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.
I have never had this trouble. I use tea tree oil and neem oil in my garden on nasties and would try them on this.
ReplyDeletehttp://www.wisegeek.com/what-is-neem-oil.htm
I put neem undiluted in a plastic spray bottle (won't break down the plastic, but tea tree will) then I just randomly spray it on the plants for foliage absorption. It is harmless and tasteless for food crops and beneficial insects. I did a post on it too.
http://lifethroughthecracks.blogspot.com/2009/06/neem-essential-oil.html
Was over 100 degrees here yesterday! Everything is so tender from being cold and shaded, but my tomatoes are finally in blossom. Hope this helps and you are well, peace
Ruralrose,
ReplyDeleteThanks for the ideas. I am allergic, though, to tea tree oil so I don't like to have it around; if it was used at the PAR garden, I would have to stay out of it!
I'll look closer at Neem as a possible help, however, our plants have been sprayed with a product (organic approved) called "Messenger" that one of our gardeners swears by as an immune-booster for plants, so we should (in theory) be covered with regard to plant health, but this has been an odd year.
I think the big instigator of the rust has been the early high heat of this summer. In years past, when May and June's temperatures were closer to the mean, the bean rust hasn't shown up.
Sorry it's so hot where you are, too!