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.
Thrips are one of the biggest threats chrysanthemum growers face. But this hasn’t put off River Flowers in the central Dutch town of Zaltbommel: they grow one of the most sensitive chrysanthemum varieties using integrated pest management. “It works, but you need discipline to succeed.”
Chrysanthemum ‘Haydar’ grows here in all its glory. When you enter the 3.5 hectare greenhouse, you are confronted with a sea of plants graduating from green at the front of the greenhouse to purple with a white edge at the back. Not many growers are keen to grow this chrysanthemum variety because of the huge threat posed by thrips. In extreme cases these small, thin insects can even mean bankruptcy, but Peter van de Werken of River Flowers in Zaltbommel is up to the challenge. “We have the resources to deal with them and we have a person working full-time on crop protection. It is more labour-intensive, but we can charge more for this plant.”
At the beginning of each plant row is a yellow sticky trap hanging from a pin mounted on the truss. Some traps have more black dots on them than others. CEO assistant Rick van de Werken takes hold of one of the yellow cards and examines it with a magnifying glass. “Look, there’s a thrip.” He points to a dot that is barely visible to the naked eye. “Last week I found two different species.” He shows us a picture on his phone. “We need to be fully alert to keep the pressure as low as possible.”
His uncle agrees: “We base our cultivation decisions on the risk of thrips. Do we want to use the sprinklers? First we check whether that fits in with our pest management strategy. It is a huge threat and difficult to get to grips with, or at least it has been until recently.”
Until 2014, the growers fought the pest with chemicals and the predatory mite Cucumeris. “Every year we started off using Cucumeris in the spring, but things would often get out of hand between weeks 35 and 45, so we had to correct with chemicals,” says Teun de Leeuw, the company’s crop protection specialist. “That immediately killed off all the biological life, including the other natural predators. The biological balance got out of kilter and we had to rebuild the biology from scratch. We were always falling behind.”
So he decided to try something new: correcting with Nemasys nematode spray. “I had heard of this before and thought: this will enable the bio to continue to do its job,” he says. The nematodes did the trick and got the number of thrips back under control. Since then, the nursery has hardly ever needed to use chemicals to tackle an outbreak.
“This doesn’t mean we can sit back and relax, though,” Van de Werken adds. “Thrips get into your crop in three ways: through the windows, through the door or from the soil. To minimise the risk in the soil, we only grow one variety of chrysanthemum in each greenhouse. Luckily we don’t have any growers as neighbours, so there is less risk of contamination through the windows. We also carry out intensive chemical thrips control measures on the new cuttings for two weeks. And lastly, Teun is always on the case.”
Teun works on crop protection full-time. He checks the plants and the sticky traps daily. “We sit down with Alliance once a week. I keep an eye on the cost structure, they input their experience, and when the number of thrips rises and the biological balance gets out of kilter, we decide together whether we need to change the strategy.”
Focus on biological control
Nematodes are not the only thing they use to keep the numbers of thrips down. They also use tapes, fungi and turkey feed. According to Piet van Boven, bio-insecticides advisor at BASF, growers are increasingly looking for a biological solution. “Firstly because the list of legally permissible pesticides is getting shorter and shorter, and secondly because pesticides are detrimental to the biological life in the greenhouse. It takes time and energy to build that up again,” he says.
For the last four years he has been recommending Nemasys nematodes. Cage tests have revealed that the effectiveness of these nematodes is around 40-60% in the soil and 60-70% in the crop. Van Boven: “Of course, you can’t translate these results directly to the commercial setting, but they do show a continuous effect. We see nematodes as part of the package of control measures and we get good results in combination with predatory mites.”
Thrips determine cultivation choices
However, it is important to follow the nematode protocol. Among other things, that means leaving the leaves wet for two hours. “Sufficient moisture is vital,” van Boven adds. “We recommend spraying with a normal spray boom. This produces the best nematode distribution and avoids dripping.”
But the chemicals company is also on a learning curve. “We used to think that the best time to apply nematodes was in the dark, at around 4 am. But new insights have revealed that spraying them in the late afternoon can also be very effective.”
For de Leeuw, that means no more getting up at the crack of dawn, although at this time of the year the plants do start the night wet, which increases the risk of rust. “It’s always something to bear in mind, but as mentioned, the thrips determine our cultivation choices,” he says.
Chemicals as a back-up
Discipline is and remains the key to success. Van de Werken and de Leeuw discovered this in September last year, when disaster was narrowly averted. “When it came to harvest time, we suddenly noticed that the flowers in some of the bays ready for harvesting were damaged,” van de Werken says. “We went to look for the cause and found insect-damaged tapes. It turned out that we had had an infestation of mice, attracted by the bran in the tapes. Because the tapes had been eaten, the thrips had had a field day. The whole balance was out of kilter. We bought some cats and tackled the thrips with nematodes and a bit of chemistry. It took more than 15 weeks to restore the balance in the greenhouse. We have learned to be even more alert now. It was a really tense time, because if you don’t get an outbreak like that under control, you might as well shut down. You would simply go bankrupt.”
So it is extremely important to have some chemicals that can still be used, he believes. “As a grower I only feel confident in heading down the biological control path if we can continue to use chemicals as a back-up. If the government allows us some leeway in terms of chemicals, we will be happy to use biological control methods in return. Chemicals are a must when you are experimenting with biological pest management. You have to have something up your sleeve if things go wrong.”
Netherlands-based River Flowers grows chrysanthemum ‘Haydar’, one of the most sensitive chrysanthemum varieties to thrips, which they control using integrated pest management. They keep numbers down with nematode sprays, but discipline is a must. One employee specialises in crop protection full-time, and the nursery is constantly optimising its methods.
Text and images: Marjolein van Woerkom.
The predatory bug Orius has been used to control thrips in sweet pepper for many years with great success, but the results have so far been disappointing in ornamentals. Researchers Marjolein Kruidhof and Gerben Messelink now think they have found a solution. With a new method of using the bugs that involves supplementary feeding, thrips can now be successfully controlled in chrysanthemums.
Thrips are the biggest threat to ornamental growers’ crops. Research into biological predators for this pest has been going on for many years. Good results have been achieved with predatory mites, but this has often failed to eliminate the problem because the predatory mites only attack the young larvae. The predatory bug Orius is a very effective weapon against thrips in both the larval and adult stages but it has trouble establishing in ornamental crops. Numerous ways of overcoming this problem have been investigated, ranging from banker plants to feeding stations, but there has been no real breakthrough. Until now, that is.
In the spring of 2017 the Wageningen University & Research Greenhouse Horticulture business unit in the Netherlands started experimenting with a new approach to thrips control in chrysanthemum cultivation. Instead of starting off with chemical crop protection products, the researchers are now introducing biological agents in the cuttings phase. The predators are given high-quality supplementary food so that they can form a strong population or a “standing army” to nip the outbreak in the bud.
“The results that have been achieved this time are due to good coordination between two projects: the PPS Thrips project, in which we are looking for a good alternative supplementary food source, and the Green Challenges project, in which we are optimising the role of biodiversity in crop protection and achieving paradigm shifts,” says researcher Marjolein Kruidhof.
In chrysanthemum cultivation, there is usually only a short time window in which you can start using biological control, according to Kruidhof. “Also, the presence of chemical residues delays the growth of populations of natural predators,” she says.
The researchers experimented with a biological start using the predatory bug Orius. They ordered cuttings that were almost pesticide-free, rooted the cuttings themselves and added the bugs a few days before the plants went into the greenhouse. “A biological start is a real change in thinking,” says Kruidhof’s colleague Gerben Messelink. An important part of this strategy is the supplementary feeding, he stresses. “After a series of trials in which we compared different types of food, we ultimately went with Artemia, the cysts of the brine shrimp. This is a potentially good food source and has a long shelf life.”
Trials using Artemia as a feed supplement for predatory bugs had been carried out before but with only moderate results, he says. “The quality of the Artemia that is available on the market at present is good enough for feeding predators like Macrolophus in tomato but not for Orius.”
The researchers therefore got together with the University of Ghent to come up with a good quality food source. Meanwhile, the Israeli company Biobee had also started producing high-quality Artemia which the researchers were able to use in subsequent experiments.
The results exceeded expectations. The number of Orius rose substantially as a result of the supplementary feeding. Having started with fewer than one bug per cutting, by the end of the production phase the researchers were counting 40 bugs per plant. What’s more, the natural predator seemed to respond very well to the availability of food. “It turns out that they are highly mobile,” says Kruidhof. “This has potential because it allows you to manage your biological control better. Plus it means you will very likely be able to reuse the bugs. If you end up with 40 bugs per plant, it would be a shame to spray them dead. That’s destruction of capital. You might be able to lure the adult specimens to new cuttings with targeted supplementary feeding.”
More effective than predatory mites
The impact on thrips damage was significant. “In the control section, in which no Orius or Artemia were used, half the younger leaves were damaged by thrips,” says Kruidhof. “The figure for the plants with the bugs was less than two percent.” The predatory mites did less well than the predatory bugs in terms of thrips control, despite the fact that they had built up a good population with the chosen food source. Researchers still found about 20 to 25% thrips damage on plants following the use of these biological predators. “So Orius really are more effective than predatory mites because they also attack adult thrips,” says Messelink.
“We have proved that the system works,” says Kruidhof. “We can build up the population of bugs by using biological controls and good quality nutrition right from the start, and this population provides good thrips control even in the presence of another food source.” However. that doesn’t mean that this method can simply be replicated in the commercial greenhouse setting. “We still need to optimise certain aspects,” she says. “For example: when is the best time to introduce the bugs? Should they be used in the rooting phase or can they be brought in later? How many bugs should you use? What will your feeding strategy be? How much food should you provide?”
This method of control is based on one generalist. What do you do as a grower if you also have to deal with leaf miner or aphids? “Growers will have to control leaf miner with additional biological measures or selective chemicals. Aphid control can become a problem, but the expectation is that high densities of this predatory bug will also keep aphids under control. Other possibilities for controlling aphids are parasitic wasps, gall midges or perhaps other predatory bugs. We therefore want to investigate whether other types of bugs can be combined with Orius to deal with aphids.”
Crop protection specialist Helma Verberkt of the Dutch growers’ organisation LTO Glaskracht sees this as an excellent development. “It is a good addition to developments in the commercial greenhouse setting, where good results have been obtained in recent years using predatory mites,” she says. “For use in practice, there will need to be enough affordable, good quality Artemia available and it is important to ensure that Orius is compatible with other biological agents and pesticides used.”
The question is also whether cutting suppliers and producers will be willing to come on board. Cuttings with few or no crop protection product residues are currently hard to find. “It’s a bit of a chicken-and-egg situation, but I think we will manage,” says Messelink. “There’s also a real change in thinking going on among cutting suppliers. More and more growers want to start biological control earlier and are asking for cuttings with fewer or no chemical residues. Cutting suppliers are also looking for alternative options. I think biological control is the solution.”
“We have shown that it works now, and that is quite a breakthrough,” Kruidhof adds. “We plan to carry out another greenhouse trial this year and we expect growers themselves to start developing the strategy further as well. As a result, the market for pesticide-free cuttings will only get bigger and more demand-driven. So producers and suppliers will have to meet that demand.”
Both projects are funded through the Top Sector Horticulture & Propagating Materials and are being implemented within this sector with funding from the government, various crop cooperatives and Koppert. The projects are coordinated by LTO Glaskracht Nederland.
Researchers in the Netherlands have made a breakthrough in controlling thrips in chrysanthemums. By starting biological control early on and providing good quality nutrition, it is possible to build up a good population of the predatory bug Orius. This population controls infestations well, even in the presence of food.
Text and images: Marjolein van Woerkom.
Supplementary feeding of predatory mites with a pollen preparation has outgrown the trial phase. A large number of growers is successfully using this method. While pest numbers are low, predators that also eat pollen have the chance to build up a vigorous population. Dutch growers Wesley Klauwi from sweet pepper nursery Zuidgeest Growers and cucumber grower Bart de Groot explain how they do it.
“Snack peppers are different from standard pepper varieties, and you have to learn to respond to that.” Wesley Klauwi is responsible for crop protection at Zuidgeest Growers, a nursery famous for its Vitapep orange snack pepper. “Caterpillars and aphids are the biggest problem at this nursery. We have the other pests well under control, even though we have had a lot of pressure from thrips here over the last couple of years”, he explains.
The sweet pepper nursery gained experience this year with supplementary feeding of predatory mites with Nutrimite, a preparation based on cattail pollen. It is highly nutritious for predatory mites and unattractive to pests. What’s more, this pollen doesn’t produce allergic reactions.
In the first week of January, Amblyseius cucumeris was used to control thrips on the four hectare site in Maasdijk (south-west Netherlands). A bag was hung on every twelfth plant, and Amblyseius degenerans was added two weeks later. The rows in the greenhouse are 50 metres long. Klauwi opened the tubes halfway down the rows. He then provided three to four batches of supplementary pollen at 14-day intervals.
He disperses the product with a small leaf blower, first around the places where he has distributed the A. degenerans and then around the whole greenhouse. “We want to see plenty of predatory mites round about March, and we have achieved that at all our sites,” he says.
Supplementary feeding of natural predators is becoming more and more popular. Marcel Verbeek of Biobest says that about half of his customers now feed pollen. The major advantage of this method is that it allows natural predators to develop well at a time when there are not yet enough pests to sustain them. Predatory mites in a sweet pepper crop can often survive simply on the pollen from the flowers, but a cucumber crop produces no pollen at all. This makes it much harder to build up a good population of natural predators.
Several predatory mites eat the pollen preparation, namely A. degenerans, A. swirskii and Eurseius gallicus. A. cucumeris also responds to the preparation but less vigorously than swirskii and degenerans. “We are seeing good results. Proponents are finding that it makes the predatory mites more active and more vital. Others believe that the mites can get lazy or that they would prefer to eat pollen than catch pests.” Verbeek doesn’t agree.
Sometimes it is hard to make a sound choice. The advice is to disperse a total of 0.5 kg per ha each time. Supplementary feeding is not cheap but it delivers good returns because of the increased numbers of predatory mites in the crop.
“We are certainly seeing plenty of Amblyseius degenerans running around on the flowers,” says Klauwi. “Thrips are under control and this predatory mite also tackles spider mite. We hope that Orius will help with pest control in around week 25.” They prefer the combination of A. cucumeris, A. degenerans and supplementary feeding with pollen. “As far as we’re concerned, supplementary feeding is the future.”
Verbeek: “Our advice is to build a resilient population of natural predators before problems start arising in the crop. Sometimes this even starts with the breeder. Some growers are already releasing predatory mites at the propagation stage as well as providing supplementary feeding with the preparation.”
Gradual start keeps down costs
“Supplementary feeding doesn’t come cheap,” says Bart de Groot, Aad and Ruud Zwinkels’ partner from Kwintsheul in the Westland area. They have been using the pollen preparation at the 28,000 m2 cucumber nursery for a couple of years now.
The cucumber growers plant three times a year. To begin with they release A. swirskii at a rate of one bag per four plants to control thrips and whitefly. When the first spider mite appears, they add Phytoseiulus. Although the preparation is very effective for the predatory mite population, they decided last year to take a more gradual approach to keep costs down. In April 2015 the pressure from whitefly increased and there were not enough swirskii present to tackle the problem, so they decided to start supplementary feeding again.
This year, the course of events is the same as in 2014. De Groot is using 0.25 kg pollen per hectare per week on this fast growing crop. “But we still notice that this is saving us a round of predatory mites,” he explains. “Incidentally, we don’t have a lot of trouble from thrips. It’s mostly whitefly that we need to keep under control.”
Fan is faster
The leaf blower they used for dispersing the preparation in the first two years has now been replaced by a fan on the pipe rail trolley as dispersing the pollen with the leaf blower took too long. The grower can now get the job done in 45 minutes. He does it early in the morning before the vents are opened. He positions the trolley so that the fan is about half a metre above the wire. Then he rides down eight rows in the 300 metre-long greenhouse. The following week he changes the pattern and takes the eight rows in between.
The advantage of this method of dispersal is that the grower gets a good picture of the condition of his crop in a short space of time. “It means I can see straight away whether the plants are growing well and if there are patches of whitefly, spider mite or other pests remaining.”
Combining bio and pollen
This year, biological control is once again going according to plan. When the third crop starts, De Groot will be using a high dose of standard bags of swirskii, one for every two plants. He wants to keep this population vital until the end of the crop with supplementary feeding.
“We are noticing that supplementary feeding with the pollen preparation is adding a new dimension to our biological control. We’ve seen for ourselves how predatory mites can build up a good population when they get a varied diet, in other words a combination of pests and pollen. With more and more chemical pesticides being banned, I see this as a good strategy for the future,” Verbeek adds.
The number of sweet pepper and cucumber growers feeding predatory mites pollen preparations is on the rise. The varied diet of pests and pollen creates a good, resilient population of natural predators. Although this strategy means the money has to be spent before the benefits are felt, this trend looks set to continue.
Text and images: Pieternel van Velden.
More and more research is revealing that endophytes – microorganisms that live in the plant without harming it – can significantly boost a plant’s resistance to pests. These findings prompted researchers to investigate the potential of endophytes in pest control in greenhouse horticulture. Experiments in tomato, sweet pepper, bedding plants and chrysanthemum have shown that while the fungal isolates tested thus far don’t deliver complete pest control, they do significantly inhibit population growth.
Endophytic fungi are therefore of particular interest alongside other control measures, but there are still many unanswered questions about how they work and how to use them. A recently launched fundamental project on endophytes is expected to provide more basic knowledge to support applied research into endophytes.
The study of microbial ecosystems in humans, animals and plants has been the focus of much research in recent years. Just as gut flora is essential for good health in humans, microorganisms in plants also play an important role in resilience to pests and diseases. Precisely how this works is not always clear. Fungi can have a direct effect on pests by secreting certain metabolites, but it has also been shown that fungi and bacteria in plants can accelerate resilience in the plant (known as priming).
Some of these fungi are also known as entomopathogenic fungi, such as those of the Beauveria, Metarhizium, Lecanicillium and Isaria genera. Many of these fungi are used as a product in crops to control insects such as whitefly and thrips. We are increasingly discovering that most of these types of fungi can also grow in plants without harming the plant. Over the past two years, Wageningen University & Research in the Netherlands has been running a number of studies looking at the effects of endophytes on pests that are relevant to greenhouse horticulture.
Inhibiting aphid growth
Aphid control in greenhouse horticulture is still often based on the use of chemical crop protection products, but new regulations and customer requirements are making chemical control increasingly difficult. The alternative – biological control with natural predators – is not always as effective. Aphids are known for their ability to grow explosively on plants, making it difficult for natural predators to get the infestation under control fast enough. Measures that could inhibit the explosive growth of aphids would therefore be a welcome addition.
A study funded by the Dutch Horticulture Product Board was set up to investigate whether endophytic fungi could inhibit the growth of aphids in sweet pepper and the bedding plant Calibrachoa. Many isolates produced no effect at all, but the fungus Lecanicillium muscarium was able to inhibit the increase in aphids by 25-30% in both Calibrachoa and sweet pepper. This may not seem very much, but on a rapidly growing aphid population and in combination with other pest control methods, it can make a big difference. In further research, it is being investigated whether these effects actually result in better control when combined with natural predators.
Another major problem in greenhouse horticulture is the western flower thrips, or Californian thrips, Frankliniella occidentalis. This pest is particularly difficult to control in ornamental crops, partly due to the ever diminishing package of chemicals available and growing resistance to pesticides. In a large public-private project (Masterplan Thrips), various endophytic fungal isolates are now being screened for their effectiveness against these thrips in ornamental crops.
In the fight against thrips, increased plant resilience would be a welcome addition alongside other measures. More than 40 fungal isolates have already been screened, some of which show significant inhibition of 40-50% in the population growth of thrips. Here too, therefore, what we are seeing is not complete control but inhibition of growth. However, the results are promising and the expectation is that they will provide a very useful addition to the various measures for keeping thrips in check. In research carried out in other countries, good results have also been achieved on the tobacco thrips in onion, with endophytes reducing thrips damage by 80%.
The next step is to take a look at potential applications in greenhouse horticulture. As with aphids, the question in terms of thrips is how to combine endophytes with biological pest control. A delayed development time could be beneficial for predatory mites, which would then have longer to work on the susceptible stages (predominantly L1), but there may also be effects that impact negatively on predatory mites. These and other predators could be affected by certain substances that enter their prey (the pest) via plants containing endophytes. So it is important to test the effects in the overall system of natural predators.
The initial results with endophytes in greenhouse horticulture indicate that there is definitely potential for using these fungi to increase resilience to pests. However, there are still a lot of questions to be answered in the research: for example, what spectrum of pests they are effective against and whether they have any adverse effects on some pests and plant pathogens. Other very practical questions concern the methods of inoculation and longevity during cultivation. It has been found that there are several types of microorganisms in plants (bacteria and fungi) that interact with each other but also with the host plant. These interactions are complex and as yet not fully understood, but they will certainly affect the behaviour of introduced endophytes.
The basic questions surrounding the plant microbiome are being investigated in a new fundamental endophyte project led by Leo van Overbeek of Wageningen Plant Research. In this project, he initially wants to determine how endophytes can best be introduced into the plant. He is looking at methods of application in practice, such as via treatment of seed or young plant material, possibly in combination with irrigation water treatment.
The researchers are also taking a close look at how endophytes behave in a plant, for example which parts of the plant they spread to which also contain the various pests and plant pathogens.
Using modern DNA sequencing and other so-called ‘omics’ technologies, including metabolomics, the research is also determining how and to what extent the microbiome of the plant is influenced, based on a) the presence of the causative agent, b) the presence of the endophyte applied, and c) the combination of both. This should shed light on how pests and endophytes respond to each other and what factors play an important role in that.
The hypothesis is that endophytes will affect the composition of the microbiome, which would be expected to have an effect on the metabolism of the plant and, in turn, on pests and diseases. The researchers hope to be able to correlate measurable effects with parameters that provide an indication of a plant’s resilience. This fundamental project is expected to culminate in an integrative model that indicates how to boost resilience in plants by applying endophytes. The model will then be used to develop new technologies to make plants more resilient to pests and diseases.
Fungi and bacteria that live in plants can help make the plants more resilient to pests and diseases. It has been shown in a range of crops that population growth in aphids and thrips can be inhibited by certain endophytic fungi. Further research is looking at developing practical inoculation methods for different crops, integration with natural predators, endophytic behaviour in plants and the underlying mechanisms that increase plant resilience with endophytes.
Text and images: Gerben Messelink and Leo Overbeek, Wageningen University & Research.
Vegetable growers don’t like to admit that they have mealybug. A group of cooperating parties therefore sent a questionnaire to growers in 2015. From this it appears that mealybug is a tricky pest to control and it is becoming increasingly prevalent in vegetable production, especially in tomatoes, sweet peppers and eggplants. The method of control varies. A clear-cut biological strategy is still lacking. Various companies and research centres are now working on effective, affordable control methods.
Mealybugs live on plant sap and tend to live in colonies. Due to their uptake of so much sap plants can loose vigour. The pests often live on the fruit, in the axils of the stems or at the base of the plant. For example in sweet peppers they live under the crowns of the fruit and in tomatoes often initially at the base of the plant, in the clips and low on the stems.
Growers often overlook mealybugs because they hide themselves so well in plants axils or in the greenhouse construction to escape their natural enemies and/or difficult environmental conditions. Only during peak periods do they emerge on mass.
Males and females
Adult males and females differ greatly in appearance. Adult females are covered with a protective waxy layer, usually have legs, no wings and are 0.4 to 0.8 mm long. The sexually mature females produce a sex pheromone to attract males.
Fertilized females lay hundreds of eggs, usually in an egg sac that consists of a white fleecy mass. This protects the eggs from predators, pathogens, drought and excessively high air humidity. The eggs also hang more easily on the plants in these egg sacs. After laying the eggs the females dry out. Unfertilised females and fertilised females that are overwintering can survive for several months. Female mealybugs go through five developmental stages: eggs, three nymph stages and the adult stage. The optimal conditions for the development of mealybugs are 26ºC and 60% humidity. Each stage takes six to 16 days. Adult males are winged and are about 1 mm long. They don’t have any mouthparts and therefore cannot feed. They survive only a few days to mate. The males go through six development phases as they mature to the adult stage.
In 2015 Biobest and growers association LTO Glaskracht Nederland looked closely at the problem. They contacted growers and crop protection advisors and invited the growers via the organisation’s website to complete a questionnaire about their experiences with mealybugs and how they deal with the problem. In total 89 growers answered the questions of which 43 grew tomatoes, 25 sweet peppers, seven aubergine and seven cucumbers. In addition, they visited ten growers. Specimens were collected and identified by a European specialist at species level.
Two harmful species were identified: Pseudococcus viburni in sweet peppers, eggplant and tomato and Phenacoccus solani at a sweet pepper nursery.
P. viburni is the most common species found in Dutch greenhouse vegetable crops. This originates from neotropical areas. Under greenhouse conditions development takes one to two months. This species can easily survive the cold and overwinters mostly in the first nymph stage in bark or in the ground.
One pepper grower also discovered P. solani. It is the first time that it has been found in a Dutch greenhouse although this species is prevalent worldwide. It is a major pest in sweet peppers in Spain. At first glance it seems to be whiter than P. viburni. This type is polyphagous and can settle on more than 30 plant families. This mealybug develops in 15 to 33 days at a temperature between 20 and 30ºC.
Found year round
One of the questions was whether growers ever had or still have trouble with mealybugs. The survey showed that this pest occurs in the greenhouse the whole year round if its spread is not stopped in time. Just 40% of the growers who answered the survey managed to eradicate the pests. On a few nurseries the pests spread so much that it was impossible to bring them under control using the usual methods.
The problem is the greatest in tomatoes. Of the 43 participating growers 19 had suffered problems and it is was still present on 11 nurseries. Of those participating in the survey the area infected with mealybug rose from 7 ha in 2013 to 10 ha in 2015.
Infected plants return about 10% less. Growers certainly waste just as much money searching for and controlling the pest.
Good hygiene measures and identifying the problem on time remain the first steps of control. Growers appear to be very creative at identifying and monitoring the mealybug. They reduce the infection by steaming the sub-surface, burning the infected stems, and using insect glue on substrate slabs and the greenhouse structure.
Most growers control the problem locally. Growers that suffer problems year round blanket spray two or three times when the young plants arrive. On these nurseries new colonies continually appear even after the entire greenhouse has been disinfected. The females escape the control and hide in the greenhouse structure (often next to the meter cupboard). Young larvae, the crawlers, are immediately seen on the young plants.
Many growers use the neonicotinoids Calypso or Gazelle with strong wetting agents to improve the control. The mealybug hotspots are sprayed two to four times after each other with an interval of four to seven days, depending on the level of infection. The old hotspots are checked every four weeks.
Gap in a strategy
A clear biological control strategy is not yet available. The survey shows that experiences with biological pest control are still very limited and the introduction of natural enemies are often too late and carried out with too few predators. Vegetable growers prefer to use biological solutions to limit residue on their products, but this approach needs to be effective. Natural enemies and green pesticides will play an important role in an integrated approach in future.
Various researchers from companies and research institutes are working on the problem and hope to be able to offer effective and affordable methods to growers as soon as possible. Biobest is experimenting this year with predators. Larvae of Cryptolaemus (ladybirds) and lacewings seem to have potential. They can clean up the first hotspots, but the biological strategy has yet to be fine-tuned into affordable solutions for growers.
Several parasitic wasps have also been reported some of which are available commercially. However, these do not offer a solution in the short term.
Based on the survey, a literary review and practical experiences, it is meanwhile possible to provide advice on how to prevent the development of mealybug or to slow it down.
Spray the infected plants and contaminated areas before the change of crop three to four times with a neonicotinoid combined with a super wetting agent and/or remove infected plants and dispose of them in rubbish bags. Remove the old crop and plant remains. Disinfect the ground and substrate. Clean the entire greenhouse with formalin or hydrogen peroxide and disinfect materials. Renew the substrate annually. Properly inspect plant material when in arrives at the nursery.
2. Scouting and monitoring
Detect the first mealybug areas fast. The pests hide in crevices and cracks under cloths, slabs, gutters, gutter edges and between pipe rail supports and greenhouse pillars. Inform and instruct personnel. Mark the infected plants and contaminated trellis with tape. Use yellow sticky traps with sex pheromones to attract the males.
3. Physical control
Remove infected material; pick leaves (pick the stem bare). Spray with soap or an oil.
Control is a matter of patience, monitoring and persistence. The crawlers are easy to kill but the adult females are difficult to control with insecticides because of their protective waxy layer. For good, long-lasting control it is recommended to use a broad action substance that works against mealybug. Take note: this should not be used with natural predators. Substances with systemic activity via the plant sap are usually more effective. Spray frequently because the hot spots often return in the same place (blocks of three sprays with a 7 to 14 day interval, repeat after six weeks if necessary). Spray the stems well. Mealybugs often take cover in the axils. Use a wetting agent to ensure good contact with the pests and their waxy layer. Use a lot of water.
Mealybug is an increasing problem in greenhouse cultivation. A stocktake in 2015 highlighted two common types. Growers address the problem in various ways: hygiene, spraying, a mechanical approach (burning, glue, brushing away) and the use of natural predators. However, these control methods are not enough. Further research is being carried out.
Text: Marleen Arkesteijn, Juliette Pijnakker and Joke Vreugdenhil
Images: Marleen Arkesteijn and Biobest
Koppert Biological Systems is introducing videos featuring the most prevalent pests and their natural enemies in the lead roles. The close-up visual material shows how pests develop in the crop and how natural enemies combat them.
Fascinating scenes are taking place in nature all the time, but most of the encounters between insects and mites, for example, cannot be seen with the naked eye. Koppert Biological Systems is capturing high definition visuals of the pests which growers have to deal with on a daily basis and show how their natural enemies do their valuable work.
The new videos will provide useful visual material for growers, agricultural consultants, academic institutions and those interested in sustainable solutions for the production of food and flowers. Koppert wants to create a greater awareness of the natural solutions that are available for horticulture, so chemical agents are not always necessary.
A total of 23 videos are in the making and will feature pests such as whitefly, spider mite, aphids, thrips, mealybugs, leaf miners, black vine weevil and Tuta absoluta. The videos of whitefly and a number of predatory insects are now available:
The rest will be released in the coming weeks and will be added to Koppert’s Youtube channel and Vimeo account. Depending on the demand, the videos can be made available in other languages.
Source/photo: Koppert Biological Systems.
Combating aphids with biological crop protection agents is everything but easy. This is why Biobest is involved in relentless research into new ways to get rid of aphids. The result? The hoverfly, Sphaerophoria rueppelli, is being deployed in the battle.
Many commercial crops are plagued by a plethora of aphid varieties that can create a tremendous amount of damage. A lot of preventive pest control strategies have already been explored. Many of these focus on the use of parasitoids. Although these are quite effective, they still aren’t effective enough to be truly reliable. According to Biobest, the biggest problem is that every parasitoid attacks only a limited number of hosts.
The latest weapon in the war against aphids, Sphaerophoria rueppelli, is a native species that is very common throughout Europe and in numerous Mediterranean countries. Its larvae are highly efficient predators of various ahipd vaieties, including Macrosiphum euphorbiae. Not only do hoverflies feast on aphids, they also consider whiteflies, thrips, and spider mites to be a delicacy. ‘Sphaerophoria rueppellii will go actively in search and fly long distances to detect even the first signs of an aphid colony,’ explains Yann Jacques, Product Manager for Macrobials at Biobest. ‘The Sphaerophoria System is therefore also a preventative system. It is a perfect complement to our existing range of parasitoids and predators.’
Adult hoverflies are virtually harmless, as they feed only on pollen and nectar. It’s the larvae, however, that are the leading players in the war against aphids. Adult females prefer to lay their oval-shaped greyish white eggs in large colonies of aphids, to ensure that their offspring will have plenty of nourishment. Each female can lay up to 20 eggs a day, and up to 400 eggs in all. The green larvae that are hatched can consume an average of 200 aphids during their larval stage, which lasts nine days at a temperature of 25°C. They will also feed on other pests, such as whiteflies, thrips, and spider mites. ‘What’s so interesting about this system is that the hoverflies can be deployed concurrently with aphid parasitoids. Hoverfly larvae will devour only the non-parasitised aphids. By deploying both, the number of aphids will be reduced even more dramatically,’ concludes Jacques. S. rueppellii is highly efficient when deployed in sweet pepper crops, but it looks as if this system will also promote aphid control substantially in other vegetable, fruit and decorative plant crops.
Koppert Biological Systems successfully completed the test phase of a mobile app plus online dashboard that identifies and analyses problems in the field.
This iPM app developed by Koppert USA makes use of innovative technology and consists of two components: a scout app with an intuitive user interface, and an online dashboard. The scout app allows growers to enter data into the system directly, while the dashboard provides insights into pests and diseases that can subsequently be used to analyse, treat and manage the problem.
The iPM app is composed of three modules: a mapping module with custom-designed maps and scouting templates for indoor and outdoor applications; a graphic module to gain insight into the development of pests and diseases and analyse the effectiveness of treatments, and a treatment module to apply chemical, biological or cultural treatments. Following the launch of the app on the US market, the app has now been successfully tested in a number of European countries.
Growers can use the app for centralized data storage that can be consulted from anywhere in the field. The raw data can be stored and edited for further analysis. The scout data are downloadable for offline use by the customer. Maps and templates are customized to suit various scouting techniques and crops. The app is an all-in-one tool designed to link scouting, analysis, treatment and management.
The scouting software helps cut costs by providing accurate insight into pesticide efficacy, while the improved timing of biological applications increases the efficacy of the control agents. This reduces the need for pesticides, thereby improving crop health and increasing yield.
The app is currently only supported by iOS platforms, but Koppert is working on the development of an Android version. iPM Dashboard is a personalised management system that is available by subscription.
More information: http://www.koppertipm.com/scout.html
Source/photo:Koppert Biological Systems.
Aphiscout, Koppert Biological Systems’ new parasitic wasp mix, is taking natural crop protection against aphids to a higher level.
Koppert Biological Systems introduced Aphiscout at IPM Essen with the campaign ‘Looking for trouble!’. This new crop protection agent detects the early signs of an aphid infestation and gives growers reliable information about the correct strategy to use. ‘Parasitic wasps are geared to detect aphids and parasitize them long before they are visible to the human eye,’ explains product manager Tim Bossinga.
Aphiscout is a mix of the Praon volucre, Aphidius colemani (see photo), Aphidius ervi, Aphelinus abdominalis, and Ephedrus cerasicola parasitic wasp species. Each of these has its own preferences and collectively they can combat the most common types of aphids. According to Koppert this makes Aphiscout the ideal form of basic protection against aphids. The parasitized aphids also provide information with regard to the best types of parasitic wasps to be released in a given large-scale offensive. ‘It’s like sending out scouts before planning your combat strategy,’ says Bossinga.
Aphiscout comes in a cylindrical package containing 250 mummies. Koppert developed a special NectarPad that is placed inside the container and contains enough sugar water to ensure that the parasitic wasps will go into battle bursting with energy. The packaging has been provided with an ingenious hanging system, in which the adhesive side of the label can be used to fasten the container around an object such as a wire or a plant stem. Besides its applications in greenhouse horticulture, Aphiscout will also be very useful to fruit growers.
Source/photo: Koppert Biological Systems.