How to Manage Aphids on Sweet Peas: What We Tried and Learned

If you’ve found aphids gathering on your sweet peas, you’re not alone. I’ve heard from quite a few people dealing with the same problem, and this summer we had our own experience with just how quickly they can multiply.

The best place to start is with regular checks and removing small colonies as you find them. Beneficial insects can help, and a spreading infestation may need additional treatment. Here’s what we tried on our farm, how the products work, and what I’ll change for our next sweet pea crop.

Early Detection and Monitoring

Aphids feed on plant sap and often gather on tender new growth and the undersides of leaves. Check those areas regularly, especially once you’ve spotted the first few.

For a small patch, you can squish them with your fingers or knock them off with a stream of water. Use enough pressure to dislodge the aphids without damaging the sweet pea vines, then check the plants again to see whether they return. Look at neighboring plants, too.

Early this summer, I spotted a small patch in our sweet peas. We’d never had much trouble with them before, so I squished them and moved on.

This year turned out to be different. The aphids multiplied and spread through almost all of our sweet pea rows. We spent hours walking the rows and shaking plants by hand, but by that point we weren’t keeping up.

That was my first lesson: removing the aphids is only the first step. Following up matters just as much.

Beneficial Insects

Lacewing larvae, ladybugs, and hoverfly larvae are among the natural predators that eat aphids. Supporting the beneficial insects already around your plants is a useful part of managing them.

Plant flowers nearby that bloom at different times so there’s a steady supply of nectar and pollen. Leave some planted areas for shelter, and avoid unnecessary insecticide applications that could kill the predators you’re trying to encourage. It also helps to learn what their eggs and larvae look like so you don’t mistake them for pests and remove them. UC IPM has a helpful guide to recognizing and protecting beneficial insects.

I wanted to control the aphids with as little impact on bumblebees and other insects as possible, so I ordered 10,000 lacewing eggs.

The larvae are the aphid-eating stage, so eggs need time to hatch before they can help. Unfortunately, our shipment was delayed. By the time it arrived, most of the eggs appeared to be dead, and barely any hatched. I later ordered live larvae, but the infestation had already grown much larger.

If you’re considering releases, you can purchase green lacewing eggs on cards or live green lacewing larvae. Ask the supplier about timing, quantities, handling, and compatibility with any sprays you’re using. Larvae need prey, so releasing them into completely pest-free plants may not help them establish.

Biopesticides

These are the products we used during a widespread outbreak. A tiny patch of aphids may only need removal and regular follow-up.

BotaniGard 22WP and PrincipLE WP

I used BotaniGard 22WP and later PrincipLE WP. Both contain the insect-killing fungus Beauveria bassiana, although they use different strains.

When the fungal spores land on an aphid, they germinate and penetrate its outer covering. The fungus grows inside the insect, eventually killing it. This infection is known as white muscardine disease.

The process takes several days. Product guidance notes that visible control can take 7–10 days after the first spray, depending on conditions. Starting early and getting good coverage matter.

These biological insecticides take time to work. I can’t separate out exactly how much each contributed on our farm because we were using several methods during the same outbreak.

PyGanic

When the aphids continued spreading, I ordered PyGanic, which works quickly on contact.

PyGanic contains pyrethrins, which disrupt an insect’s nervous system, causing rapid paralysis and death. Because it works on contact, the spray needs to reach the aphids directly. Thorough coverage is important, including where aphids gather beneath leaves.

I sprayed in the early mornings, and we eventually brought the aphid population under control.

Pyrethrins come from chrysanthemum flowers, but they can also harm bees and other beneficial insects exposed to the spray. Follow the label’s restrictions and avoid exposing visiting bees.

You can find the home-garden product here: PyGanic Gardening. Its label excludes plants grown for sale or research, so commercial growers need a formulation labeled for their use.

With any spray, follow the current label for your crop, growing site, application rate, protective equipment, and re-entry requirements.

Mosaic virus

Aphids can pick up viruses while feeding on infected plants and pass them to other plants as they feed. Their needlelike mouthparts pierce plant tissue, allowing them to introduce a virus.

During our outbreak, the sweet peas began showing mosaic symptoms. Getting rid of the aphids doesn’t cure plants that are already infected, and we lost a few varieties when the vines collapsed before their seeds could finish ripening.

If you notice just a few plants with suspected mosaic virus, remove the whole plants promptly, bag them, and put them in the trash. This removes a potential source of infection and can help reduce further spread, though other plants may already be infected before symptoms appear. Keep monitoring the remaining plants and managing aphids.

Because we were growing for seed, I wanted to understand whether the virus could be carried in the seeds we planned to sell. I sent plant material to a diagnostic lab.

The lab detected pea enation mosaic virus (PEMV-1). Pea seed-borne mosaic virus (PSbMV)—the one I was particularly worried about—was not detected in the submitted sample.

Those findings helped us understand what was happening and were a huge relief.

For anyone seeing unusual symptoms, testing can help identify what you’re dealing with. “Mosaic” describes a symptom pattern; it doesn’t identify a particular virus on its own.

Companion planting around sweet peas

I usually leave feverfew, blue borage, yarrow, and nasturtium growing around the base of our sweet peas. As the season progresses, they can get big enough to spill into the walkways. This year, we removed them to make the rows cleaner and easier to get through.

Looking back, I think we also removed habitat that had been supporting beneficial insects.

Flowering plants can provide nectar, pollen, shelter, and alternative prey for insects that help manage pests. Companion planting won’t guarantee aphid-free sweet peas, but it can help support their natural predators.

Along with bringing those flowers back, I want to add alliums. I’ve grown them alongside sweet peas, ranunculus, and anemones in the hoop house for a few years, and they seem to have helped keep aphids down there. That’s my observation, and I’d like to see how they do in the field.

Other options to consider are sweet alyssum, flowering dill, and cilantro allowed to bloom. These plants provide food for beneficial insects. Research with sweet alyssum in lettuce has shown benefits for aphid management, while flowering herbs such as dill and cilantro support natural enemies of pests. That research isn’t specific to sweet peas, but these are useful plants to consider when creating habitat nearby.

My plan for the next sweet pea crop

The biggest change will be getting started earlier.

• Keep companion plants while leaving room to work. I’ll plan space for flowering plants so we can support beneficial insects without losing access to the rows.

• Have a beneficial-insect plan ready while the plants are small.

• Remove small aphid colonies promptly and keep checking. I’ll follow up on affected plants and inspect nearby vines to see whether the population is spreading.

We still brought in a good sweet pea seed harvest this season, and we’ve been drying, cleaning, and sorting the seeds. It’s been satisfying to reach this part of the process and see the results of our work.

I’m looking forward to sharing this year’s sweet peas and putting these lessons to use in the next crop.