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Common treatments include hand removal, B. thuringiensis (Bt), assassin bugs, and lacewings. Chemical application is not recommended, as it is often more damaging to beneficial insects than target pests and leads to chemical resistance.

White flies: White flies are sap-sucking insects that are significant pests in a wide variety of vegetable crops (Figure 19i).

There are three primary whitefly species that impact vegetable crops in the U.S.: the sweet potato, greenhouse, and the banded-winged whitefly (Natwick et al. 2016). Adults of these species are small (1.52 mm) with yellow bodies and wings covered in a white, waxy powder. Most life stages are found on the undersides of leaves, where the adults and nymphs feed. Commonly affected crops include beans, broccoli, cabbage, cauliflower, cucumber, eggplant, melon, peppers, squash, tomato, and watermelon.

Plants with heavy infestation levels may appear stunted, have yellowing or silvering of the leaves, and have defoliation resulting in reduced yields. Honeydew, excreted during feeding by whiteflies, can reduce the quality and marketability of vegetable crops. Perhaps the most damage caused by whiteflies is their role as a vector for more than 100 different plant viruses.

Natural enemies can be effective in reducing or controlling pest levels in greenhouses. Common biological controls are predators (lacewings, bigeyed bugs, lady beetles), parasites (specifically Encarsia formosa, a parasitic wasp), and fungal entomopathogens. Insecticidal soaps and oils can provide some control of whiteflies, but active compounds must cover the undersides of leaves where the insects hide. Thrips: Thrips are tiny narrow insects that are a common and persistent pest of vegetable crops in both greenhouse and outdoor systems (Figure 19j). Of the hundreds of species affecting vegetable crops, the Western Flower thrip and the Onion thrip are the most pervasive. Thrips, like other insects mentioned here, are sucking insects that drain water and nutrients from the leaves, leaving them discolored with silvery feeding scars and wilting of plant components.

Thrips: Thrips are tiny narrow insects that are a common and persistent pest of vegetable crops in both greenhouse and outdoor systems (Figure 19j). Of the hundreds of species affecting vegetable crops, the Western Flower thrip and the Onion thrip are the most pervasive. Thrips, like other insects mentioned here, are sucking insects that drain water and nutrients from the leaves, leaving them discolored with silvery feeding scars and wilting of plant components.

All life stages may be damaging, as eggs are commonly laid inside plant tissue, leaving a scar. Typically, the larval and adult life stages are going to be the most damaging due to plant feeding behavior and the risk of transmitting viruses to the plant. Thrips complete their lifecycle in 3-5 weeks.

Thrips can be hard to see directly on the plant, depending on the species. Shaking the leaf over a white piece of paper can help make them more visible. Treatment options vary according to species. Biological controls include lacewing larvae, pirate bugs, and predatory thrips.

Management of the culture environment and prevention is key to preventing thrips. Use of sticky traps placed at the base of plants or examination of the underside of leaves for feeding scars are ways to monitor for presence of thrips. Thrips can be prevented by using proper sanitation protocols for culture equipment, only using seedlings grown in-house, and preventing weedy areas or overgrown vegetation near the plants or greenhouse.