What Are Thrips?
Thrips are common in both outdoor and indoor gardens. They damage plants by scraping at leaves, flowers and fruits, and sucking out the juices. They are active – flying away or leaping when disturbed. Feedings take place in large groups. Substantial damage often occurs from thrips. They are a common pest for cannabis crops. When it comes to vegetables, thrips seem to prefer beans, squash, onions and carrots.
Numerous flowers are susceptible to thrip damage including roses and gladioli. Light, yellow and white blossoms are attractive to the larvae and adults. One a plant is infested, viruses are often spread including necrotic spot virus and tomato spotted wilt.
How to Identify Thrips
Adult thrips are tiny, with a length of 1/25th of an inch. They are slender and have a black, brown, yellow or straw color, with two pairs of wings. Unless a magnifying glass is used for identification, thrips look like little dark threads. The wings are feathery and fringed. The nymphs have a similar appearance with a smaller size, and a lighter yellow or green coloration.
Nymphs often have red eyes, with undeveloped wings. One good way to get a good look at thrips is by shaking them out of the plant onto a white piece of paper. More than 4500 species have been identified, but the belief is there are nearly 6000. Some thrips attack plants, while others are beneficial. Beneficial thrips consume other insects frequently attacking plants. Unfortunately, when trying to prevent or treat a thrip infestation, both the beneficial and harmful species destroyed because telling them apart is extremely difficult.
Western flower thrips (WFT) and onion thrips are most common in the United States but have spread to other continents, including South America, Australia, and Europe due to transport of infested plants. They also attack the flowers of specific crops, young cucumbers and capsicum.
The western flower species of thrips attack weeds, ornamental crops and vegetables. There is also a strain that attacks greenhouse crops including cannabis, eggplant, cucumber, capsicum, chrysanthemum, rose, gerbera and carnation. Numerous species attack weeds including Amaranthus, cape gooseberry and black nightshade.
Thrips thrive when conditions are dry and hot, which means they tend to be more problematic in the western growing regions of the U.S. and are the most damaging insect pest of onions in California.
Thrips on Cannabis
Thrips are one of the most common pests in cannabis growing. Although, it is not one of the biggest threats your crops can face, it is important to be aware of symptoms and how they can damage your plants. It is always best to be proactive and prevent thrips, as well as other pests, from making your marijuana plants their home. Thrips can reproduce up to 12 times per year, which can make them difficult to combat once they have settled.
Thrips Life Cycle
When a female is unable to find a mate, asexual egg production occurs. Unlike most caterpillar species, thrips eat a hole in the plant to lay eggs. This provides the eggs with protection from predators and unfavorable weather conditions. Once hatched, the thrips’ life cycle continues as they begin consuming plant matter.
Most thrips have two larval nymph stages prior to maturing into adults. Some species have as many as five larval stages. Once the development of the nymphs is complete, the pupation stage occurs. Thrips then become adults. When the weather is warm, 8 to 15 days are necessary to complete this process. In colder weather, the process requires more time.
The thrips’ life cycle includes a stage called diapause for certain species. This stage is like suspended animation. Eggs, pupae and adults can survive by going into this stage. The lifespan for thrips is approximately 45 days.
What Does Thrip Damage Look Like?
Damage from thrips includes:
- Distortion of fruit and young leaves
- Spotting on flowers
- Yellow speckles on the leaves
- Older leaves have a silvery appearance
- Excrement leaves black spots behind on the leaves
- Small insects on the underside of the leaves or in the flowers
- Small white patches
- Pale, splotchy and silvery leaves
- Damaged fruit and shoots
- Stunted growth
- Discolored petals
- Wilting and scarring
Thrips cause a wide range of damage including small patches of white, silvery specks and streaks. The damage occurs when the plant cells are sucked from numerous types of garden plants, shade trees, flowers and fruits. When an infestation is present, plants often become stunted with damage to the fruit and flowers. Damage also results from viruses spread by thrips.
The leaves of the plant turn silvery, splotchy and pale before dying. Injured plants become scarred, discolored and twisted. Thrips impact the aesthetics of plants by noticeably damaging the shoots, leaves and fruit. Thrips on cannabis during the flowering stage often results in severe damage if not identified and remedied quickly. These insects rarely cause the death of shrubs or trees.
The impact on specific vegetables and herbaceous ornamentals is much worse due to accompanying viruses that are easily spread to young plants. Learning how to identify and get rid of thrips is important because feedings can stunt the growth of the plant, resulting in distorted papery leaves with little pale spots and prematurely dropping leaves. Infested plants become discolored with rolled leaves. The petal tissue becomes dark and discolored due to feedings prior to the opening of the buds.
Certain plants can become severely stunted early in the season. The Cuban laurel species of thrips cause pod-like and tightly rolled terminals on Ficus foliage between the summer and fall. Western flower thrips usually attack herbaceous plants, but large enough numbers will damage flowering woody plants including roses. Thrip feedings cause dark spots and streaks, and deformed buds that become incapable of opening.
The surface of citrus fruits and avocados become scabby, silvery and brown, but the flavor is not affected. When there are eggs on grapes, dark scars often develop with a lighter halo. Raspberries, nectarines and apples become scarred or deformed while developing.
The foliage and shoot tips of blueberries can be distorted by the citrus species of thrips, resulting in smaller yields of fruit. Knowing how to get rid of thrips is critical because once damage is seen, it may be too late to save the plant. The damage caused by thrips is comparable to mites and different species of true bugs including the symptom of dark specks of fecal matter. Before deciding which method to use to get rid of thrips, make certain the insect has been identified correctly.
Some species of thrips can spread viruses such as Impatiens Necrotic Spot Virus and Tomato Spotted Wilt Virus. These viruses can kill specific herbaceous ornamentals and vegetables. Virus symptoms may resemble other plant disease symptoms or nutritional issues. Wilting, streaking, or necrotic brown or black spots are symptoms of viral infection.
How to Get Rid of or Kill Thrips Naturally
The best natural methods to get rid of thrips include:
- Apply Trifecta Crop Control combined with Beauvaria
- Hang blue sticky traps
- Predatory insects
- Prune the plant
Thrips are one of the most difficult pest infestations to treat with Crop Control alone, mostly because of their anatomy. You need to spray their thorax region in order to suffocate them, but most people are spraying with fine mist atomizers which, while great for mites, does not manage to get the product delivered to the underbelly of the thrips where their breathing mechanisms are located.
Using a deluge sprayer like a paint sprayer can help with this. Crop Control works very well as a preventative for thrips, which is what we recommend. But as with any infestation, it will require diligence to address thrips. Apply Trifecta Crop Control Super Concentrate at a dilution ratio of 2oz per gallon.
There is a beneficial fungus called Beauveria which can be used in conjunction with Crop Control and really helps with breaking a thrip infestation. When used in conjunction with Trifecta Crop Control as part of your IPM, thrips should never become an issue.
It is important to note that Crop Control will kill off and break down the beauvaria. The two products can be used in rotation to allow each to perform its function. Beauvaria can be applied 2 days after Crop Control in a weekly application.
NOTE: the Beauveria will drive fungal spore counts rather high, though. This can create a failure on a TYM test for commercial cannabis growers. Using Crop Control as a rinse after a Beauveria treatment seems to help mitigate this.
Thrips are very attracted to bright colors. Blue sticky traps are recommended and are another tool that can be added into the mix that helps quite a bit. Place the traps close to the infected plants.
When there are only a few thrips on cannabis plant, the injured areas can simply be pruned. Plants can be pruned by cutting them right above the nodes and branches as opposed to cutting off the terminals. Avoid shearing as it stimulates thrip-susceptible new growth. Certain species can be controlled by pruning during certain seasons.
How to Prevent Thrips Naturally
These pests can be prevented naturally by:
- Applying Trifecta Crop Control as part of Integrated Pest Management (IPM)
- Row covers
- Reflective mulch
- Remove all nearby weeds
Applying Trifecta Crop Control Super Concentrate as a preventative is the best way to prevent thrips naturally. Apply as follows or click here to view and/or download our complete Application Guidelines.
- .5oz per gallon applied once per week during veg
- 1oz per gallon applied once per week during flower up to 2 weeks before harvest
Row covers will help keep thrips and other insects away from young plants. The covers should be placed prior to the emergence of the plants or when planting. Covers are only necessary when the plants are young because this is when they are the most vulnerable. When the temperature is warmer or the plants are bigger, the covers should be removed to prevent overheating, and to allow enough space for growth. Furrow or drip irrigation is often necessary when covers are used.
Reflective mulch reflects light, disrupting the ability of the thrips to find the plants. Reflective materials are only effective when a low number of pests are present. Reflective mulch decreases the number of pests attacking young plants including winged aphids, whiteflies and adult leafhoppers. Reflective mulch is an effective option for vegetables and flowers with virus sensitivities.
Numerous species of this pest frequently move into different areas or gardens when grasslands and weedy areas start drying out during the summer or spring months. Susceptible plants should not be planted in these locations. Nearby weeds should be removed to make the area less enticing to the thrips.
Thrips Management in Greenhouse Using Biocontrols
Thrips have numerous enemies such as green lacewings. Biological control should only be used in conjunction with a planned IPM program.
Neoseiulus cucumeris a predatory mite smaller than 1 millimeter long. It attacks thrips larvae and eggs on foliage and flowers. Neoseiulus pierces its prey and sucks fluids out of them. Apply the predators directly on your crop. For each square yard, introduce 100 mites.
Tips for introducing neoseiulus include:
- Predators should be introduced the moment you detect thrips
- Release the predator mites upon delivery whenever possible
- Temperatures for release need to be 50 to 85 degrees Fahrenheit
- Before distribution, allow an adjustment to the greenhouse temperature
- Humidity level for release should be 70 to 90 percent
- Distribution needs to be evenly sprinkled among the plants
- Development requires a relative humidity level a minimum of 65 percent
- Storage is possible for one to two days in a dark, cool area with a relative humidity level of 85 percent
As a predatory soil mite, hyposapis consume thrips pupae. Hypoaspis can decrease the population of thrips by 30 to 60 percent. When you introduce this predator at planting time, you can achieve control for between six and eight weeks. You should use this mite along with another natural thrips enemy consuming all life stages taking place on the plants.
You can also use hypoaspis for the effective decrease of fungus gnat larvae. For each square yard, you need to introduce between 100 and 300 mites. Tips for introducing hypoaspis include:
- Introduce the predator mites as quickly as possible once delivered
- Your soil needs to be moist as opposed to wet
- Before planting, mix the mites into your growing media or sprinkle them over the soil
- A minimum temperature of 60 degrees Fahrenheit is required for good activity
- Compatible with beneficial nematodes and BT
- You can use mites as a preventative measure
- Numerous pesticides will negatively impact hypoaspis
- You can achieve control for six to eight weeks by releasing at planting time
- You should talk to your supplier for pest and disease control for pesticide side effects on beneficial organisms
This is a minute pirate bug consuming both immature and adult thrips additionally feeding on other prey including spider mites and aphids. As with most biocontrol agents, orius is not a rescue treatment. You should not use orius with a high population of thrips. Tips for introducing orius include:
- Use one adult for every two feet or per square yard where pests are located
- The temperature needs to be 70- to 90-degrees Fahrenheit
- Introduce the predators immediately when thrips are found
- Do not use pesticides for two months before using orius due to susceptibility
- Reintroduction may be necessary every two to three weeks depending on scouting
- You can use neoseiulus cucumeris in combination with orius
- Apply during the early evening or cool morning
- Encourage mating by shaking the material in clusters on the leaves
- Do not introduce under bright sunlight
- Do not disturb the material for a few days
- Side shoots should be pruned before introduction to enable orius eggs to be laid
- Orius should not be introduced close to sticky cards
- To increase effectiveness, place orius close to hot spots
Amblyseius swirskii is an extremely effective generalist predatory mite that can be used to contain immature thrips, cyclamen mites, two-spotted spider mites, broad mites, and whiteflies in fruit, ornamental and market crops.
Adults are pear-shaped, 0.5 mm long, with long legs. The eggs are transparent and round and 0.14 mm in diameter. A. swirskii lay their eggs on leaf hairs and along the veins on the inner surface of leaves. Eggs hatch in about 3 days.
Like other generalist insect predators, A. Swirskii can sustain its population even when thrips are no longer present on the plants and will start working as soon as thrips begin to surge. A. swirskii is not susceptible to diapause so it can be introduced in the winter. It is also tolerant of high temperatures. A. Swirskii needs more heat than Neoseiulus cucumeris to develop fully.
The introduction rate provided below is simply suggestive. Specific conditions need to be considered such as type of crop, climate and temperature and the severity of the infestation.
- Introduce to crop quickly upon receipt
- Use 25 for every square yard for preventative
- Use 50 for every square yard for light curative
- Use 100-300 for every square yard for heavy curative
- A. swirskii population starts to develop when the temperature regularly exceeds 68-72°F