How to Manage Whitefly Infestations in Your Greenhouse

If there’s one pest that makes greenhouse growers grit their teeth, it’s whitefly. These tiny sap-sucking insects may look harmless at first, but give them a few warm days and they’ll explode in numbers, leaving your tomato leaves yellowing and sticky with honeydew. The good news? We’ve learned how to manage whitefly infestations using tried, tested, and chemical-free methods.

Spot Them Before They Settle In

Whiteflies tend to lurk on the underside of leaves, and you’ll often notice them fluttering up in a cloud when disturbed. Early signs include yellow mottling on leaves, sticky honeydew, and the sooty mould that often follows.

Check the underside of leaves every few days, especially on tomatoes, cucumbers, chillies, and aubergines, which whiteflies seem to love most.

Hang Up Yellow Sticky Traps

One of the easiest and most satisfying tools in our pest control kit: yellow sticky traps. These are irresistible to adult whiteflies and can help reduce their numbers before they lay more eggs. We hang them low among the plants and replace them as they fill up.

They’re not a complete solution, but they’re a great first line of defence and a good monitoring tool too.

Keep Air Moving

Whiteflies thrive in warm, still conditions, which is pretty much what most greenhouses offer by default. We counter this by keeping vents open on warm days and using a small solar-powered fan to improve airflow. Not only does this discourage pests, but it also reduces fungal disease and helps with pollination. Win-win.

Introduce Beneficial Insects

Our best allies in the war on whiteflies are tiny parasitic wasps like Encarsia formosa. These microscopic heroes lay their eggs inside whitefly pupae, killing them from the inside out. It sounds grim, but it’s incredibly effective, and completely natural.

We introduce these good bugs early in the season, before the whitefly population booms. Timing is everything.

Remove Heavily Affected Leaves

If a plant is heavily infested, we don’t hesitate to remove the worst-affected leaves. It helps reduce the population quickly and allows beneficial insects to catch up. Bag and bin these leaves, never compost them so they’re not accidentally spreading the problem.

Keep Plants Healthy and Stress-Free

Stressed plants are more vulnerable to pests. We make sure our greenhouse crops are well-fed, consistently watered, and never overcrowded. Strong plants can tolerate more pest pressure and recover quicker if an outbreak occurs.

Regular feeding with seaweed extract or compost tea keeps our plants resilient and boosts their natural defences.

Wash Them Off (Literally)

Sometimes we go old-school: hose down the undersides of leaves with a gentle spray. It knocks eggs, nymphs, and adults right off the plant. We do this early in the day so everything dries quickly, and we repeat it weekly if needed.

It’s basic, but incredibly effective in combination with other methods.

Clean Thoroughly Between Seasons

Whitefly pupae can hide in plant debris and greenhouse corners. At the end of the season, we clear out old plants, scrub down the frame and benches, and disinfect pots. It sets us up for a clean start next year and fewer problems down the line.

Managing whitefly infestations in your greenhouse doesn’t mean reaching for harsh sprays. With vigilance, a few natural allies, and good growing practices, we can stay one step ahead of these persistent pests and keep our crops thriving.