Lentils Major Pests and Disease and their Management

Lentil (Lens culinaris), a crucial leguminous crop, holds great significance in regions such as North America, South Asia, North Africa, Europe, and Australia. The management of insect pests in lentil cultivation is essential for ensuring optimal production levels. Numerous insects, both in the field and during storage, pose threats to the crop, requiring an integrated approach to their management.

The use of chemicals in the management of insect pests and diseases in lentils should always be approached with caution and responsibility. It is important to apply only approved pesticides and fungicides that are specifically labeled for use on lentils. Always adhere to the recommended dosages to minimize environmental impact and ensure crop safety. Consultation with a local agronomist is highly recommended before any chemical application to ensure that the selected products are appropriate for your specific conditions and to promote sustainable agricultural practices.

Lentil Pests and Their Management

Major Field Insect Pests

Lentils are vulnerable to a variety of insect species in the field. Key pests include aphids (e.g., Aphis craccivora, Acyrthosiphon pisum), leaf weevils (Sitona spp.), Lygus bugs (Lygus spp.), and cutworms (Agrotis ipsilon). Additionally, species such as thrips, bud weevils (Apion arrogans), and pea moths (Cydia nigricana) also affect lentil plants. These insects not only damage the crop through feeding but also act as vectors for transmitting viruses, exacerbating the extent of damage.

**Aphids (*Aphis craccivora koch***)

Aphids are polyphagous and feed on tender leaves, stems, and pods. They have a rapid reproductive cycle. Aphids can reproduce both sexually and asexually, enabling females to generate offspring without the need for mating. This method of asexual reproduction contributes to their rapid population growth. They typically live between 17 and 20 days and can produce between 29 and 34 nymphs. Their feeding deforms plant parts, reduces growth, and can lead to severe yield losses. Both nymphs and adults suck the plant sap from the tender leaves, stems, and pods and mostly colonize the young leaves and growing points, which become characteristically deformed. Aphids also transmit viral diseases, which further decrease crop productivity.

Management

A nominal threshold for action in lentil plants is 30 to 40 aphids per 180° sweep of a 38 cm (15 inch) diameter insect net. This threshold is particularly relevant when few natural enemies are present and the number of aphids remains constant or increases over a two-day period. You can examine the field to detect infestations, especially from the beginning of July till mid-August, when flowering and pod development occurs. Management strategies for controlling aphids include early sowing of crops to mitigate infestation risks. Additionally, preserving natural enemies, such as predatory Coccinellidae (ladybugs), larvae of syrphid flies, spiders, lacewings, and parasitoids like Aphidius colemani, is crucial. The application of entomopathogenic fungi, such as Metarhizium anisopliae and Beauveria bassiana, can also be effective. Chemical control (insecticides) is widely used, although biological control methods mentioned above are considered sustainable alternatives.

**Leaf weevils (*Sitona spp.***)

lentil pod-borer

Leaf weevils are most harmful in regions like Europe, West Asia, and North Africa. The adults of Sitona species feed on young shoots, creating characteristic semicircular notches along the leaf edges. Although this feeding behavior typically occurs early in the season and does not usually impact yield, it can become problematic under certain conditions. If weevil populations reach high levels and lentil seedlings are stunted due to unfavorable environmental factors, the plants may struggle to recover, leading to economically significant damage. However, the larvae of Sitona species are the primary concern, as they feed on root nodules, significantly affecting the plant's ability to fix nitrogen (N₂). This damage can severely compromise plant health and yield potential, making larvae the most serious threat posed by leaf weevils.

Monitoring for leaf weevils primarily involves assessing feeding damage to estimate population density rather than counting adults. The ideal timing for assessment is typically the last week of May to the first week of June (for the North Hemisphere), coinciding with peak foliar damage and weevil migration. During early flowering (late June and July), when larval populations peak, you can examine the roots for larvae or feeding injury.

Management

Control measures for managing leaf weevil infestations include chemical applications with insecticides and cultural practices such as crop rotation and reduced tillage. Crop rotation with non-host crops can be effective. However, adult pea leaf weevils are strong fliers and may still infest nearby fields. Reduced tillage practices can promote the population of beneficial insects, which can prey on the weevils.

Lygus bugs (Lygus spp.)

Lygus bugs are prominent, particularly in North America. They overwinter in ground debris and crop residues, emerging after the snow melts in spring. Their ability to pierce tender leaves, stems, buds, petioles, and developing seeds makes them particularly destructive. Most importantly, they cause seed damage known as "chalky spot syndrome," reducing market value. This condition manifests as pitted, crater-like depressions on the seed coat, often accompanied by a discolored, chalky appearance. Such damage can lead to substantial economic losses, as lentils exhibiting more than 3.5% chalky spot damage face price discounts based on symptom severity. The impact on yield is severe, with reductions of up to 50% due to direct feeding or chalky spot formation and an average yield loss of approximately 30% without effective control measures.

Lentil Lygus-bugs

Effective scouting for Lygus bugs is crucial to mitigate damage to crops. Given that lentils grow close to the ground, traditional sweep netting can be ineffective, and the presence of these pests may be overlooked. However, once lentils enter the bloom and podding stages, sweep nets can be used to assess adult populations, with a threshold of one Lygus bug for every three sweeps indicating a need for insecticide treatment.

Management

Several natural control agents can help manage Lygus bug populations. One notable example is a wasp from the family Mymaridae, which parasitizes the eggs of Lygus bugs, offering potential biological control. One of the few parasitoids targeting adult Lygus bugs is the tachinid fly Alophorella sp. Crop rotation programs for Lygus bugs have shown only partial effectiveness due to the pest's reliance on multiple host plants throughout its life cycle. Insecticides are also commonly used to control these pests.

**Cutworms (*Agrotis Ipsilon***)

Cutworms, specifically Agrotis ipsilon, are cosmopolitan and polyphagous pests known for their nocturnal feeding habit. During the day, the larvae remain hidden below the soil surface, under clods of soil, or in other shelters, making them difficult to control. The first two larval stages typically feed on the foliage, while older larvae cut the plant above the root crown, often leaving it to wither and dry before moving on to other plants. This behavior can lead to severe crop damage, particularly when cutworm populations reach epidemic levels.

Regular scouting of crops from early spring to June is crucial to monitor for expanding bare areas, missing plants, and wilted, notched, or shot-holed plant tissue. Scouting is often more successful in the evening when the cutworms are active.

Management

agrotis-ipsilon

Control measures for Agrotis ipsilon are challenging due to the pests' subterranean habits and sporadic population dynamics. Large populations can cause significant damage, and by the time the pest is identified, they may have developed into later life stages that are less susceptible to insecticides. Effective management strategies include deep plowing of fields between crops to expose larvae and pupae to predators and sunlight, as well as destroying their hiding places. To manage cutworm populations, farmers can also utilize poison baiting with Bacillus thuringiensis (Bt) mixed with wheat bran, and mechanical removal of caterpillars is recommended. The economic threshold for Agrotis ipsilon in lentil crops is 2 to 3 larvae per square meter within the top 7 cm of soil, highlighting the need for timely intervention to protect the crop.

Minor Field Pests

Several minor insect pests threaten lentil crops, though their impact is generally less severe than that of major pests. Thrips (e.g., Thrips tabaci and Frankiniella spp.) damage leaves and flowers, reducing plant vigor, while bud weevils (Apion arrogans) primarily affect the flowering stage by destroying buds. Pea moths (Cydia nigricana) can bore into lentil pods, causing unnoticed damage to seeds. Pod borers, like Helicoverpa armigera, occasionally inflict damage in specific regions, and the Lima-bean pod borer (Etiella zinckenella) can significantly harm developing seeds in various areas. Management for these pests often involves insecticide applications during flowering or early pod-setting.

lentil pod-borer

Pod Borer (Helicoverpa armigera hunber )

Lentil Major Diseases

**Fusarium wilt (*Fusarium oxysporium f. sp. lentis)***

Fusarium wilt is a severe soil-borne disease first recorded in India in 1934. The pathogen invades the plant's xylem vessels, blocking the flow of water and nutrients, resulting in wilting. Affected seedlings typically exhibit sudden drooping, followed by drying of leaves and, eventually, the death of the plant. In mature plants, the browning of the vascular system is evident from the roots up to the stem. The fungus can persist in the soil for three to four years, even without a host, making it difficult to eradicate. Fusarium wilt thrives in areas with low soil temperatures and high water retention, leading to significant yield losses, especially if the disease strikes before the pod stage.

Management involves biological control practices, such as applying antagonistic microorganisms like Bacillus subtilis and Trichoderma harzianum, and cultural practices ,sush as crop rotation with cereals that are not susceptible to the pathogen. Chemical treatment of the seed with fungicides is also applied. You should always consult a licensed agronomist before using any chemicals, and you should follow the label instructions.

**Ascochyta blight (*Ascochyta lentis)***

Ascochyta blight, is another destructive disease affecting lentils. It can attack all above-ground parts of the plant, leading to lesions on leaves, petioles, stems, and pods. The lesions, initially tan-colored, turn dark brown on pods and seeds, and in severe cases, the stem can be girdled, causing the upper parts of the plant to die. The disease spreads through rain splashes and infected seeds, especially during periods of wet weather, with optimal infection occurring at temperatures between 50 to 59°F or 10 to 15°C.

Ascochyta-on-leaflet

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Management of Ascochyta blight includes crop rotation, restricting lentil cultivation to once every four years, using certified disease-free seeds, and applying hot water treatments (55°C or 131°F for 25 minutes) or sun-drying seeds to reduce seed-borne inoculums.

Botrytis grey mold (Botrytis cinerea)

Botrytis grey mold (BGM) affects all aerial parts of lentil plants, leading to crop losses that can exceed 50%. The disease begins with dark green lesions on the lower foliage, which eventually turn greyish-brown and spread across the leaves. Severely affected leaves fall off, leading to plant decline. BGM thrives in humid conditions with temperatures ranging from 15 to 25°C (59 to 77°F), and the fungus spreads via wind-borne conidia, infected plant debris, and seed-borne inoculum.

Botrytis-late-season

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Managing Botrytis grey mold requires cultivating resistant varieties such as Pant L-639 and Pant L406, adopting delayed sowing and wider row spacing to prevent dense canopies, and applying fungicides to affected crops. You can also focus on weed control and optimal fertilization, especially avoiding high nitrogen levels.

**Rust (*Uromyces viciae-fabae)***

Rust, is one of the most destructive foliar diseases in lentil cultivation, with the potential to cause total crop failure. The disease manifests as yellowish-white pycnidia on the underside of leaves stems, and pods, followed by the appearance of brown uredial pustules that can merge into larger lesions. Rust thrives in high humidity and overcast conditions, spreading through spores that persist in plant debris or seeds.

Managing rust involves applying foliar fungicides and cultivating resistant lentil varieties like Pant L-639, Pant L-406, and Pant L-8. It is always recommended to consult a local agronomist before using chemicals.

Other Lentil Diseases

In addition to these major diseases, lentil crops are also affected by other diseases like Anthracnose (caused by Colletotrichum truncatum), White Mold (caused by Sclerotinia sclerotiorum), and Powdery Mildew (caused by Erysiphe polygoni). Though less common, these diseases can still lead to yield losses and require targeted management strategies.

It is highly advised that farmers consult a licensed agronomist before applying agrochemicals and always use certified and suitable products. Farmers should always strictly follow label instructions and recommend dosages. Over-application or misuse of pesticides and fungicides can harm beneficial insects, contaminate the environment, lead to pest resistance, and harm consumers' and users' health. With responsible pesticide use, farmers can protect their crops effectively while protecting the ecosystem's health.