News » 12.10.2026 - How greenhouse airflow influences biological control and plant communication
Horizontal airflow (HAF) is central to greenhouse climate management, but airflow velocity at the crop canopy must be balanced against the flight requirements of biological-control agents. According to Frank Giglia, Owner of Signature Supply, the practical target is 0.2 to 0.4 m/s (40 to 80 ft/min) at canopy level.
"The optimal canopy-level airspeed to balance fungal prevention with beneficial insect flight and establishment is 0.2 to 0.4 m/s." At velocities below approximately 0.15 m/s, stagnant boundary layers can persist around leaves, increasing localized humidity and condensation risk associated with diseases such as Botrytis and powdery mildew. At 0.2–0.4 m/s, airflow is generally sufficient to remove excess moisture from leaf surfaces while maintaining conditions in which flying beneficials can function.
Frank describes this range as "the sweet spot" for commercial IPM systems. Above approximately 0.5 m/s, however, the biological trade-off becomes more significant. Micro-parasitoids such as Encarsia, Eretmocerus and Trichogramma can have difficulty maintaining directional flight as velocity increases.
"When air is pushed too hard, these sub-millimeter insects drop out of the air column to cling to leaf undersides, reducing their host-searching radius to a single pot."
Predatory mites such as Phytoseiulus persimilis, Amblyseius swirskii and Neoseiulus cucumeris are less affected mechanically because they move across plant surfaces. However, stronger airflow can increase drying and potentially reduce localized humidity important for mite development.
Adjusting airflow around beneficial releases
Airflow management can therefore be incorporated into biological-control release protocols. He recommends temporarily reducing HAF operation immediately after releasing flying beneficials.
"Turn HAF fans off or run them at minimum variable-frequency drive (VFD) speed, around 20–30%, for 2 to 4 hours immediately following a release."
Predatory midges require additional consideration. "Aphidoletes aphidimyza is most active during dusk and nighttime, when mating and host-searching flights occur," Frank recommends maintaining airflow toward the lower end of the target range during this period.
"If using predatory midges for aphid control, reduce HAF speeds to the lower end of the window, 0.2 m/s, between dusk and dawn." Measurement location is also important. Airspeed should be measured at crop level using a sensitive hot-wire anemometer rather than near the fan or beneath the greenhouse trusses.
"HAF fan jets lose velocity as they travel down the bay, meaning canopy air is typically 40–60% slower than the open air stream just below the trusses."
Communication between potted plants
Containerization does not eliminate communication between plants. Frank says that while individual pots largely prevent the formation of shared root systems and common mycorrhizal networks, plants can exchange information through airborne chemical signals and light perception.
When plants experience pest pressure, pathogen attack or mechanical damage, they can release volatile organic compounds (VOCs), including herbivore-induced plant volatiles. Neighboring plants can detect these compounds and alter their defensive physiology. Some volatile blends can also contribute to the recruitment of natural enemies.
"Potted nursery plants actively communicate with one another." In addition to airborne signaling, plants respond to changes in the red-to-far-red light ratio created by surrounding vegetation. According to him, this can occur before direct shading develops and may trigger shade-avoidance responses such as stem elongation, upward leaf orientation, and changes in branching.
Implications for commercial crop management
The greenhouse environment therefore links airflow, biological control and plant signaling. Strong HAF currents can improve moisture removal and temperature uniformity while simultaneously dispersing volatile chemical signals and interfering with flying beneficials.
"High airflow from horizontal air flow (HAF) fans rapidly disperses volatile plumes, diluting chemical warning signals between plants while simultaneously drying microclimates."
For commercial growers, the practical objective is not maximum airflow, but appropriate airflow at the crop level. Monitoring canopy velocity, adjusting fan operation around biological releases, and considering crop density can help integrate climate control with IPM and plant physiological responses.
Frank will be in Ontario around the Canadian Greenhouse Conference and available for meetings.
Source: www.floraldaily.com
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