What you see: Brown lines on your wax beans (or green beans or other snap beans/string beans).
What it is: Pod flecking or russeting, which can have various causes.
Eat or toss: These should still be fine to eat.
Green beans and wax beans (and all of the the beans collectively known as “snap beans” or “string beans”) can develop a brown pattern on their surface for a number of reasons. Storing them in a too-cold environment, for example, can trigger unsightly brown patches, which are totally fine to eat. Scientists call this “russeting” and sometimes refer to such a pattern as “flecking” (though flecking can also refer to spots that are part of the bean’s genetically programmed coloration).
In the case of the pod flecking or russeting pictured here, however, Jim Myers, a professor in the horticulture department at Oregon State University, said it appears that these wax beans bear battle scars from holding off a microscopic pathogen. Basically, he said, they detected an intruder and then killed off some cells, which created a defensive wall. Scientists call this a hypersensitive response or programmed cell death response.
“When the cells die, the pathogen is usually stopped in its tracks,” he wrote in an email. So the pathogen never took hold. “These beans are probably not fighting off an ongoing infection – it was a prior infection.”
(Other plants use similar tricks. See it in potatoes here.)
For us human observers, the defensive fences of dead cells look like brown dots and lines. While the damage left by cold temperatures is similar (a too-cold environment causes some cells to die and turn brown), Myers said that beans with “chilling injury” tend to have larger and more amorphous brown lesions. In the case pictured here, Myers said the plant pathogen would have been so effectively stopped that it’s unlikely to have left anything problematic behind. The brown color is from the bean itself.
Some plant pathogens are more likely to make their way to beans like these during a wet growing season. Spores often ride in on gusts of wind. They also tend to lie in wait in soil. Maybe a raindrop’s splash in a puddle sent a contaminated droplet onto the beans.
SOURCES:
- Jim Myers. Professor, Vegetable Breeding and Genetics. Oregon State University. College of Agricultural Sciences. Department of Horticulture.
- Snap Beans Shipping Point and Market Inspection Instructions. United States Department of Agriculture. Agricultural Marketing Service. November 2002.
- Hodges, Laurie, “G90-993 Basic Cultural Practices for Commercial Production of Green (Snap) Beans” (1990). Historical Materials from University of Nebraska-Lincoln Extension. 1016. Accessed November 2024.
