Brisbane Local Food

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Hi all,

Just wondering if anyone can help me identify this pest and help me treat my beans. Every time I grow beans they seem to take off and then once they start flowering the leaves start to wilt and drop off and tumourous growths appear around where the leaves join the stems and sometimes at the base of the plant. I thought it was something I was doing wrong the first two times but this time I decided not to blame myself as I planted them in good soil in a position they love. Managed to get them growing really well but then the same thing happened. I picked off a couple of leaves that were wilting and found tiny bugs/larvae inside. They have a brownish/creamy casing and a very tiny - about 1-2mm long. I'm presuming this is the problem but can't seem to find any info about it or how to treat the beans online.

Any pearls of wisdom??

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Hi Vanessa,

I'm no bean-expert but the bugs could be a cause or a symptom - in that bugs will usually attack a sick plant which is exactly what happened to my coriander when it got too hot and it decided to bolt. You'll have to excuse me if I ask the obvious, I'm not sure what you've tried and what you haven't. Did you re-plant in the same area as the previous failed crop? There might be something in the soil even if you've put new stuff in. What variety of beans are you trying to grow? What is the soil like if you dig 20-30cm down? I had a problem with drainage which caused some tomato plants to wilt and here I was assuming they weren't getting enough water. Aphids can also transmit viruses (mosaic for example) which can affect beans from what I've read.

Can you take some photo's so we can try and identify the bugs in question and maybe someone who knows more about beans than me (not hard) can help you out. Good luck!
Thanks Brent,

I have planted in three different spots now and ended up with the same problem. I was doing some more searching online and think the culprit could be the bean fly. I've been out to check the leaves and I think there are some spots on them where the larvae would have eaten into the leaf and then gained access to the main vein and then the stem of the leaf. The plant was perfectly healthy before this happened, healthier than any of my previous bean crops with plenty of leaves and heaps of flowers. I was looking forward to a good yield this time : (

The soil here isn't the best - we have clay soil. This was a completely new garden bed when the beans were planted and I mixed in lime to break up the clay and some cow manure.

Will attempt some photos but I'm not sure if my camera is good enough for the little blighters.

No sign of any other insects apart from the usual katy-dids around the place.

Thanks for your help!
The symptoms suggest bean fly ... my beans have the same problem. It is supposed to be the reason why many people plant Snake Beans in the summer rather than the more conventional beans. But even SBs will succumb if they are growing in less than ideal conditions.

It does depend on the soil a great deal - lime may not be the best solution here to break up clay since it increases the pH - on the amount of water and the heat. In more sheltered spots I have had bumper crops of Purple Kings for example. In the spot they are today, the PKs and the Blue Lakes are stressed with the heat and more subject to these attacks.

It is usual to have some pest damage but with really healthy plants the damage is minimal and doesn't kill or inconvenience the plants much. Never expect to have no pest damage - just expect it to be very minor.

So far my Dutch Pole Bean plant has produced vast quantities of pods, the one plant is in a very exposed position and next door to a PK which is growing well but not setting much fruit. Both are in a new above-ground 300L bed with a soil-less mix, compost, worm castings, gypsum. There's some Blue Lakes too which are not setting much fruit, either.

Beans like lots of calcium (Gypsum is clay breaker and a good cheap source of calcium which doesn't change the pH), lots of potash (potassium or K(alium)) and phosphorus (P) they make a lot of their own nitrogen if conditions are right for the rhizobia (symbiotic bacteria living in the plant roots) to flourish.

As with a lot of gardening though, you do you best and see what happens and adjust the conditions next time.

Try the Dutch Pole Bean seeds from Saturday - just wait for them to thoroughly dry, then soak the seeds in tap water for 12 hours, plant them into separate pots and transplant when they start to look sturdy - about 2-3 lots of leaves. DPBs are enthusiastic growers and should give you lots of pods - pick when they are around 3 - 4 inches long when they are very sweet and fleshy, much bigger and they start to get tough.
Thanks Elaine, looks like bean fly it is. Will try the DPBs when they're dry.

I'm happy to accept some loss but this has almost totally wiped out my beans. There are 1 or 2 setting but I'm not sure if they'll make it.

Thanks for your advice.
Hi Ness, could you put a pic up (wish i could do the same but a camera is my xmas pezzy) I think i might have the same prob?
Thanks for posting these pictures Venessa. I often see these yellow specks on my beans, now I know this is evidence of bean fly...
I had a sneaking suspicion we had the same problem last year but I didn't look closely enough to find the problem. I noticed ants like you did but I think they're after the larvae.
Finally got round to it - sorry it took so long!

Above is general destruction and what my beans look like now - no leaves on the bottom half: I picked most of them off in an attempt to stop the invasion and the others just fell off because they were dead.

The bean fly lays its eggs on the leaves then when the larvae hatch they burrow into the leaf until they get to a vein and then travel into the stem of the leaf.

I actually found one of the larvae today - have never seen them before but definitely confirms my suspicions.

This last one is the pupa which is what I was discovering to start with.

Hope that helps!
Beans seemed so easy to grow 20 years ago.I have given up on most green beans.
I still get the same problem with snake beans in summer as well. Has anyone tried Butter beans? var. "Cherokee Wax" in your gardens instead of green beans during summer ? these are said to be resiliant to bean fly attack.?. I have yet to try DPBs but will give them a go.I was at Dads today and he has a great crop of purple beans just dripping from the vines without any signs of bean fly or any disease problems at all.
I often think that Bean fly attack and Sclerotinia sclerotiorum ( a pathogen) is difficult to diagnose. I still find it difficult to decide which is which in the earlier stages of development. Pathogen, predator or both?...
Destructive little things.. I'm about to try some beans in the tomato bed because blight has ended the crop early & the tom's need to move elsewhere. I hope I have more luck with beans - i'll try the varieties suggested here. Thanks for posting the pics and here's hoping you can salvage the remaining survivors!

Did a Google on bean fly and it took me back to ... Brisbane Local Food! I too have clay soil and the same symptoms with the dwarf beans. Now I know the spots on the leaves are bean fly damage.

Thanks for the informative post, Elaine.

Update August 2011: in light of last summer's experience, the Dutch Pole Beans did not fare as well as the home-saved 'Joe's Beans' I got from Jane at Benaraby. Whatever they are or were, they are the closest I've grown to being bean-fly resistant. It's an enthusiastic climber, the beans are flattish but not as flat as the Dutch Pole, but sweet fleshy and crisp. If Jane has some spare seed give them a whirl this summer. The Winged Beans seem to be bean-fly resistant as well but it is a wholly different taste and texture of bean.


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