When you purchase through links on our site, we may earn an affiliate commission. Here’s how it works.
Beans are one of the easiest vegetables to grow, and when they pop a bunch of pods all at once, even a beginner gardener will feel like they’ve done a great job. Each year, some beans with spots show up in the garden, which is a shame, especially when it pours rain. Beans with brown spots are often sick with bacteria or fungi, but don’t worry—you might be able to save them.
As a green bean enthusiast who loves growing and cooking with fresh beans, nothing is more disappointing than cutting into a beautiful green pod only to find unappealing brown spots. These blemishes definitely detract from the vibrant color I expect from healthy green beans. But what actually causes these spots to form?
After researching and consulting with produce experts. I’ve discovered the primary culprits behind brown spotting in green beans are
- Bacterial infections
- Sunscald
- Freezing injury
- Age and deterioration
Understanding the specific causes can help prevent and treat brown spots when cultivating and storing green beans.
Bacterial Brown Spot Disease
One of the most common causes of brown spots on green beans is a bacterial infection known as bacterial brown spot. The bacterium Pseudomonas syringae pv. syringae is responsible for this troublesome plant disease.
Here’s what happens:
- The bacteria infiltrate leaf pores and wounds on bean plants.
- Under cool, wet conditions they rapidly multiply, spreading through tissues.
- On pods, small dark brown greasy spots emerge on surface.
- Spots expand and may coalesce, covering large areas.
Wet, humid weather promotes growth and spread of the bacterial cells leading to more severe spotting. Overhead irrigation and rainstorms help disperse the bacteria.
Once bacterial brown spot takes hold, there is no cure. Prevention with good cultural practices is key:
- Avoid overhead watering to limit spread of bacteria.
- Space and prune plants for good airflow.
- Remove any diseased leaf and plant debris.
- Rotate bean crop locations year to year.
While unsightly, the spots do not affect bean flavor and small amounts can be cut away. But severe infections warrant discarding pods.
Sunscald
Sudden intense sunlight exposure can also cause brown blemishes on green bean pods known as sunscald. Here’s the mechanics behind this abiotic disorder
- Beans growing in shade/partial shade experience rapid solar heating.
- Photosystems cannot adjust quickly enough to increased light.
- Tissues burn in reaction to photooxidative stress.
- Sunken brownish lesions form on exposed pod surfaces.
Providing beans consistent sunlight exposure rather than sudden shifts prevents sunscald. Trellising and proper plant spacing helps minimize this environmental stressor.
Freezing Injury
Freezing temps can wreak havoc on green bean plants, leaving behind telltale brown discolorations called freezing injury:
- Prolonged exposure to temps below 32°F damages cell membranes.
- Water leaks out and oxidizing enzymes are activated.
- This causes browning, pitting, and necrotic lesions.
A late cold snap can create scattered brown spots on pods while a hard freeze can kill entire plants.
To avoid freeze damage, choose resistant varieties, cover plants, harvest beans pre-frost, or grow beans under protective covers/enclosures.
Age and Deterioration
Finally, plain old age and deterioration will eventually cause green bean pods to develop brown spots and blemishes:
- During storage, natural enzymatic processes and oxidation occur.
- This causes the bright green chlorophyll to break down.
- The underlying brown pigments become visible, causing spots and dullness.
While not harmful, these spots signal that beans are past their peak freshness. Storing beans properly delays the aging process:
- Refrigerate unwashed beans in perforated plastic bags.
- Blanch and freeze beans for long-term storage.
- Keep beans away from ethylene-producing fruits.
- Monitor for excessive moisture, shriveling, and softening.
With optimal storage conditions, crisp texture and vibrant color can be maintained for 7-14 days refrigerated.
Evaluating Severity of Bean Spotting
Not all brown spots indicate beans must be discarded. Here are some guidelines:
-
A few minor spots can be cut away and beans eaten.
-
Moderate spotting is mostly cosmetic but beans should be used soon before spoilage.
-
Major spotting means quality loss has occurred and beans should be avoided.
-
Pervasive, wet decay spots signal bacteria/fungi and require throwing out pods.
My advice is to promptly use up beans at first signs of spotting to enjoy their optimal texture and flavor. But occasional minor spots are not dangerous to eat when beans still appear fresh.
Keeping Beans Spot-Free
To prevent disappointing brown spots, be diligent about these best practices:
-
Select disease-resistant varieties suitable for your climate.
-
Water at soil level and increase airflow to discourage bacterial spread.
-
Avoid extreme temperature shifts and grow beans under protective covers in cold climates.
-
Harvest beans at their peak and store properly in cool, slightly humid conditions.
-
Check beans frequently for deterioration and use promptly. Discard any with major discoloration or decay.
With careful precautions during cultivation, harvest, and storage, you can minimize troubling spots and enjoy maximum quality in your fresh green beans.
Brown Spot Bean Plant Diseases
Brown spots on beans are a common sign of bean disease. Many of them show up at the same time, which makes it hard to tell if the disease is caused by fungi or bacteria. But if you look closely, you might be able to tell the difference between candida bean spots and bacterial ones. This will make treatment easier.
- Large brown spots show up on bean leaves because of anthracnose, and the damage is worst near the soil line. It could spread quickly and kill the whole plant if nothing is done. Beans that have been infected with anthracnose quickly get white fungal bodies on their surfaces when they are picked and brought inside.
- Bacterial brown spot starts out as small wet spots on leaves that quickly turn into dead spots with a yellow edge. The spots on the leaf sometimes merge with each other or the dead parts fall off, making it look torn. Spots on the pods are brown and sunken, and young pods come out bent or twisted.
- Bacterial blight is a bacterial disease that looks a lot like bacterial brown spot, but the bean pods will also get soggy spots on them. Soon, they get bigger and turn rusty. If it’s humid, they may leak a yellow fluid. Seed abortion or discoloration isnt uncommon.
- Halo blight is different from other bacterial blights because its leaf spots are red-orange and have green-yellow halos that are different sizes. When temperatures go above 80 degrees Fahrenheit (26 degrees Celsius), spots will almost completely go away. ). When it rains, these sores may leak a cream-colored liquid.
Treating Spots on Bean Plants
Beans with spots shouldn’t cause you to worry, but they do need to be treated right away. If you act quickly, you can save most or all of your harvest. You can choose a chemical that kills the right kind of organism if you know whether the spots are caused by a fungus or bacteria. Treat fungal infections using neem oil, applied every 10 days for several weeks. A copper-based fungicide is more likely to kill bacterial diseases, but it may take more than one treatment to get a good harvest. Avoid going into the bean patch when the leaves are wet in the future to keep these diseases from spreading. Keep bean leaves and other shed material off of the ground, since these dead tissues can harbor pathogens.
Brown Spots on the Leaves of Green Beans
FAQ
Can you still eat green beans with brown spots?
How do you treat brown spots on green bean plants?
What are the symptoms of bacterial brown spot in beans?
Why do my green beans have rust spots?