Research on seaweeds for plant parasitic nematode management: Part 1

What was the title of your PhD research and where did you do the work?
Tasmin: “Plant Parasitic Nematode Infection in Turf: Novel Approaches for Management using Seaweeds. My main supervisor was Professor Alan Gange from School of Biological Sciences at Royal Holloway, University of London. The work had an Industrial supervisor; Dr Andy Owen, International Technical Manager at ICL, and was a BBSRC iCASE studentship.”

So the focus is plant parasitic nematodes (PPNs) for turf, did you get an impression of how large a problem this is for the industry?
Tasmin: “Yes, I completed an industry questionnaire chapter which allowed me to quantify that, and basically there is a recognition across the industry of the issue, but most respondents did not see it as one of the key problems facing turf managers. However, for the few turf managers out there where PPNs are an issue – they are searching desperately for the right solution to implement. It is a big problem for them at that time.”

Tamsin Williams

So why look at seaweeds as a mechanism for management of the problem?
Tasmin: “We were looking for a sustainable solution for the PPNs in turf, and actually, there was quite some anecdotal evidence for some seaweed types having a positive effect on the problem. My industrial supervisor at ICL (Dr Andy Owen) had run some small-scale trials with alkaline extracted seaweeds giving very positive outcome. Hence the development of the project. This approach was completely vindicated whilst researching for our published meta-analysis paper (Williams, T. et al., 2021. Evaluating the use of seaweed extracts against root knot nematodes: A meta-analytic approach. Journal of Applied Soil Ecology 168 1-8) which showed certain seaweed extracts could help control root knot nematodes in some crops, but the effects were dependent on seaweed type; Ascophylum nodosum seaweed extracts had the greatest control effect, and alkaline extraction versions seemed to have been the most studied. The results did seem to be variable depending on the PPN type and crop group, so not 100% success for all PPNs or in all crops, but still very positive.”

What were your key experimental findings?
Tasmin: “My pot-based trials using alkaline extracted Ascophylum nodosum demonstrated significant reductions (P<0.01) in PPNs from seaweed applications (three applications at label rate at 21-day intervals), but these trials were in a fairly controlled environment. Things got more complicated when I took the research into the field. Over the course of three field trials – I did see reductions in PPN numbers from the same seaweed application schedule, but the natural variability of PPNs I measured meant the results did not always demonstrate a significant reduction. However, on balance we reduced PPNs and certainly significantly lowered the variability, as we published in the European Turfgrass Society Conference paper. (Williams, T. et al., 2020. Ascophylum nodosum extract use on plant parasitic nematode abundance and diversity on a
golf green. Rasen 3. 84-85). I think there is clear evidence of efficacy of the method, and with greater replication and trial site selection it could have been much clearer.”

What was the mode of action, how was an alkaline seaweed extract working? Did you investigate that?
Tasmin: “The mode of action will be multi-faceted, but we showed in one experiment how applications of alkaline extracted seaweeds can up-regulate defense genes and defense signaling pathways to potentially allow the plant to defend better against PPN attack. This was essentially an elicitor response. Allowing the plant to display a range of defense mechanisms. This work was completed on a model plant species (not turfgrass), so there needs to be an element of caution when translating this response to turf species – but I suspect it is highly likely (especially looking at the current areas of research being carried out on the benefits of seaweed applications). A second mode of action was the slowing of the rate of hatching from PPN egg masses. There was still some hatching of juvenile nematodes but a delayed hatching or a more spread hatching period could allow the plant to better prepare for defense or reduce the overall impact of the PPN infection.”

A Criconema nematode

What is best advice for a turf manager who suspects they have a PPN problem or are managing turf with a history of PPN issues.
Tasmin: “Firstly, monitor and measure the severity of the problem, it is important to get a positive identification of the issue and the species involved. So, collect samples and send off to a Turf Disease Centre and have the turf properly assessed and the nematode species and populations counted.
Secondly, from the work I have completed, use an Ascophylum nodosum seaweed (I exclusively used the SMX product from ICL) with an alkaline extraction and make preventative applications at recommended rate in the period leading up to the key stress periods. My trial work showed positive results following three or four applications at 21-day intervals. I tested greater than recommended rate applications – and they did not seem to add any benefit, but perhaps more frequent applications at standard rate would be useful (however this was not tested). Of course, it also makes sense to try and reduce the stress the turf is under, to provide greater turf resilience, for example by raising height of cut a little, if possible, by spreading wear, managing moisture in the rootzone and ensuring the plant is not deficient in any nutrients etc.”