For commercial growers, the appearance of the infamous two-spotted spider mite (Tetranychus urticae) is more than just a nuisance; they are a direct threat to the aesthetic value and marketability of your crop. Particularly the high-stakes world of ornamental production, where a single visible web can render a plant unmarketable, waiting for damage to become obvious is a strategy for failure.
The key to protecting your margins isn't a stronger chemical; it’s a more sophisticated monitoring program. Spider mites have evolved to be the ultimate greenhouse survivors, and your first line of defence must be detecting them before they reach their exponential growth phase.
Resistance: Why chemicals aren't enough
If you feel like your miticide applications aren't as effective as they used to be, you aren't imagining it. Spider mites have the highest documented resistance to pesticides of all insects, with resistance recorded against more than 90 active ingredients.
This rapid evolution is driven by their unique biology. Through a process called arrhenotoky, unfertilised eggs develop into males. When a female mates with her own offspring, intense genetic recombination occurs, leading to a high frequency of mutations and the rapid development of resistance. Relying solely on a chemical "silver bullet" is a losing game; an Integrated Pest Management (IPM) approach is the only way to stay ahead.
Monitoring: Walking the line
There is no substitute for regular, disciplined crop walking. Because spider mites do not fly, traditional sticky traps are ineffective for monitoring their presence. Instead, you must be the eyes of your operation.
What to Look For
- Stippling: The earliest sign of infestation is light-yellow stippling on the leaves. These tiny spots occur when mites pierce plant cells with their needle-like mouthparts to suck out the contents.
- Location: Focus your monitoring on the undersides of new and medium-aged leaves. Be sure to check "hot zones" first—areas near heating pipes, south-facing edges with high sun radiation, or spots where the crop is particularly dry.
- Webbing: If you see silk threads draped over the canopy, you have reached a late-stage infestation. Spider mites use this webbing to protect their eggs and to "hitch a ride" on air currents or worker clothing to move throughout your facility.
Essential Tools
At a minimum, every grower should carry a x10 or x20 hand lens. Without magnification, identifying the translucent eggs (only 0.13 mm) or the straw-coloured larvae is virtually impossible until the population has already exploded.
The biological arsenal
Early detection allows you to deploy natural enemies when they are most effective. In a professional IPM program, we categorise our beneficials by their specific roles:
The specialist: Phytoseiulus persimilis
Phytoseiulus is the "gold standard" for curative control. This predatory mite is highly voracious, capable of consuming up to 20-25 eggs or 7 adult spider mites per day. It breeds faster than its prey at optimal temperatures (20–25°C) and can completely eradicate a colony. However, because it only eats spider mites, it cannot be used preventatively; it will starve if the pest is absent.
The preventative powerhouse: Neoseiulus californicus
For long-term protection, N. californicus is indispensable. Unlike Phytoseiulus, this mite can survive on a diet of pollen or alternative prey when spider mites are scarce. It is also far more tolerant of the hot, dry conditions that often cause other biologicals to fail. Releasing these via breeding sachets provides a continuous "walk-out" of predators over several weeks.
The early bird: Amblyseius andersoni
In the early season or in cooler greenhouses (as low as 6°C), A. andersoni is your best ally. It is one of the few predators that can actively hunt the diapausing (overwintering) forms of spider mites as they emerge from cracks and crevices in the spring.
The hotspot hunter: Feltiella acarisuga
When you find a dense hotspot, the predatory midge Feltiella can be a game-changer. The adults are excellent fliers and will actively seek out the largest mite colonies to lay their eggs. Their larvae are incredibly voracious, consuming up to five times more prey than Phytoseiulus.
Start winning the battle today
- Establish a "Bio-First" Culture: Train your staff to recognise the difference between the pale, round eggs of the pest and the larger, oval, pinkish eggs of predatory mites.
- Prioritise Hygiene: Always scout infested areas last. Mites are easily carried on clothing, and you can inadvertently become the primary vector for an outbreak.
- Manage the Microclimate: Low humidity is the enemy of most predatory mites. Occasionally boosting humidity or misting leaf undersides can dramatically improve egg hatch rates for your beneficials.
- Respect the Residuals: Before releasing predators, check your spray history. Many common insecticides (like pyrethroids or neonicotinoids) have residual toxicity that can kill your beneficial mites for weeks or even months after application.
Master your IPM strategy
Detecting the first mite is only half the battle. Knowing which predator to release, at what rate, and how to support their establishment is what separates the professionals from the rest.
If you are ready to move beyond "bucket science" and build a truly resilient pest management system, we invite you to explore our advanced course: Spider mites and their natural enemies.
Don't wait for the webbing to appear. Start your monitoring program today and let biology do the heavy lifting.
