Not another year of no tomatoes!
May 18, 2010 7:54 AM   Subscribe

[Tomato Help] Baby tomato plants are turning bronze or yellow on the leaves. What is it? Pest or disease? Visual here.

All grown organically in potting soil mixed with sterilized manure. They are kept in a solar greenhouse on cold nights (less than 45 Fahrenheit) and are placed outdoors when the temperature rises above 50 Fahrenheit.

The markings on leaves developed over the weekend.
posted by Etta Hollis to Home & Garden (9 answers total) 2 users marked this as a favorite
Best answer: Possibly overwatering. I have seen the same with mine in the past and it was after I had let them get too dry and then given them a good soaking. Try to keep the soil evenly moist, and try not to get water on the leaves.
posted by priorpark17 at 8:10 AM on May 18, 2010 [1 favorite]

over- or under-watering could be the culprit

but it could also be a nutrient deficiency, possibly magnesium or potassium
posted by jammy at 8:27 AM on May 18, 2010

Pests can be seen. I don't think it's a deficiency, though they can be induced by overwatering, in the case of nitrogen. I think this may be early blight, which shows up when soils are cold and water is allowed to sit on the leaves for several hours.

45 degrees fahrenheit is way too cold for tomatoes. 50 is the minimum that they tolerate without succumbing to disease, but they won't even produce unless nights are over 55 degrees. I would start more seedlings- started now and kept warm, they will probably eclipse these plants in a month.
posted by oneirodynia at 8:52 AM on May 18, 2010

Response by poster: Oneirodynia- I'm in the North East where 45 is fine for our tomatoes. They are a variety that is used to the colder spring weather. And since we aren't out of the frost/freezing period yet we keep them indoors at night where it's well above 55.

It doesn't look like early blight because the stems aren't affected and there are no dark parches really. We had late blight wipe out everything last year, so we're diligent about keeping watch for it.
posted by Etta Hollis at 9:06 AM on May 18, 2010

That looks like sun scald to me.
posted by mneekadon at 9:06 AM on May 18, 2010

Yeah, sun bleaching. Was it a clear, sunny day?
posted by bonehead at 9:38 AM on May 18, 2010

Sorry, meant to say verticillium, not blight. You'll know it's that if the leaves droop in the next couple of days. They may not ever turn black anywhere, it depends on the type of verticillium infection. If not, and no other symptoms show up, probably a deficiency as jammy says.

I'm in the North East where 45 is fine for our tomatoes. They are a variety that is used to the colder spring weather.

What variety is that? You can look up what diseases it's bred to be resistant to if you have a name. That would rule out a lot of guessing from a photograph.

That looks like sun scald to me.

It does, but the leaves are deformed as well as being yellow. That seems more like disease or deficiency. If no other symptoms show up, and the color never changes, then sunscald is likely.

Deficiencies in young plants can often correct themselves. However one of the deficiencies that jammy pointed out, phosphorus, is prevalent in young tomatoes at temperatures below 55 degrees because plants cannot take up that nutrient at those temperatures. The deficiency goes away when temperatures warm up. Nitrogen deficiency also shows up in older leaves, while the newest stay green (nitrogen is mobile in plants). Like I said above, this can be induced by overwatering, and is much more common when temperatures are below 50 degrees, and nitrifying bacteria are much less active.

Even in tomatoes bred for cold weather areas (and other plants that have high phosphorus and nitrogen requirements), these deficiencies exacerbated by cold soil can still be a problem.
posted by oneirodynia at 8:32 AM on May 19, 2010

Response by poster: Thanks everyone. We're pretty sure they weren't watered on a regular basis over the weekend. They're now perky and looking much better.
posted by Etta Hollis at 5:11 AM on June 4, 2010

Glad to hear that you've healed your plants, Etta! We were having some similar tomato issues, and after reading this thread, we also found this page from Colorado State University, all about tomato problems and figured we'd share it with our fellow gardening MeFites.
posted by hatta at 3:04 PM on July 21, 2010

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