One of the great things about working at the Plant-a-Row-for-the-Hungry garden, besides getting to hang out with a cool bunch of gardeners, is that it adds a lot to my gardening experience. This week, it added “bean rust” to the list of plant diseases with which I am now familiar.
This is what bean rust looks like on the top of a leaf:
And this is what it looks like on the underside of a leaf:
This bean variety is State Half Runner. The poor plants were already beset with Mexican bean beetles, but this is, potentially, worse.
I had brought my copy of Ellis and Bradley’s Organic Gardeners Handbook of Natural Insect and Disease Control with me on Wednesday morning (our usual work time) to look up what was wrong with our cucumbers (another post…). It definitely came in handy! Photos on page 34 made the problem easy to identify, and this is what the book says:
As this fungal disease progresses, leaves turn yellow and drop. Spots also appear on pods and stems. . . Rust usually develops in late summer. To control, spray sulfur as soon as you see indications of the disease. Plant cultivars that are rust-tolerant, such as ‘Burpee Stringless,’ ‘Kentucky Wonder,’ ‘Roma,’ ‘Spurt,’ and ‘Sungold,’ to prevent problems.
After reading this, we looked up sulfur in the index, to learn more:
Sulfur is probably the most commonly used organic fungicide, although plain sulfur is more a protective measure than a control. Sulfur doesn’t kill fungal spores, but it does prevent them from germinating on the plant surface. Another useful control is lime-sulfur, which can kill recently germinated disease spores. (page 348)
And then we found this:
A severe limitation to the use of sulfur is the foliar damage it causes in hot weather. (page 369)
In essence, we have a problem. If the rust progresses – and in this hot weather it will – the plants could lose all their leaves, which would definitely impair production. If we use a sulfur spray, the leaves could become damaged in this hot weather, which would impair the plants’ production. It’s almost one of those “danged if you do and danged if you don’t” situations. Our fearless leader, however, has decided to try the sulfur.