Metarhizium anisopliae for Cardamom – Control Root Grubs, Borers & Thrips Naturally

Your cardamom clumps are the backbone of Idukki's economy. But every season, root grubs, borers and thrips cause serious damage, often destroying entire clumps before you even notice.

The root grub problem in Idukki cardamom:

The root grubs of a small, greenish blue beetle (Basilepta fulvicorne) are short, stout, pale white in colour and often assume a shape resembling the letter 'C'. These grubs feed on cardamom roots. Symptoms start as yellowing of leaves, which later result in the drying up and death of the plant. Once the roots are destroyed, the entire clump collapses – there is no recovery. Heavy infestation of root grub has been documented in local varieties of cardamom across Idukki, including in on‑farm trials conducted by KVK Idukki and ICRI. Chemical pesticides provide only temporary relief and harm soil health.

The borer problem:

The cardamom stem borer (Conogethes punctifieralis) – also called capsule borer or panicle borer – is the most destructive pest. The larvae bore into pseudostems, causing "dead heart" – the central shoot withers and dies. When panicles and capsules are attacked, developing capsules drop prematurely, causing yield loss of up to 50%. Chemical pesticides often fail because borers are inside stems and capsules, where sprays cannot reach.

The thrips problem:

Thrips scratch the surface of developing capsules, causing chaffy, underdeveloped, low‑quality capsules. They also transmit viral diseases. Thrips are notoriously difficult to control with chemicals because they develop resistance quickly.

Metarhizium anisopliae is the KAU and KVK‑recommended natural solution for all these pests.

KVK Idukki recommendation for root grub:

KVK Idukki has conducted on‑farm trials assessing Metarhizium anisopliae for root grub control in cardamom. The recommended dose is 25g of Metarhizium anisopliae per plant mixed with cow dung. This treatment achieved a yield of 2.4 tons per hectare and generated an income of ₹3,50,000 per hectare. This is significantly better than the farmer's practice of drenching Chlorpyriphos, which yielded only 1.7 tons per hectare and generated ₹2,80,000 per hectare. The Metarhizium treatment also resulted in a higher benefit‑cost ratio (2.4 compared to 1.7 for chemicals).

KAU recommendation for root grub:

The Kerala Agricultural University (KAU) recommends soil drenching with formulations of entomopathogenic fungi like Metarhizium anisopliae (NBAIR strain Ma6) at 10g per litre of water (5‑10 litres per plant). Mix 10g of Metarhizium powder in 1 litre of water and apply 5‑10 litres of this solution per plant as a soil drench around the root zone. This effectively targets the root grubs that are feeding on your cardamom roots.

Scientific study evidence from Idukki:

A three‑year study (2021‑2024) was carried out in Idukki district, Kerala, to evaluate bio‑intensive pest management modules. One of the tested modules (BIPM‑2) employed soil‑applied entomopathogenic fungus Metarhizium anisopliae (2% w/v) for root‑grub suppression. The study demonstrated that Metarhizium effectively reduces root grub populations without the negative impacts of chemical insecticides, which can destabilise cardamom ecosystems and leave residues in the harvested product.

For stem borer and capsule borer control:

Research studies have shown that entomopathogenic bio‑control agents, including Metarhizium anisopliae at 5 ml per litre of water (for liquid formulations), are on par with neem‑based oils for the management of stem borer. Metarhizium infects both the larvae and adult stages of borers. The fungal spores penetrate the borer's cuticle, grow inside, and kill the insect within 3‑7 days. Since the fungus can persist in the environment, it provides longer‑lasting protection than chemical sprays.

For thrips control:

Research at the Indian Institute of Horticultural Research (IIHR) has shown that application of Metarhizium anisopliae at 1×10⁷ spores per ml resulted in significantly higher yield (3.1 kg per plant) and very low thrips incidence (only 3.6 thrips per plant) compared to the untreated control, which yielded only 0.825 kg per plant and had 11.42 thrips per plant. Metarhizium is effective, non‑chemical, pesticide‑free, eco‑friendly, conserves biodiversity, and has no phytotoxicity.

How to apply Metarhizium anisopliae on cardamom (Bactostore method):

For root grub control (KVK and KAU recommended):

• Take 25g of Metarhizium powder per plant

• Mix with well‑decomposed cow dung (enough to form a paste)

• Apply this mixture around the base of each cardamom plant, in the root zone

• Repeat every 4 months during the growing season

• Alternatively, soil drench: Mix 10g of Metarhizium powder in 1 litre of water and apply 5‑10 litres per plant as drench

For foliar spray (for borers, thrips, and other foliar pests):

• For liquid formulation: Mix 3‑5 ml of Bactostore's Metarhizium anisopliae liquid in 1 litre of water. For 1 acre, use 1‑2 litres of liquid diluted in 200‑400 litres of water.

• For powder formulation: Mix 5‑10g of Bactostore's Metarhizium powder in 1 litre of water. For 1 acre, use 1‑2 kg of powder diluted in 200‑400 litres of water.

• For better results, add 2 kg jaggery (gur) to the mixture and let it sit overnight – the sugar feeds the fungus, boosting spore germination.

• Spray thoroughly on both sides of leaves, on stems, panicles, and capsules. Pay special attention to the base of pseudostems where borer larvae enter and the root zone for grub control.

• Spray in early morning or late evening when humidity is high. Cloudy days are ideal.

• Repeat every 10‑15 days during the active pest season.

Three golden rules for cardamom farmers:

1. Apply in early morning or late evening – UV rays kill Metarhizium spores. Cloudy days are best.

2. Keep the soil moist for 2‑3 days after soil application – the fungus needs moisture to germinate and infect grubs.

3. Never mix with chemical fungicides – they will instantly kill the beneficial fungus.

Buy from Bactostore. We deliver fresh Metarhizium anisopliae – liquid or powder – to all Idukki cardamom areas. Mention "Cardamom pest control" for a 5% discount.

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