Frenching

Rather than steamy backseat interludes, frenching describes the way leaves can become discolored or distorted.

Frenching of tobacco (R.J. Reynolds Tobacco Company, Bugwood.org) CC BY 3.0 US

Frenching most commonly occurs in cotton and tobacco, but it may also be seen in citrus, sorrel, squash, and tomatoes. Peppers seem to be exempt from this condition, but no one knows why.


​Is frenching a disease?

Well, yes, and no, and maybe. Since frenching is not entirely understood by botanists, its causes are currently referred to as “frenching factors”. These factors include predominantly fungal diseases, insufficient iron, poor drainage, alkaline soils, and temperatures above 95°F. [It sounds like I just described my yard!]


In some cases, frenching is caused by specific bacteria commonly found in the soil (Bacillus cereus, Macrophomina phaseolina), the latter being one cause of damping-off disease. Frenching is also more likely when plants are grown in soil that stays moist during a drought. [I guess this means I should back off on watering my heavy clay soil quite so much in summer…]


How to identify frenching

While there are many ways that leaves can turn the wrong color or take on an abnormal shape, frenching has some consistent characteristics:

• short internodes
• leaf thickening
• vein darkening
• chlorosis along leaf margins
• loss of apical dominance*
• downward curling
• rosette, or witches’-broom growth
• slowed overall growth

*Apical dominance refers to some plants’ natural tendency to have one main shoot that actively inhibits the growth of other shoots.

Frenching seen in tobacco leaf with dark veins and chlorotic margins (R.J. Reynolds Tobacco Company, Bugwood.org) CC BY 3.0 US

These symptoms can be mistaken for aster yellows at first, but roots are not affected. This condition, regardless of its cause, starts out as tiny pinheads of chlorosis. New leaves are narrower than normal with wavy edges. As these leaves grow, only the midrib gets longer, pulling the leaves into strap-like shapes that end up looking more like stiff strings than leaves.


Scientists have found that autoclaving soil eliminates the frenching effect, but I’ll bet none of us have that option. There isn’t much we can do about the weather, either, but there are things we can do that will reduce the chance of frenching in our home gardens. Those actions include improving drainage, monitoring and maintaining a good soil pH, and feeding and irrigating plants regularly should do the trick.


Have you seen frenching in your garden? Which plants were affected?