Thrips are tiny insects that puncture the outer layer of host plants, sucking out the content of the cells. This results in discoloration, stippling, scaring or silvering of leaves and fruit surfaces and a reduction in the production of the plant. If there is a high infestation of thrips they can cause the leaves to wither. Thrips can move long distances by floating where the wind takes them or by being transported on infested plants.
Thrips Reproduction and Life Cycle
Thrips life starts by hatching from an egg and developing through two actively feeding larval stages, two non-feeding stages and finally becoming a fully mature adult. Late-instar larvae’s appearance and behavior greatly change and are called prepupae and puae, even though thrips do not technically go through the true stages of being a pupal. The light prepupae and puae drop to the soil or leafs littering or lodging within plants. Thrips either have puae (and eggs) on lower leaves or are enclosed within plant tissues. Most plant-feeding thrips lay their long, circular to kidney-shaped eggs into buds, leaves or other locations where the larvae can feed. Thrips can have up to 8 generations a year. With warmer weather, the life cycle from egg to adult can be completed in 2 weeks.
Thrips Identification and Habitat
For the most part adult thrips are slim, elongated and have fringes on the outline of their long, narrow wings. Larvae are slim or oblong and elongated in shape, with no wings. They can range in colour from dark brown or black to translucent white or yellowish. There are a few species of thrips that come in bright colours, such as the larvae of the predatory thrips that is reddish-orange. It is important to distinguish between species when pest management methods need to be used. Identifying thrips species may reveal that they are harmless under specific situations and may not need to be controlled.
- -Onion thrips (Thrips tabaci)
- -Western flower thrips (Frankliniella occidentalis)
- -Cuban laurel thrips (Gynaikothrips ficorum)
- -Myoporum thrips (Klambothrips myopori )
- -Predatory thrips (Franklinothrips orizabensis)
- -Avocado thrips (Scirtothrips perseae)
- -Greenhouse thrips (Heliothrips haemorrhoidalis)
- -Citrus thrips (Scirtothrips citri)
When thrips feed on plants it can damage their shoots, leaves and fruits. They can also drastically affect the cosmetic appearance of the plants by causing the leaves to become papery, creating colour breaks in the petals and cause its fruits to have tiny, pale spots on them. Many species of thrips will feed on fungal spores and pollen. When thrips feed on pollen, it can leave unsightly pollen deposits that will reduce the longevity of the flower. When the eggs of the thrips are laid on grapes, the fruit tends to develop dark scars that surround a lighter “halo”. Thrips can also cause brown to silvery, scabby scarring on citrus fruit and avocados surface, but will not damage the flavor or quality of the fruit itself. That being said, rarely do thrips actually have the power to kill or threaten the survival of shrubs and trees. Ornamental plants and specific vegetable crops are more vulnerable to major injury from thrips feeding on them, along with giving plant thrips-vectored viruses and tomato spotted wilt, especially when an infestation occurs on young plants. You are able to find thrips on apples, avocados, blueberries, roses, cucumbers, grapes, nectarines, peppers, tomatoes and other citrus and woody plants, depending on their variety.
Thrips Control Methods
Thrips are a difficult pest to control, which is why it is best to use an integrated management system that includes the use of natural enemies, good cultural control methods and the use of the least-toxic insecticide that will still eradicate thrips. It is important to know that the presence of thrips does not mean they will damage your plants and they may not even be present by the time you try a control method. Before taking action to control thrips, make sure that the pest thrips is the bug that is actually causing the damage. If there are plants that you suspect are infested by the thrips-vectored viruses, it can be easily diagnosed by sending a sample from the plant to a lab that test for plant pathogens.
For optimal control and prevention, grow plants that are well-adapted to the soil and weather conditions in your area. Keep plants well irrigated and avoid applying excessive amounts of nitrogen, this will promote the population of thrips. Some varieties of thrips damage light-coloured, fragrant roses. Rose cultivars can be an effective control method, with sepals that stay tightly wrapped around the bub up until the blooms open.
Pruning is another control method that works well. It is important that you destroy injured and infested terminals. Cut the plants just about the crotch of the branch and nodes instead of shearing off terminals.
Using hot caps, row covers and other types of cages with a fine mesh can eliminate thrips from eating your vegetables and other young herbaceous plants. Any kind of covering that excludes insects and allows the light and air to penetrate can be used. For coverage on sturdy crops that do not grow tall, floating row covers can be put on top of the beds with no frames or hoops. As for plants with sensitive tips that are easily damaged, use hoops, plastic tunnels of wire strung up between posts and prop the covers up. Using wood, plastic or wire frames that are covered with nylon, muslin or other fine mesh can be used for many years. It is most effective to apply the covers before crops have emerged and left on while they are still young and most vulnerable to damage. Once the temperatures get warmer or plants become larger, take off the covers to give them enough space to grow. At this point, light irrigation is necessary when using row covers.
Damage done by thrips is unsightly and does not typically warrant the use of insecticide. Thrips can be a difficult pest to manage and control effectively due to their mobility, feeding behavior, and protected egg and pupal stages. Injury usually goes unnoticed until after the tissue grows and explants. Therefore, the thrip that caused the damage is often gone. There is no pesticide application that can restore the appearance of the damaged tissue. If plant viruses are a problem, insecticides typically do not kill thrips fast enough to stop the transfer of the virus. Using cultural control methods such as row covers is the more effective way to prevent infection.
Be sure to carefully read the label for cautions and proper application. It is extremely important to never spray on days that are windy. Contact insecticide that do not leave persistent residue is most effective for greenhouse thrips. These particular insecticides have low toxicity to people, pets and pollinators. Adequate contact insecticides include neem oil (Schultz Garden Safe Brand Neem Oil, Green Light Neem), insecticidal soaps (Safer), pyrethrins combine with piperonyl butoxide (Garden Tech Worry Free Brand Concentrate, Ace Flower & Vegetable Insect Spray), azadirachtin (Safer Brand BioNeem, AzaMax), and narrow-range oil (Monterey Horticultural Oil Bonide Horticultural Oil). For these insecticides to be most effective, they must thoroughly cover shoot tips, buds, and any other vulnerable plant part where thrips could be living and feeding. If plants have a history of unexplained damage, start treatment early when thrips our first observed. Unless told otherwise by the label on the product, periodically repeat application if thrips are still present.
It has been seen that spinosad (Monterey Garden Insect Spray, Green Light Lawn & Garden Spray with Spinosad 2, Captain Jack’s Deadbug Brew) is usually more effective against thrips. This particular chemical lasts a minimum of 1 week and can move short distances into plant tissue to reach the part of the plants that thrips feed on. Adding horticultural oil to the mixture has the potential to increase the resistance within plant tissue. This particular insecticide is a fermentation product and can be toxic to natural enemies such as predatory mites and bees for a minimum of 24 hours after it has been applied. Do not apply to plants that are flowering.
There are a few chemicals that you should avoid using. Avoid foliar sprays of other organophosphate insecticides (e.g., malathion), pyrethroids (e.g., bifenthrin, cyfluthrin, permethrin and fluvalinate) or carbamates (carbaryl) along with Systemic organophosphate acephate (Orthene, Lilly Miller Ready-to-Use Systemic). Avoid using these chemicals as they are highly toxic to natural enemies and pollination. The use of these chemicals can cause outbreaks of spider mites, can damage plants after application and are not particularly effective on most varieties of thrips.