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 may also occur in citrus, sorrel, squash, and tomatoes. Peppers seem exempt from this condition, but no one knows why.
 
Is frenching a disease?

Well, yes, and no, and maybe. Since botanists do not entirely understand frenching, its causes are currently called frenching factors. These factors include fungal diseases, insufficient iron, poor drainage, alkaline soils, and temperatures above 95°F. Frenching is also more likely when plants are grown in soil that stays moist during drought conditions.

In some cases, specific bacteria commonly found in the soil, such as Bacillus cereus and Macrophomina phaseolina, the latter being one cause of damping off disease, cause frenching.

How to identify frenching

Leaves can turn the wrong color or take on an abnormal shape for many reasons, but frenching has some consistent characteristics:

• Short internodes
• Leaf thickening
• Vein darkening
• Chlorosis along leaf margins
• Downward curling
• Rosette, or witches’ broom growth
• Slowed overall growth
• Loss of apical dominance*

*Apical dominance refers to some plants’ natural tendency to have one main shoot that actively inhibits the growth of others (think Christmas tree).

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, except the roots are not involved. Frenching, regardless of its cause, starts as tiny pinheads of chlorosis. New leaves are narrower with wavy edges. As these leaves grow, only the midrib gets longer, pulling the leaves into strap-like shapes that look 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 proper soil pH, and feeding and irrigating plants on a regular schedule.