The leaf webber, also known as the semi-looper or inchworm, is a common pest that infests green gram crops. This pest belongs to the order Lepidoptera and the family Noctuidae. The adult moth has a wing of about 20-25 mm and is light brown in color. The larvae are pale green with a darker head capsule and can grow up to 25 mm in length.
They feed on the leaves and pods of green gram, creating a characteristic webbed appearance. It takes the leaf webber 30 to 40 days to complete its life cycle. The female moth deposits her eggs on the lower part of green gram leaves. After a few days, the larvae emerge and feed on the leaves. As they expand, they build protective webs around themselves. Before pupating in the ground, the larvae go through several molts.
The adult moth emerges after roughly 10 to 14 days, and the cycle repeats. Green gram crop leaf webber infestations can be managed in several ways. Crop rotation, intercropping with non-host plants, and timely sowing reduces pest populations. Predatory insects and parasitoids can also be added. Chemical control can be used sparingly with other management strategies.
Leaf Webber Management in Green Gram
Identification of Leaf Webber
Leaf webber, scientifically known as Eucosma critica (Eucosmidae: Lepidoptera), is a common pest of red gram and other pulses in India. This pest is widely distributed throughout the country. The adult moths are pale brown and have a wingspan of about 20 mm. They have golden or yellow-brown forewings, three dark zigzagging lines, and some darker patches. On the hindwings, the number of crossing lines is reduced to two.
Female moths lay eggs singly on the young leaves or shoots of the host plants. The young larvae initially roll the leaves of the host and feed on the tender shoots. Later, they create webs by joining the leaves and feeding from within. This results in stunted growth of the main shoot of the plant.
The Life Cycle of Leaf Webber
The female moth lays eggs on the young green gram and other pulse leaves or shoots. The larvae feed on tender shoots after hatching for 3-4 days. After merging leaves, larvae feed from within webs. They undergo several instars before pupating. After 10–12 days, the adult moth appears. The 20-mm-wingspan adult moth lays eggs singly on host plants to finish the life cycle.
Causes/Conditions Favorable for Leaf Webber Spread in the Field
Hot, dry weather is ideal for leaf webber infestations, particularly when the crop is vegetative and reproductive. Plants may be more vulnerable to infestation due to inadequate moisture, nutrient deficiencies, and bad crop management techniques. Pests may find shelter in weeds and agricultural residue, which may also aid in spreading the pests.
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Damage Symptoms of Leaf Webber
- The larvae of leaf webber cause damage by boring into tender shoots of folded leaves and feeding from within.
- The terminal leaves get spun together, causing damage to the growing tip of the plant.
- The green larvae live in a single rolled leaf or two leaves spun with silk threads.
- In later stages, they may spin several leaves together, forming a mass of congregated leaves that are partially eaten.
- They feed on tender leaf tissue between the veins, resulting in areas cleared of the outer epidermis, and leaves may turn brown or die.
- Severe infestations can reduce leaves to a skeleton of hard parts, leading to smaller pods and reduced yields.
Yield Loss Due to Leaf Webber on Green Gram
Green gram yield losses from leaf webber infestations can be major, ranging from 10 to 60%. The amount of yield loss can be greatly impacted by the infestation’s severity and the attack’s timing. Early identification and prompt methods of control can reduce the damage pest causes.
Leaf Webber Management in Green Gram by Cultural Method
- Early planting of crops can avoid high infestation of pests.
- Removing weeds and crop residue can reduce the hiding places of pests.
- Balanced use of nitrogenous fertilizers to maintain plant health and avoid nutrient deficiencies.
- Providing adequate moisture through proper irrigation practices can help reduce the impact of hot and dry weather conditions.
- Crop rotation can help break the pest cycle and reduce infestations.
- Planting trap crops like marigolds to reduce the pest population.
Leaf Webber Management in Green Gram by Biological Method
- The use of natural enemies like parasitic wasps, spiders, and predatory insects such as lady beetles and lacewings can help control leaf webber populations.
- Encourage natural enemies by planting nectar-rich flowers and avoiding broad-spectrum pesticides.
- Releasing biocontrol agents such as Trichogramma chilonis, a parasitoid wasp, can help reduce leaf webber infestations.
- Microbial insecticides like Bacillus thuringiensis (Bt) and Beauveria bassiana, which infect and kill the leaf webber larvae, can also be effective.
Leaf Webber Management in Green Gram by Chemical Method
- Insecticidal formulations containing cypermethrin or decamethrin can be applied at fortnightly intervals to manage leaf webber populations.
- Endosulfan 35 EC can be sprayed on the infested crop at a rate of 2.0 L in 700 L water per acre to control leaf webber infestations.
- Care should be taken to follow recommended dose rates and safety precautions.
Leaf Webber Management in Green Gram by Organic/Natural Method
- Parasitic wasp species of Trichogramma can be used as a biological control method to manage leaf webber populations.
- Other larval parasitoid species, such as Brachymeria ovata, Grotiusomyia nigricans, Sturmia albincisa, Nemorilla maculosa, and species of Apanteles and Toxophroides, can also be used to control leaf webber infestations.
- Integrated pest management techniques, such as crop rotation, intercropping, and maintaining healthy soil, can help prevent or minimize leaf webber infestations’ impact.
Preventive Measures for Control of Leaf Webber
- Plant-resistant varieties of green gram that are less susceptible to leaf webber infestations.
- Monitor your plants carefully and take action if a critical number of plants show symptoms of infestation.
- Perform crop rotation, which can help disrupt leaf webbers’ life cycle and prevent population buildup.
- Remove weeds from the cultivation site, as they provide shelter and food for leaf webbers and other pests.
- Sow nectar-producing plants around the fields to support natural predators of leaf webbers.
- Pheromone traps can determine the number of leaf webbers and disrupt their mating behaviors, reducing their population and preventing further crop damage.
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Conclusion
Leaf Webber damages green gram yields. Rolled, webbed leaves with larval feeding are symptoms. Effective management methods include cultural, biological, chemical, and preventive steps like crop rotation, resistant varieties, and pheromone traps. These methods can control the pest and protect green gram yields.
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