A Proactive Pest Management Guide for Greenhouse Production

Postiva Fungicide control of powdery mildew on Gerbera Daisy

Postiva Fungicide control of powdery mildew on Gerbera Daisy | Syngenta

The warm, humid environment of greenhouse production creates perfect conditions for pests to threaten healthy plants. Unwanted visitors, from aphids and fungus gnats to powdery mildew, can rapidly multiply and devastate crops. This is why it is crucial to implement proper scouting techniques throughout production, as early action can minimize damage.

Growers should inspect new plants for insects and diseases before introducing them into production areas and frequently inspect the upper and lower surfaces of leaves, stems, and growing media. It’s also important to understand how to scout for the most common greenhouse pests.

Female black fungus gnat

Female black fungus gnat | EBKuai

Watch Out For: Fungus Gnats and Shore Flies

While adult fungus gnats are primarily a nuisance, larvae feed on plant roots and stems, allowing soilborne pathogens to enter and cause disease. Adult fungus gnats are dark, mosquito-like insects, with long legs, one pair of clear wings, and a Y-shaped vein in the wing pattern. Larvae are legless, thread-like, and transparent. Scout for fungus gnats with yellow or blue sticky cards placed where the insects are likely to congregate and check them weekly.

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Shore flies don’t typically feed on plant tissue and instead favor algae or decaying organic matter. Adult shore flies are slightly larger than fungus gnats and resemble small houseflies with stockier bodies. They have shorter legs and antennae than fungus gnats and are also stronger, faster fliers. The wings on the shore fly have distinct white dots, which is helpful for identification. Shore fly larvae are white, wedge-shaped, and do not have distinctive heads. Shore flies are typically spotted where water and algae accumulate and can be easily scouted using yellow or blue sticky cards.

Thrips Injury On Impatiens taken by Nancy Rechcigl

Thrips injury on Impatiens | Nancy Rechcigl

Watch Out For: Aphids and Thrips

Aphids are soft-bodied insects with long legs and antennae, and range from greenish-yellow to dark green, dark brown, and black. They are often found feeding in groups on new growth and use their piercing mouthparts to extract fluids from stems, leaves, and other plant parts, which leads to distorted growth. When scouting for aphids, hold white paper under plants and shake or tap the foliage to dislodge pests or whitish cast skins. This will help reveal colonies that might be hidden in the foliage.

Adult thrips are tiny, elongated insects with featherlike long, narrow wings, while immatures are wingless. They vary in size and color ranging from yellow, yellow with a dark abdomen, red, black, or a combination. They feed by scraping and piercing plant tissue and sucking out the sap and cellular contents from leaf tissue, flower buds, and/or unexpanded shoot tips. As a result, leaf stippling (silvery streaking), scarring, and distortion can occur. Sticky cards and white paper should also be used when scouting for thrips. Place the white paper under open flowers, gently tap the flowers, and use a 10x magnifier to examine the insects that fall out. For thrips that feed in buds or shoot tips, clip off several plant parts and put them in a jar with 70% alcohol. Shake the solution to dislodge any thrips.

Botrytis On Rosemary taken by Nancy Rechcigl

Botrytis on rosemary | Nancy Rechcigl

Watch Out For: Botrytis

Botrytis blight, or gray mold, is the most common disease that affects ornamental plants. It is particularly threatening to newly propagated material like germinated/young seedlings and unrooted cuttings. Initial Botrytis infections result in water-soaked spots on foliage and flowers and can spread quickly. When scouting for symptoms of infection, look for small, light brown spots or tiny flecks on flowers, V-shaped, tan-brown lesions on flowers, and fuzzy brown or gray spores.

Monarda with powdery mildew colonies that have coalesced.

Monarda with powdery mildew | Elise Lobdell

Watch Out For: Powdery Mildew

Powdery mildew fungi form white, talcum-like spots on leaves, stems, and flowers. While powdery mildew is often first observed on the upper surface of the leaves, both sides may develop white spots, called “colonies,” so it is important to check both sides of the leaf. Over time, the colonies increase in size and number to cover the plant’s surface. If not controlled, severe infections will cause leaves to turn yellow, brown, and then drop, resulting in reduced plant vigor and growth. Additional infection symptoms include yellow or brown leaves and stunted growth.

Adopt an Agronomic Program

Effective pest management requires a well-rounded approach, beginning with rigorous scouting practices to prevent initial infestations. However, even with proactive scouting, it is crucial to implement a robust agronomic plan to protect plants from pests that enter the operation. An agronomic program provides a framework for product rotation that leverages the strengths of products with different modes of action and mitigates the risk of resistance development. By integrating regular scouting, sound cultural practices, and a strategic agronomic approach, growers can help reduce risks throughout the growing season and ensure healthier plants.

Learn more about agronomic programs at GreenCastOnline.com/Solutions.

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