CO₂ enrichment, the deliberate increase of CO₂ concentration in a greenhouse, offers potential to accelerate plant growth and improve yield and product quality. "Elevated CO₂ increases the rate of photosynthesis, so the plant produces more carbohydrates", explains Emilia Mikulewicz with consultancy company Cultiva EcoSolutions. "But if nitrogen in fertilization is supplied abruptly or irregularly, part of it isn't immediately incorporated into proteins. This raises the pool of free amino acids (FAA) in the phloem—making the sap exceptionally attractive to aphids."
© Cultiva EcoSolutions
Emilia explains that aphids then reproduce faster and transmit viruses more easily. "For the grower, this means one thing: more expensive IPM. The lack of synchronization between CO₂ and nitrogen management can trigger uncontrolled pest pressure and disrupt the entire protection system. Today, it's increasingly clear that aphid pressure depends not only on the total nitrogen dose, but also on its form, the size and frequency of applications, and how well they align with growth conditions inside the facility."
According to Emilia, the key is steady, calm delivery of nitrogen. "With stable, continuous N nutrition and adequate light, the plant can incorporate nitrogen into proteins efficiently and avoid building up excess FAA even under CO₂ enrichment. This smooth nitrogen processing prevents sudden physiological shocks. Avoid abrupt corrections after cloudy periods or low-radiation days." It's also important to respond to low nighttime transpiration, high humidity, low VPD, or drops in substrate temperature—all of which slow nitrate reduction.
© Cultiva EcoSolutions
"To limit aphid pressure during CO₂ enrichment," she continues, "maintain a stable predominance of nitrate over ammonium and urea forms—especially under cold or low DLI conditions. Keep EC stable and make gradual nutrient adjustments instead of abrupt daily changes. The physicochemistry of the root zone is critical: high dissolved oxygen, favorable redox conditions, proper solution temperature, and the absence of stagnation all support efficient protein synthesis and help reduce the FAA pool."
Ongoing monitoring is essential. "Track fast-responding indicators such as NO₃⁻ in sap, conductivity, or the Brix:NO₃⁻ ratio, and watch aphid pressure on reference plants. In practice, some CEA operations compare Brix values of leaf sap with nitrate content as an indirect measure of the C:N balance. When Brix increases while NO₃⁻ remains stable or decreases, it typically signals a lower FAA pool and reduced attractiveness of the phloem to aphids. But this index isn't standardized—the result depends on sampling protocol, plant species, leaf position, time of day, and the plant's water and potassium status. It's best used for trend tracking within the same block, and nutrition decisions should always combine data and IPM observations."
© Cultiva EcoSolutions
CO₂ enrichment enhances photosynthesis and biomass gain, but its effectiveness depends on the plant's ability to form strong, resilient tissues. "Under limited transpiration—caused by high humidity or cool nights—calcium transport through mass flow is hindered. A potassium surplus can also displace Ca and Mg from the cation complex. When Ca supply to meristems drops, fewer Ca pectates form in cell walls, increasing susceptibility to micro-damage and pest punctures. This can offset the benefits of CO₂. The best results come with a balanced K:Ca:Mg ratio and a stable root-zone environment. Only then does higher carbohydrate production translate into durable tissue quality and lower pest sensitivity."
"When CO₂ levels are raised, always intensify scouting for 10–14 days and lower intervention thresholds by one level," advises Emilia. "This precaution helps manage the risk associated with rising FAA levels. Control vegetative growth through climate management—especially night VPD—and by adjusting the form of nitrogen. The goal is to moderate excessive young tissue development, which aphids prefer."
Aphid populations can surge very quickly. "In such cases, biological interventions like Beauveria bassiana may act too slowly—the fungus typically takes 3–5 days to work. During that time, aphids still feed, reproduce, and spread viruses. If biological products are applied only after a spike in FAA, it's often too late. The pest population surpasses the threshold, and chemical correction becomes necessary. That's why, under elevated CO₂, growers should closely monitor biological control performance and shift treatments toward prevention. Avoid long delays between the first signs of rising FAA and bio-interventions, and increase application frequency during high-risk periods. This proactive timing is key to effective IPM under dynamic plant physiology."
It's also becoming common practice to protect biologicals by applying them during non-conflict windows—separating bioproduct applications from oxidants and strong acidification events on the same day. "Recording the full chain from sensor → decision → result ensures traceability and confidence that biological treatments operate under optimal conditions."
"CO₂ raises potential," concludes Emilia, "but nitrogen discipline determines whether IPM costs rise along with it. Manage nitrogen form and timing, maintain cation balance, and control vegetative growth. With this foundation, biological and targeted interventions work faster, cost less, and carry a lower risk of resistance."
For more information:
Cultiva EcoSolutions
cultivaeco.com
Dr Emilia Mikulewicz, Ph.D.
Email: [email protected]