Researchers have found three species of predatory bug in the Miridae family that can limit the establishment of the harmful predatory bug Nesidiocoris tenuis in tomato crops. “Omnivorous predatory bugs could potentially be a great help in biological pest control,” researcher Gerben Messelink says.
In recent years the bug Nesidiocoris tenuis has become a serious problem in tomato growing. Although it controls whitefly and tomato leaf miner, the insect causes so much damage to the crop that growers tend to view it as a pest rather than a predator. These Mediterranean plunderers puncture fruits and flowers and cause necrotic rings which lead to stems breaking off. They inhibit plant growth, resulting in deformed plants. Tips fall off and production stagnates.
“Tomato growers in southern Europe have been using Nesi to control Tuta absoluta for years,” says researcher Gerben Messelink of Wageningen University & Research’s greenhouse horticulture business unit in Bleiswijk, the Netherlands. “Various other predators such as nematodes and parasitic wasps have been tried as well, but Nesi appears to be the most effective. Southern Spanish growers therefore mainly see this creature as a useful predator.”
But things are different hundreds of kilometres to the north, where Nesi is a serious problem for Dutch tomato growers. Crop damage is severe and the predatory bug is difficult to control selectively. Chemicals also have an adverse effect on Macrolophus, a relative of Nesi, giving pests such as whitefly free rein and disrupting the whole biological control system in the greenhouse. What’s more, this creature develops faster than related species. “It is a thermophilic insect, so when the temperature in the greenhouse is 20°C the population is already growing strongly,” Messelink says.
Omnivores in a spectrum
To tackle this problem, in 2015 WUR teamed up with the growers’ organisation LTO Glaskracht Nederland and submitted a project proposal, “Pest control with omnivorous predatory bugs”. This public-private partnership launched in 2016, financed half by the Dutch Ministry of Agriculture and half by the private sector. The private funding for this project comes from the Dutch tomato, gerbera and rose growers’ cooperatives, Stichting Programmafonds Glastuinbouw (the Dutch greenhouse horticulture programme fund foundation) and Koppert Biological Systems.
“Nesi is a predatory bug in the Miridae family, just like Macrolophus,” Messelink explains. “Miridae are omnivores that not only use plants as food but also serve as predators. There are many different species of Miridae and they are all located in different places in this spectrum. One species eats more plant, the other more prey. Macrolophus is a predatory bug that is very pest-oriented and only causes limited damage to plants. Nesi, on the other hand, quickly causes a lot of damage but is also a good pest controller.”
Messelink and his colleague Ada Leman ran a greenhouse trial last year in which they investigated whether establishment of this insect in tomato is limited if a population of other bugs is already established in the crop. To determine whether Nesi also affects the densities of its relatives, controls with these bugs without the notorious predator were also set up.
The greenhouse trial was carried out in large insect cages with one tomato plant per cage: grafted Brioso plants with two stems. The effect was assessed using three types of new predatory bug, which the researchers brought in from southern Europe. “We investigated the effect these three species had on pest control and we looked at the development and establishment of these insects in tomato and their secondary effects on Nesi. The result was quite spectacular,” the researcher says. “Nesi was able to establish in all treatments, but what we saw was that where we had built up a population with the new species first before introducing Nesi, establishment was reduced by an average of 90%.”
The final population density of the predatory bug among its three southern European cousins averaged 85%, 92% and 95% lower than the controls respectively. There was no significant effect the other way round.
Whitefly and cotton whitefly
“We confirmed in the laboratory that the adults of the three new species feed on the young Nesi nymphs, but it is not yet clear what effect Macrolophus has on the insect,” Messelink says. “We have observed that Macrolophus is often squeezed out in the greenhouse, and in the laboratory too we have noticed that this bug doesn’t feed on young Nesi nymphs. So using these new species could offer an advantage over Macrolophus. But it’s important to find out whether they are just as effective in controlling the main pests.”
Now that the researchers have established that the three southern European bugs control tomato leafminer, this year they are looking into the effect these species have on greenhouse whitefly and tobacco whitefly.
Messelink is enthusiastic about the initial result. “You have to view the predatory bugs as a standing army. If you can deploy the new species preventively, if they can control different pests, tackle Nesi and don’t damage the crops, then we will be taking a big step forward in biological control.”
At the end of the day, the researchers want to be able to offer growers a total package. “We are looking for a predatory bug that controls an infestation as effectively as possible and doesn’t damage the crop,” Messelink says. “I have high hopes. I think these insects will be a big help in biological control in the future.”
Experience in rose and gerbera
As part of the same study, the researchers also investigated the use of omnivorous predatory bugs in gerbera and rose. “We think that this insect can offer a solution in these crops too,” researcher Gerben Messelink says.
“Whitefly, caterpillar, Echinothrips – all these pests can be controlled with predatory bugs, so it is possible but we still need to do more research. We have observed that this insect has difficulty establishing in gerbera, mainly because of the mildew control technique that’s currently used. Growers spray the crop, and it is not so much the toxic value that eliminates the predator; research has shown that spraying under high pressure ‘blows away’ the predator. So if we can find another way of controlling mildew, we can also build up a population of predatory bugs in the crop and control pests that way.”
The researchers are also trialling building up a population of these predators in rose. “Rose is a woody plant, which makes it difficult for this insect to establish. Bugs prefer hairy, herbaceous plants. But we might be able to keep these predators in the crop by using a host plant, for example. We have already demonstrated that we can control Echinothrips in rose effectively this way.”
Three species of predatory bugs in the Miridae family can limit the establishment of their harmful cousin Nesidiocoris tenuis in tomato growing. Researchers looked at the effect they have on pest control. They investigated the development and establishment of these three southern European predators in tomato and their secondary effects on Nesi. The final population density of Nesi with the three predatory bugs tested was around 90% lower than in the control. It is likely that these omnivorous insects could ultimately also offer a solution in rose and gerbera.
Text and images: Marjolein van Woerkom.
Dutch chrysanthemum growers are feeling quite optimistic about thrips control. After years of high pest pressure, growers are getting more adept at integrated pest control, thanks to meticulous scouting, a good predatory mite, supplementary feeding and biological crop protection products. Of course, there isn’t a one-size-fits-all approach that works for every nursery. Chemicals are still an indispensable part of the mix as a backup. Growers and suppliers outline the latest developments.
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Even finding a thrips to take a picture of for this article isn’t easy. It’s the middle of May and we’re looking for a specimen on the sticky traps at Kamuro Flowers, Frank, Rick and Arthur van Zeijl’s 38,000 m2 year-round chrysanthemum nursery in the Hook of Holland.
That’s extremely good news, especially when you consider that the chrysanthemum sector has some difficult years behind it. With the use of chemical controls declining, thrips were popping up everywhere, posing a real threat to the crop. Frank van Zeijl: “About this time last year there would be at least thirty on each sticky trap. This year is different. Partly because of the weather, because by April we hadn’t had an extended period of warm weather in the Netherlands.”
More thorough scouting
But that’s not the whole story. The van Zeijl brothers have also changed their crop protection strategy, including introducing more thorough scouting. In 2016, their company, which grows disbud chrysanthemums like Anastasia, Astroid and Siberia, joined Zentoo, a quality mark that guarantees 100% pest-free flowers. To make this a reality, members have to follow a strict protocol for scouting and thrips control. Since last year every member has had one person responsible for monitoring the protocol.
“Scouting is more important now than ever before,” van Zeijl says. “Our supplier Van Iperen does that for us. They not only check the sticky traps, they walk through the crop as well. Because the sooner you discover a hotspot, the better. Once a week we also spray with NeemAzal-T/S or Azatin, which are both products of natural origin. They work well with Phytoseiulus persimilis, which we use against spider mite. We don’t use the predatory mite Transeius montdorensis because we regularly get bugs and the biological products we use are also effective against them.”
Production scaled up
Unlike the van Zeijls, however, many other growers are opting to use this “new” predatory mite against thrips this year. Two or three years ago, Royal Brinkman (with its partner Agrobio) was the first supplier to achieve good results in thrips control with montdorensis, at chrysanthemum nurseries in Bommelerwaard, the Netherlands. Koppert and Van Iperen (with its partner Bioline) subsequently also stepped up production of this natural agent.
Grower Michel Grootscholten of Monster, the Netherlands, who grows chrysanthemums on 11 hectares, has been using this predatory mite to control thrips since 1 January. “It’s been around for a while but I used to find it too expensive. A few other growers got through the summer very well with montdorensis. After that, all three suppliers scaled up their production, which brought the price down, fortunately. I don’t yet know whether it will turn out to be a good thing for us. We have got thrips under control now, but other pests have been grabbing their chance, like caterpillars and snails. So in mid-May I started using NeemAzal-T/S and the bacterial preparation Turex, two biological agents that fit in well with our biological system. But the system isn’t watertight yet. It’s important for us growers – and the suppliers – to share knowledge.”
Knowledge-sharing is already happening, but mainly between groups of growers. Supplier Van Iperen coordinates crop protection for all Zentoo growers, for example, but it does more than that. Throughout the year, adviser Richard van Spronsen collects data from all the affiliated nurseries – including from washing and counting, for example – and compares the results obtained.
Van Spronsen: “Of course, every nursery and every season is different, but we are building up a database of information this way. As yet there is no such thing as one ideal strategy. Some Zentoo growers are controlling thrips with Transeius montdorensis, some are using our recently revamped bugline with Amblyseius cucumeris, and the van Zeijl brothers only use biological products. Whether the predatory mites are supplementary fed with prey mites differs from one grower to the next. There are a lot of unanswered questions around that, but my impression is that it works. We are continuing to work with the growers to see which integrated solution is the most effective. What is certain is that pesticides – biological or chemical – are still indispensable.”
Products of biological origin
Daniel Cornelisse, adviser at crop protection product manufacturer Nufarm, can confirm that. “Growers usually use chemicals to enable them to get off to a clean start or to supply insect-free plants. Broad-spectrum chemicals are becoming less and less readily available. We will continue to lobby for selective chemicals because it’s important for growers to be able to firefight. For instance, Nocturn (pyridalyl), a selective pesticide for controlling thrips, was approved for Dutch chrysanthemum cultivation last year.”
The focus at Nufarm is on plant protection products of natural origin, Cornelisse says. “We invest in products that fit in well with integrated pest control, like NeemAzal-T/S, which is made from neem tree extract, and Dipel DF, a bacterial preparation. We want to help create a robust integrated system in chrysanthemum cultivation.”
Lianne van Wijk, technical advisor at Certis, also has the same message. “Combining natural predators with biological products makes the system strong. Not least because the products that growers cite – Azatin and Turex, but also BotaniGard – also control other insects apart from thrips. We are constantly looking for products that fit into this system. For instance, NEMguard, a biological agent against nematodes, has just been approved. Of course, chemical pesticides such as Winner are still indispensable.”
Thrips has been a serious problem for chrysanthemum growers in recent years. But Dutch growers are increasingly winning the battle against the pest: mainly because they are scouting much more thoroughly, but also because many nurseries are successfully using predatory mites to control attacks. Biological products are an indispensable link in this integrated approach. It is important for suppliers and growers to continue to develop and share knowledge.
Text: Karin van Hoogstraten.
Images: Studio G.J. Vlekke.
Viruses are among the smallest pathogens infecting other living organisms. Plants are also susceptible to a large number of viruses that can cause serious diseases.
Viruses consist solely of a piece of genetic material (RNA or DNA) and a protein coat, or capsid. They therefore cannot survive independently and need other organisms to multiply and spread. Plant viruses replicate in plant cells and use insects (especially aphids and whitefly), mites, nematodes, soil fungi and even humans and our tools to move from one host to another. There are specific interactions between viruses and their vectors. Cucumber mosaic virus (CMV) is transmitted by aphids, for example, and tomato spotted wilt virus (TSWV) by thrips.
Therefore, controlling viral diseases not only entails starting with clean and certified plant material but also involves monitoring and controlling the transmitters (vectors) of plant viruses. Vigilance is essential, because new viral diseases can appear in plants when changes in populations of viruses and their vectors give rise to new situations.
Crop protection products are sometimes unfairly labelled as losing their efficacy against pests or diseases. On closer investigation it becomes clear that these products don’t always end up in the right place or are not being taken up properly. In that case, adjuvants can be indispensable if you use them in the right combinations. Uptake can sometimes increase by as much as six to eight times.
Substances that support the use of crop protection products and enhance their effect are on the rise. A year ago, no fewer than 101 different ones were registered with the Dutch Board for the Authorisation of Plant Protection Products (CTGB). Thirty companies are involved in the development and distribution of these products.
One of these is the Dutch manufacturer SurfaPLUS, which is actively promoting their correct use in a series of events for consultants and users. Director Hans de Ruiter sees it as his mission to do this. That’s hardly surprising, since in his previous job he was project leader at Wageningen University & Research, where he was intensively involved in research into these substances. But this research rarely if ever takes place in the public domain these days. Instead, he has it carried out by private research institutions. After all, there’s no question that this extremely useful work must go on.
Variety of effects
“Adjuvants” is actually a collective term for products that work in a variety of ways. An important function that is particularly relevant to open-field cultivation is reducing spray drift. This keeps the active ingredients where they need to be to do their job. Another function is reducing volatilisation during spraying or after contact.
These products can also ensure that droplets of the solution stay on the plant or leaves and that the active ingredient is more evenly distributed. In other cases, the products can improve contact by “gluing” the active ingredients to the leaf surface. Lastly, they can boost uptake of active ingredients by making them soluble or making the plant’s waxy cuticle more permeable.
Every adjuvant therefore has its own characteristics, and some do several things simultaneously. “That’s important,” de Ruiter says. “because we know from the research how poor the uptake of active ingredients can sometimes be without these products.”
To start with a concrete example, de Ruiter cites the “Vertimec case”. This product, which is based on the active ingredient abamectin, is authorised for the control of spider mite, thrips and leaf miner in both ornamental and vegetable cultivation. In tomatoes, for example, it can be used three times per cultivation cycle, and more often in ornamentals. Vegetable growers tend to use it sparingly because it has an adverse effect on biological controls. But with the emergence of pests and diseases that are difficult to control, such as tomato russet mite, growers sometimes need to reach for the chemicals.
De Ruiter: “I hear complaints from growers that a product is becoming less effective at the correct dosage. The story goes that certain insects or mites have become resistant. But it doesn’t have to be that way. If you use the right adjuvant, a product generally does what it’s designed to do. In fact, an effective combination of the two products can actually reduce the risk of resistance.”
Abamectin is a product that is inadequately absorbed by the leaves when sprayed on its own. With the correct adjuvant, uptake can increase by six to eight times. It is poor uptake that increases the risk of resistance.
Combination works better
In 2014, research was carried out at the Westland Demo Nursery (Demokwekerij Westland) into the effect of abamectin and Hasten, an adjuvant based on an esterified canola oil, on an infestation of Californian thrips on sweet pepper. The treatments were as follows: untreated (water), 100% abamectin, 100% abamectin with Hasten, 50% abamectin and 50% abamectin with Hasten.
Thrips control with abamectin on its own was no higher than 15-25%. The combination with the adjuvant worked two to three times better. Previous research into spider mite control in cucumber yielded the same outcome.
In the summer of 2016, Botany BV carried out research into a combination of the adjuvant Elasto G5, a glycerol-based polymer, and XenTari, a biological agent based on Bacillus thuringiensis, against the golden twin-spot moth in sweet pepper. The treatments consisted of untreated (water), XenTari, XenTari with Elasto G5, and Elasto G5 on its own. Both pupae and adult moths were released into the crop and the researchers waited until various stages of caterpillars were present. A total of three treatments were carried out at weekly intervals.
The trial showed that the adjuvant improved the effect of the active ingredient. The product provided better coverage on the crop and improved distribution of the active ingredient (see graph).
These were mild substances that did not cause any damage and left no residues behind. Nonetheless, a warning would not be out of place, says De Ruiter. “Adjuvants can also boost the effect of products. They can make ‘hard’ products even harder.”
The use of Elasto G5 has also proven its worth in another way: in combination with inhibitors. In 2014, Delphy ran a trial with the adjuvant in combination with Alar (daminozide) in pelargonium which revealed that the use of inhibitors can be reduced by half. “That cuts costs for growers quite substantially, because inhibitors are expensive. It depends on the crop and the variety, but we have sometimes seen costs cut by as much as 44%.”
The days of pioneering with adjuvants are over, says de Ruiter. They have since found wide acceptance and the trial results are better than in the past, when some substances were too aggressive. The gentler products are gaining ground. “Of course, we have to keep on investigating new opportunities and we need to communicate the results we obtain with caution.”
Hence the events, which are held fairly regularly. Incidentally, SurfaPLUS is not the only company doing research into these substances. Crop protection product manufacturers such as Bayer Crop Science and Certis include them in their programmes, and the Dutch companies Modify and GreenA are also active players.
Adjuvants that enhance the effect of crop protection products are gaining ground. Not only do they get the active ingredients working better, they also help to avoid resistance. The right combination can halve the need to use inhibitors in some crops, delivering substantial savings. It’s important to know which combinations are the right ones because an adjuvant can also reinforce a product’s adverse effects.
Text: Pieternel van Velden.
The fungus Mycosphaerella, also known as Didymella bryoniae, can cause serious problems, particularly in cucumber cultivation. It can infect leaves, stems, flowers and fruits. The fruits can be affected on the inside (internal fruit rot) and the outside (external fruit rot).
Generally speaking, the first infections in crops grown under glass are caused by ascospores (sexual spores) which enter the greenhouse mainly via the air. For infection to take place, there needs to be high relative humidity (RH >85%). Internal fruit rot is caused by the fungus penetrating the fruit via the flower. Stems, older leaves and the outside of fruits become infected via damage (wounds). The risk of infection can be somewhat reduced by aiming for lower RH in the greenhouse.
It is thought that mildew-tolerant varieties are slightly more susceptible to Mycosphaerella, perhaps because growers of these varieties use fewer mildew products which also help to control this fungus, such as Collis, Rocket and Fungaflor.
Images: BASF and Wageningen University & Research.