4 steps to rid your greenhouses of pests to start the horticultural season off on the right foot

Start the horticultural season off right

Horticulturalists are beginning to open their seasonal greenhouses, start their seedlings and receive their first transplants. This is the perfect time to do a thorough cleaning. Here are a few tips for starting the season off strong!

Diapausic pests: an underestimated problem in greenhouses

The main pests in the horticultural industry can withstand the cold and are capable of surviving the winter in unheated greenhouses. The two-spotted spider mite (Tetranychus urticae) easily makes it through the cold months on the ground and in surrounding trees. The eggs of the greenhouse whitefly (Trialeurodes vaporariorum) can withstand several days at the freezing point. Thrips winter in fissures and cracks and on the ground, in plant debris.Unfortunately, you can’t count on the cold to kill pests in your greenhouse.

Four simple steps: Clean, disinfect, identify and introduce

It’s important to carefully clean and inspect everything in your greenhouse before the new season begins. Most pests easily survive the winter on the ground, in weeds, folds in the plastic sheeting and at the base of posts. Bacteria and other pathogens can survive in crop residues (e.g. bacterial cancer can survive up to 24 months in organic matter). A good cleaning will reduce the risk of disease and pathogenic organisms during the season.

1. CLEAN THE GREENHOUSE — By removing weeds and plant matter in and around the greenhouse.
2. DISINFECT THE GREENHOUSE — By cleaning with soap, dormant oil or other suitable cleaning products. A good cleaning will kill most pests in your work areas (e.g. potting table), on the ground and on or in your trays, bins and gardening tools.
3. IDENTIFY THE ENEMY — By planting pest indicator plants two weeks before your transplants are scheduled to arrive.
4. INTRODUCE ALLIES — By introducing ground-dwelling predatory mites, which reduce pest populations and establish themselves in the greenhouse for the season.

Pest indicator plants

Now’s the time to plant pest indicator plants. By attracting pests, they confirm the presence of pests in your greenhouse. Indicator plants include beans (spider mite), eggplants (aphids and whiteflies), chrysanthemum (thrips) and marigold (thrips).

Have your indicator plants in place two weeks before your transplants arrive. Place them where pests are likely to encounter them (entrance door, ventilation, warm areas, etc.). If you find pests on these plants, you will be able to disinfect again or adjust the number of predators accordingly.

Introducing ground-dwelling predatory mites

CIt can be difficult to apply disinfectant in some areas, like the underside of concrete slabs or plasticized carpets. Introducing ground-dwelling predatory mites in these areas will reduce pest populations during the season.

Stratiolaelaps scimitus is a generalist predatory mite used to control sciaridae, thrips and other ground-dwelling pests. As prevention, it reduces thrips populations by up to 30% by consuming the nymphs and pupae found on the ground. S. scimitus adapts to various substrates (potting soil, coconut fibre and rock wool) and can be added to pots. One or two introductions at the beginning of the season are enough to get the mites established in the greenhouse for the season.

See the Stratiolaelaps scimitus sheet