Garden Word of the Day
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Pea Leaf Weevils
While adult pea leaf weevils (Sitona lineatus) are chowing down on the leaves and growing tips of your legumes, their miscreant offspring are underground, gnawing away at the nitrogen fixing nodules found in and around the root system. Originally from Europe, pea leaf weevils are now found around the world.
How can you tell if pea leaf weevils are attacking your plants, and what can you do about it?
Pea leaf weevil damage
Scalloped leaf edges and gnawed-off stumps where growing tips used to be are the first signs that these invasive pests have reached your garden. Leaf scalloping tells you that adult pea leaf weevils are feeding. What you can’t see without digging up the plant is all the damage being done to the root nodules. Larval feeding can completely halt nitrogen fixation, resulting in stunting, chlorosis, and plant death. All legumes are susceptible to pea leaf weevil feeding, though lentils are less likely to be affected. I have no idea why. Larvae may also burrow into young pea pods and start feeding on young peas.
Pea leaf weevil identification
Pea leaf weevil adults are one-fifth of an inch long, grayish-brown, and rather slender in physique. If you look closely, you may be able to see three pale lengthwise stripes down the thorax. Larvae are milky white with a dark head. Like other grubs, they tend to hold themselves in a C-shape. These larvae have no legs and are about the same size as adults. Eggs are white at first but turn nearly black just before hatching.
Pea leaf weevil lifecycle
These pests tend to have one generation each year. After overwintering in protected feeding grounds, adults fly and walk to new territories where female pea leaf weevils will lay 1,000 to 1,500 eggs on or near young legume plants. When those eggs hatch, the larvae enter the soil where they go through five developmental stages or instars. They feed heavily on the nodules that allow legumes to convert atmospheric nitrogen into a form they and neighboring plants can use for food. While these pests feed on all legumes, they only reproduce on peas and fava beans.
Pea leaf weevil management
Commercial growers apply insecticidal seed treatments before planting, but that’s probably not an option for the home grower. The good news is that black clock beetles, ground beetles, and rain beetles all love to eat pea leaf weevils. By mulching and applying aged manure and compost around your legumes, you can encourage these beneficial insects. This will also provide your legumes with any nitrogen they may need.
As always, avoid using broad-spectrum pesticides. Those chemicals end up killing off all your helpers. Bacillus thuringiensis (Bt) can also be used against these pests, but it only works on the weevils it touches. Eggs and larvae will be unaffected. These other tips can help protect your peas and other legumes from pea leaf weevil damage:
I hope that pea leaf weevils never find your garden.
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