Resistance to bean and pea weevils

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I’m hoping for a bit more discussion about weevils! What are your experiences? Has anyone noticed weevil resistance in any legumes that are in an area with high weevil pressure?

Here in the Portland, OR area growers struggle quite a bit with weevils in their legume crops. Some areas seem safe while others seem vulnerable to infestation levels. Fear of weevils prevents many people from growing a larger legume crop.

On my farm we have issues with weevils in common beans, snap and soup peas, chickpeas, and favas. Over the last few years I’ve noticed nearly all peas are attacked, most chickpeas, many but not all favas, and only some common beans. Runner beans seem to be unaffected, which is amazing.

Within common beans, bush beans seem more susceptible, with some pole varieties showing complete resistance over several years. We’ve been growing “Borlotti Gaston” from Ayers Creek/Uprising Seeds for years and have never seen any weevils. Which makes me wonder if they may have a genetic resistance.

I’ve been troubled by how indiscriminately weevils have attacked diverse bean mixes. I suspect there are genetic and environmental factors involved, as with many pests and disease. But I’ve also been picking thru our diverse mixes to replant unaffected seeds, in hopes we may trend toward resistance that way.

I haven’t positively identified our weevils, maybe that would be helpful. Brief research suggests Acanthoscelides obtectus, maybe Zabrotes subfasciatus, possibly Sitona lineatus, maybe others.

I understand that seeds can be frozen to kill off weevils, which is particular common in seed production, but I’m interested in genetic resistance, especially for a storage food crop.

Here is a good overview of the weevil situation, which links to a journal article from Crop Science and the Legume Innovation Lab at Michigan State. Sounds like their breeding line called “AO-1012-29-3-3A” has resistance to A obtectus and they are hopeful about crossing with susceptible varieties.

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Found this short discussion on Permies from 2021 about breeding weevil resistance in favas.

Also found this lively forum thread from 2019 about pea weevil resistance led by Joseph!

I can’t seem to find it anymore but years ago I saw a youtube of a lady growing medieval food crops in southern Oregon, she seemed to think overwintering legumes might be the solution because the harvest comes earlier in the season before the weevils are active.

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An overabundance of any pest suggests a depauperate ecosystem devoid of pest-predators. Allocating some space to habitat can help, as can mixing multiple species of plants together in the garden. Native plants in general are often highly beneficial for predators, as the predatory species generally have coevolved with the native plant ecosystem.

In terms of adaptation and development of pest resistance, that’s a numbers game both in terms of diverse genotypes and sheer numbers of individual plants. A lot of times, people tell me they simply don’t have the space for that. However, those folks are often growing linear rows of crops. One can plant much more densely in a bed than in a row. I get much better results with beans planted in beds rather than rows. Mixing in other plants that have differing root structures and requirements can also help break up the continuity of the crop, helping to prevent the pests from moving directly from one infested plant to its neighbor.

Some folks argue that an infested plant should be uprooted and removed; i don’t do that. I let the bugs eat what they want. They may decimate my crop but have never eradicated it. Sometimes plants can look really bad but bounce back later when conditions improve.

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I’ve also read that, for favas, planting late is a strategy. If your favas aren’t the first to flower, the majority of weevils will go decimate your neighbour’s crop instead (they can migrate a few kilometres).

This obviously isn’t a solution, but perhaps it suggests that it would be worth experimenting with staggered planting.

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There’s a 2025 update at the beginning of this post suggesting the PNW weevils are becoming resistant to freezing. :face_with_spiral_eyes: (though he doesn’t say what temperature he freezes at… it should be at least -18c / 0f and in small batches)

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