden.  It is much easier to maintain a clean garden than a messy one since many pests and diseases hide in garden debris and over winter there.
An iris garden should not be overwatered, overcrowded, or overfed if it is to be healthy.  In warmer climates overhead watering spreads diseases, overcrowding keeps the air from circulating and overfeeding makes large, but soft, rhizomes. 
Only the most often encountered Iris diseases and pests are included here.  The Iris Borer is perhaps the #1 problem.  Infestation by this pest may cause other diseases, or other diseases may begin without the borer being present at all.  There may also be secondary diseases to consider. 
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Leaf Spot – Bacterial and Fungal

Leaf spotting may be caused by a bacterium or a fungus. Both produce rather similar symptoms, but with practice they can be told apart. The prevalence of leaf spotting was probably behind the old custom of cutting down the foliage of bearded irises after the blooming season. This practice may actually have been helpful, at least with bacterial leaf spot.

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Fungal Leaf Spot: Fungal Leaf Spot is common. As many as eight different leaf-spot fungi attack different sorts of irises, but the symptoms are all the same. Small spots appear anywhere on a leaf (but more usually toward the tips) and grow to about ¼ inch in diameter, with a yellowish center and a distinct brown border. The spots do not get soft and run together as in bacterial leaf spot, but they can become so abundant that the whole leaf is destroyed. Heavily infected plants are seriously weakened and will fail to thrive. Like bacterial leaf spot, fungal leaf spot occurs most often during wet weather.
In areas with dry summers, fungal leaf spot comes on with the autumn rains. Fortunately, systemic fungicides work quickly to limit the spread of the disease. For the sake of appearances, badly spotted leaves can be removed. Even more so than with other diseases, fungal leaf spot can be prevented by avoiding crowding (the disease spreads from plant to plant) and by cleaning up dead foliage thoroughly in the fall and burning it. Some authorities say that if you can keep this disease out for two years, it will not recur unless brought in on new plants. Some gardeners recommend soaking rhizomes in a solution containing benomyl before planting as a preventative or sprayed with this solution if the disease is found on the leaves.
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In Year 2000, Scorch was a major problem in many gardens.  In Year 2001, there was more Leaf Spot in areas of Central and SW Kansas.
Bacterial Leaf Spot: begins at the margins or tips of the leaves and produces soft, watery areas that spread rapidly and run together, working downward through the leaf. Eventually the whole leaf may die. This form of leaf spot is relatively uncommon and occurs during long spells of wet weather. It is found mostly in northeastern North America.
The only cure is to cut off any infected leaves well below the spotted region, using tools that are dipped in a bleach solution between cuts to sterilize them. Always put cut leaves into a container to prevent walking on the infected leaves and spreading the disease in this manner. Also, don’t allow irises to become so crowded that air cannot easily circulate amongst them.
Since the spores that cause leaf spot can live over winter on garden debris, it is important to keep a clean garden. Be sure to remove old dead Iris leaves. Keep an eye out for the onset of leaf spot during wet weather – starting as small yellow and brown spots appearing near the tops of the leaves first. The spread of the disease slows or stops when the weather dries off.
Starting in the spring when conditions for leaf spot are favorable, some gardeners recommend a regular spraying program. Start spraying about six weeks before bloom. Spray again if rain should wash it off. Fungicides such as Captan, Fore, Bravo, Daconil, Kocide and Bayleton are all effective in the control of leaf spot. Using two of these fungicides alternately is better than using one of them exclusively, since resistance to a given fungicide can build up with repeated use. The availability of any particular chemical depends on state and federal regulations. Consult your local Extension Agent for possible sources of these chemicals.
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Bacterial Soft Rot

How to Deal with Soft Rot
Jim Loveland
(Copied from AIS Region 18 Bulletin – Fall 2000)

I have been asked many times how to deal with soft rot. That’s a good question with a difficult answer. Once I notice soft rot that has invaded my iris patch, I immediately check each plant to see if old bloomstalk rhizomes are rotting or if it’s a new rhizome. If it’s in the old bloomstalk rhizome I will cut out, then pull all the dirt away from around the rhizome and the area I cut.
At this point I sprinkle Comet on the affected area. Comet is a drying/bleaching agent. I also cut the leaves down to 8-10 inches to allow air and the sun into the area that has been infected. I cut the leaves on plants surrounding the affected iris too. I have even gone as far as to remove tree branches so the infected area gets more sunlight.
Over the last few years I’ve learned that the sun will cure a lot of diseases infecting plants, and iris diseases are no exception. In smaller gardens of 30-50 iris, you might consider planting them further apart than on to one and a half feet. This will allow for better air circulation. Now if the infected area is very extensive, I may decide to dig all infected plants, cut out all the rot, let them lay out in the hot sun for a time. Usually two to four hours is sufficient time for the rhizomes to dry.

You can dip rhizomes in a ten-percent bleach solution to disinfect the rhizomes, then immediately rinse well. You can use a spoon to scoop the rot out, then sprinkle Comet on the infected area. Use whatever method works best for you. In smaller gardens I would most likely dig out the infected area for this, in my opinion, is the best cure method. In my case I grow hundreds, do I use other methods as explained above.

A friend from worked asked if I would teach her how to take care of her iris by thinning and transplanting them.  Although these were "orphan" iris, they were prized by the her because they originally were grown by her grandmother.  We grabbed up our shovels and headed to her back yard.  With the first lifting, we noticed the pungent odor associated with bacterial soft rot.  I suggested the treatments listed in this article. Other photos from the infected clump are below.  Much of the foliage had a few brown leafs.
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Soft Rot is a very smelly, soft, mushy bacterial – Erwinia carotovora -- rot which affects the rhizome and the base of the fan. It causes the fan to tip over and can usually be detected by the foul smell. The bacteria which causes this 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.
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All six (6) of these photos illustrate the damage caused by Bacterial Soft Rot.  
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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.
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There are a number of ways to deal with rot. All are most effective if you detest 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; 4) Resort to Chemicals.
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When this disease is present, the rhizome should be dug, the infected tissue scraped away with spoons or melon scoops, and the rhizome allowed to dry in the sun and replanted in another location. The rhizome may be soaked in a 8-1 or 10-1 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.
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 Agramycin (a Streptomycin) or Benlate works. Also soil sulfur is a slow acting soil acidifier, it would see appropriate for use with Siberians.
Remember – keep watch to spot softness at the base of the leaf fan and toppling fans that have separated from the rhizome. 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 spring and late fall.

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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. All descriptive damage was similar – brown leaves, leaves not easily pulled away from the clump, and no noticeable foul smell. There was much discussion everywhere. 
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These three photographs were taken of Iris Plants in Dallas, Texas in 2000.  Diagnosis = Scorch
The following is quoted from iris-talk on May 4, 2000, from Dana Brown in Lubbock, Texas:
"I also have some scorch. Although I have had one or two cases of this before on any given year it has never been like this. I am compiling a list of cultivars to send to Cindy Rivera at her request. I too have looked for a common denominator and I think it might be tied to early spring growth and a light freeze. I theorized that maybe the varieties that were damaged are more susceptible to freeze damage thus weakening the plant and allowing scorch to attack.
"I spoke with several people about this during the national and everyone seems to have their own horror story. It also seems to be the year for scorch. An awful lot of people seem to be having a problem with it. I wonder how many of them had little to no winter as compared to normal. That is the only thing that makes this year different for me. Maybe the lack of winter allowed varieties that are cold sensitive to start their growth early and then when we had a little freeze it zapped them. Now, for the hole in that theory, 2 pieces of the same cultivar, 18" apart, one scorched and the other is growing and blooming its fool head off.
"One other observation, the scorch is MUCH worse in the beds I dug last year. In the 2 year and 3 year old beds there is little to no damage with 80% coming from the 3 beds that were planted new last year? Too much fertilizer, compost, tender loving care???? Next question is, will the victims love or should I just dig them up and throw them away? Some of them were 1999 introductions and some of them were historics. I don’t want to lose them all either way. I notice some of them have little bits of green growth (new?) under all that damage. Should I cut off all of the damaged foliage? Comments, suggestions??

Scorch is an iris disease of unknown cause, and luckily it is of rather rare occurrence. Discussions about the reasons for scorch are contradictory and confusing. Scorch has unique symptoms. Leaves at the center of the fan begin to die at the tips, but cannot be pulled free of the rhizome. Scorch begins with withering of the central leaves and within a few days the leaves turn a characteristic rusty red-brown, beginning at the tip and spreading down toward the base. Soon all the leaves are affected. When the affected plant is dug up, the roots (not the rhizome!) are dead and hollow. 
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Some cases of scorch can be treated by digging up the rhizome and letting it cure in the sun on asphalt paving for a week or so. This is called the "Hot Asphalt Treatment." Whatever the scorch organism is, heat seems to destroy it.
Scorch is not very contagious, and if it spreads at all, the agents are likely to be aphids. Control of these insects can limit the disease. Scorch does not appear to be particularly contagious since it will occur only in scattered spots of large plantings.
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These two photographs were taken in Garden City  and Manhattan, Kansas.  Diagnosis Unknown, perhaps Scorch.  Note the characteristic brown leave tips.  Note also the apparent healthy neighboring iris clumps.  This random damage is typical of Scorch. 

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The article below appeared in Tall Talk, September 2000, p 28.

Scorch Identified
By John Burton, Hamilton, Massachusetts

For at least the last forty years, the iris disease called "scorch" has been identified as a specific ailment with fairly well defined symptoms, but with no known cause. It has been referred to as a disease of unknown origin. At the AIS Convention in Omaha this year, there was a research report presented, and the Region 21 Bulletin described the identification of the organism responsible for the scorch symptoms.
Scorch is characterized by the dieback from the tip of the center leaves of the fan and the dieback of roots beneath the rhizome, but the rhizome remains relatively normal in appearance. The outer leaves may die back in drought without being scorched, and the center leaves of the fan may die back first as a result of either borer or rhizome rot, again without being scorched. In the latter case, borer presence in the fan or rhizome or rhizome rot is usually readily visible.
A research team from the Botany Department of the University of Iowa suspected that the symptoms might be explained by the malfunction of the conducting tissue of the central part of the plant and, using electron microscopy, began examining this tissue in scorched and healthy plants. They did find that the diseased plants had phloem vessels (those that carry food) blocked by material of a kind produced by cells under stress. Further study showed that they also contained particles of an organism of a type called a mycoplasma-like organism (MLO). These organisms, which are somewhat like a bacterium without a cell wall, were only found in the phloem of plants with scorch symptoms. This type of organism is found in some other plant diseases, and generally can’t be grown outside of living plant cells or transmitting insect tissue. So far, the team has not been able to track the insect vector or compare this MLO with other known MLOs.
The fact that MLOs cause scorch suggests that both antibiotics and heat can be used to cure scorched still under study, but heat is a safe and easy way to solve the problem. The research team found that subjecting the scorched rhizomes to a temperature of 104 degrees F, for three to four days completely cured the treated rhizomes. Re-sprouted plants showed no symptoms and showed no MLOs under the microscope. This temperature and time can easily be obtained in an incubator or a food dehydrator. In fact, growing untreated scorched plants in un-air-conditioned green houses caused some of them to be cured by the heat, thereby making it harder to prove that the treatment was effective. A closed greenhouse or cold frame would probably work in a sunny week. Fortunately, the heat did not kill the irises, only the MLOs.
With the cause identified, it should now be possible to track the insect or insects that spread scorch, and perhaps find plants which serve as a source of infection to the insect. It also has been confirmed that scorch cannot be transmitted by soil, water, or direct contact between plants.
From IRID-ISM, publication of the Iris Society of Massachusetts, Volume 10, Number 2, Fall, 1990.

 

The following is taken from the AIS Bulletin #292, January, 1994, pp 36-39.

SCORCH REVISITED AND A NEW THEORY
Raymond Smith (Indiana)

For the past 43 years I have been growing TB irises and hybridizing for rebloom. Over this period there has been scorch ranging from 1 to 2 percent in both named sorts and seedlings. Ordinarily all sick plants were culled, but if special, and retained, they recovered fully in from one to three years.
The purposes of this article are (a.) to review the research articles on scorch that have appeared in AIS publications over the last forty years, (b.) list observations concerning possible causal conditions, and (c.) to suggest a theory that might serve as a working hypothesis for further research.
In April, 1954, guy Rogers of Texas wrote a classic description of scorch, "It is first manifest by the tips of leaves becoming brown. Gradually the brownness continues downward until most, if not all of the greenness of the fan is gone. The roots are withered or have entirely lost their vitality depending upon the extent of the drying up process … The rhizomes will be perfectly firm and will yield no visible symptoms of bacteria or fungi." (A.I.S. Bulletin 133, 38)
In an article on diseases of rhizomatous iris in California, J. G. Bald et. al. reported that plant pathologists had examined diseased irises submitted by Guy Rogers and had found nematodes of a kind different from those causing root-knot. "Scorched plants consistently contained the fungus Fusarium; some contained a watermold, probably a species of Pythium. (A.I.S. Bulletin 144, 79)
The accumulated knowledge concerning scorch was summarized in 1959 in Garden Irises by A. W. Dimock, a professor of plant pathology at Cornell University. In addition to many fungi such as Fusarium and Pythium he also found Rhizoctonia from roots of "scorched" plants, but he said that none of these organisms were isolated consistently or exclusively. Furthermore, he was unable to reproduce the disease by inoculating healthy plants with any fungus. He concluded his statement with the sentence, " … we know of no treatment that will eliminate or prevent scorch." (Garden Irises, L. F. Randolph, 1958, 96)
A further note on Scorch was reported by the AIS Scientific Committee in 1962. Dr. Bald had found in examining discolored areas on the rhizomes of scorched plants from California and Texas that all contained a similar organism which appeared to be a Pseudomonas. He said that this suggests a possible relationship between the organism and the disease. (A.I.S. Bulletin 164, 92)
In 1969 Dr. Bald conducted a series of experiments on lilies and irises and reported that the bacterium Pseudomonas is "the cause of scorch disease of rhizomatus iris …" He concluded that the disease usually attacks "when blooms are developing and expanding … It can destroy the root system in a short time." (A.I.S. Bulletin 195, 26)
However, an article by Julius Wadekamper in 1972 questions the Pseudomas conclusions. He first adds to the definition of scorch symptoms by noting that, "The roots of a plant that shows new symptoms of scorch in the leaves are already shriveled."
Wadekamper found at least four types of fungus in the diseased roots, but concluded that the fungi "were secondary and were present as a result of the deteriorating tissue and not a cause of the initial deterioration." He further found it impossible to transmit scorch to irises by bacterial inoculation and therefore concluded that a pseudomonas cause of scorch has not been proven and is in serious question. (A.I.S. Bulletin 204, 21)
[Injection included from Wadekamper article printed in A.I.S. Bulletin 204, 21, "Mr. James Seeden of Minneapolis noted eggs of an insect on scorched plants that he did not find on healthy plants. These were identified to be Diptera of the family Mycetophilidae and were present on scorched plants as a result of the condition of the plants and not as a cause." What if these finds are not totally substantiated? What if the massive swarms of flying ants which invaded my garden in 1999 carried the cause of Scorch Disease? The fall of 1999 has been the only year of encountering these insects, and spring of 2000 has been my first year to encounter scorch. Is this coincidence too simple?]
Six months later Wadekamper published the results of three experiments related to scorch. The first indicated that, contrary to some suggestions, ozone did not produce scorch in irises.
In the second study, seven different plants were treated with diseased iris plant sap from roots, rhizomes and leaves. A leaf from each treated iris was mascerated and then one half of each leaf was then rubbed with the diseased plant sap, the other half with distilled water. No differences were found between the halves of the experimental plants for any of the seven.
In the third experiment, root and rhizome sap from both healthy and diseased plants were compared by electron microscope to search for difference in virus particles. Again no significant differences were found. These three negative findings suggest that either the variables, that is ozone, sap from diseased plants and virus particles are all benign when applied to healthy plants, or that the experimental designs were incapable of producing detectable differences. (A.I.S. Bulletin 206, 63)
In 1978 publication of The World of Irises included a fine summary chapter of iris diseases written by John Weiler. He summarized knowledge of scorch to that year and added that although reports of the incidence of scorch is greatest in the tier of southern states, neither the cause nor the control of the condition is known. (The World of Irises, Bee Warburton, 1978, 346-7)
The next mention of scorch in the Bulletin was an article by Paul Black in which he reported a devastating incidence (up to 70%) in his own plantings. He noted the universality of the disease throughout the United States with the exceptions of Washington, Oregon, Utah and Idaho. Also it has been found throughout bearded iris classifications, as well as in the non-bearded Louisianas. In his own gardens most scorch appeared during times of rapid growth, and that it seems to occur most often in clean, well kept gardens which suggested to him that it might enter the plant through a damaged root system due to cultivating or weed pulling. As treatment, Paul began incorporating the fungicide Terrachlor Super-X into the soil and practically eliminated the disease. He found that the use of Terrachlor liquid drench worked equally well. He began regular use of Terrachlor Super-X at 9 lbs. per acre but cautions that this is three times the normal dosage and may not be proper. Also a fungicide at this dosage could be affecting any fungi or bacteria present. His treatment worked, but possible efforts on plants or soil were undetermined. (A.I.S. Bulletin 252, 32)

Conditions Conducive to Scorch

I have noted the following conditions accompanying cases of scorch in my garden.
  1. Root Damage: rototilling, hoeing
  2. Leaf Damage: virus, fungi, bacteria, and rabbits, tramping from animals.
  3. Rhizome Damage: borer, crown rot, soft rot
  4. Competition: closely grown seedlings
  5. Herbicides: soil chemical build-up
  6. Insecticides: e.g. Cygon a bit strong can initiate leaf desiccation
  7. Soil pH: either excess acidity or alkalinity
  8. Lack of trace minerals: weak plants
  9. Lack of humus: weak plants
  10. Lack of Nitrogen, Potassium, Phosphorus, Lime: poor growth
  11. Roots of trees or other ornamentals
  12. Major changes in climate
  13. Any combination of the above
  14. Weather conditions:  
    dry - augments tilling danger
    hot - augments crown rot
    wet - compacts soil, eliminates oxygen, augments water borne diseases.
Any of the above or any combination of them places the iris under stress. Light stress seems to be beneficial. Shallow cultivation appears to cause a spurt of growth. The competition of a weed trying to grow in a raspberry patch may cause it to reach twice its normal height. A clump of irises run over by a truck may recover with amazing rapidity. Scientists have known for some time that stressed plants send salicylic acid as a signal causing the plant to initiate its natural defenses – nicotinic acid, or whatever. If the assault is moderate, the plant will build a partial immunity to the injury. It has recently been shown through a study in which a bacterial gene capable of salicylic acid transformation, was placed into tobacco, that the usual immunity was not acquired. The authors concluded that the immunity is dependent either upon the accumulated salicylic acid or to protein expressed by genes activated by the acid. (Science 261, 754 (1993))
If however, the attack is severe relative to the condition of the iris, the iris will go into scorch. The hypothesis presented her is, then, that scorch is a condition rather than a disease. It can be caused by many things, any of which, singly or in combination, can cause the plant to scorch. It is stress that causes an internal reaction in the plant. It is as if the plant says to itself. "I cannot cope with this situation," and goes dormant for a time.
The fact that the plant reacts favorably to mild stress suggests that the initiating factor might be an auxin such as gibberellic acid. It wasn’t long ago that this was on the market as a week killer that acted by stimulating excessive growth.
If scorch is caused by some internal growth inhibitor, it should be possible for one of our botanists or biologists to come up with a counter measure that could save a lot of valuable irises.
In conclusion I have hypothesized that scorch is a dormant condition of a bearded iris rhizome (or a Louisiana iris) brought about by stress. In response the plant generates a growth inhibitor that kills all roots and top growth. Recovery occurs naturally and usually within a period of one year.
It may be possible to accelerate the recovery process as is done with dormant iris sees, by simply soaking in water. We need not know the name of the inhibitor to experiment with methods of amelioration. Wasn’t it the Aztec Indians who discovered that an offering to the gods by including a piece of fish in each hill of maize produced remarkable results? Growers can try such remedies as soaking rhizomes in normal solutions (or even stronger) of salt, sugar, household bleach, fungicides, germicides, alcohol, acetone, Rootone, epsom salts, calcium chloride, sulphur, or whatever. A valuable rhizome may be worth a try.

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Rabbits

This next article started out as a joke. We were discussing routine business at our annual November Thanksgiving local club meeting in Garden City. We talked about "hopping" into a couple of vehicles and driving over to Johnson, Kansas to tour a member’s garden next spring. She suggested we bring our shotguns for rabbit control !!!!!!! She no longer has her dog and is now overwhelmed with rabbits eating her iris foliage.
Sparked by the idea of chatting with others from Region 18 in the electronic Internet group and by getting advice other than shooting rabbits, I posted to the group. Responses were received by the end of my day. Here are a few of them:
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Our moderator Judy Eckhoff wrote: "… The furry little creatures are a problem for me also. They don’t seem to eat on my iris but do love fresh tulip greens and other tender plants. New shrubs were being eaten to the point I had to put a fence around them. One thing I’ve found to slow them down is to sprinkle garlic salt, hot pepper sauce, etc. around the foliage. It helps. I now have a cat and am seeing fewer rabbits."
Sherryl Fitzpatrick wrote: " … When I lived in Alabama, the rabbits would eat all my impatiens and tender plants. I noticed they never touched my neighbors and she said she sprinkled bloom meal around all newly planted plants. It really seemed to work for her."
Jim Loveland - I could not quote Jim but he added: Best way to deal with them … unless of course you live in town you could get in serious trouble shooting a gun. ….. Maybe sprinkle some nice cayenne on moistened leaves …. Then watch them spit, dance or whatever they do. Just have your digital camera handy so we can add these pictures to the web site." Jim – here is that picture!

Jon Cliburn helped by saying: "At some stores like Wal-Mart etc, or Sports shops that have hunting sections you can buy small bottles of fox urine that hunters use to disguise their human scent. Used sparingly, it will discourage the little critters, a couple of pet cats or a dog will work also, but then there is nothing better than rabbit & dumplings or fried rabbit!"
Our RVP and Secretary Ray & Judy Keisling posted: "Hi all – I will take fried RABBITS (wrabits) over turkey (buzzard) any day for my holiday meat anytime. We will take this opportunity to wish everyone a happy Thanksgiving and hope that you have all your Iris planted…. "

 

Steve and Jane Amy finished the thread saying: "We sprinkled blood mean all around one year. It’s great fertilizer also. We also had two labs and a blood hound mix. The dogs thought that blood meal was the greatest stuff. ….. I saw her (the black lab) hot on the heels of a rabbit a couple times … Have a wonderful Thanksgiving! I’m waiting for the picture of Nancy to come out with her shotgun!"
I can identify with lab (as in laboratory) and with the blood since I am a "vampire" in a hospital Laboratory. I posted back … to Steve … "you may be waiting a mighty long time … it is pheasant season in SW Kansas right now. I’m after birds right now. That sure would be a sight to see though … I’ll see what I can do in the future. Happy Thanksgiving to everyone …"
I sent everyone’s input to Joanne Snowbarger. She was elated and I received back a very nice thank you card … with Wrabbits pictured. Joanne is seriously thinking of getting another dog.
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