Thrips are insects in the order Thysanoptera, with approximately 6,000 described species. Their name is derived from a Greek word meaning “woodworm”, and in English, “thrips” is used as both singular and plural. There is no such thing as a single “thrip”!
These insects are very small — typically less than half an inch long — with slender bodies and narrow, fringed wings. They are usually translucent white or yellow in color but can sometimes be brown or black. Considered a sister group to the true bugs (order Hemiptera), the oldest known thrips fossils date back to approximately 270 million years ago. Other fossil thrips, from about 100 million years ago, are notable as the earliest evidence of plant pollination by an insect.
While some extant thrips pollinate flowers that they feed upon, many thrips species are notorious for the damage they cause to plants while feeding. Plant damage by thrips includes galls — that is, abnormal outgrowths of plant tissues — as well as curling or rolling of leaves. Streaks, speckling, and small white patches may be indicative of thrips damage, with more severe infestations leading to stunted flowers or fruits. Serious pest species include the western flower thrips (Frankliniella occidentalis) and onion thrips (Thrips tabaci), which both have a broad host range including many flowers, fruits, and vegetables.
1) Basil (Ocimum basilicum)
Native to the tropical regions of Central Africa and Southeast Asia, basil is a popular herb used in cuisines from around the globe. Many varieties of basil have been cultivated, ranging in color from vibrant green to deep purple and ranging in flavor from peppery to citrusy. Basil is easily identified by its glossy, oval leaves with smooth or lightly serrated margins. The leaf forms a slight cup shape and is arranged oppositely along the square stem.
Basil flowers are small and white or pink, arranged in terminal clusters. Basil is an annual herb but can sometimes be grown as a perennial in warmer climates. It can be started from seeds, either sown directly into the soil or germinated indoors, or from seedlings or cuttings.
This herb grows best in locations with 6 to 8 hours of full sun and thrives with moist but well-drained soil. As a hardy and low-maintenance plant, it can grow in containers or in a garden and is tolerant of a variety of conditions, though it cannot tolerate cold temperatures below 40°F.
The intense scent and oil from basil are famed for their pest-repellent properties and are reported to repel thrips as well as many types of flies. In addition to planting, basil can be harvested and scattered around the garden, burned as incense, or rubbed on the skin to provide further insect repellent applications. Basil is a common companion plant with tomatoes, asparagus, brassicas, and peppers, but should not be planted with cucumbers or fennel as it will compete for resources.
2) Catnip (Nepeta cataria)
Also known as catwort or catmint, catnip is a species of plant native to parts of Europe and Asia. This short-lived perennial resembles other members of the mint family, with a square stem and opposite leaves. The foliage ranges in color from brown or gray to a bluish-green, with triangular leaves and coarse-toothed leaf margins. The flowers of the plant are small and bilabiate, either pink or white in color, and occasionally with small purple spots.
Catnip is easy to grow, and thrives indoors or outdoors, though it can grow quickly, therefore care should be taken to avoid it becoming overgrown in a garden. A perennial plant, catnip prefers loamy or sandy well-drained soil and areas with at least six hours of direct sunlight. In hotter areas, some shade can be beneficial for growth. Catnip is drought-tolerant, and soil should be kept moist but not soaking, and it cannot tolerate cold temperatures or high humidity. It can be grown from seed but is also easily propagated by cuttings.
Most famous for the intense attraction that many cats have towards it, catnip is most frequently used as a recreational substance for domestic cats. Larger cats, such as leopards, cougars, and lynx, react in a similar manner, though lions and tigers may react to catnip but do not show consistent behaviors.
Catnip is popularly used as an insect repellent, with the same active compound that attracts cats, nepetalactone, shown to be a deterrent to flies as well as thrips, termites, cockroaches, beetles, and other pest insects. Studies have also shown that cats that have rubbed on catnip plants may do so to reduce mosquito bites. The same compound can also attract beneficial insects such as lacewings. As a companion plant, catnip grows well when paired with brassicas, squashes, beans, and root vegetables, but it should not be planted with rue or parsley since they may inhibit its growth.
3) Oregano (Origanum vulgare)
Sometimes called wild marjoram, the oregano plant is a woody perennial native to the Mediterranean region. It is common as an ornamental plant and as a culinary herb. The leaves are spade-shaped and olive green, with pink or pale purple flowers borne in clusters, though cultivars may vary somewhat in appearance. Oregano grows well in full light or partial shade with well-drained soil, either in a container or in a garden. It can be readily grown from seed as well as from split plants or cuttings.
It is a common companion plant with many vegetables, especially tomatoes, which benefit from its antifungal, antiseptic, and anti-pest insect properties. The essential oil of oregano contains many compounds such as thymol and carvacrol, which contribute to its strong flavor and its use as a pest deterrent.
Interactions between oregano and insect communities can be complex. For example, oregano can attract aphids away from other plants while also attracting hover flies (family Syrphidae), whose larvae prey upon aphids and other small insects. Oregano does not grow well with basil, chives, or mint since it requires much less soil moisture. Thrips will feed on oregano, so while it may attract them away from other plants, infested oregano leaves or other plant parts should be removed to prevent thrips from spreading.
4) Chives (Allium schoenoprasum)
A close relative of garlic, shallots, and onions, chives produce edible leaves and flowers that are commonly used for their mild flavor. The only Allium native to North America as well as Europe and Asia, they are easily recognized by their grass-like leaves and slender conical stem. The flowers are pale purple, star-shaped, and bunched together in a dense inflorescence. Chive flowers can also be used in dried bouquets.
This plant thrives in full sun with well-drained soil, usually planted in clumps either indoors or outside. They grow well as companion plants with nearly everything, except for plants with drier soil requirements such as rosemary, sage, thyme, and oregano. Peas may also be stunted somewhat by being planted near any members of the Allium genus.
In general, chives repel most insects, yet their flowers are highly attractive to bees and other pollinators. In addition to repelling Japanese beetles and carrot rust flies, chives may also draw thrips away from other plants. Though chives tend to have a repellent effect, some thrips species will still attack them, so chives can be used as a sentinel but should have damaged leaves removed and plants should be carefully inspected before relocation or harvest.
5) Garlic (Allium sativum)
Originally found in Central Asia and Iran, garlic has a long history of human use and consumption due to its powerful flavors and medicinal properties. With flat, blade-like leaves and pink or purple flowers arranged in a spherical cluster, the garlic plant is most easily identified by its pungent smell that is concentrated in its bulb. Many cultivars exist, and garlic can be grown from seed but is almost always propagated asexually by planting individual cloves.
Plants can be grown closely together, in loose, well-drained soil with plenty of sunlight. Garlic plants will tolerate a wide range of soil conditions and are typically hardy with few pests or diseases. Indeed, the odor of garlic repels many garden pests, ranging from bunnies and moles to a variety of insects. The repellent effects of garlic are due to the presence of sulfur compounds, including allyl methyl sulfide, which causes “garlic breath” in humans. Since this compound cannot be digested, it is passed to the blood and ultimately is excreted by the lungs and the skin (so, brushing your teeth won’t help reduce the stench from eating too much garlic).
In addition to its many medicinal uses, garlic is a popular companion plant for many fruits, vegetables, and flowers since it repels a variety of both crawling and flying insects — including thrips. However, like other Allium, it should not be planted with peas. Beans, sage, parsley, and asparagus also do not typically pair well with garlic. In addition to its use as a plant growing in the garden, garlic cloves can be harvested and mixed into a spray that can function as a more concentrated pest repellent when it is applied to plant leaves or to insects directly.
Extra Tips to Deter Thrips From Gardens
Thrips have few natural predators themselves, though green lacewings, anthocorid bugs, phytoseiid mites, lady beetles, and certain parasitoid wasps can function as natural enemies. As thrips are challenging to get rid of once established, the most effective method for managing the spread of thrips is to prevent them from entering areas like greenhouses and removing infested plant parts or isolating infested plants. Thrips are poor flyers, so movements by people or airflow should be evaluated to prevent accidental relocations to greenhouses.
Methods for deterring thrips in gardens include reducing weeds and debris, regularly inspecting plants for damage, and physically removing thrips by dislodging them by spraying with water (or soapy water). While chemical control can be used, thrips readily develop resistance to insecticides and can be difficult to reach since they often hide in flowers and buds.
Using certain plants that repel thrips is another strategy that can benefit overall garden health and reduce the risk of a thrips infestation. The following article describes several plant species that are often used to repel thrips. Most of the plants with thrip-repelling properties are in the mint family, Lamiaceae, or the amaryllis family, Amaryllidaceae.
