1
point
How do you keep weevils from destroying beans if you don't have a freezer?

Bean    northern California

Every year I find a few weevils in one or two varieties of beans when it's time to plant them. I know the usual way to prevent eggs from hatching is to make sure the beans are dry and then put them in a chest freezer at 0F for a few days. But I was wondering how bean seed was protected before freezers were available in climates where it doesn't get below 30F or so.


Posted by: Tanya in the Garden (128 points) Tanya in the Garden
Posted: April 4, 2013




Answers

2
points
A very interesting question! In the case of protecting stored grains/seeds etc from insects, it appears that one traditional method of protection is the use of other plants as natural insecticides. e.g. in China, plants such as neem and chilli are used as a natural insecticide for grain storage. In Ghana, tobacco leaves which can not be sold are used by the farmers to protect their grain. However, there is very little information on how these plants are applied to the stored commodity (see this document from the FAO http://www.fao.org/docrep/x2230e/x223...)

The traditional use of plants as insecticides led to interest from scientists who are keen to find alternatives to chemical pesticides. Many chemicals are being withdrawn from use on the basis of environmental concerns and an alternative is desperately needed to improve global food security.

I have been scanning the scientific literature on bean weevil feeding in order to try and come up with an answer to this and I think that the answer must lie in the control of the adults on the plants prior to egg laying. Due to their importance as pests of stored seed/grain, weevils have received some attention and have been subject to a number of experiments ultimately aimed at controlling them post-harvest.

An area of interest in the literature is the use of botanical essential oils to repel or kill insect pests. Essential oils have received attention as in addition to the antimicrobial and antifungal activities, they also have insecticidal activity as both fumigants (spraying of gas) and contact insecticides.

One study I found (Sertkaya, 2013; see image) recorded a 100% adult mortality when bean weevils were exposed to preparations of the essential oils of thyme and oregano. The oils of rosemary, basil and lemon balm also caused insect mortality, but to a lesser extent. It is worth noting that these studies were done in the laboratory and not on plants out in the field but I wonder if it may be worth conducting a little home experiment by rubbing some thyme or rosemary oil onto the leaves of your plants?

Additional information

Acanthoscelides obtectus (bean weevil) life cycle

Adult bean weevils overwinter indoors in stored seeds or outdoors in protected areas. The adults become active when the bean plants are flowering and and they lay their eggs either in holes they have chewed in the pod, or in natural wounds. The larvae hatch in 20-30 days and move through the pod to the seed. The larvae burrow through the seed coat and feed on the interior. The larvae pupate inside the seed and exit by chewing a circular hole in the seed. Newly emerged adults will migrate to new bean plants and after mating, females will again lay their eggs in the pods to complete the cycle. The entire life cycle can be completed in as little as 21 days in favorable conditions, allowing 6-8 generations to be produced each year!

Female weevils that emerge from stored seed behave slightly differently and will lay their eggs close to the seeds. When the larvae hatch out, the will move to the seed and bore through the coat.....In addition to the adults, I would imagine it is at this point - as they are moving to the seed - that they are susceptible to the insecticide (neem, rosemary etc)


Posted by: Lindsay McMenemy (2 points) Lindsay McMenemy
Posted: April 5, 2013


Tanya in the Garden commented,
Thanks, I have a few more things to try: scattering rosemary branches among the bean towers; putting essential oil of thyme or neem extract on a piece of cotton taped to the inside lid of the mason jars with beans; storing beans in a jar filled with dried lemon balm leaves or rosemary leaves.

But I wonder if it's known when the bean weevils lay their eggs in the beans: in the green pods? in the drying pods while still on the plant? in the drying beans indoors?

over 6 years ago.

Lindsay McMenemy commented,
Tanya, I've added some extra info into my answer about the life cycle of the weevil (this makes it more visible to others who may have a similar question than posting as a comment) as well as a link to the excellent extension document written by Gerald Ghidiu where I found most of the information- hope it helps. I think the things you plan to try out are great ideas and I'd love to hear how you get on
over 6 years ago.

Tanya in the Garden commented,
Lindsay, thanks for the additional info. I found this in the extension document: "All stages of bean weevils are killed by super-cooling in a deep freeze at 0°F for 4 days, or placing beans in cold storage at 32°F for 58 days. However, both of these methods may slightly reduce seed germination. Storage in a refrigerator, which is usually about 40°F, stops insect development but does not kill the insects." So that adds 2 more things to try: Putting the small jars of saved beans in the fridge with thyme oil or neem extract, and storing some jars in the freezer for a couple months.
over 6 years ago.



2
points
I've been given a couple ideas I'm going to try this year so I'll pass them along so you can try them too. The 1st is to spray the beans with a dish detergent/ water mix on the beans,repeat every 3 weeks for 9 weeks. The other way I'm trying is to sprinkle the jar with diatomaceous earth, a natural insecticide that dehydrates insects. Don't use the diatomaceous earth method on seed stock and triple rinse your beans before eating, better safe than sick.


Posted by: J.D. Archer (31 points) J.D. Archer
Posted: April 5, 2013


Tanya in the Garden commented,
Does the type of detergent matter? How much detergent per pint of water? Why is DE bad for seed stock?
over 6 years ago.

J.D. Archer commented,
original dawn unscented is what I was told but I'm looking for a healthier alternative. DE is 90% silica, a strong dessicant. Putting this on your beans would be like powdering them with salt.
over 6 years ago.



1
point
If you consider preventing adults from laying eggs in the first place, you can use bay leaves. Just place them with the beans into the bag/container and they'll repel the weevils.

http://www.wikihow.com/Get-Rid-of-Wee...


Posted by: Mehmet Ali Doke (2 points) Mehmet Ali Doke
Posted: April 5, 2013


Tanya in the Garden commented,
I placed bay leaves in all my mason jars of saved beans this year. And I still had weevils in my favorite beans.
over 6 years ago.

Tanya in the Garden commented,
Perhaps one bay leaf per jar was not enough. Or it was too late!
over 6 years ago.



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