Frenching - a general discussion

[deluxestogie]

Frenching. Clemson Univ.

Frenching (nonpathogenic causal agent)
This disorder has been associated with toxins produced by a
nonpathogenic bacterium, Bacillus cereus, and other
nonpathogenic microorganisms. Frenching is more
prevalent on wet, poorly aerated soils. This problem can be
more severe on neutral or alkaline soils and is sometimes
associated with lack of available nitrogen or other minerals.
Proper drainage and fertilization can be beneficial. Do not
plant in alkaline soils and avoid heavy applications of lime.

http://www.arec.vaes.vt.edu/content/dam/arec_vaes_vt_edu/southern-piedmont/Documents/04-Discon17.pdf

If you see top leaves that are ripply or curly-cue, then the tobacco plant is exhibiting signs of Frenching. If you search for information on the subject, most of what you will find is a discussion about a specific bacterium, and vague suggestions about remedies.

Commercial tobacco growers don't plant tobacco close to shade trees, so the impact of underlying tree roots is not discussed in the literature of any extension services that I've explored. Home growers, by contrast, sometimes must (or choose to) plant near or beneath a tree canopy.

In my own tobacco growing, I have seen Frenching on several occasions. One was apparently related to my having applied ag lime (dolomitic lime) in excess. All the other times were confined to plants that grew in the neighborhood of a tree (a giant maple, or even a young, dwarf fruit tree).

Excessive shade causes general stunting. More moderate shade may, of itself, lead to taller (lankier) plants with larger, thinner leaves--as is done with shade cloth (~40% shade) for commercial wrapper production. This tree shade only works if the shade is from tall trees that are far enough from the tobacco that their root zone is not intruding into the soil beneath the tobacco. So a line of taller trees well away to the south of the tobacco, but close enough or tall enough to shade the tobacco for less than a third of the day, may allow for "shade-grown" leaf.

My guess on the effect of tree root intrusion on tobacco is twofold:

1. Tree roots reduce the soil water content, and may lower the standing water table. So tobacco grown in such a circumstance may require additional watering, when compared to tobacco growing in nearby, open areas.
2. Tree roots extract various minerals (in addition to N-P-K) from the soil. The nature of this varies, no doubt, from one tree species to the next.

The signs of Frenching are signs of malnutrition that results from failure to absorb adequate levels of certain minerals. Mineral absorption from tobacco roots requires a suitable pH. This pH varies for each mineral, and also depends on the soil concentration of that mineral. So, a pH that is either too high or too low for the given concentration of a particular mineral will result in deficiency. Depending on the class of tobacco, a reasonable pH range for tobacco growing is 5.2 to 6.2.

Bacillus cereus is a common soil bacterium. Its mere presence does not cause Frenching. A pH above about 6.2 enhances its growth. It does produce a toxin that can inhibit mineral absorption by tobacco roots, but this seems to be meaningful only when the pH is high (6.2 to 6.5 or above). Excess application of lime to the soil is a frequent trigger for overgrowth of B. cereus and Frenching.

Similar signs of Frenching seems to occur when tree roots "steal" the required minerals. It may be (I have not verified this) that Frenching from tree root intrusion may be prevented by simply increasing the fertilizer application.

Soil testing (often done for only a modest cost) by a local agricultural extension service can inform a home tobacco grower about adjusting soil pH, as well as fertilizer requirements. A discussion from the Univ of Georgia is here: http://caes2.caes.uga.edu/commodities/fieldcrops/tobacco/guide/documents2013/5Fertilization2013.pdf

Other threads on Frenching:
http://fairtradetobacco.com/threads/2929-Frenching
http://fairtradetobacco.com/threads/1067-Is-This-Tobacco-Frenching

From my 2013 grow log:
7/18/2013
Frenching

Here is a single plant, within a bed of 16 plants, that demonstrates the metabolic abnormality commonly termed "frenching." Notice that the lower leaves of the plant appear normal, while the top leaves exhibit symptoms of frenching.

The subject of frenching, along with some lovely photos, was recently discussed in another thread. The best I can figure out, from available publications, is that the symptoms of frenching result from a single metabolic abnormality that can be triggered by a number of different causes. But the most common cause seems to be from the overgrowth of a bacterium (Bacillus cereus) in soil that presents favorable conditions for its growth (poor drainage, high pH [low acidity]), and is the result of a waste product produced by that bacterium.

...a definite rise in soil numbers of [Bacillus] cereus accompanied frenching.

Although frenching occurred over the full range of pH suitable for the plant, it was more infrequent [i.e. less frequent] at high acidities (pH 4.6-5.2). The severity of the symptoms tended to be greater at low soil acidity....

[Sodium nitrate] prevented appearance of symptoms in the plant temporarily.

http://link.springer.com/article/10.1007/BF01666124#page-2

Causal agent: metabolite of Bacillus cereus

http://www2.ca.uky.edu/agcollege/plantpathology/ext_files/DiagnosticImagesTobacco.htm#Frenching

Frenching is more common in poorly drained and high pH soils.

http://www.uky.edu/Ag/Tobacco/Pages/Frenching1.html

What I find unique is that only a single plant displays symptoms of frenching.

8/10/2013
And in a tale of redemption, now that the VA Bright bed has recovered from the monsoons, the leaf above the frenching leaves are looking normal.

Bob

 

[SmokesAhoy]

First one maybe Frenched? Second one is what it should look like.



This was planted into sod. No tree roots but possible stress from the sod roots that while they'd been burned down with roundup still hadn't rotted away yet by the time it was transplanted.

 

[deluxestogie]

Or it could be residual effect from the roundup.

Bob

 

[SmokesAhoy]

Could be a lot of things. Probably not evil Monsanto though.

 

[deluxestogie]

https://www.ipmimages.org/browse/subthumb.cfm?sub=777&area=62

Bob

 

[SmokesAhoy]

So frenching could be a blanket term for a plant under stress of unknown origin? Because I've seen it before in other beds in other years under different growing conditions.

 

[deluxestogie]

Frenching is a sign, rather than a specific disease. It is usually a sign of a generalized malnutrition that results from the roots' inability to absorb nutrients that are present in the soil--because of pH abnormalities or toxic exposure from the waste products of an overgrowth of Bacillus cereus. It compromises linear growth. So, untopped plants can show rosettes of new leaves at the top, with little or no spacing between them on the stalk. Also, linear growth that is slower than growth of the lamina results in the characteristic wavy leaves. The causal conditions may be only temporary during a single growing season.

If you can identify a different, specific causative agent for these signs, then it is best labeled as a disorder caused by that specific agent. Since sub-lethal exposure to herbicides has an effect that differs by the dose and by the specific product, that is probably a better description (i.e. herbicide toxicity) than simply using the visible sign, "Frenching." This is despite the fact that many herbicides function by directly causing malnutrition in the plant. (Some of them directly nuke the function of mitochondria within plant cells. Others cause root uptake functions to fail.)

BUT...severe stress can lead to the visible sign, Frenching, as evidenced by the Frenching I'm seeing in proximity to trees. If I were thorough, I would collect multiple soil samples at a range of distances from the suspect trees, and have them analysed. That would allow a more objective discussion.

Bob

 

[DistillingJim]

The last week has been horrible here. Little sun and excessive rain. I've noticed some definite Frenching on quite a few of my plants. Hoping that if the sun reappears it may remedy somewhat or that it at least wont effect smokeability.

 

[bdm56]

Is there any noticeable difference in smoking tobacco derived from a plant with this condition ?

 

[deluxestogie]

Severely affected leaves are so shriveled and puny that they aren't worth harvesting. I can't recall ever having cured the leaf. Leaf that is in any way damaged does not cure as consistently or as nicely, although most of it can be salvaged for some use, and kilned. Is there any noticeable difference in smoking? Probably, yes.

Bob