Post-Season Questions FAQ: Why does this newly dug clump have so many shoots coming up? Is it healthy?
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|The cluster of shoots in one area is typical of Leafy Gall Disease, caused by the bacterium Rhodococcus fascians. The plant will not die but it will produce many thin stems.
Once a plant is infected, there is no cure and the tubers must be discarded to prevent spread of disease. According to research from Oregon State Univ, the bacteria can't survive long in soil without plant matter, but CAN be transmitted via tools to other plants. So sterilize your digging tool after finding one of these clumps to avoid spreading it. The soil will be fine for next year's plants.
(Commentary and control measures below adopted from http://www.science.oregonstate.edu/bpp/Plant_Clinic/IS IT CR...)
There have been field observations which imply that populations of R. fascians may persist for one or two years in soil in which diseased plants have been growing. R. fascians will also love in water, although this is a passive process as these bacteria have no ability to move on their own. On infected plants, bacteria are primarily limited to the surfaces of the leaves, petioles and stems, although some underlying cells may become infected. There is no evidence that R. fascians can systemically infect plants. The disease is primarily spread by taking cuttings from infected plants, and it is difficult to know if the plants you have are clean, because the bacteria can be present on plants for months before symptoms develop. Plants affected by R. fascians often grow with less vigor, have an abnormally short stature, may produce fewer flowers, and may have less root growth, although this varies with the plant species.
Control measures for the crown gall (Agrobacterium) and leafy gall (Rhodococcus fascians) bacteria:
1. Make every effort to start with clean plants. Do not take cuttings from symptomatic plants or plants in close proximity to diseased plants. Agrobacterium infection can be systemic in some plants, and plants can also harbor R. fascians without showing symptoms.There are also varietal differences in susceptibility to both bacteria; use indexed tissue culture derived plants for those cultivars that appear particularly susceptible.
2. Start with clean planting trays, preferably new. Used ones must be washed free of all organic debris before treating with a disinfectant such as Greenshield, household bleach, or Physan 20.
3. Potting mix or field soil should be pasteurized (60 minutes at 160 F aerated steam) before use.
4. Knives or razor blades should be changed or sterilized between plants during propagation.
5. Keep plants off the greenhouse floor and solid surfaces. Runoff water can disperse the bacteria.
6. Immediately remove and destroy any diseased plants plus any neighboring plants or trays.
Plants can be infected with R. fascians for up to several weeks prior to symptom development, so even though the plants may look healthy, they could be infected. It’s best to toss them out. Clean up and discard all old leaves and other plant debris. Soil can harbor both Agrobacterium and R.fascians.
Bacteria need water for movement, infection, and multiplication. Minimize the length of time leaves are wet; apply irrigation under conditions where leaves can dry in 1-2 hours. Good ventilation will help.
|Interesting! I came across a tuber that looked like this earlier this week...sure wish I could remember which. Think I pitched it.
Dahlias -- the gift that keeps on giving!
|I threw away one like this last year , misdiagnosed it as Crown Gall though it was not quite as far along as the photo here .|
|Here's another take on this, quoted from a dahlia grower that was on the ADS scientific board:
"Fasciation has many causes....bacterial, hormonal, viral, and environmental like cold, Fungi, mites, insect damage, chemicals, and genetic mutation. ...Interestingly fasciation is not contagious but if a bacteria was the causal agent then that can possibly infect other plant's thru contact....and there is no enzyme involved here.....And it is never to be confused with Crown Gall."
So according to this grower, Leafy Gall (bacteria) is only one of the reasons for the mess of multiple shoots.
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