Hartley Magazine

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Banish Bugs in your Greenhouse

Pest control starts long before the question- “What do I spray?”

This month greenhouses take center stage in the gardening year. However, insects can come along with the show. I’ve turned to Sue Nicol, a Seattle consulting horticulturalist and arborist ([email protected]) for advice on indoor pest management. Sue says, the first question all greenhouse owners should ask themselves- “Is this a healthy place for plants and people?”

Sue then outlined a series of simple steps in integrated pest management that will allow you to say “yes!”to that question every time you enter your own greenhouse.

1. Test for Stress

It’s true- robust plants resist pests and disease. Stressed plants are more vulnerable. The first step is to control the traumatizing factors. A greenhouse environment is actually easier than in the open garden.

Consider the big three temperature, light requirements and fertilizing. Research the specific growing requirements of your plants and meet them. For instance, there’s a big difference between the needs of tropical plants and temperate ferns.

#2. Know your Enemy

Five common greenhouse pests are aphids, mealy bugs, scale, spider mites and thrips. Start with physically keeping bugs out- screen all openings, including fans. Quarantine incoming plants and check for unwanted critters.

Sue recommends a hand lens or a simple ten-power loop for hunting down offenders. Turn over leaves, look in stem crotches. Colored sticky squares attract flying pests and allow quick identification. Get to know which plants are most at risk-often citrus-and inspect those first at least once a month.

3. Clean up Common Culprits

“Ninety percent of pest control,” Sue says, “is cleaning the plants.” Her weapon of choice is a strong spray of water for knocking off sucking insects like aphids. Scale can be wiped away with a damp cloth or (gently) a rough sponge.

Expect to clean more than once before eradication. Regularly sweep and hose off benches, floors and cracks. Keep a soil floor well weeded so pests have no place to hide.

4. Spray Last, not First

For a major infestation, Sue advises using an ultra-fine horticultural oil spray followed up three days later with a plant wash down. Faced with an outbreak of thrips and long-tail mealy bugs in a client’s greenhouse, Sue sprayed the oil once a week for a month. Three days after each application, she thoroughly washed the plants. The regimen was successful-no thrips, and few mealy bugs left. Another plus? Bugs don’t gain resistance to the smothering effects of oil.