Skip to content 
Botrytis can destroy my marketable yield fast. A few humid nights can turn pruning wounds into stem rot and cause gray mold on leaves and trusses.
To prevent Botrytis in an Almería tomato greenhouse, I control dew point and VPD, dry the canopy early, prune only when plants are dry, and remove crop debris fast. This reduces wet hours and cuts infection pressure without sacrificing yield.
A dashboard view of moisture risk and plant stress.
Almería is one of the world’s most concentrated greenhouse regions, so small management mistakes scale into big losses. NASA explains how this region’s plastic-covered agriculture supports very large output. NASA Earth Observatory<1> That scale is the reason I run humidity control like a daily production system, not an emergency response.
Why does Botrytis spread so fast in tomato greenhouses?
Botrytis is not “random.” It follows moisture and weak tissue. When leaves stay wet and wounds stay wet, Botrytis wins.
Botrytis spreads fast when humidity stays high, leaf wetness lasts for hours, and pruning creates fresh entry points. If the crop dries slowly, infection risk rises even before I see gray spores.
Wet scars are common infection entry points.
University guidance confirms that gray mold thrives under high humidity in greenhouse settings. University of Minnesota Extension<2> I use that as a simple rule: if I reduce wet hours, I reduce disease pressure.
I also keep a second rule: Botrytis outbreaks often start where the crop is stressed or crowded. So I look for the places where air does not move well, not only the places where the thermometer looks high.
What humidity control metric works best: RH, dew point, or VPD?
RH is easy to read but it can mislead me. Dew point and VPD tell me what the plant actually experiences.
I use dew point to avoid condensation and I use VPD to keep transpiration stable. RH is useful, but dew point and VPD explain why Botrytis risk changes even when RH looks similar.
Dew point and VPD show moisture risk clearly.
Michigan State University Extension explains why VPD matters for greenhouse growers and how it connects to plant water loss and stress. Michigan State University Extension<3> I use VPD because tomatoes are more stable when transpiration is stable. When VPD is too low for long periods, the crop does not “pull” water well, leaves dry slowly, and disease pressure rises. When VPD is too high, the crop stresses and fruit quality can drop. So I aim for stable, moderate conditions.
My daily humidity goal is not “low RH.” My daily goal is “no long wet hours.”
How do I lower humidity in Almería without losing CO₂ and yield?
If I vent too hard, I throw away CO₂ and can slow growth. If I vent too little, I trap moisture and invite Botrytis.
I lower humidity by combining early-day drying, uniform canopy airflow, and staged ventilation. I reduce heat load first so I do not cool into a wet greenhouse.
Air must move through the canopy.
I separate two jobs: air exchange and canopy airflow. Air exchange removes moist air. Canopy airflow removes wet pockets. Many outbreaks happen when exchange exists but airflow is weak at crop level.
I also avoid humidity traps caused by cooling choices. Fan-and-pad evaporative cooling has limits and can add moisture, especially when outside air is already humid. University of Florida IFAS explains how fan-and-pad systems work and why performance depends on outside conditions. University of Florida IFAS Extension<4> In practice, when humidity is high, I use shading and ventilation first. I do not push more water into the air.
For structure and airflow capability, these pages help me connect greenhouse type to ventilation performance:
- https://cfgreenway.com/multi-span/
- https://cfgreenway.com/wide-span/
- https://cfgreenway.com/sawtooth/
- https://cfgreenway.com/shade-net-rainshelter/
What pruning and sanitation routine prevents Botrytis at the source?
A perfect climate plan fails if my team prunes wet plants and leaves debris inside the greenhouse.
I prevent Botrytis by pruning only when plants are dry, removing debris the same day, and creating a daily “dry-out window” so wounds dry quickly.
Dry pruning and fast cleanup reduce infection pressure.
Penn State Extension stresses sanitation and highlights that heating and ventilating can prevent high humidity, often by extra venting early in the day. Penn State Extension<5> That fits my routine.
My routine is simple:
- I dry the canopy early when conditions allow.
- I prune later when plants are dry.
- I remove leaves and stems fast.
- I avoid leaving dead tissue in the crop.
- I keep airflow uniform so one corner does not become the “disease corner.”
This workflow often reduces chemical dependence. It also protects yield because the crop stays cleaner and more stable.
If I want this to run consistently across teams and shifts, I use automation and clear control staging. That is why I connect climate and operation logic using:
https://cfgreenway.com/solutions/smart-auto-control/
Conclusion
To prevent Botrytis in an Almería tomato greenhouse, I reduce wet hours. I control dew point and VPD, dry the crop early, prune only when plants are dry, and remove debris fast. This protects marketable yield without sacrificing growth.
External Links Footnotes (Authority Sources)
1> https://science.nasa.gov/earth/earth-observatory/almerias-sea-of-greenhouses-150070
<2> https://extension.umn.edu/disease-management/gray-mold-tomatoes
<3> https://www.canr.msu.edu/news/why_should_greenhouse_growers_pay_attention_to_vapor_pressure_deficit_and_n
<4> https://edis.ifas.ufl.edu/publication/AE069
<5> https://extension.psu.edu/botrytis-or-gray-mold
—
## Internal References (CFGET)
– **CFGET Homepage**
– **Commercial Greenhouse Systems**
– **Smart Auto & Control Solutions**
– **Pest Barriers**
– **Multi-span Film Greenhouse**
– **Wide-span Greenhouse**
– **Sawtooth Greenhouse**
– **Shade Net & Rain Shelter Systems**
– **Contact**
—
## Internal Blog References (Related CFGET Articles)
– **Choosing the Best Greenhouse for Tomato Plants: Key Design and Climate Considerations**
Choosing the Best Greenhouse for Your Tomato Plants: Key Considerations?
– **How to Set Up a Commercial Greenhouse: An Essential Guide for Growers and Agribusinesses**
How to Set Up a Commercial Greenhouse: Essential Guide for Growers & Businesses?
– **Hydroponic Greenhouse Systems: Investment vs Yield, ROI Models, and Payback Periods**
Hydroponic Greenhouse System Investment vs Yield: Real ROI Models, Break-Even Yield & Payback Years?
– **How Much Does It Cost to Build a Smart Greenhouse? Hidden Costs You Should Know**
How Much Does It Cost to Build a Smart Greenhouse? What Are the Hidden Costs?
– **Why Sawtooth Greenhouses Beat the Heat with Zero-Energy Natural Ventilation**
https://cfgreenway.com/sawtooth-greenhouses-beat-the-heat-with-zero-cost-natural-ventilation/
