Key Pests Affecting Cashew Trees and Their Management

Cashew (Anacardium occidentale) is one of India’s most commercially important plantation crops, contributing significantly to foreign exchange earnings through the export of cashew kernels and cashew nut shell liquid. Yet, despite its economic value, the crop is constantly under threat from a range of insect pests. More than 180 insect pest species have been documented on cashew, and when pest pressure goes unmanaged, yield losses can be severe. Understanding the biology and damage patterns of key cashew pests – and knowing how to respond – is the foundation of effective orchard management.

The tea mosquito bug: the most damaging cashew pest 🔗

Of all the pests that attack cashew, the Tea Mosquito Bug (TMB), Helopeltis antonii Signoret (Miridae: Hemiptera), consistently causes the highest economic losses. Under severe outbreak conditions, yield losses attributable to TMB in Indian cashew plantations can reach 40-50%. Three species of Helopeltis are commonly found on cashew – H. antonii, H. bradyi, and H. theivora – with H. antonii being the most predominant along the east coast from Tamil Nadu to Odisha, while H. theivora dominates in the northeast.

How TMB damages the plant 🔗

Both nymphs and adults are responsible for damage. They feed by piercing plant tissues, extracting fluids, and injecting enzymes – including polyphenol oxidase – from their salivary glands, which leads to browning and scab-like lesions on affected plant parts. The pest primarily targets tender shoots, inflorescences, and developing nuts. As feeding wounds accumulate, fungal pathogens like Botryodiplodia theobromae and Phytophthora enter the damaged tissues, causing dieback of shoots and blighting of inflorescences – compounding the direct feeding damage.

Feeding on premature and mature fruits causes desiccation, reducing both the size and quality of nuts, while die-back from blight further limits the tree’s ability to grow and produce. The pest population peaks during February-March, coinciding with the full blossom stage when trees carry the most tender, sap-rich growth.

Management of tea mosquito bug 🔗

Biological control offers some of the most sustainable options for TMB management. Research in Karnataka cashew plantations found that the weaver ant Oecophylla smaragdina was the most effective predator against TMB – trees fully colonized by this ant recorded the least TMB damage. Studies show that colonization by red ants led to a yield increase of up to 400% by the third year, with a cost-benefit ratio more favorable than chemical pesticides. Egg parasitoids such as Telenomus cuspis, Chaetostricha sp., and Erythmelus helopeltidis are also recorded as promising biocontrol agents. Among entomopathogenic fungi, Lecanicillium lecanii and Metarhizium anisopliae have shown notable effectiveness in reducing TMB populations in field trials.

Cultural management includes removing self-sown neem plants in and around cashew orchards (which serve as alternate hosts), regular orchard monitoring during the flushing and flowering season, and avoiding late-season pruning that stimulates tender growth during peak TMB activity.

Chemical control remains the dominant practice in commercial plantations. A three-spray schedule is recommended: the first spray at the new flush stage (November-December) using monocrotophos 0.05% or lambda-cyhalothrin 0.003%, the second at the flowering stage with carbaryl 0.2%, and a third spray at the pea-nut stage with monocrotophos 0.05%. Trees harboring weaver ant colonies should not be sprayed, to preserve this natural ally.

Stem and root borer: the silent tree killer 🔗

The Cashew Stem and Root Borer (CSRB), Plocaederus ferrugineus L. (Cerambycidae: Coleoptera), is widely regarded as the deadliest insect pest in all cashew-growing regions globally. Unlike foliar pests that reduce yield, CSRB can kill the tree entirely – making early detection and prompt action critical.

Damage symptoms and biology 🔗

The grubs bore into the bark and feed on the phloem and xylem tissues of the trunk and roots, creating irregular tunnels that arrest the movement of plant sap, ultimately causing tree death. During the initial stages of attack, gum exudation and frass – a mixture of chewed wood fibres and excrement – appear in small quantities at the base of the tree. As infestation advances, the canopy takes on a sickly, yellowing appearance, leaves drop prematurely, and twigs begin to die back. In severe cases, large accumulations of frass and gum are visible, and the bark splits – at which point the tree is unlikely to recover.

Adult beetles emerge around November-December, but different life stages can be found throughout the year. During the onset of monsoon, a healthy tree turns deep green while an infested tree remains noticeably yellowish – a useful field diagnostic.

Management of stem and root borer 🔗

Cultural and mechanical control is the first line of action. Trees showing yellowing or dieback should be removed immediately along with their roots by digging a pit of about two feet around the trunk base, and destroyed – a practice called phytosanitation. Tree bases should be kept clean and weed-free to enable early detection of frass and gum.

Post-extraction prophylaxis (PEP) is the standard curative approach. All grubs, pupae, and adults are carefully extracted from infested trees by chiseling, and the exposed cavities are then treated with insecticides to prevent re-infestation. Research found that chlorpyriphos 20 EC at 0.2% gave the highest recovery rate among trees treated after grub removal. More recently, imidacloprid 17.8 SL at 2.0 ml/litre has shown superiority over other treatments in PEP trials.

Biological control for CSRB is still developing. Entomopathogenic fungi – Metarhizium anisopliae and Beauveria bassiana – have been tested against CSRB larvae, with neem oil (5%) and neem cake also evaluated as plant-based management tools. However, the cryptic, concealed nature of the borer inside bark and wood means natural enemies rarely reach it, making biological control alone insufficient at present.

Minor pests: leaf miners and leaf and blossom webbers 🔗

While TMB and CSRB are the major threats, two secondary pests – the Leaf Miner and the Leaf and Blossom Webber – regularly cause damage in nurseries, young plantations, and during specific flush periods, and should not be ignored in an integrated management program.

Leaf miner (Acrocercops syngramma) 🔗

The Leaf Miner is a notable cashew pest during the post-monsoon period, with peak incidence occurring during October-November when trees produce new flushes. The tiny larvae mine the epidermal layer of tender leaves, feeding on the mesophyll just below the surface. This produces characteristic blistered, greyish-white patches that enlarge into holes as the leaf matures. Nursery seedlings and young plantations are far more vulnerable than mature trees.

Fortunately, natural enemies play a meaningful role here. Larval parasitoids including Chelonus sp. and Sympiesis sp. can manage leaf miner populations by up to 50% in Kerala and Goa, often making spraying unnecessary except in severe nursery infestations. When chemical intervention is needed, profenophos at 1.5 ml/litre or lambda-cyhalothrin at 0.6 ml/litre is effective.

Leaf and blossom webber (Lamida moncusalis) 🔗

The Leaf and Blossom Webber, Lamida moncusalis (Pyraustidae: Lepidoptera), causes damage through caterpillars that web together the terminal portions of new shoots and flower panicles, feeding within these silken shelters. This leads to defoliation, loss of inflorescences, and reduced fruiting. The pest completes its life cycle in about 37 days, with pupation occurring in leaf webs or in the soil.

For biological control, the braconid parasitoid Apanteles sp. and the green lacewing Chrysoperla sp. are documented natural enemies of this pest in Kerala. Chemically, spraying lambda-cyhalothrin at 0.6 ml/litre or profenophos at 1.5 ml/litre during the flushing period provides effective control. Removing and destroying webbed shoot tips manually is a simple but useful cultural practice that reduces larval populations before chemical intervention becomes necessary.

Integrated pest management for cashew: a combined approach 🔗

No single control method is sufficient for managing the full spectrum of cashew pests. Effective cashew pest management requires integrating cultural, biological, and chemical strategies – and timing each intervention to coincide with the most vulnerable pest stage and the most susceptible crop growth phase.

Cultural practices form the base: regular monitoring from November onwards, removal of dead wood and infested plant parts, maintaining clean tree bases to detect CSRB early, and avoiding conditions that favor pest buildup. Biological control should be actively conserved – particularly weaver ants for TMB and larval parasitoids for leaf miners. Insecticide sprays should be avoided on trees with established ant colonies. Chemical control, when required, should follow the recommended spray calendar – targeting the new flush, flowering, and nut development stages – using registered insecticides at prescribed dosages. Rotating between chemical groups helps prevent resistance development, a concern especially relevant for a long-lived perennial crop like cashew.

Good recordkeeping of pest incidence, spray timings, and yield outcomes across seasons allows growers to refine their IPM strategy year on year – and is increasingly recognized as a hallmark of professional orchard management.

What do you think? Given that the weaver ant Oecophylla smaragdina has shown impressive results against the Tea Mosquito Bug without any chemical input, do you think biological control methods receive enough attention in commercial cashew farming? And with the Stem and Root Borer capable of killing entire trees undetected for months, how should farmers prioritize early monitoring in their annual crop calendar?

References

1. https://link.springer.com/chapter/10.1007/978-981-19-0343-4_59
2. https://epubs.icar.org.in/index.php/IJAgS/article/view/55868
3. https://horizonepublishing.com/index.php/PST/article/view/7327
4. https://en.wikipedia.org/wiki/Helopeltis_antonii
5. https://link.springer.com/chapter/10.1007/978-81-322-2089-3_34
6. https://agris.fao.org/search/en/providers/122648/records/647356aa53aa8c8963068555
7. https://link.springer.com/article/10.1007/s42690-022-00912-5
8. https://cashew.icar.gov.in/pestsite/cashew-stem-root-borer/
9. https://arccjournals.com/journal/agricultural-science-digest/D-6098
10. https://www.entomoljournal.com/archives/?year=2020&vol=8&issue=4&ArticleId=7351
11. https://www.academia.edu/51665474/Management_of_cashew_stem_and_root_borer_Plocaederus_ferrugineus_L_by_microbial_and_plant_products
12. https://cashew.icar.gov.in/pestsite/leaf-miner/
13. https://cashew.icar.gov.in/pestsite/leaf-blossom-webbers/