Monsoon Fungus Every Year? Check the Film Before the Soil

Every monsoon, the same story repeats. The rains arrive. The farm looks green. And then, slowly, something starts going wrong at the base of the plant. Leaves yellow. Stems soften. Crops that looked healthy a week ago begin to collapse. Fungal disease during monsoon is one of the most frustrating problems a farmer faces because it is invisible until it is already too late. Most farmers blame the soil, the seeds, or the rain itself. But here is what rarely gets discussed: the microclimate sitting directly under your mulch film may be doing more damage than anything above it.  

What the Film Is Quietly Doing to Your Soil 

Mulch film covers the soil to retain moisture, regulate temperature, and suppress weeds. In dry seasons, this works exactly as it should. But in monsoon, the same properties that make film useful can work against you if the conditions are not managed correctly. Here is what changes under the film during heavy rain:

• Moisture levels under the film rise sharply and stay high for longer
• Air circulation between the soil and the film surface drops close to zero
• Soil temperature stays warm while surface humidity stays high
• Organic matter trapped under the film begins to break down faster

This combination of warm, wet, still, and enclosed is precisely the environment where fungal pathogens thrive. It is not the film causing the problem. It is the microclimate the film is creating when it is not matched to monsoon conditions.  

Not All Mulch Film Handles Monsoon the Same Way 

Not all agriculture mulch film behaves the same way in high-humidity conditions. The difference between a film that traps moisture and one that manages it comes down to colour, installation, and drainage.

Film Type	Monsoon Behaviour	Fungal Risk Level
Black film (no drainage)	Traps heat and moisture under surface	High in waterlogged zones
Black film (with drainage)	Manages moisture if installed correctly	Moderate
Silver / Bi-Colour film	Reflects surface heat, reduces under-film temperature	Lower
Transparent film	Allows heat build-up, worsens humidity	High, avoid in monsoon
Biodegradable film	Begins breaking down in high humidity	Medium, check decomposition rate

The takeaway is simple. Black film in a high-humidity monsoon zone without proper drainage creates the warmest, wettest environment under the surface. That is where fungal pressure builds fastest. Silver or bi-colour agricultural mulching films reduce the under-film temperature by reflecting surface heat, which slows the rate at which humidity accumulates. It does not eliminate fungal risk, but it reduces the conditions that invite it.  

Your Planting Holes May Be Inviting the Fungus

This is one of the most overlooked causes of monsoon fungal attacks and it has nothing to do with the film material itself. When planting holes are cut too large, a gap forms between the stem of the plant and the film edge. During heavy rain, this gap becomes an entry point. What happens through an oversized planting hole:

• Rainwater carries soil particles and fungal spores directly into the root zone
• Soil splashes back upward through the gap, landing on the lower stem
• The gap stays wet longer than the surrounding film surface
• The enclosed warm air under the film creates the ideal temperature for spores to germinate

The fix is straightforward. Cut planting holes as close to the stem diameter as possible. Use a circular cutter rather than cutting free-form with a blade. A tight seal between the film and the stem dramatically reduces splash-entry during monsoon rain.  

What Loose Film Edges Do During Heavy Rain 

Most farmers focus on what is happening above the film. The real problem during the monsoon is often what is happening at the edges. When film edges are loosely anchored, monsoon rain lifts them. Water runs underneath. Soil disturbed by rain splash gets carried in. The wet soil under the film never fully dries out between rain events. Signs your film edges are failing during monsoon:

• Visible soil deposits appearing near the base of plants under the film
• Fungal symptoms appearing first at the edges of beds, not the centre
• Film corners lifting after heavy rain events
• Wet soil visible under the film when you check edge anchoring

Fungal infections that start at the bed edges and spread inward are almost always related to poor edge anchoring, not poor soil quality. Anchor film edges at least 8–10 cm deep. On monsoon-heavy farms, pressing a line of soil along the full edge length, not just at intervals, keeps water from running underneath during sustained rain.  

Fungus Already Spreading? Here Is What to Do 

Sometimes the diagnosis comes too late. The fungal attack has already started under the film before you identified the cause. Here is what to do mid-monsoon if pressure is building:

• Check planting holes first: widen or re-seal any gaps where soil splash is entering
• Lift and re-anchor any loose edges: stopping water entry is the first priority
• Improve drainage channels around beds: standing water near edges will keep finding a way under
• Avoid adding irrigation: most fungal pressure during monsoon comes from excess moisture, not lack of it
• Consider partial film removal on beds with severe waterlogging: ventilation sometimes matters more than moisture retention at this stage
• Do not pull the entire film if only edge sections are affected: targeted fixes cause less disruption

 

Which Crops Suffer Most Under Monsoon Film? 

Some crops feel this problem more sharply than others. In Eastern India, these are the ones most commonly affected during monsoon:

Crop	Why It's Vulnerable	Common Fungal Issue
Chilli	Shallow roots, sensitive to wet soil	Phytophthora root rot
Brinjal	Dense canopy traps humidity at base	Stem rot, wilting
Tomato	Long crop cycle overlaps full monsoon	Early and late blight
Strawberry	Low-growing, close soil contact	Botrytis, grey mould
Cucumber	Sprawling growth, high soil moisture	Pythium rot

If you grow any of these crops through monsoon, film colour, planting hole size, and edge anchoring deserve more attention than any fungicide you apply after the fact.  

The Fungus Will Return Until You Fix What's Below 

Soil quality matters. But if fungal attacks are returning to the same beds, the same crops, and the same edges every single monsoon, the soil alone is not the full answer. The microclimate under your agriculture mulch film the temperature, the moisture, the air movement, the seal around planting holes, shapes what grows there just as much as what is in the ground below it. Fix the conditions first. The fungal pressure follows.  

Frequently Asked Questions

Q1) Does mulch film make fungal attacks worse during monsoon? Not by itself. Film creates a microclimate that can favour fungal growth if drainage is poor, edges are loose, or planting holes are oversized. The film is not the cause, the conditions it creates can be. Q2) Which mulch film colour is safest to use during heavy monsoon? Silver or bi-colour film reduces under-film temperature by reflecting surface heat, which slows humidity build-up. Black film works too, but needs proper drainage and tight installation in high-rainfall conditions. Q3) Why do fungal attacks always start at the bed edges and not the centre? Loose edge anchoring allows rainwater and soil splash to enter under the film. The edges stay wetter the longest, making them the first point where fungal conditions develop and spread inward. Q4) Can I reuse mulch film that was on a fungal-affected bed last monsoon? Not recommended without thorough cleaning and sun-drying. Fungal spores can survive on film surfaces between seasons. Using the same film on a new crop cycle can carry infection from the previous season. Q5) Is removing mulch film before monsoon a better option for fungal-prone farms? It depends on the crop stage. Mid-season removal exposes soil, invites weeds, and loses moisture benefits. A better approach is improving drainage, re-anchoring edges, and switching to silver or bi-colour film before the season starts.