Thrips are slender, tiny insects. These insects have fringed wings. These insects feed by puncturing the outer layer of host tissue. After that, they suck all the nutritive content from it. This results in stippling, discolored flecking, stippling, and silvering of the surface of leaves.
Feeding by thrips is accompanied by black varnishlike flecks of frass. These species of pests are plant feeders that discolor and scar flower, leaf, and fruit surfaces. They distort plant parts.
Most of the species of thrips feed on pollen and fungal spores. Also, they are often innocuous. However, pollen feeding on plants such as African violets and orchids may leave unsightly pollen deposits. Also, it may result in a reduction in the longevity of flowers.
Few species of thrips work as beneficial predators. They feed on other mites and insects.
Thrips can easily move and cover long distances. They do this by floating with the wind or transported on infested plants.
New Zealand is the place of origin of thrips. Later they spread to Southern California. Spreading to many of the areas of the state.
Thrips Life Cycle
Thrip hatches from an egg. These insects develop via two feeding and two nonfeeding larval stages. After this, they grow up to form the prepupa and pupa. Finally, they attain the adult stage.
Late-instar larvae show rapid changes in behavior and appearances. They are known as pupae and prepupae.
Females of many plant-feeding species lay their cylindrical, elongate, kidney-shaped eggs on or into buds, leaves or other places where the larvae can feed.
Thrips are extremely active species of insects. They feed in large numbers. They fly or leap away if disturbed. Host plants include beans, onions, squash, carrots, and many other garden vegetables. You can also find these insects on many flowers, especially roses and gladioli.
Both wingless larvae and adults are attracted to yellow, white and other light-colored flowers. They are the main cause of spreading the impatiens necrotic spot virus and tomato wilt virus.
Feeding by these insects can damage leaves. Their feeding can also stunt plant growth. The leaves usually become distorted and papery. The infected leaves may develop tiny pale spots. As a result, the leaves may drop prematurely.
Infested parts may become discolored and rolled. Petals may show “color break,” which is dark or pale discoloring of petals.
These insects are not easy to control. If management becomes necessary, make use of an all in one program that combines the use of natural enemies, good cultural practices, and the use of least-toxic insecticides that will be effective.
If thrips are the sole cause of plant damage, the larvae and adults can be monitored by gently shaking foliage or flowers or by branch beating onto a light-colored sheet of beating tray, white paper or small white cloth.
For thrips that feed on unexpanded shoot tips or buds, remove the plant parts that have thrips on them. To see thrips on such plant parts, place them in a jar that has 70% alcohol. Now, shake intensely to displace the thrips. To see thrips more easily, strain the solution through filter paper.
You can monitor adult thrips by hanging yellow bright sticky traps near host plants.
Green lacewings, predatory thrips, minute pirate bugs, mites, and few parasitic wasps assist in controlling plant-feeding thrips.
If you want to encourage and conserve naturally occurring populations of these beneficial insects, do not create dust and consider regular rinsing of dust off of small plants. Also, avoid the use of persistent pesticides. You can also try growing different types of plant species.
Where thrips become a major problem, see if it has pest has specific natural enemies helpful to control the spread.
For example, green lacewing larvae and a minute pirate bug, Macrotracheliella nigra, are important killers of Cuban laurel thrips. Euseius species mites are killers of citrus thrips.
50% of eggs of greenhouse thrips in Southern California are killed by a tiny, small wasp, Megaphragma mymaripenne. After the insect feeds inside during its larval stage, then the emerging adult parasite leaves behind a very large round hole in the tiny thrips egg.
Thrips that feed on several plant species generally relocate themselves into landscapes and gardens when plants in grasslands or in weedy areas begin to dry in during summer or spring.
Do not plant susceptible plants near these areas, and control weeds that serve as an alternate host to pest thrips.
Provide proper cultural care to keep plants healthy and improve their tolerance to damage from thrips. Water the plants well, and avoid overuse of nitrogen fertilizer, which may cause higher populations of thrips.
Spent and old flowers can nurture thrips, so their disposal and removal become necessary.
Prune and destroy infected and injured plant terminals when looking after a few small plant specimens in your garden.
Do not shear plants. Shearing is the clipping of dense foliage in order to maintain an even surface on formal hedges or creating specific shapes (topiary). Shearing stimulates the growth of thrips.
Prune by cutting plants just above nodes and branch crotches rather than shearing off terminals. Prune during fixed times of the year to control a few types of thrips.
Some Cuban laurel thrips can withstand the winter because of the protection offered by the leaves they gall. Rather than pruning avocado from February to April, pruning in January may reduce thrips scarring of fruit.
Pruning during January can help to induce extra avocado growth flush during the May fruit set and can also help to reduce thrips scarring of fruit. When succulent foliage is in excess during spring, thrips remain and feed on leaves and avoid moving to fruit.
Pruning the interior parts of citrus trees can increase mite populations in the exterior canopy. This causes a reduction in fruit scarring by citrus thrips.
Hot caps, row covers and other types of cages that have a very fine mesh can exclude other insects and thrips from young herbaceous plants and vegetables.
Apply row covers before crops come up from the ground or to pest-free plants during planting. Once plants grow large or temperatures get warmer, remove the covers to give enough growing space. This will also help to avoid overheating.
Furrow or drip irrigation is necessary while making use of row covers.
You can use any type of row covers that excludes that allow air penetration and light but exclude insects entry.
For crops that never grow too tall, floating row covers (spun-bonded polyester, vented polyethylene, point-bonded polypropylene) are placed on top of beds with no hoops or frames.
The crop itself lifts the light fabric as it grows. For plants that grow straight upright or have very sensitive tips that may face damage when getting pushed against covers. Always make use of plastic tunnels, hoops, or wire strung between the posts to hold covers.
Wire, wood or plastic frames covered with nylon, muslin, or other fine mesh can be used for many years.
Mesh or mulch that reflects light interferes with a few flying insects’ abilities to locate the plants.
If at the beginning the plants are pest-free and relatively small when compared with the surface area that is covered with reflective material, reflective mulch can help to delay or reduce the level to which young plants become infected by winged aphids and adult leafhoppers, whiteflies, and thrips.
In vegetable crops and flowers that are sensitive to insect-vectored viruses, the effort and cost of using reflective mulch may be right. This is because the mulch can be more effective than insecticides in delaying or preventing infection of small plants.
As plants grow bigger, reflective mulch becomes less effective. Other management methods become necessary. Reflective mulch stops to repel insects by the time the plant canopy covers more than about half of the soil surface.
Synthetic mulch application methods includes the following steps:
- Transplant seedlings via holes in the mulch.
- Apply the mulch before plants come out from the soil and leave a very narrow, mulch-free strip along the planting row.
- Lay a very lightweight material that allows air and light penetration over the top of a crop that is strong enough to lift the material as it grows.
Mulch may improve the growth of few crops by increasing the levels of light, keeping soil warmer for the complete night, reducing weed growth, and preserving soil moisture.
Mulch can also have some negative effects on plants. It can increase crop chances to develop root diseases. It can prevent the use of overhead watering. Finally, use of mulch makes it very difficult to know if you are maintaining proper soil moisture in the rooting zone of a plant or not.
Most recyclers will never accept plastics with soil on them for recycling.
Although thrips damage is ugly, it does not usually ask the use of insecticides in landscapes and gardens. Feeding injury does not become obvious until after tissue grows and expands.
Thus, by the time damage is visible on distorted terminals or ripening fruits, the thrips that cause the heavy damage usually move away.
No pesticide application can improve the condition of damaged plants. Plants will remain in a state of damage until the injury is pruned off, leaves drop or new unblemished fruit is produced.
Where plant viruses are the cause of the problem, insecticides are not able to kill thrips fast enough to avoid the movement of the virus from thrips to plants.
Making use of row covers or other methods to limit thrips infestation is the best and most effective way to prevent infection by thrips-vectored viruses.
Thrips can be very difficult to control with insecticides. This is because of their feeding behavior, mobility, and protected egg and pupal stages.
Failure to treat the proper plant parts, improper timing of application and inadequate spray coverage when using contact materials are the few common mistakes that can prevent very effective insecticides from actually controlling the infestation.
Before you use a pesticide, try learning about the biology of your pest species. Also, read the label of the available products to know their area of application and effectiveness.
Insecticides Most Compatible with IPM
Contact insecticides that leave no persistent residues can be very effective for greenhouse thrips and other pests that feed openly on plants.
These products have very low toxicity to pets, people and pollinators. These products have relatively very little adverse impact on biological pest control. This is because they leave no toxic residues that may kill natural enemies.
Contact insecticides mainly include Insecticidal soaps, azadirachtin, neem oil, pyrethrins, and narrow-range oil.
To be highly effective, contact sprays must be applied to thoroughly cover buds, shoot tips, buds and other plant parts where thrips are present.
Unless directed otherwise repeat the application of pesticides to eradicate thrips completely.
Greenhouse Thrips Management
Greenhouse thrip is very dangerous and can infect many plant species but mainly is a pest of evergreen, broadleaved perennials. It is found mainly on the fruit clusters and on the underside of leaves or other parts of plants that touch each other.
They are very sluggish and the adults do not fly. These insects feed in groups. initially, they start feeding on a small part of the plant. Later, they slowly spread to the other parts of the plant.
To detect thrips early and ensure proper removal of new infestations, pruning off colonies is the best option and can be very effective.
You can easily control Greenhouse thrips with a thorough and deep application of contact sprays. Sprays of liquids such as natural pyrethrins (plus piperonyl butoxide), horticultural oil or insecticidal soaps to the underside of infested leaves will greatly help to control thrips.
Repeated applications are very necessary. Remember that greenhouse thrips have natural enemies in the natural landscape. Use pesticides and insecticides only when the infestation is too heavy. Use natural and least toxic sprays.