Scott Adkins, Josh Freeman, Sam Hutton, Hugh Smith, Gene McAvoy, Crystal Snodgrass, Mathews Paret, and Norm Leppla were some of the people who were there.
Several species of thrips that are not native to Florida have spread there and are hurting vegetable, ornamental, and agronomic crops badly. Crop damage is caused by thrips feeding and egg-laying damage, plant diseases being spread by thrips, the cost of control methods, and the loss of pesticides due to resistance. The Western flower thrips (Frankliniella occidentalis), which was brought to north Florida in the early 1980s and quickly took hold, is the main thrips that hurt tomatoes. Central and southern Florida didn’t have to deal with the western flower thrips as a business problem until 2005 (Frantz and Mellinger 2009). Other invasive species, such as the melon thrips (Thrips palmi) and the chili thrips (Scirtothrips dorsalis), do not hurt tomato plants.
When the western flower thrips first came to Florida, growers in all parts of the state used broad-spectrum insecticides on a regular basis. This has led to the classic “3 R” situation: resistance to insecticides (even new, lower-risk insecticides), a rise in thrips populations because natural enemies and native species that compete with thrips have been killed, and the introduction of other pests that are caused by broad-spectrum insecticides. There are a number of scientific papers that look at the situation in Florida (Funderburk 2009; Frantz and Mellinger 2009; Weiss et al. 2009).
The western flower thrips is the most efficient vector of Tomato spotted wilt virus (TSWV). This virus is one of about twenty known species of tospoviruses (Sherwood et al. 2001a, b). Epidemics of tomato spotted wilt (TSW) occur frequently in numerous crops in north Florida. Historically, it was thought that TSW occurred sporadically in central and south Florida. Most of the infections were limited to a few plants in a field. These were transplants, mostly peppers, that came from planthouses in Georgia. Secondary spread (i. e. , within the field) away from the initial site of infection was rarely, if ever, seen. In the last 20 years, growers and scouts have started to report a few cases where secondary spread has become more common. TSW has sometimes shown up in fields in south Florida where transplants did not come from Georgia or other places where TSW is already common.
Tomato chlorotic spot virus (TCSV) and Groundnut ringspot virus (GRSV) are two recently emerged tospoviruses in Florida. In south Florida, TCSV and GRSV were often found in solanaceous plants and weeds showing tospovirus-like symptoms. They were also found together with TSWV in tomato and pepper (Webster et al. 2015). Tospoviruses were only found in tomato spotted wilt virus in other survey locations in north Florida and the rest of the continental US. TCSV was found in tomato in Ohio, and GRSV was found in tomato in South Carolina and New York. All of these were the first reports of these viruses in tomatoes. Currently, TCSV is the predominant tospovirus in south Florida and has also become widespread in the Caribbean. TCSV and GRSV usually infect plants that are solanaceous, but more and more non-solanaceous hosts have been found for TCSV in Florida and the Caribbean recently. These hosts are weeds like purslane (Portulaca oleracea), sweet basil (Ocimum basilicum), lettuce (Lactuca sativa), and a few others. They are also hosts for annual vinca (Catharanthus roseus) and a few other ornamental plants (Estévez and Adkins, 2014; Raid et al. 2017; Warfield et al. 2015). Because different tospoviruses cause similar symptoms in all of these hosts, it is necessary to use serological or molecular tests to find out exactly which virus is present.
Like TSWV, TCSV and GRSV are transmitted by thrips. These new tospoviruses are spread by Western flower thrips and common blossom thrips (Frankliniella schultzei) (Webster et al. 2015). Concern should be raised about the fact that tospovirus-related diseases are starting to show up more often and in more places in south Florida. Although these new tospoviruses are closely related to TSWV, biologically based thrips management and integrated management strategies for TSWV may also work for these new tospoviruses. For example, metalized (UV-reflective) mulch may help.
Finding strange spots, scars, and deformities on the leaves of your prized tomato plants? The culprit could be tiny insects called thrips that suck juices from the foliage in stealth mode. Here’s a guide to identifying thrips damage on tomatoes and controlling these pesky garden pests.
What Are Thrips?
Thrips are tiny slender insects, measuring only 1-2 mm in length. Various species prey on different crops, but the common tomato thrips is Frankliniella occidentalis. These insects have fringed wings and tend to range from translucent yellow to dark brown or black in color.
The thrips lifecycle consists of egg, larval, pupal and adult stages. The adults overwinter in plant debris before becoming active in spring. After mating, females use their saw-like ovipositor to insert eggs into the leaves and stems of host plants. The larvae are wingless and feed on plant juices. As they mature into pupae and adults, they develop wings to disperse to new plants.
How Do Thrips Damage Tomato Leaves?
The primary damage to tomatoes is caused by thrips larvae and adults feeding on the undersides of leaves. Here are some typical symptoms
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Speckling – Numerous tiny white or silvery dots appear on the upper leaf surface. This is due to loss of chlorophyll from thrips saliva and scraping.
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Discoloration – Leaves become bronzed, yellowed or curled due to the toxins in thrips saliva.
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Scarring – Feeding scars look like white or silvery streaks running parallel to the veins,
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Black spots – Frass or fecal droppings from thrips appear as black dots on leaves.
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Stunted growth – Heavy infestations affect the plant’s vigour and reduce fruit yields.
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Leaf deformation – Young leaves may become twisted or curled due to feeding damage.
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Flower injury – Buds and flowers can become scarred and deformed.
How to Check for Thrips
It takes a keen eye to spot thrips because they are so tiny. Here are some tips for close inspection:
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Shake the plants over a white sheet of paper to dislodge thrips.
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Use a 10x hand lens to scan leaves closely, especially the undersides.
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Hold damaged leaf against sunlight to see tiny moving specks.
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Peel back the top layer with clear sticky tape to uncover hiding thrips.
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Cut open buds or flowers to find thrips larvae.
Focus on new growth which is most vulnerable to infestation. Also check for tiny black dots and shedding skin which are signs of thrips presence.
Effects of Thrips Damage
Moderate thrips feeding causes cosmetic damage but rarely kills tomato plants. However, it can have more severe consequences:
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Reduced photosynthesis lowers plant vigor and fruit yields.
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Scarring damages fruit appearance and marketability.
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Viruses like tomato spotted wilt are transmitted by thrips.
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Growth of sooty mold on frass-coated leaves blocks light.
So it’s important to control thrips, especially in greenhouses and commercial farms where populations can explode quickly.
How to Get Rid of Thrips on Tomatoes
Here are some effective organic and chemical options for controlling thrips:
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Insecticidal soap – Spray plants to kill larvae and adults on contact.
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Neem oil – Deters feeding and disrupts thrips life cycle.
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Spinosad – Organic insecticide derived from Saccharopolyspora bacteria.
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Pyrethroids – Fast-acting synthetic chemicals like bifenthrin and zeta-cypermethrin.
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Beneficial insects – Predatory mites and minute pirate bugs feed on thrips.
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Sticky traps – Blue or yellow traps catch adult thrips.
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Strong water spray – Knocks thrips off foliage to prevent further damage.
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Remove debris – Dispose plant waste to eliminate thrips overwintering sites.
Rotate chemical treatments to prevent resistance. Also, target the undersides of leaves and new growth. Combining multiple tactics offers the best control against thrips infestations.
Preventing Thrips on Tomato Plants
Here are some cultural practices to deter thrips problems in the tomato patch:
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Use disease-resistant tomato varieties which are less stressed and vulnerable.
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Avoid excess nitrogen fertilization which makes plants more succulent.
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Control weeds around crops to remove alternate thrips hosts.
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Use reflective mulch to deter thrips from finding young plants.
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Apply kaolin clay spray which creates a physical barrier against feeding.
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Use row covers to exclude thrips until flowers need pollination.
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Rotate tomato crops to different beds year to year.
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Monitor and treat early before thrips populations explode.
With diligent inspection and integrated pest management, you can protect your tomato plants from these tiny sap-sucking saboteurs! A little effort goes a long way to produce flawless ripe tomatoes for summer salads and salsas.
Tomato Spotted Wilt Virus
TSWV is circulatory and replicative, which means that the virus moves through the blood of insects and copies itself inside their bodies. The cycle of getting and spreading the virus starts when larvae eat infected plant matter (de Assis Filho et al. 2005). The virus gets into the insect’s midgut and then to different cells and organs, such as the salivary glands. The virus is spread to a plant that isn’t already infected when plant tissue is injected with saliva during feeding (Figure 1).
In crop systems, the virus is transmitted by adult thrips. Importantly, adult thrips that have not acquired the virus as larvae are not able to transmit the virus. Only certain species of thrips are able to transmit TSWV (Sherwood et al. 2001a, b). Aphids and whiteflies are not vectors. At least seven species of thrips are vectors of TSWV. The virus has a worldwide distribution, with a known plant host range of over 926 species.
Epidemics of TSW occur in many geographic regions worldwide. When and how bad epidemics are in a certain cropping system depend on how the thrips vector, the pathogen host plants, and the pathogen itself interact with each other. TSWV has been found to infect natural plant species that grow close to crops that are susceptible. In some cases, natural plants are a major source of adult thrips that carry the virus to crops that are susceptible. In other situations, susceptible crops are the source of viruliferous adults invading new fields.
The unusual virus-vector relationship is a challenge in efforts to manage TSW (Momol et al. 2004). Primary spread of the disease (i. e. three quarters of plant infections start when virulent adults from outside sources, such as cultivated and uncultivated plant hosts, come into contact with the crop for the first time. Adults persistently transmit, which means they are infected for life, and insecticides don’t stop them from spreading because infections only take a short time to take hold during feeding (Momol et al. 2004).
Secondary spread (i. e. plant infections that happen within a crop are caused by virus-carrying adults that got the virus from eating an infected plant as a larva and then move to another plant in the same crop. For secondary spread, thrips need to colonize and reproduce on infected plants within a crop. Control of the larvae before their development to adults is effective in preventing secondary spread. Most viral infections in north Florida are caused by primary spread, but some secondary infections happen late in the spring (Momol et al. 2004). The fact that there haven’t been any TSW epidemics in central and south Florida in the past suggests that the Florida flower thrips isn’t a good way for uncultivated plant species to get TSWV. The western flower thrips is better at getting and spreading TSWV from pepper in the lab, but this one can do it too (Avila et al. 2006). The eastern flower thrips, melon thrips, and chilli thrips are not competent vectors of TSWV.
Table 1 lists different types of tactics effective in managing primary and secondary spread of TSW. Each type of tactic is discussed in the text that follows.
Management Programs for Western Flower Thrips and Tomato Spotted Wilt Virus
Adult eastern and Florida flower thrips do little to no damage to tomatoes, and they keep the western flower thrips away, which is good. There has been no damage seen even when 20 to 25 of these native species were on each flower (Funderburk 2009; Demirozer et al. 2012). All species of thrips adults eat flower petals and other parts of flowers, but this doesn’t hurt the flowers’ value. The western flower thrips adults that live in tomato flowers do damage by laying eggs in the small fruit (Salguero Navas et al. 1991). About one western flower thrips adult per flower is safe, but growers need to do something when this number is reached.
Thrips feed by sucking the contents of the epidermal cells of the plant. When feeding occurs on fruit, it results in a damage symptom called “flecking” (Ghiudu et al. 2006), which may not become evident until the fruit ripens although the feeding occurred on immature fruits. Adults of the western flower thrips and larvae of all species cause flecking (Figure 2). It’s okay for there to be at least two larvae per small, medium, or large fruit in a field on average (Funderburk 2009; Demirozer et al. 2012).
Because there are a lot of native flower thrips on the flowers of fruiting vegetables, beating out the harmful invasive species, it is important to be able to correctly identify the species before making management decisions. A small container with 70% alcohol should be used to hold a few flowers on a regular basis (Figure 203, Funderburk et al. 2019). The container can be shaken to get the thrips out, and then a professional can look at it under a microscope with at least 40X power to figure out what kind of thrips it is. This is one way to figure out how the relative abundance of different types of thrips changes during the growing season. Figure out what kind of thrips a plant has is hard, so growers should have a skilled scout do it for them. Contact your county agent for advice and help.
Thrips densities in flowers can be determined by picking the flowers and placing them on a white board. If you gently tear open the flower, the thrips will fall out onto the board. The adults and larvae can be easily told apart and counted. In the field, you can’t tell the difference between Florida flower thrips, western flower thrips, and eastern flower thrips. For scouting purposes, counting the thrips on ten flowers from a few different spots in a field is usually enough to get a good idea of how common each species is. Examine small, medium, and large fruits directly for thrips, taking care to look under each calyx. Examine and count the thrips on at least four fruits from each of several locations in the field. It is important to keep an eye on the small fruits often because that’s when the eggs are usually laid, during the flower stage. Larvae on the small fruit are the first sign that something is wrong.
The ultraviolet-reflective mulch in the typical raised-bed plastic mulch production system of Florida repels the migrating adults of the western flower thrips and this reduces the primary and secondary spread of TSW. The use of ultraviolet-reflective mulch also reduces the influx of eastern flower thrips and Florida flower thrips (Momol et al. 2004). This cultural tactic is most effective from early to midseason before the plants grow to cover the mulch. Application of certain fungicides and other pesticides reduces the UV reflectance and hence the efficacy of the mulch. A single application of copper and mancozeb fungicide can reduce the reflectance by approximately 49%.
Acibenzolar-S-methyl (Actiguard®) is a systemic acquired resistance inducer that influences the salicylic acid pathway in the plant. This product has been shown to reduce the incidence of infection of TSWV (Momol et al. 2004). Its use has minimal impacts on populations of the flower thrips. The product is particularly effective against bacteria and it is an excellent replacement for foliar pesticides for bacterial and fungal disease control.
When invasive western flower thrips got to Florida, they were probably already resistant to most of the common types of broad-spectrum insecticides. Resistance has been documented for pyrethroid, carbamate, and organophosphate classes of insecticides. Flaring of western flower thrips and the non-target pests is possible when any broad-spectrum insecticide is used. Because of this, they are being phased out of tomato crops as safer, more selective insecticides from different chemical classes become available (Table 2). There are some organophosphate and carbamate insecticides that can kill western flower thrips, but they should only be used on certain plants. Their use may be warranted but only in particular instances when nontarget effects would be minimal. In this case, it would be near the end of the growing season, since the label shows re-entry and pre-harvest intervals.
The most efficacious insecticides for western flower thrips in tomato and other crops are in the spinosyns class. No other insecticide class provides this level of control. However, some level of resistance to spinosyns has been documented in pockets in Florida (Weiss et al. 2009). The label for spinosyns has a limit on the number of applications per season. Growers should always follow the label and not exceed the label wording. Only use Insecticide Action Committee group 5 insecticides (spinosyns) a maximum of 2 sprays per crop. Avoid sequential sprays on sequential crops. Cyantraniliprole and acetamiprid have performed best after the spinosyns in the trials. Other insecticides that are very good at getting rid of western flower thrips adults and larvae are flonicamid, spirotetramat, and Requiem® (terpenes). Western flower thrips can be controlled with azadirachtin, potassium salts of fatty acids, and other insecticides that can be bought in stores (Table 2).
The goal of management is not to kill as many thrips as possible, but to keep damage from happening. High levels of dimpling and flecking are only bad, and they can be lowered to levels that aren’t too bad by controlling western flower thrips adults and larvae. When different insecticides from different chemical classes need to be used more than once during the growing season, it is important to do so. In north Florida, it may be necessary to use insecticides three to five times a week to keep dimpling and flecking from doing too much damage. The weekly applications are sufficient as well to prevent secondary spread of TSW (Momol et al. 2004). In the past, these applications included spinosad and certain broad-spectrum organophosphate insecticides. The organophosphate can be replaced with the newer, safer insecticides (Dripps et al. 2010; Srivistava et al. 2013).
This Pest LOVES Drought… Here Is How To Treat Thrips.
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