Alfalfa also attracts numerous pests that can weaken the crop canopy, hinder regrowth, and reduce forage quality. Better identifying these pests, knowing when they establish themselves, and recognizing the damage they cause allows for more targeted action in the field. Discover our solutions for protecting your alfalfa crops.
Alfalfa weevil
The alfalfa weevil (Hypera postica) is a weevil whose larvae cause the majority of the damage, especially in spring, with peaks often observed in April and May. These larvae devour the foliage, causing sometimes significant defoliation in infested fields. In the field, they are primarily identified by their green appearance, marked by a light lateral band. This pest is well-known in Europe, including France, and warrants particular attention during the early growth cycles and in seed production.
Alfalfa snout beetle
The Alfalfa snout beetle (Otiorhynchus ligustici) acts on two levels: the adults attack the foliage while the larvae burrow into the roots. This dual pressure can lead to wilting, stunted growth, or even the death of some plants. The adult is a large, grayish-brown weevil with a convex body and fused wing covers that prevent it from flying, while the larva is white, legless, with a brown head. Adults become active as early as April, but the larvae enter a longer life cycle, which can last for almost a year.
Alfalfa leaf beetle
The Alfalfa leaf beetle (Colaspidema barbarum , syn. C. atrum) is a beetle in the Chrysomelidae family that can cause heavy foliage consumption, with a marked impact on the second growth. The larvae are the most damaging part, although the shiny black adults are already easy to spot in the field. The eggs are laid in mucilaginous clusters, while the larvae, initially yellowish then darkening, have a hairy appearance or are speckled with pigmented patches. Adults appear as early as April, and the larvae are most prevalent between May and June.
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Pea leaf weevil
The Pea leaf weevil (Sitona lineatus) is a small, grey-brown weevil with a very short rostrum, easily recognizable by the semi-circular notches it leaves on the edges of the leaflets. Adults can weaken young seedlings when their feeding is extensive, while the larvae attack the nodules and roots, sometimes resulting in a noticeable delay in growth. Overwintering adults generally emerge in April, egg-laying occurs from May to July, and then new adults appear in summer. On alfalfa, its presence is not always immediately obvious, but the leaf damage is very characteristic.
Cowpea aphid
The Cowpea aphid (Aphis craccivora) colonizes young shoots, leaves, and inflorescences, where nymphs and adults feed on sap. In cases of severe infestation, growth and flowering can be disrupted, and the presence of honeydew often attracts ants. Wingless individuals are black, small, often less than 2 mm, with rather pale legs and black cornicles; winged forms are also very dark. This highly polyphagous species is widely reported on Fabaceae, which explains its regular presence in alfalfa stands.
Pea aphid
The Pea aphid (Acyrthosiphon pisum) can become a problem when colonies develop heavily on alfalfa. It then causes phloem sucking, resulting in deformed or yellowing leaves as they grow. This aphid typically measures between 2.2 and 3 mm and varies in color from light green to pink, with long antennae, an elongated tail, and prominent cornicles. Overwintering eggs can hatch as early as February, leading to numerous generations throughout the year, especially when conditions are favorable.
Pea thrips
The pea thrips (Kakothrips robustus , syn. Frankliniella robusta) is a small, inconspicuous pest, but its effects can be significant on shoots and flowering parts. Both larvae and adults cause superficial punctures that weaken tissues, resulting in shriveled or sterile inflorescences, as well as visible shiny punctures on the pods. Flights generally begin as early as May, peaking in June, and egg-laying often continues through June and July.
Alfalfa plant bug
The Alfalfa plant bug (Adelphocoris lineolatus) pierces stems, buds, and pods, particularly in seed-producing fields, where it can cause abortions and damage to reproductive organs. The adult insect has an oval, elongated shape typical of Miridae, and its larvae may resemble aphids at first glance, but they move much faster. Its presence becomes especially noticeable at the end of the growing season, between June and August, a period when monitoring floral and fruiting structures is crucial.
European tarnished plant bug
The European tarnished plant bug (Lygus rugulipennis) also belongs to the Miridae family and primarily attacks buds, flowers, and pods. Its feeding can lead to aborted buds, flower drop, and malformed seeds. This pest is most commonly observed between June and August in seed production, where its impact is less on vegetative mass than on the crop’s reproductive potential.
Alfalfa flower midge
The alfalfa flower gall midge (Contarinia medicaginis) is a very small fly whose larvae develop directly within the floral tissues. They cause gall-like deformities, blocking productive flowering and preventing normal seed formation. Adults measure only 2 to 3 mm, while the legless, orange larvae are found inside the affected flowers. The floral galls are a very clear warning sign in the field. This pest is reported in several regions of Europe and is most prevalent during the flowering period, from spring to summer, depending on the area.
Alfalfa moth
Cydia medicaginis is considered a major seed pest in Europe. It is the larvae that cause damage by attacking the pods and developing seeds.
Alfalfa seed weevil
The Alfalfa seed weevil, or Tychius aureolus , is a small, light brown beetle measuring 2 to 3 mm. When disturbed, it drops to the ground. Both adults and larvae contribute to losses, but it is primarily the larvae inside the pods that reduce the number of viable seeds. The first infestations can occur as early as April or May, with peaks occurring more frequently in June and July.
Leaf miners
Leaf miners, grouped here in the Agromyzidae family, are active in their larval stage. The maggots burrow tunnels between the two epidermal layers of the leaves, creating mines visible through the leaf. This damage reduces the active photosynthetic surface area and can also degrade the quality of the harvested forage.
Leafhopper
The leafhopper, in particular Empoasca fabae, causes yellowing and then necrosis of the edges of leaves, associated with stunting of the plant.
Orange sulphur
The alfalfa butterfly or orange sulphur (Colias eurytheme ) is the larva of a butterfly in the Pieridae family and causes sometimes significant defoliation. The caterpillars, usually green, develop on the foliage and can rapidly reduce the available plant mass.
Tobacco whitefly
The tobacco whitefly (Bemisia tabaci) belongs to a species complex widely distributed in warm regions. Both larvae and adults pierce plant tissues, causing chlorosis and general weakening of the plant. The honeydew they produce then promotes sooty mold growth and leaves sticky surfaces, further degrading crop quality.
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