Problem with Beans

Question: Hello UMD Extension, 

The bean plants pictured were planted in a raised garden bed (3.5'x12'x2' deep) filled with a 50/50 mix of soil/compost delivered from a local mulch supplier.  They were planted as seeds, late (mid-June) approx. 2" deep.  There are 3 varieties, green pole-beans, purple bush beans, and yellow wax (bush) beans.  All plants sprouted and did well for about 2 weeks, growing nicely.  Suddenly, a few plants (4) abruptly withered and died overnight (July 8/9).  There had been some leaf spotting and damage at the margins prior that I'd equated to water issues, and quite a bit of splashed dirt on the leaves from a series of downpours when they were about 4-6" tall, but nothing I would have thought particularly concerning as the plants continued to grow.  From the original 4 plants, I have now lost an additional 12 plants in 2 weeks in the same manner (about 40% of the plants), with several more looking questionable, and very few plants growing vigorously.  

Plants that I pulled didn't show any obvious cankers or sores on the stalks, but the roots did feel spongy and almost hollow.  Given their rapid decline and the fact that it seems to be spreading down the rows from the original infected plants, I suspect it might be something fungal/bacterial, but I'm not sure how best to treat it.  If I can prevent further spread, I'd like to know how!  Further, if I lose this crop, I'd be curious to know if there is anything "safe" to plant in these beds in future years that wouldn't be affected by the same blight.  I'm having similar issues with my peppers, submitted separately.  But given that I'm seeing similar effects in legumes and nightshades, I'm worried it's not host-specific.

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied July 21, 2023, 12:35 PM EDT
response: Hi- the leaf discoloration (3rd photo) is due to one or more environmental factors and not a disease. Bean leaves often develop these spots due to high heat, fertilizer burn, moisture stress, etc. Leaf color in the non-symptomatic plants looks ok so the light green color in the 3rd photo is probably due to a compromised root system unable to pull in sufficient nutrients.  There are soil-borne diseases that can affect plants individually or in groups or rows depending on the presence of the pathogen and environmental conditions. Bean root rots are favored by saturated or slow-draining soils. Spongy roots are one symptom of root diseases like pythium and fusarium. Southern blight is a fungal disease that causes browning of lower stem tissue and stunting/wilting and can infect bean and pepper.  We are wondering if the soil mix is holding excessive water due to a high clay content and/or excessive watering. This would make root rot infections more likely but can also directly contribute to slow or poor growth and wilting symptoms, due to a lack of air available to root systems. Browning of leaf margins is often a symptom of extreme moisture stress or burn from fertilizer salts or pesticides. Although in beans, it's also a symptom of leafhopper feeding.  Remove any dead and dying plants, calibrate watering so soils are moist but not wet, and let us know if symptoms change or worsen.  Jon

responder: The Question Asker Replied July 24, 2023, 4:09 PM EDT
response: Good afternoon, Jon and Extension Experts,  Here is the latest Bean Casualty with some additional photos.  You recently responded about Southern Blight potentially affecting my bell peppers.  I see similar traits here.  The roots seem to be intact, though they are hollow below the first branch of feeders.  There seems to be dead tissue moving up the stem internally.  Externally, there appears to be some browning right at the base (this wasn't super evident until the plant was pulled).  I don't see any white mycellia or obvious tells of a fungal infection but the stem damage seems to track with the peppers.  I'm curious if these photos confirm anything.  Beyond doing a deep "turning over" of the soil next year, is there a way to avoid further spread this year, or in future plantings in the same bed, beyond pulling the affected plants to reduce the latent soil population?  Based on the links provided with respect to Southern Blight it seems like it is difficult to get rid of.  I'll do some digging on my own, of course, but any suggestions on how to save what's left of the garden this year, and what to plant next year that will resist it if still present, would be very much appreciated.  On Fri, Jul 21, 2023 at 12:35 PM Ask Extension <<personal data hidden>> wrote:

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied July 25, 2023, 12:13 PM EDT
response: Hi- the bean plant symptoms are consistent with Southern blight. The disease could have been in the soil or brought in on transplants, compost, or manure. Removing and discarding all affected plant parts in the trash is the most important step. There are no resistant pepper, tomato, or bean cultivars.   Some sources recommend that growers practice deep soil turning to bury the fruiting bodies (sclerotia). They look like tan to light brown mustard seeds and can be found at the plant base. If you see sclerotia on plants you could remove the top 2--3 inches of soil within a 4-in. diameter of the plant stem. This will remove sclerotia that have detached. Flipping the soil so that the subsoil is above the topsoil will greatly reduce soil health and crop production. We don't recommend it.  Southern blight is reported as a minor problem every summer when the weather becomes hot, wet, and humid. It is relatively rare for gardeners to see it two years in a row. Jon