Whole Leaf Tobacco

Sunscald??

deluxestogie

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It could possibly be sun scald. I've found that it can occur if a puddle of water remains on top of the lamina in bright sunlight. Just watering plants in the sunlight does not appear to do that.

Bob
 

skychaser

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Looks like sun scald to me too. It often happens on newly transplanted seedlings that weren't hardened off. I don't know why it sometimes occurs on plants that are well established. Puddling water on a leaf in very hot sunny weather can do it, but I've seen it happen with no water involved. I've seen half a leaf scald on one side of the mid rib while the other half looks perfect. It's usually not to serious or wide spread, so I wouldn't worry too much.
 

deluxestogie

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Skychaser grows a whole lot more tobacco each year than I do. His specific goal of seed production (including government phytosanitary inspection) also means that he observes individual plants more closely than a typical tobacco farmer. So his anecdotal experience is valuable.

The term, "sun scald", already assumes a cause, even though the actual cause of what we call sun scald is unclear to me. This year, with some truly scorching heat (for SW Virginia), I've been forced to water my tobacco at times other than my preferred early morning or just before dusk. So I decided to go whole hog. I have been showering my entire tobacco plants from the top, in the noon-day sun when necessary. From having regularly engaged in this generally discouraged approach to watering, I must conclude that just drenching the leaf beneath a hot sun has no relationship to sun scald.

I did observe that occasional mud lugs that lay flat on the soil, and over which somewhat muddy water pooled, showed sun scald. That could have been from lensing of sunlight by the standing water, or might just as likely be the resulting, ideal bacterial soup resting against a drowned leaf that was unable to breath, with its stomata pressed against the wet soil.

A more specific description of what Jim's photo in the first post illustrates is patchy necrosis (death) of laminar cells. Bacterial and fungal growth usually radiates from one central focus. As it spreads, roughly circular or oval areas are affected. Sometimes it follows the rectangular area demarcated by two bounding, secondary veins.

"Achlorosis" is loss of chlorophyll from otherwise healthy cells. But necrosis is dead tissue through and through. After curing, achlorosis often is no longer identifiable, whereas necrotic lamina will simply leave a hole.

There are all sorts of other causes of patchy leaf necrosis. The pattern of the injury in space and time is key to diagnosing these. I can't tell you how many times I've scanned through, from start to finish, all the tobacco disease photos from IPM Images: https://www.ipmimages.org/browse/AreaSubs.cfm?area=62

Bob
 

Jim232118

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Thanks for the replies, very informative and beneficial as always. The past week has been 105 - 109 degrees with no rain. I’ve been watering at dusk to try and help as much water absorb as possible. Is there anything I should do?
 

CT Tobaccoman

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Is this sunscald or could it be something else?
Sorry, so late to reply. In 15+ years growing tobacco in Connecticut, I have never heard of sun scalding happening on a growing plant. Sun scalding only occurs after plants are cut or leaves are picked, and left in the direct sun too long, A living tobacco plant loves the sun, and a little rain water on the leaf will never cause sun scalding.
 
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