New priorities for the proving ground

Growers were updated on research into disease control and the flower lines under trial at this year’s Cut Flower Centre’s open day.

Fusarium control in column stocks has been one of the research interests for the AHDB-supported National Cut Flower Centre in Lincolnshire for several years.

The soilborne disease, caused by F. oxysporum, is an ongoing problem in the crop which the Centre has tackled by screening varieties for susceptibility, demonstrating any effects of steam-sterilising the soil, and investigating fungicides. But work as part of a larger cross-sector AHDB project, to develop detection tests that will allow scientists to track how levels in soil wax and wane in response to cultural practices and control measures, is offering hope for a clearer picture of where crops are at risk and for more sustainable control strategies.

Speaking at the Centre’s annual open day in August, NIAB EMR geneticist Andrew Armitage said DNA tests are available to identify the majority of Fusarium species affecting different crops but they can’t distinguish between forms of F. oxysporumthat are adapted to attack only stocks or only daffodils, for instance, or harmless strains that are abundant in soils. With recent advances in identifying genes that are shared by, or unique to, these various forms, scientists have now been able to design a DNA-based quantitative test for the strain that affects column stocks. “It works on very small volumes of soil or plant tissue and will tell you how much of the fungus is in a soil sample,” he said.

He added that there was scope to offer the test as a laboratory service for growers or develop it further into one that could be conducted on a nursery.

The project isn’t stopping there. Because F. oxysporumis far from alone among Fusariumspecies in causing disease, the team has been working on a test that can describe a soil’s wider fungal community. “It will capture a whole range of soil pathogens as well as Fusariumspecies and host-adapted F. oxysporum,” said Dr Armitage. “It’s primarily a research tool at present but will have applications for assessing soil health before planting.”

Now the form of F. oxysporumspecific to column stocks can be accurately identified, and levels measured, the research team is aiming to find out how much of the fungus needs to be in the soil in order to have any economic effect on a crop. At the same time, stocks varieties are being trialled in the Cut Flower Centre’s polytunnel where the soil has been inoculated with the pathogen, to see which may be more or less susceptible to the disease. This summer’s unusually hot weather saw the disease quick to take off. “It took just two weeks to devastate most of the plants,” said Centre manager Lyndon Mason. “Plots of lisianthus, which is also susceptible to fusarium, were untouched, confirming the specificity of the different forms.”

Some of the Centre’s funding this year has also been put to use looking into another, more recent disease problem for stocks growers.

Downy mildew is normally controlled by various protectant fungicides but warning signs that the pathogen had developed resistance to some emerged from the Netherlands earlier this year – and the disease has now led to widespread losses there. Mr Mason told the open day that it wasn’t until May that he started being contacted by UK growers finding their standard spray regime failing to control mildew.

“There was no doubt the mildew strain was more aggressive than we were used to,” he said. “The Centre was able to react quickly and allocate funds to screening the pathogen’s sensitivity to nine crop protection products.”

The laboratory tests, by Fera, on samples collected from five nurseries showed that the pathogen has developed resistance to the active substance metalaxyl-M which Mr Mason says explains why it was so difficult to keep under check this year. Paraat, Percos and Revus were the most effective, giving 90% control at best. “We’ll now be able to design a spray programme from the results,” he said. “But spraying will probably have to start earlier in the season in future, as soon as the crop is planted.”

The rapid response to the concern over downy mildew was due to a change in priorities for work at the Centre, which now sees it better able to address pest and disease issues more quickly. New product development still forms a major part of its research effort, however.

Among the new lines under trial this year are umbellifers such as ammi and Daucuscarotaas bouquet fillers, astrantia, lysimachia and monarda.

The cuttings-raised scabious variety Scoop, now in 16 colours and which has looked so attractive in trials, flushed in week 28 from a week 18 planting. Some plants were then cut back to see how well they would rejuvenate. The return that growers would need to justify its harvesting cost, though, is still holding back large-scale production.

Veronica has been trialled for a further year, to investigate season extension. Planted on two dates and pinched either two or four weeks later, Skyler colours white and pink both responded to the treatment, with the first flush from the first pinch to the week 18 planting, flowering in week 28. It had no effect on the blue variety, all plants flowering at the same time.

Zinnia and dahlia have both been trialled in previous years, when they won universal acclaim for their rich colours, but a limited vase life is hindering retail potential. Nevertheless the Centre has not given up on them and is working with cut-flower treatments company Floralife to see if a nutrient product rich in calcium, applied weekly to plots in the polytunnel, could help harvested flowers meet vase-life specifications. In particular, it’s hoped that the calcium content could strengthen the cell walls in the neck of zinnia stems.

While no difference has been found between treated and untreated stems this year, the company’s Emma Bradford said the difference observed in stem length looks like it could be an effect from the foliar feed. “We’ll look again next year when growing conditions will hopefully be more as normal,” she said.

Fera senior mycology diagnostician Ann Barnes examines a leaf under the microscope in the Crop Health and Protection (CHAP) mobile crop science laboratory at the Cut Flower Centre’s open day. Growers had been invited to bring along plant samples for on-the-spot provisional diagnosis of any pest attack or disease infection. The laboratory is one of four the CHAP scheme has invested in to give growers, agronomists or agrichemical companies access to state-of-the-art monitoring and testing equipment ‘in the field’.

Innovation in novel treatments

Growers can look forward to a new generation of biologically based treatments for pest and disease control, according to Warwick University microbiologist Dave Chandler.

At the Centre’s open day he said new products were being developed using, for instance, naturally occurring peptides – molecules similar to proteins – that have no effect on mammals but do have insecticidal properties.

Another area of research is the use of synthetic double-stranded RNA which, applied to plants, can turn off target genes in insects or pathogens. “A lot of investment is going into this,” he said. “This could be a game changer for crop protection. The future is very exciting.”

Dr Chandler is leading AHDB’s project, AMBER, which is helping growers of ornamentals achieve better results from currently available biopesticides.

From benchmarking work on commercial nurseries the researchers have found that, except in the case of aphid control, biopesticides are as effective as grower standard treatments but that the basics of spray application need improving. “Label guidance is hard to follow and there is a lack of independent data on the application frequency and timing of new products coming through,” he said.

Analysis at Silsoe Spray Applications Unit, where a wind tunnel can replicate how growers apply biopesticide sprays, has shown that the water volumes generally used are far higher than is appropriate, said Dr Chandler. High water volumes don’t equate to better crop penetration but lead to run-off, waste and reduced effectiveness.