THIS IS THE WAY - to kill tomato blight fungus
June 11, 2021 7:08 AM   Subscribe

I have early tomato blight. It struck fast and took down both cherry tomatoes. I know it's early blight - that same bed was affected late last year. It's starting to affect my big healthy tomato plants in another bed. I need the DEFINITIVE way to solve this problem before all my tomatoes die.

I've posted in both local gardening groups with very little help. One person says neem oil? I'm ok with pulling out the big guns (as long as they are non-toxic). I don't want to waste time with 'cute' solutions that won't work. And time is of the essence. I need this, like, yesterday.

Yes, I realize I need to amend the soil in the future. I just don't have time for that this year.
posted by kitcat to Grab Bag (13 answers total) 1 user marked this as a favorite
Neem oil isn't going to help -- it can protect your plants against insects but blight is a fungus. What you want is a fungicide.

Here is a page from UMN ag extension. There is a list of fungicides at the bottom that you can try. Some of these are expensive and/or hard to come by in garden-sized quantities.

The other thing you can do is make sure that you protect your uninfected plants from infection, cleaning off tools etc., but if it's crossed to the other bed it's probably too late for that to work very well.
posted by goingonit at 7:31 AM on June 11

Oh sorry I missed the non-toxic requirement...

Apparently oil can be fungicidal as well?
I thought it was just for insects -- TIL! As this page says, what you want is "clarified hydrophobic extract of neem oil" if you're getting neem oil, but other horticultural oils should work equally well because the active ingredient of neem oil shows no fungicidal activity.

You have to spray the not-yet-infected plants as oils are ineffective against ongoing infections, they just stop new spores from germinating.

There are some other good things on the "cultural practices" section of the UMN page, and particularly you may want to prune some of the lower leaves and stems from your healthy tomato plants to minimize soil contact, and avoid overwatering.

Also...baking soda might work?
posted by goingonit at 7:37 AM on June 11

Response by poster: I need it to be non-toxic in both senses of 1) Doesn't harm the ecosystem and 2) Is safe while young kids and pets are around. I really do need both one thing that kills existing fungus and one that prevents further spread I guess.
posted by kitcat at 7:42 AM on June 11

Yeah I wouldn't apply any of the commercial fungicides on things that a child/pet might accidentally eat. I don't know if you can fence off the already-afflicted tomatoes with chicken wire or something, and then be more aggressive on them, while trying oil or baking soda on the other ones?
posted by goingonit at 7:46 AM on June 11

The Extension Service link mentioned copper as a fungicide, so maybe this article on organic treatment of tomato blight is useful. If this happened last year too, it's probably in the soil and you'll need to rotate out tomatoes next year and the year after or replace the soil.
posted by fiercekitten at 7:59 AM on June 11 [1 favorite]

We've solved it in our garden by rotating tomato locations. Over 5 or so years the blight seems to abate from the soil. As for this year, we never solved it without rotating crops. Super GL!
posted by sydnius at 8:00 AM on June 11 [1 favorite]

Be aware that copper fungicides are still toxic to mammals including kids and pets!!
posted by goingonit at 8:10 AM on June 11 [2 favorites]

At our community garden, we recommend that growers choose a blight resistant variety of tomato, like on this list, so that gardeners don't spread the disease to each other.
posted by xo at 8:47 AM on June 11

Response by poster: Update: I bought a copper fungicide. I'm not sure I'll use it. I haven't figured out yet HOW toxic it is, like, would you have to actually eat a leaf of the plant to be affected? Or is it like, brush up against the plant and you're in peril?
posted by kitcat at 11:24 AM on June 11

Odd as it may seem, I have sprayed skim milk on plants showing signs of fungal infection and it has helped. I heard of this from somewhere a long time ago and I don't know if it's verified, but it is a no-harm thing for most critters and supposedly makes it hard for fungal stuff to survive.
posted by mightshould at 11:54 AM on June 11 [1 favorite]

Also, blight can be stored in the soil, so don’t plant your tomatoes in the same bed next year.
posted by dbmcd at 11:56 AM on June 11 [1 favorite]

Here is an MSDS for a fungicide concentrate that's 10% copper octanoate. It may cause minor skin and eye irritation, and if you eat more than 2000 mg/kg of it you could be in trouble (so that's like an ounce and a half for a 50lb child). And this is the concentrate, so you'd be diluting it 20-30x. Long story short I wouldn't be too worried.
posted by goingonit at 11:56 AM on June 11 [2 favorites]

Also, while tomato leaves are not particularly toxic as toxic plants go, they can still make you ill, so if you have plant-nibbling pets or children, you should probably take steps to keep them away from the tomatoes as a general rule….
posted by GenjiandProust at 1:18 PM on June 11 [3 favorites]

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