Why May Is the Most Important Month in Your Greenhouse IPM Calendar

Greenhouse IPM in spring is not reactive — it's foundational. May represents the narrow window between the lower-pressure winter period and the exponential pest buildups that warm summer temperatures accelerate. Greenhouse whitefly (Trialeurodes vaporariorum) and fungus gnats (Bradysia spp.) are two of the most economically damaging pests in commercial greenhouse production, and both share a critical vulnerability: their populations are far easier to regulate when biological control is established preventatively, at low pest density, than when it's deployed curatively against an established infestation. If your greenhouse IPM biocontrol program isn't in place by mid-May, you're already behind the curve.

Building Your Whitefly Biocontrol Program in Spring

Greenhouse whitefly management relies heavily on the parasitic wasps Encarsia formosa and Eretmocerus eremicus, which parasitize whitefly nymphs on the undersides of leaves. Enermix — a combination card product containing both Encarsia formosa and Eretmocerus eremicus — provides broad-spectrum coverage against greenhouse whitefly and covers the temperature variation typical of spring production. Encarsia formosa performs best at temperatures between 64°F and 81°F; Eretmocerus eremicus functions well at higher temperatures, making the combination product well-suited to the transitional conditions of a May greenhouse. Introduce parasitic wasp cards at the start of the crop or as soon as new plants arrive, at weekly intervals, maintaining a preventative release schedule throughout the production cycle. Monitor with yellow sticky traps — placed at canopy height — to track adult whitefly populations and evaluate whether your release rate is sufficient.

Biological Control for Fungus Gnats in Commercial Greenhouses

Fungus gnat pressure in commercial greenhouses peaks wherever moist growing media and organic-rich substrates are found — which, in May, means propagation areas, plug trays, and recently transplanted crops. The two standard biological controls are Steinernema feltiae nematodes and the predatory mite Stratiolaelaps scimitus. Steinernema feltiae — in Entonem OMRI — is applied as a drench to moist growing media, where the nematodes actively seek out and kill fungus gnat larvae in the soil. For best results, apply to media that is already moist, and water again after application to drive nematodes down into the root zone. Stratiolaelaps scimitus — the predatory mite in Entomite — is a soil-surface predator that feeds on fungus gnat larvae, thrips pupae, and other small soil-dwelling pests. Introduce Entomite at the start of the crop cycle as a preventative measure, particularly in propagation houses where gnat pressure is typically highest.

Scouting and Monitoring: The Foundation of Effective Greenhouse IPM

No greenhouse IPM biocontrol program delivers consistent results without a rigorous scouting protocol. In a commercial greenhouse, weekly scouting is the minimum standard — in high-pressure periods or with new crop introductions, twice-weekly inspection of representative plants is justified. Map your greenhouse in zones and assign scouting routes that cover all sections systematically. Record pest counts per sticky card, per plant, and per zone. Track the presence of biological control agents alongside pest counts — evidence of Encarsia parasitization (black mummies on leaf undersides), predatory mite activity, or nematode-killed gnat larvae in potato trap slices all confirm your program is working. Read the comprehensive IPM scouting guide for monitoring protocols that support data-driven release decisions.

Chemical Compatibility: Protecting Your Biocontrol Investment

One of the most preventable failures in greenhouse IPM spring setups is the inadvertent destruction of biological control agents through incompatible pesticide applications. Any fungicide, insecticide, or growth regulator applied to your crop must be checked against published compatibility tables before application. Many commonly used fungicides have significant residual toxicity to predatory mites and parasitic wasps. Establish a formal chemical use log for your operation, record every application with date, product, and rate, and require that all biocontrol introductions be scheduled relative to the most recent spray date. Visit the greenhouse growing solutions page to build a complete spring biocontrol schedule tailored to your crop mix and production timeline.