A newsletter reader contacted me to see if I could help with a problem. His broad beans consistently fail. I’ve always found broad beans remarkably easy and not had any problem to speak of or solve. Hopefully this will help him, but if you have had and solved this problem, or have any other ideas on it – please comment below.
Broad Beans
His Question:
I grow on my Allotment and I’m very happy with the results. My runner beans and French beans are excellent. The only problem I have every year are the broad beans. I’ve tried over wintering them, then planting them spring time. Then the problem, every year. I’m not sure if it’s blight or rust, but the plant just turns brown and blotchy then the crop fails. The worst part of it is that I love broad beans, typical!
I’m sure someone will have a logical answer. Also, I did a bit of a Google, copper sulphate comes up, however I don’t like using chemicals. Unless there’s another way, I’d rather not grow them.
Well, this is a puzzle to which I’ve no obvious easy solution. Usually a problem like this has one of three root causes; disease, soil or cultivation. Knowing you’re an experienced grower, that leaves soil or disease. What I’d suggest is this:
Soil
By ‘soil’, I mean the nutrients in the soil. Assuming the soil has had fertiliser or has had compost or manure added, the first thing I’d do is check the pH. Ideally for broad beans this should be between 6.5 and 7.0. All the legumes like a high pH. They’ll still grow fairly well at a lower pH, but they’ll grow better with a sweeter soil.
Broad beans particularly like potash (potassium) so some additional potash applied at the start of the growing season is always beneficial. A good organic source of potash is wood ash. Other organic sources like chopped banana peel (if you have a lot) or seaweed meal or chicken manure pellet will also boost the potassium level, as will any inorganic fertiliser with potassium / potash in the name like potassium chloride or sulphate of potash.
Finally, it may be a micro-nutrient (trace element) deficiency. Beans are particularly susceptible to a zinc deficiency. Testing soil for trace elements is a job for professionals with a laboratory, and pricey. More cost-effectively, just apply a trace element fertiliser. S-Chelate’s Cultiv-8 is approved by the Soil Association for organic growers.
Disease
Firstly, the better the soil, the better the plant will grow and be able to resist any disease.
It’s unusual to get a disease affecting just one of the legumes, but possible. You mention copper sulphate, copper is an antifungal and copper sulphate a component in Bordeaux mixture which was the standard blight preventative for potatoes. Incidentally, Bordeaux mixture used to be organically approved, but no longer.
Finding a fungicide approved for use by home growers for use on edibles is not easy. Sulphur based, Mildew Clear for Edibles from Neudorff may possibly be helpful. Read and follow the instructions carefully.
Final thought
One last thing, if it is some disease lingering in the soil or a deficiency, growing in a completely different area of the plot may escape the problem
If the soil type is something like heavy clay then I’d suspect a brown rot of some sort.
But, more likely, especially if it is broad beans only, is “chocolate spot”. I suggest your correspondent has a look at the photos on the RHS web page (search terms: “rhs”, “chocolate spot” and “broad beans”).
Rust is possible, but much less debilitating, and only affects late-sown broad beans.
I also have a problem with broad beans only, all other beans being ok, and it is similar to the first enquiry, although I do manage to get a few beans. However, I also notice round bite marks all around the edges of the leaves making them look fluted. I suspected flea beatle and have tried many things alongside crop rotation but it still happens every year. Any suggestions for this?
The round bite marks are caused by the pea and bean weevil. I get it every year on my allotment but still get a good crop of broad beans. I have never seen the culprit so they must come out at night. They don’t do too much damage so best to leave them be.
I suspect Dave Lester was right in suggesting ‘Chocolate spot’ was the main problem. This is caused by a species of Botrytis that thrives in humid conditions. Doing anything to reduce this should help (although weather conditions are the most important).
Leave more space between rows and sowing the beans in the more ‘open’, exposed parts of the garden or allotment might help a little.
It didn’t sound like chocolate spot to me, but certainly a possibility. Adding potash to the soil helps the plant fight off the fungus.
My go to for most problems is to get the soil right so the plant can shake off the problem. Sometimes it works! 🙂