sigh. Southern blight

9 years ago

QUESTION: Tactics for dealing with southern blight (Athelia/Sclerotium rolfsii) found on one plant (of 2) in a 4x4 bed? Aside from removing the top couple inches of soil in the area the affected plant occupied, is there a relatively environmentally friendly drench available to home gardeners? Will a bleach drench and/or boiling water drench do anything? I don't have much garden space, so the idea of doing without that bed for a few years (I have no desire to grow corn or grains) is a bit disconcerting.

BACKGROUND, SHORT VERSION: pulled a plant that was in bad shape and found mycelium girdling at crown and confirmed one small cluster of mustard-seed-like sclerotia clinging to plant just under the soil line. Plant is 1 of 2 tomatoes in a new 4x4 bed, soil is fairly clayey with below-average tilth even though amended with compost. Mycelium was visible on plant crown only, not on soil surface. The plant next to it was still going strong, but I pulled it.

DETAILED VERSION: Well, this is interesting. We recently went through a period of a week of rain and cool temps (60s during days, 50s/high 40s during nights), and some of my tomato plants, some of which already had some early blight, were unsurprisingly looking very sad afterward. So I went out there yesterday to pull the cruddy ones and noticed that my Black Beauty tomato plant was basically almost completely dead. I figured it was a combination of root distress from wet feet and the EB. I cut it off the trellis, then pulled the stump and found the crown was girdled by some kind of white mycelium.

I at first thought it was just some unidentifiable fungus taking advantage of the cold, wet conditions and plant matter made susceptible by the EB, so I bagged it with the rest of the plant debris and kept about my business.

Last night, I had a nagging suspicion that I should look into it more, so I researched tomato diseases involving white mycelium and realized it could be timber rot (Sclerotinia sclerotiorum) or southern blight (Athelia rolfsii).

This morning, I opened up the bag and pulled out the stump and saw a cluster of about half a dozen mustard-seed-like sclerotia just below the soil line.

The Big Beef plant next to the affected plant was still going strong but, since we're at the point where fruit ripens very slowly, I pulled it to deny any existing fungi a new host.

So I'm wondering what strategies I have at my disposal. This is a disease I have no experience with, and it's a bit of a surprise, actually. Not one of the baddies I expected to be dealing with in my garden.

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Comments (4)

gorbelly
Original Author
9 years ago
FYI for those also dealing with this problem: I did some research, and it turns out that many tomato rootstocks (Maxifort, Estamino, etc.) are highly resistant to southern blight. So maybe next year I'll try my hand at grafting.
PcolaGrower
8 years ago
Hey Gorbelly - So I'm pretty sure I just experienced my first encounter with southern blight. It started with one plant and has since moved to a couple around it. I was seeing what you did to deal with it. I have pulled the affected plants and have trashed the first couple inches of soil around it. I'm thinking it was made worse sue to some cutwoem damage at the base of the stem and also because I had some wood mulch fairly close to the stem. All my other plants seem to be okay at the moment. If you have any suggestions, let me know.

Thanks,

Kevin

The first victim

White fungus at the stem base

This is actually a piece of mulch that was right up against the stem (mustard seed looking stuff)

Second victim

Stem base, no seeds though
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gorbelly
Original Author
8 years ago
Yep. That's southern blight. Do NOT till the bed until you have removed the soil from around the area and thrown it away. Replace with fresh soil. Make sure to disinfect all tools used in a way that prevents potential spread of the organism.

I worked in a lot of organic matter this spring and drenched with B. amyloliquifaciens and B. subtilis and use a lot of coffee grounds (which supposedly are a food source that various Trichodermas like) in the bed where I had it last year. So far, so good.

Luckily for me, and, it seems, for you, southern blight doesn't strike until very late, but the down side of that is that I won't know for sure that my efforts have been successful until the end of the season. If they're not, I will try grafting with Maxifort next year.

One thing that my efforts seems to have helped is that the bed where I had bacterial wilt problems last year doesn't seem to have those problems this year. Of course, it could also be that what I'm growing there is a variety less prone to the disease. But that's encouraging for me, as it's very hard to find a rootstock that resists both bacterial wilt and southern blight.
dirtmechanic
8 years ago
My current working hypothesis is that the theory of abundant organic matter being a great idea has to be balanced against the rate at which fungal elements are supported by the atmosphere in that region. I was caught in a feed the soil loop once. The sheer number of pathogenic particles overwhelmed me. Most fungi and virus need more than a few particles to take hold of a host. Perhaps its worth your consideration to have more dirt in your soil.