biological crop protection
Hyperparasites in the crop can completely disrupt biological crop protection. Sweet pepper growers in the Netherlands know a thing or two about that. But where there’s hope, there’s life: in October 2015 a multi-year, fundamental research project was launched that aims to unravel the interactions between hyperparasites and their environment. Once these are sufficiently well-known, attractants may turn out to be an answer.
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Plant bugs like the European tarnished plant bug and the common nettle bug are a serious problem in crops such as aubergine, cucumber and chrysanthemum. Even in small numbers they can do considerable damage: abortion of the flower in aubergines, stem and fruit damage in cucumbers and splits in chrysanthemums. As soon as growers spot bugs or bug damage, they feel they need to intervene fast with products that are harmful to the biological predators they are using for other infestations, marking the beginning of the end of their biological pest control.
Bugs usually enter the greenhouse from outside. They can arrive early in the season but most sightings of bugs, particularly the most harmful species, the European tarnished plant bug, are reported in the summer months. A good method of spotting and monitoring the presence of bugs can help growers decide when to use pest control products. It would be even better if bugs could be effectively eliminated from the plants with traps.
Pheromones and plant aromatics
A trap with a pheromone attractant for the European tarnished plant bug (Lygus rugulipennis) was originally only available for outdoor use, mainly in strawberry crops. Producers of biological pest control Entocare biocontrol C.V. and Wageningen University & Research have been working with a number of growers in the Netherlands to study and optimise the use of the trap and pheromone in the greenhouse. This trap is now available for detecting the presence of the European tarnished plant bug in various crops (aubergine, cucumber).
The traps were tested in a season-long trial and show peaks in the occurrence of bugs (Figure 1). The relationship between the numbers of bugs caught and the damage they cause is currently being investigated more closely. The level of the peaks and the increase or decrease in the numbers captured in weekly counts help the grower decide which crop protection measures to take.
Trapping bugs certainly helps control them but as yet it is unclear what proportion of the bugs already present can be eliminated with traps. The distribution of bugs across the greenhouse is very irregular: catches in traps show no evidence of bug hotspots.
During the trial it was discovered that the luring effect of the pheromone works best in the presence of plant or crop aromatics. A simple pheromone trap catches fewer bugs than a trap with the smell of the crop in the background. But it is mainly the males that are attracted by the smell of the pheromone, so the researchers have set about finding attractive alternatives to lure females as well. Their main focus is on plant aromatics.
Several plant substances that seem to attract the females have already been identified. Lab trials indicate that the concentration at which the aromatic is offered is critical, however (Figures 2 and 3). Too little fails to attract them while too much scares them off. Some substances are attractive to both males and females (substance B) while others only attract males (substance D) or only females (substance A). The research is now focusing on finding the right substances, or combination of substances, and on finding a formulation that will go on producing the right intensity of aromatics over a long period of time in practice.
Trap colour and shape
The funnel trap with pheromone which researchers are currently using needs to be further optimised for catching bugs. Video recordings of males landing on these traps showed that less than five per cent of landings on the trap actually resulted in capture. The colour and the shape of the trap will be studied in more depth in future research, along with ways of further optimising the trap. If a combination of pheromone, plant aromatics and better traps proves successful in trapping both males and females, this will open up new opportunities for tackling the bug problem.
Besides observations, the aim is also to improve biological control with an effective combination of attractants and biological agents. To begin with, the researchers are looking at a biological agent based on an insecticidal (entomopathogenic) fungus. They are investigating whether it is possible to use attractants to target fungal spores better in the crop in order to increase their effectiveness in controlling bugs. With a modified formulation of the fungal spores and an effective method of transferring them to the bugs, it has been shown that it is possible to get at least three to four times more spores onto a bug.
The next question is whether this combination of methods (luring, infecting and transferring) actually helps combat the infestation. Further research on this will be taking place during the coming year.
For some years now, scientists and growers have been working together to come up with a better monitoring and control plan for the European tarnished plant bug. A pheromone trap that captures males has already been successfully tested. Research into attractants for females has yielded some new substances that are effective, offering new options for controlling this bug.
Text and image: Rob van Tol (Wageningen UR), Maedeli Hennekam and Daowei Yang (Entocare biocontrol).
Controlling thrips in cut flowers biologically may be difficult but it’s not impossible. Supplementary feeding with pollen can help to build up and maintain a vigorous predatory mite population. But this strategy isn’t without risk, since pollen is also a food source for thrips. This was the starting point for a research project on roses which also looked at how other predatory mites react to supplementary feeding.
Supplementary feeding of biological predators with pollen preparations is a strategy that is becoming increasingly popular. In vegetable production, particularly in cucumbers and sweet peppers, a lot of growers are using this method to build up a healthy population of predatory mites. But is it also suitable for ornamentals, an area in which pest tolerance is low?
Entomologists Gerben Messelink and Ada Leman of Wageningen University & Research in the Netherlands are studying the development of Californian thrips in roses and their control with a range of predatory mites. Part of this research involves supplementary feeding with pollen, a method that has raised questions in the past.
Taking no chances
“Biological control in ornamental production is no easy option,” Messelink says. “Pest tolerance is so low that it is difficult to build up a good biological balance. A few thrips on a glue trap are enough to trigger panic.” In other words, growers don’t want to take any chances if there is a risk of infestation, especially with Californian thrips. But there are not enough chemicals available to control or correct an infestation.
The entomologists’ research is focused primarily on getting biological agents, in this case predatory mites, better established in the greenhouse and the crop. They call this the “standing army principle” – an army that is on standby ready for deployment.
If biological agents are difficult to establish in a crop, banker plants can sometimes help. These are plants on which useful predators establish readily and then spread throughout the crop. But this method doesn’t work for predatory mites because they don’t fly and only move around slowly.
Pollen a firm favourite
Amblyseius swirskii has so far proved one of the most successful predatory mites for controlling thrips in ornamentals. But to do its job, this creature must be in tip-top condition. As thrips pressure is kept as low as possible, there isn’t very much food around. Fortunately these mites are omnivores and are happy to tuck into a good meal of pollen. So providing pollen to help build up the predatory mite population would seem an obvious choice.
And yet there’s a danger lurking in this method. Thrips also like to feed on the same pollen. So the question is whether providing pollen actually does more harm than good. There is also the risk that the predatory mites could become lazy and leave the thrips in peace.
So the researchers first wanted to get a clear idea of how both thrips and predatory mites would react to supplementary feeding. They studied a thrips population fed with cattail pollen, maize pollen, Ephestia (Mediterranean flour moth) eggs and cysts of Artemia (brine shrimp). The thrips population remained lowest in the control treatment without supplementary feeding and increased most in the treatments with pollen and Ephestia. “We noticed that the number of eggs laid by the thrips tripled on average when pollen was given,” says Messelink. This confirms that thrips love pollen and thrive on it.
The predatory mite A. swirskii was studied separately and was given the same food sources. This study also showed that pollen and Ephestia had a considerable impact on egg laying.
Supplementary feeding needed
With these results in mind, the researchers devised a strategy for the rose, a crop in which a predatory mite population can be difficult to maintain. Using pollen, they quickly built up a vigorous population, and stopped supplementary feeding when the thrips started flying in. But that didn’t work: the number of predatory mites dropped to such an extent that the thrips gained the upper hand.
Messelink: “We have changed our strategy now. Supplementary feeding is still needed once the thrips have arrived. A vigorous predatory mite population can easily tackle a nascent thrips infestation despite the presence of pollen.”
The question then arises as to how much pollen is needed to maintain the population. It’s difficult to say, and it also depends on the conditions on site. The equivalent of 5 kg of pollen per hectare per week was administered in the study, but in practice it has been found that good results can also be achieved with smaller quantities.
Research in 2015 with a combination of A. swirskii supplemented with the predatory mite Macrocheles robustulus also delivered quite promising results. A. swirskii attacks the adult thrips and M. robustulus goes for the pupae that fall on the ground. The two predatory mites make a good team.
Other good natural predators
In many tests, Amblyseius swirskii has proven to be one of the better predatory mites for controlling thrips, but this has always been tested without the use of pollen. It may well be that other species are even more effective when given a supplementary food source. So in greenhouse trials with roses, A. swirskii was compared with Iphiseius degenerans, Euseius gallicus and Euseius ovalis. They were all given pollen.
The test confirmed that both I. degenerans and E. ovalis responded very well to supplementary pollen feeding – even better than A. swirskii, in fact, proving that these predatory mites are an interesting option for use in roses. Many predatory mites don’t do well in a short period of heat with low humidity, but I. degenerans appears to be reasonably resistant to that, making it a useful addition to the overall package.
If Echinothrips also occurs alongside Californian thrips, E. ovalis in combination with pollen is a good species to use. In short, various species of predatory mite are suitable for controlling thrips in roses in conjunction with pollen.
Messelink predicts that good thrips control will consist of a total approach involving a range of biological agents at different times. Close monitoring and providing supplementary pollen feeding at the right moment are also part of this mix.
In their follow-up research, the entomologists are not only looking at control with predators but also at the “push-pull” method, which is based around repelling and attracting pests. For example, the crop can be made unattractive to insects with certain smells, or the pests can be lured away with plants or smells that are more attractive to them. Increasing plant resistance also plays a role in this strategy. Research is currently being carried out in wind tunnels, in particular using smells that should scare off thrips.
Controlling thrips in rose cultivation biologically is difficult: due to the low pest tolerance, the predatory mite population has trouble establishing properly and staying vigorous. Supplementary feeding with pollen goes a long way towards solving this problem. This strategy also puts other predatory mites back in the picture. A total approach with a range of biological agents is likely to be the most effective one.
Text and image: Pieternel van Velden and 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.
Marius Mans of Mans Flowers is one of the first growers in the Dutch ornamental plant cultivation sector to firmly adhere to the guidelines of the Next Generation Growing. "You become more conscious of your energy usage and that leads to savings. But optimizing growth remains the primary objective."
Modern growers are increasingly becoming entrepreneurs who must know all about the many aspects of a modern greenhouse cultivation company. "Nowadays, regulation and control by a climate computer play an essential role in any of the larger companies", says Mans. However, despite that fact, he believes that having green fingers is still very important. "Certainly in the case of the Next Generation Growing, it is about making the right observations and using this information to choose the correct settings at the right time."
"Insight into every detail of the plant's growing process leads to many other opportunities."
In the last few years, Mans Flowers has developed the Next Generation Growing even further. He became more aware of his energy consumption, which was the first step towards making savings. However, the biggest added value is the optimal growth that he has experienced. "An optimal greenhouse climate greatly improves quality. I can now also deliver top quality products during the more difficult growing periods in the year. Insight into every detail of the plant's growing process leads to many other opportunities."
Balanced greenhouse climate
Mans has recently switched to Priva for his climate control needs. "I have made that choice because it gives me more options to achieve the ideal, balanced greenhouse climate. I get calculations in advance based upon a variety of parameters. And that helps me to take the right decision at the right time in order to achieve my goal."
"A lot of knowledge has been gained about biological control in the Netherlands, which has given us an advantage over growers from other parts of the world."
Fighting diseases and pests also has a very high priority, says Mans. "The gerbera is a bushy plant with a lot of leaves close to each other, which makes it difficult to treat diseases and fight pests. For that reason and also because we want to demonstrate corporate social responsibility, biological control is extremely important. It has to do with having the right balance and an integrated approach. A lot of knowledge has been gained about biological control in the Netherlands, which has given us an advantage over growers from other parts of the world. That helps us to be able to hold and improve our strong position in the future."
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.
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.