Seaweed Research in Turf

Research by Tamsin Williams at Royal Holloway, University of London investigated novel approaches to managing plant parasitic nematodes in turf using seaweed extracts.

The BBSRC iCASE PhD, supported by ICL, focused primarily on plant parasitic nematodes, but also explored the effects of alkaline-extracted Ascophyllum nodosum on turfgrass rooting, naturally occurring mycorrhizae, turf quality and beneficial nematodes used for insect pest management.

The results showed several potentially useful responses, but also important differences between controlled and field conditions.

Tamsin Williams

Why investigate seaweed and plant parasitic nematodes?

Plant parasitic nematodes, or PPNs, are not considered one of the main challenges facing turf managers across the whole industry.

However, where PPN populations are high enough to affect turf, they can create a significant management problem.

The research explored seaweed extracts as a possible management approach because previous small-scale work had indicated positive effects from alkaline-extracted seaweeds.

A published meta-analysis also found evidence that some seaweed extracts could help reduce root-knot nematodes in certain crops.

The effects varied according to seaweed type, nematode species and crop. Ascophyllum nodosum extracts showed the greatest control effect within the studies reviewed, with alkaline-extracted products among the most commonly investigated.

The evidence therefore did not suggest a universal response across all nematodes or crops, but it provided a basis for further work in turf.

What did the PPN research find?

Pot-based trials using alkaline-extracted Ascophyllum nodosum demonstrated significant reductions in plant parasitic nematodes.

The treatment consisted of three applications at label rate at 21-day intervals.

The results were produced under relatively controlled conditions, so further field trials were carried out to assess how the approach performed under established turf conditions.

Across three field trials, reductions in PPN numbers were also observed using the same application schedule.

However, natural variability within PPN populations meant that the reductions were not consistently statistically significant.

The research also found reduced variability in PPN populations following treatment.

The difference between the pot and field results is important. Controlled trials showed a clearer response, while the field work demonstrated the additional variability involved when working with naturally occurring nematode populations under practical turf conditions.

A Criconema nematode

How might seaweed affect PPNs?

The research investigated possible mechanisms that could explain the effects observed.

One experiment found that applications of alkaline-extracted seaweed could up-regulate plant defence genes and defence-signalling pathways.

This suggested an elicitor response, where the application stimulates the plant’s own defence mechanisms.

However, this work was carried out on a model plant species rather than turfgrass. The finding therefore cannot be assumed to translate directly to turf species without further research.

A second response involved the hatching of nematode eggs.

Seaweed treatment slowed the rate of hatching from PPN egg masses. Juvenile nematodes still hatched, but the process was delayed and spread over a longer period.

The research suggested that this could potentially reduce the impact of infection or give the plant more time to respond, although the work did not establish this as the definitive mechanism responsible for the observed field effects.

Effects on turfgrass rooting

The PhD also investigated how alkaline-extracted Ascophyllum nodosum affected plant rooting.

Pot-based trials showed a significant increase in rooting, with a particularly clear response in perennial ryegrass (Lolium perenne).

Changes in root architecture were also observed, including greater branching and more fibrous root development.

These results again need to be interpreted according to the trial conditions.

In field trials on mature turf, the research did not measure a significant increase in rooting, although trends towards greater root biomass were recorded.

Measuring turfgrass rooting reliably under field conditions is difficult, and the research highlighted the challenge of translating results from controlled pot trials directly into established turf.

Effects on naturally occurring mycorrhizae

The work also measured mycorrhizal infection within turfgrass roots.

Applications of alkaline-extracted Ascophyllum nodosum significantly increased root infection by naturally occurring mycorrhizae.

Another treatment combined seaweed with a commercial mycorrhizal powder.

In this trial, the seaweed treatment interacting with the naturally occurring mycorrhizae produced a higher level of root infection than the treatment combining seaweed with the applied mycorrhizal product.

The work was not developed further, so the research does not explain why this difference occurred.

It did, however, identify an area where further investigation into interactions between seaweed applications, turfgrass roots and naturally occurring soil biology could be useful.

Turf quality under field conditions

Not all measurements showed an improvement following seaweed application.

In field trials, the researchers did not measure improved plant quality in terms of turf colour or growth.

These trials were carried out on well-managed turf receiving fertiliser and a good level of management.

Under those conditions, it may have been more difficult to separate any additional response caused specifically by the seaweed treatment.

The finding is important because it shows that responses observed below ground do not necessarily translate into a measurable improvement in turf appearance under every set of conditions.

Compatibility with beneficial nematodes

The research also investigated whether seaweed extracts affected entomopathogenic nematodes.

These beneficial nematodes can be used within turf management to help manage insect larvae, including species used against chafer grubs and leatherjackets.

A serial dilution test was carried out using increasing concentrations of seaweed extract.

No adverse effect was recorded.

The beneficial nematodes remained alive and viable even at relatively high seaweed extract concentrations.

Under the conditions tested, the seaweed extract therefore showed no direct control effect on these beneficial nematodes.

Industry attitudes to sustainable turf management

The PhD also included an industry questionnaire using Q-methodology to explore attitudes towards different turf management approaches.

Responses broadly separated participants into three groups:

• Solution-focused negative thinkers
• Progressive positive thinkers
• Acquisition-centered traditionalists

The groups differed in how and when they would adopt different management approaches.

However, all three recognised the importance of finding more sustainable management options.

There was also a generally positive attitude towards biostimulant-based management tools.

A recurring theme was that new approaches were more likely to be adopted where they could be clearly demonstrated to work while maintaining an acceptable level of surface performance.

The research also identified demand for further sustainability-focused research to help support turf management decisions.

What does the research mean for turf managers?

The research does not suggest that seaweed extracts provide a universal solution to plant parasitic nematodes.

The first step where PPNs are suspected remains identification and measurement.

Samples should be assessed so that the nematode species and population levels can be established before a management approach is selected.

Within the research, alkaline-extracted Ascophyllum nodosum was applied preventatively ahead of key stress periods.

Positive results were recorded following three or four applications at 21-day intervals.

Applications above the recommended rate did not appear to provide additional benefit in the trials.

More frequent applications at the standard rate were suggested as a possible area for investigation, but this was not tested.

The wider management of turf stress also remains important. Measures discussed within the research included adjusting height of cut where appropriate, spreading wear, managing rootzone moisture and avoiding nutrient deficiencies.

What questions remain?

The work identified several areas where further investigation could have strengthened the results.

COVID-19 restrictions prevented another season of field trials on a site more susceptible to plant parasitic nematodes.

Further replication and more targeted site selection may also have helped clarify the field response.

The interaction between seaweed applications and the rhizosphere microbiome was another area identified for future research.

More detailed work could examine whether seaweed treatments alter the biological environment surrounding turfgrass roots and how those changes relate to plant performance.

What can we take from the research?

The PhD produced evidence of several responses to alkaline-extracted Ascophyllum nodosum.

Controlled pot trials showed significant reductions in plant parasitic nematodes and increased rooting, particularly in perennial ryegrass.

The research also found increased infection of roots by naturally occurring mycorrhizae and no adverse effect on the beneficial entomopathogenic nematodes tested.

Field results were more variable.

Reductions in PPN populations were observed, but were not consistently statistically significant, while significant increases in rooting and visible improvements in turf colour or growth were not recorded under the field conditions tested.

Those differences are important.

They show both the potential identified within the research and the need to interpret results according to the trial conditions, measurements and limitations behind them.