Large Sow Thistle Aphid

Uroleucon sonchi

Large Sow Thistle Aphid, Sow Thistle Aphid

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A close up photograph of a large sow thistle aphid infestation
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Deal with aphids organically: Method 4
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Deal with aphids organically: Method 4
Deal with aphids organically: Method 3
Deal with aphids organically: Method 3
Deal with aphids organically: Method 2
Deal with aphids organically: Method 2
Large Sow-Thistle Aphid is a relatively large insect. They're a pest of Sow-Thistle (Sonchus sp.), especially common sowthistle (Sonchus oleraceus) and prickly sowthistle (Sonchus asper). It's also a known pest of lettuce and chicory. Not to fear, however, these aphids are a favourite for ladybirds. These insects are attracted to roadside verges, agricultural land and weed-infested areas.
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These aphids can attract sooty moulds to the area infected.
An abundant food resource for predatory insects like harlequin ladybirds and their larvae.


Adults can be either a dark brown or a pinkish-brown, with a shiny finish. They're around 3mm, where some adults possess wings and some don't. They also possess black abdominal horns. Nymphs tend to look like adults but are smaller in size, are slightly paler, and lack wings.


Copious amounts of honeydew may be evident near the site aphids are present. Honeydew can encourage the growth of black mould, so this may be notable too. Damage seldom permanent.












Biological treatment

General good housekeeping can help prevent any insect pest infestation. Before planting, be mindful of the space you leave between crops and shrubs. Weeds and plant debris can facilitate a bad pest infestation. Planting strong-smelling herbs such as basil, chive and mint are believed to deter aphid activity. Aphids aggregate in areas of new growth, so be sure to check in all the nooks of plants. Aphids can also be treated with a strong jet of water to dislodge them from the plant; or, a light, soapy mixture applied to the plant or even just squashing them. A mixture of tomato leaf and distilled water is believed to deter aphids. Once the leaves are drained, dilute the remaining mix with 1-2 cups of water. Tomato plants contain the same allergens as nightshade. It's not advised to use this method if allergic to nightshade. Aphids can sometimes attract ants to the infested area because of the honeydew they produce. An ant colony will protect aphids so they can farm their honeydew. Placing ant traps near infested plants will help to prevent any secondary infestations. Aphids possess an array of natural enemies (ladybirds, wasps and lacewings, to name a few!). These can be attracted into the garden by planting a selection of indigenous plants, incorporating an insect hotel, or by letting some the garden grow wild.

Chemical treatment

Wherever possible, aphids should be tolerated on plants because they are food for other wildlife. Aphid populations tend to peak during spring, but die off when natural enemies become more apparent later in the summer. Assess the level of damage for the time of year before taking action with chemicals. When using chemicals, it’s always best to act when nymphs (immature aphids) are most active, which tends to be in the spring. Assess the plants' size. Full pesticide coverage for trees and large shrubs is expensive, if not impossible, to achieve. Likewise, apply pesticides before flowering occurs. Sprays can be indiscriminate killers, killing the useful insects as well as the bad. Contact insecticides containing natural plant oils can be more environmentally benign than synthetic pesticides. Look out for products containing natural pyrethrums, fatty acids and plant oils. Synthetic pyrethroids that are available for home use include ingredients: Deltamethrin, lambda-cyhalothrin and cypermethrin.



Predatory ladybirds will quickly attend to colonies of aphids like these.
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