Gall in dahlias

Cosey · 2023-11-10T00:46:21+00:00

Do not panic....I recently read a study that tested a small selection of imported dahlia tubers (fresh new growth) for viruses. All of them had a virus of so...

blown_dry

Cosey I like to think people are cautious rather than panicking. Gall is different from virus and it makes sense to keep it out of the operation as much as possible. I found a good page here at Oregon State University: https://bpp.oregonstate.edu/crown-gall-and-leafy-gall
I am working my way through an article summarizing what is known about leafy gall (caused by R. fascians).

Increased demand for herbaceous perennials has driven changes toward high volume production methods using growth hormones to stimulate offshoots for vegetative propagation. The leafy galls and
shoot proliferations caused by R. fascians
can be confused with the denser growth
obtained with use of plant hormones.
Growers who do not recognize that their
plants are diseased risk propagating the
bacterium along with their cuttings. The
situation is complicated by the ability of
the bacterium to persist on plant surfaces
for many months prior to the production of
symptoms (52).
R. fascians offers considerable challenges to the commercial grower. The
pathogen may be present as long as 6
months before symptoms are apparent
(18,52,103), or symptoms may be relatively mild, misleading propagators into
thinking they are working with healthy
material. There is relatively little known
regarding its epidemiology, nor have any
modern control compounds been tested
against the bacterium.

SteveM

blown_dry I found a good page here at Oregon State University: https://bpp.oregonstate.edu/crown-gall-and-leafy-gall
I am working my way through an article summarizing what is known about leafy gall (caused by R. fascians).

Thanks, some good winter reading!

Teddahlia

I read through the OSU papers over a year ago. After time goes by, you generally only remember the main conclusions and some random tidbits. One of the tidbits is that the researchers had a tough time getting the bacteria to infect plants. They need to do this so they can explain how it is spread. The lady researcher named Melody Putnam (I understand she is now retired) believes the bacteria lives on the surface of the plant for quite a long time(months) before it infects the plant . She theorized it went through "stages of growth" and one was growing on the surface of the plant. That would make sense as the bacteria needs to have the plant produce "sprouting hormones" and supposedly it does so by altering the genes of the plant to produce the hormone. Another tidbit was that the bacteria does not reside all though the plant but just on the surface layers. Avoid introducing leafy gall to your garden and one way is to not grow new plant material in the garden, but grow it in pots or a separate garden.

Krista

Wondering if anyone’s ever tried using a heat gun to sterilize soil used in potted plants that have expressed symptoms of gall?

DarcyD

Krista To save potted soil? I’d toss. Why risk Gall over something easily replaceable? Maybe I’m missing something 😊

Krista

DarcyD Yes, I’m not a risk-taker when it comes to gall, and you’re not wrong. I’m not mulling over this because I’m in a predicament, I’m just curious!

We live on a 2K sqft lot and pay for (and haul in) all the soil for our garden spaces/pots. Throwing away a pot of soil would mean needing to purchase replacement soil, and the volume of waste would take up lots of our garbage bin for the week that the city provides curb pick up for. Not the end of the world, you’re right!

But my partner is in the process of demo’ing our laundry room right now and needed a heat gun to rip up the old vinyl flooring (I’m cheering for this!). And when I heard about how hot it can heat, it just made me wonder?

Teddahlia

Leafy gall in the soil is an unknown issue. We know it spreads in water when water is allowed to go from an infected plant to another plant. That is the main way it is transmitted. There can be a long latency period(months) while the newly infected plants exhibit no symptoms and this is an issue. Removal of the infected plant any not be enough and the plants next to it may need to be quarantined or destroyed.

Krista

Teddahlia Ah I recall information (maybe from you ☺️) that implied soil without a host wouldn’t retain gall for long. I believe I read a study about gall contamination on tools and that very little time needs to pass before gall was no longer detectable; the dramatic drops happened within hours and days I believe.

I’m overthinking, but I’m wondering about those little hair roots left behind in the soil, or a half a chopped-tuber. Would that be enough host-plant matter to keep gall lurking around for the following year? I’ve heard people mention baking soil in an oven but I’m afraid I am never going to do that.

Bessie

Krista a few days ago I researched soil sterilization, again😳, just to make sure I remember correctly. I decided to sterilize a small batch of soil in the microwave. Thirty minutes at temps 180 degrees or greater. I don't have a gas BBQ, but if I did, I'd use it to sterilize soil, set to 200 degree, for 30 minutes. Aluminum baking pans would be my vessel of choice, covering the pans filled with moist soil with aluminum foil.

NCDahlia

Ah so yea I have used a propane weed torch but for dahlias I burned out a row once 50 feet long x 2ft wide. Left it for a year, then replanted the following and those dahlias was fine (I threw away all the dahlias the prior year when soil was burned). I am unsure of if it was the flame (500k BTU) or just sitting for a year.

I keep bees so I originally got to burn out the inside of "dead outs" bees that died in the winter. For bees when one burns / chars the inside of the boxes it kills all the virus / mites. I would assume perhaps the same works for dahlia / soil - but I only did it one time.

Probably is excessive because it hooks up to a standard propane tank as well. I use for my sidewalk cracks, I do not like using roundup anywhere near dahlias.

https://www.homedepot.com/p/Flame-King-500-000-BTU-Propane-Torch-Kit-Heavy-Duty-Weed-Burner-YSN500K/317903288

Krista

NCDahlia Thanks for your link to your flame torch, wow awesome!

Were you were using the torch because of a gall concern? With it, how deep below the soil surface do you think temperatures get high enough to eradicate the risk of gall? I was sort of imagining a sift n’ torch method which wouldn’t be very sustainable for a 50’ bed of course.

Someday I’d love to have enough space for bee hives — it’s very cool to hear you’re a bee keeper! Even without them, I’m with you on using chemicals that aren’t bee/pollinator friendly. ❤️

Krista

Cool Bessie, I love how you’re always down for an experiment! How did it go for you? Do you have a way to test whether the microwave method was successful? We unfortunately do not own a microwave or a gas grill.

Bessie

Krista I measure the internal temperature of the soil. Then hold that temperature for the time needed. I'm 100% confident that organisms (fungus, bacteria, pest eggs) will not survive 30 minutes in steam.

Krista

Bessie Ohhh yes, of course. Thank you for holding my not-science brain's hand!