Whiteflies are minute, winged insects that feed by piercing plant tissue and sucking out the sap. They are often found clustered on the undersides of leaves, and when disturbed, they flutter up in a noticeable swarm. Direct damage occurs as they extract plant juices, causing leaves to yellow, shrivel, and drop prematurely. Whiteflies also excrete a sticky, sugary waste product called honeydew, which encourages the growth of black sooty mold that covers the leaves and interferes with photosynthesis. Understanding which plants whiteflies favor is key to protecting a garden or landscape from an infestation.
Primary Host Plants: High-Risk Vegetables and Ornamentals
Whiteflies, particularly the Greenhouse Whitefly and the Silverleaf Whitefly, have an incredibly broad diet, infesting over 250 species of plants. They prefer soft-leaved, actively growing plants where feeding and reproduction are most successful. Many popular garden vegetables are highly susceptible, especially those in the nightshade family (Solanaceae) like tomatoes, peppers, and eggplant.
Cucurbit vegetables, including cucumbers and squash, are also frequently targeted, often experiencing significant damage and virus transmission. Other high-risk vegetable crops include beans, okra, and sweet potatoes, which are especially attractive to the Silverleaf Whitefly. Infestations can lead to stunted growth, reduced yield, and the transmission of various plant viruses.
Ornamental plants and shrubs in both outdoor landscapes and indoor environments are vulnerable. Tropical and subtropical plants are often favored hosts, with hibiscus being a common target. The Silverleaf Whitefly is particularly notorious for its preference for poinsettia, earning it the alternative name of poinsettia whitefly.
Other susceptible ornamentals include gardenias, lantana, and fuchsias, which offer the soft foliage and dense growth whiteflies seek for shelter and feeding. When purchasing new plants, inspecting the undersides of the leaves for small white insects or sticky residue is important to prevent introducing pests. Whiteflies collectively target plants with soft, tender tissue that provides easy access to the phloem sap.
Factors That Make a Plant Attractive to Whiteflies
The preference whiteflies show for certain plants is rooted in specific nutritional and physical qualities. Whiteflies require a high amount of nitrogen to synthesize protein-rich tissues and support rapid reproduction. This need causes them to prefer plants, or specific parts of a plant, that exhibit high nitrogen content.
Plants treated with high levels of nitrogen fertilizer become significantly more attractive for feeding and egg-laying. This is because the phloem sap, which whiteflies consume, is richer in amino acids and nitrogen compounds. Whiteflies are also visually drawn to specific light reflections, particularly in the yellow-green spectrum, which mimics tender, new foliage.
The physical characteristics of the leaves also play a significant role in host selection. Whiteflies prefer soft, smooth leaves with minimal defensive structures. Leaves that lack a dense layer of glandular hairs (trichomes) are easier for the insect’s piercing mouthparts to penetrate and reach the phloem. Highly preferred plants often lack defensive chemical compounds, known as allelochemicals, which deter feeding.
Plants That Naturally Deter Whiteflies
Strategically planting certain species can help reduce a garden’s attractiveness to whiteflies, as these plants possess natural repellent properties. Many aromatic herbs are effective deterrents because they release volatile organic compounds that confuse or mask the attractive scents of host plants. Basil, with its strong fragrance, is frequently cited as a plant that can repel whiteflies when planted near susceptible vegetables like tomatoes.
Other pungent herbs like rosemary, mint, oregano, and thyme also release powerful essential oils that interfere with a whitefly’s ability to locate its food source. The presence of these highly fragrant plants creates a sensory disruption, making the host plant invisible to the pests. Planting garlic and chives among vulnerable crops also contributes to a less appealing environment due to their strong sulfur-containing compounds.
Certain flowering plants also possess defensive compounds that discourage whitefly habitation. Marigolds, particularly the French varieties, exude chemicals from their roots and foliage that act as a broad-spectrum pest deterrent. Nasturtiums serve a dual purpose: their foliage repels whiteflies, and they also act as a sacrificial trap plant for other pests like aphids. These plants manage whitefly populations by disrupting the insect’s natural feeding and oviposition behaviors.