In recent years, the problem of thrips in chrysanthemum crops has got rather out of hand. Generally speaking, thrips that have survived the winter in the greenhouse result in an explosion in the pest’s populations in the spring. Chemical pesticides are not suffi cient to tackle them effectively; as a result of resistance development,
they become perceptibly less effective. Combating them using Amblyseius cucumeris is also not effective enough in practice. Research carried out by Wageningen University and Research centre (WUR) has shown that other predatory mites are better able to deal with thrips in chrysanthemum crops.
Erik van Santen: ‘The damage of thrips as well as the use of chemicals strongly reduced.
The first blow
Koppert consultant Erik van Santen, who is also head of the Dutch Ornamentals Team, developed a new approach over the past year. Together with DLV crop supervisors and the distributors Horticoop and Vos, this approach has now been tested on fi ve companies’ premises, with extremely encouraging results. The first step is to use Entonem, the soil-dwelling nematode Steinernema feltiae. For the fi rst four weeks of cultivation, this product is applied weekly by means of overhead irrigation. ‘That kills the thrips pupae still in the soil,’ says Erik. ‘It is the first blow landed by the grower, and that’s half the battle.’Capturing huge numbers
The next trump card is Swirski-Mite, the predatory mite Amblyseius swirskii, whichtackles the larvae of the thrips mite. From day 10 of the new crop cycle, A. swirskii is introduced over a period of seven weeks using a blower. That results in the establishment of a strong population: the predatory mite can be found on 70 to 90 per cent of the leaves.
The third measure is hanging up 1,000 Horiver sticky traps per hectare at the same time as the cuttings are planted. That is also very effective. ‘Between 50 and 200 thrips are counted on each sticky trap per week. If we take an average of
100 insects as a modest estimate, the grower captures 100,000 thrips weekly per hectare. Those are huge numbers.’ The fi nal measure is on-site correction by means of gentle products, particularly useful in the case of large hot spots.
Thrips under control
‘We are very pleased that we decided to start using this method,’ says Bert van Ruijven, part-owner of Arcadia Chrysanten, covering 16 hectares. ‘There were very high infestation levels of thrips. Without this approach, we would not have gained control over the pest.’ ‘We are not yet where we want to be in terms of combating thrips. The effectiveness of the nematodes is diffi cult to measure, and theAmblyseius swirskii population declined in August due to the heat. The beneficial
was clearly struggling.’ However, Bert van Ruijven will be continuing next year with
the new method.
Hardly seen any thrips
Henry Satter has a company covering 2.5 hectares. He has had good experiences with this approach. ‘While the project was running, I saw hardly any thrips,’ he says. ‘As far as the nematodes are concerned, I thought they worked well for me, but other growers have had other experiences.’ Distributing Amblyseius swirskii using ablower worked well at his business. As very little crop spraying took place to combat thrips, it was important to keep a close eye on other pests. ‘In terms of price, Koppert should perhaps do a little better. Other than that, I am pleased with how the project went.’
Mass trapping with Horiver blue seemed to be very effective. The sticky traps captured huge thrips numbers every week.
Still lessons to be learned
At Nico Kiep’s company, the approach worked reasonably well until 1 August. After that date, the thrips infestation started to get out of control. The reason is still unclear. ‘From August onwards, swirskii was less visible in the crop. Had the benefi cial really disappeared, or did that just appear to be the case? Answers are required to such questions.’ We still have things to learn, says Kiep. For instance, it is also still not completely clear to him whether releasing the nematodes really made anydifference in a positive sense. In one section of his nine-hectare company, he wants to test whether Amblyseius cucumeris (Thripex-Plus) could be more effective than Amblyseius swirskii.
Continuing along the current path
Dennis Duijvestijn of Chrysantenkwekerij Aad Persoon (4.6 hectares) is certainly seeing progress, but states that the results could be better. He has noticed lower counts on the sticky traps this year than in 2012. ‘But we are still not free from the problem of thrips. In addition, the effects vary per variety. There is less thrips damage evident on our white Anastasias, and we have not yet seen a difference in an earlier stage in the yellow Anastasias. But that variety is more susceptible. Fortunately, there are no problems in the fi nal product.’ Dennis Duijvestijn is keen to continue along the current path. ‘The approach using chemicals is simply no longer effective.’The approach works
At Middelburg Chrysanten (6.5 hectares), the approach is working as it should. These are the words of Barry Middelburg, who is responsible for matters including crop protection. ‘The idea was good, so we tested it on three hectares. The results are still not quite as good as they could be, but we are satisfi ed. Swirskii is effective against thrips. The beneficial mites can be seen in the crop from early spring.’ In Barry’s view, it is always good to try something new if the old, familiar methods seem to be becoming less effective. ‘We are on the right track.’Distributing benefi cials with an Airobug has become the standard procedure
at more and more companies
More research is needed
Theo Roelofs, a consultant at advice and research organisation DLV Plant, is involved in the project together with two colleagues. ‘Thrips is a major problem in chrysanthemum,’ he says. ‘We are pleased that Koppert is investing time and money in the development of a solution.’ DLV put forward the fi ve companies at which the methodology is being tested. According to Theo, these were not exactly the easiestcompanies; all five had above-average thrips infestation levels. He had expected that measure 3 (mass trapping using sticky traps) would prove to be of little use, following an overkill with nematodes (measure 1) and with swirskii (measure 2). ‘But that turned out not to be the case; the sticky traps were in fact very useful.’ He is reasonably satisfied with the work of swirskii; the beneficial worked well until August. From August onwards, things were more difficult at some of the companies’ premises. The effect of the nematodes was less clear. 'That is striking, because it has long been proven that soil-dwelling nematodes prey on thrips pupae. It could be due to the overhead irrigation; the question is whether the nematodes are more effective if
they are sprayed. It would be worthwhile investigating this. Otherwise the nematodes might be wrongly rejected.’
Thrips damage greatly reduced
The project got underway in 2013, and a continuation in 2014 is likely. Koppert also wants to investigate whether soil-dwelling predatory mites could tackle the thrips pupae in the soil even more strongly than Entonem and whether the distribution of Entonem could be improved further. One continually growing problem for manyproducers was quickly brought under control on the five participating companies. ‘The damage caused by thrips on their companies’ premises has declined by around 40 to 60 per cent,’ says Erik. ‘They were much better able to keep the pest under control.’ The use of chemicals has also greatly decreased. An additional advantage is that spider-mite control is going better!
Source: BioJournal Koppert
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