Why Mycorrhiza Fails: 6 Reasons VAM Doesn't Colonise Roots (and a 3-Week Check) — India 2026

Short answer: Mycorrhiza (VAM) rarely fails because the product is "fake" — it fails because the fungus never gets a living root to colonise. The six usual causes are late application, a fungicide within 7–10 days, high soil phosphorus, waterlogging, a non-host crop and dead stock. Fix those and a correctly dosed VAM product is typically colonising roots within 2–3 weeks.

VAM only works when it is applied at planting, kept away from fungicides, and given roots that need phosphorus.

Reference prices (Oct 2026, incl. GST, free delivery): Mycorrhiza VAM Powder 1 Kg is ₹2,499 (6000 IP/gm, 100 g per acre, so about ₹250 per acre). Mycorrhiza VAM Liquid 50 Ltr is ₹5,800 (₹116 per litre; at 2–3 L per acre that is ₹232–₹348 per acre).

What "working" looks like

VAM fungi (Glomus intraradices and Glomus mosseae in our liquid) live inside root cells and extend fine threads into the soil, reaching phosphorus the root cannot. Our liquid specification is a minimum of 100 spore / 1200 IP per ml against an FCO 1985 minimum of 10, with root colonisation of 70% or more as the target. Colonisation takes about 2–3 weeks, so you judge the result at day 21, not day 5.

The 6 reasons VAM fails

1. Applied too late

The fungus needs young, growing feeder roots. Applying at flowering gives it little to colonise. Apply at sowing, transplanting or the first irrigation after planting. For transplanted crops, dip roots in 10 ml per litre for 30 minutes before planting.

2. A fungicide went on within 7–10 days

VAM is a fungus. Carbendazim, Mancozeb and similar fungicides can suppress it. Keep a 7–10 day gap either side. If a drench fungicide is unavoidable, apply VAM first and delay the fungicide.

3. Soil phosphorus is already high

Plants only host mycorrhiza generously when they are short of phosphorus. Check your Soil Health Card: if phosphorus is rated High, expect little response and save the money. Medium and low P soils respond best.

4. Waterlogged or puddled soil

VAM needs oxygen. In continuously flooded paddy the response is weak; it works better in aerobic or drip-irrigated crops such as vegetables, banana, sugarcane, arecanut, cotton and fruit trees.

5. The crop does not host mycorrhiza

Cabbage, cauliflower, mustard-family crops and beet do not form VAM associations. Use NPK Consortia there instead.

6. Dead or poorly stored stock

Heat kills microbes. Store drums in shade below about 30 °C, keep sealed, and use within the 18-month shelf life (liquid). Do not buy from a seller who cannot show an IP/gm or spore count on the label.

The 3-week field check

At day 21, gently uproot two plants from a treated row and two from an untreated strip. Treated plants should show more fine white feeder roots and firmer root balls. For a definite answer, send root samples for a lab colonisation percentage; the visual check is only an indicator.

Dose and cost summary

Powder: 100 g per acre, ₹2,499 per kg covers about 10 acres. Liquid: 2–3 L per acre in 200 L of water through drip or drench. For complete nutrition alongside, NPK+VAM Consortia 50 Ltr is ₹4,699 (₹94 per litre).

Frequently asked questions

How long does mycorrhiza take to work?

Colonisation takes about 2–3 weeks; visible root and growth differences typically follow after that.

Can I mix VAM with urea or DAP?

Avoid high concentrations of DAP in the same tank; apply the VAM first and fertiliser after, and keep fungicides 7–10 days away.

Is liquid or powder better?

Liquid suits drip and larger acreage; powder suits small plots, root dip and seed coating.

Does it need to be FCO compliant?

Yes. Orgogrowth Mycorrhiza complies with FCO 1985 and is made in an ISO 9001:2015 certified unit in Mehsana, Gujarat.

Results vary with soil, crop and management; this guide gives general agronomic guidance, not a guaranteed outcome.