Grasses form an essential component of our planet’s ecosystems, providing a wealth of resources for various species, including humans. Wheat, rice, and maize provide 50% of the World’s food.

With an extensive root system that plays a critical role in their survival and prosperity, these plants have evolved various mechanisms to protect their roots from insect herbivores. These root defences range from physical and chemical traits to more indirect forms of protection. In order to understand these intricate systems and their significance, it is important to understand a little about the vast world beneath the soil, where roots reign supreme.

What’s the problem with leatherjackets?

Contrary to popular belief, bird activity induced by the presence of leatherjackets isn’t the main damage being caused to the green by these insects. I see a lot of effort being put into repelling the birds, whilst the leatherjacket problem remains unaddressed. Another example of symptoms management in action.

Meanwhile the cranefly grubs, commonly known as leatherjackets, pose a significant problem for those greenkeepers. These grubs are the larvae of craneflies or ‘daddy longlegs,’ and their diet primarily consists of the roots and stem bases of grasses. This causes noticeable damage, including yellowing and thinning of the turf, often leading to bare patches. The lifecycle of the cranefly in the UK typically begins with eggs laid in the soil during late summer and early autumn. These eggs hatch into the grubs that remain active throughout the winter months, feeding on the grass. In the spring, they transition into a dormant pupal stage before emerging as adult flies in late summer, ready to start the cycle again. Given their lifecycle and the damage they cause, understanding and effectively managing these pests is a key skill for greenkeepers.

A good place to start would be to understand what the plants themselves do to counteract these pests.

In a recent review by Ben D. Moore and Scott N. Johnson from the Hawkesbury Institute for the Environment, Western Sydney University, it was revealed how grasses employ various defensive strategies to protect their roots from herbivores. Given that grasslands cover roughly 40% of the Earth’s terrestrial surface outside of Greenland and Antarctica, and that grasses invest a significant proportion of their resources into their roots, understanding these defence mechanisms is a good place to start to look for answers to the burgeoning leatherjacket and chafer problems being faced by greenkeepers.

Key points

Some of the key learning points from this review reinforce a lot of what we currently understand, but also point to deeper defence mechanisms we can perhaps exploit in trying to minimise the damage to turf from the increasingly prolific cranefly grubs and chafers.

1. Physical Defences: One of the primary defence mechanisms grasses use involves physical structures that deter herbivores. These include structural macro-molecules such as lignin, cellulose, suberin, and callose, as well as silica and calcium oxalate. Root hairs and rhizosheaths, unique to grasses, may also play defensive roles. The researchers note that only lignin and silica have been proven to negatively affect root herbivores so far.
2. Chemical Defences: Grasses also employ a range of chemical defences against root herbivores. Some potential chemical resistances include nitrate, oxalic acid, terpenoids, alkaloids, amino acids, cyanogenic glycosides, benzoxazinoids, phenolics, and proteinase inhibitors.
3. Indirect Defences: The researchers also highlighted the role of indirect defences, where grasses recruit natural enemies of root herbivores. An example is maize, which can attract entomopathogenic (damaging to insects) nematodes via the emission of (E)-β-caryophyllene.
4. Cost-Benefit Analysis of Defence Mechanisms: The study also discusses the cost and benefit of these defensive investments. The optimal defence theory (ODT) suggests that the allocation of resources to these traits is driven by the relative costs and benefits of this investment. This theory has yet to be fully applied to root defences, but the researchers suggest that chemical defences may be as important, if not more so, for roots due to their value to the plant and lower tolerance of damage compared to shoots.
5. Knowledge Gaps: Despite these insights, the researchers also acknowledge that there are still significant gaps in our understanding of grass root defences. For instance, the role of salicylic acid, a known plant defence hormone, in grass root defences against herbivores is not well understood. Similarly, the potential role of furfural, a compound found in many plants and known for its pesticidal properties, remains unexplored in the context of root herbivore resistance.

In summary, grasses employ a range of physical, chemical, and indirect defences to protect their roots from insect herbivores. Further research is needed to fully understand these mechanisms and to explore other potential defences, but meantime, we can take some of this knowledge and apply it now to our greenkeeping practices. Here are some suggestions:

Practical applications

Here are a few maintenance practices you can add to your greenkeeping programme to help your turf resist insect damage.

BioActive KitoPlus

A natural soil improver derived from chitin-rich shell fish for greenkeepers to promote a healthy
sward.

BioActive KitoPlusTM Easy is an effective soil improver enabling the growth of healthy, vigorous plants of good colour and with the ability to resist damage from abiotic and biotic stresses. This product can improve both the rhizosphere and phyllosphere, and therefore boost beneficial microorganism populations, including mycorrhizae, enabling improved nutrient assimilation.

BioActive KitoPlusTM Easy can facilitate via the stimulation of natural defence mechanisms:

• Reduced likelihood of fungal infection in turf
• Effective action against plant viruses
• Increased plant resistance to attack by pests
• The development of healthy plants and healthy soils, which are less likely to support populations of root feeding nematodes
• Alteration of the environment in the rhizosphere & phyllosphere to shift the microbial balance in favour of beneficial organisms and to the detriment of plant pathogens
• Improved resistance to both biotic and abiotic stresses
• Increases photosynthesis, vegetative growth and plant vigour
• Stimulation of growth-promoting microbes and antagonistic biological control agents
• Complexation of plant nutrients, aiding assimilation

Application: BioActive KitoPlus Easy 1500 m² green:  300 ml diluted in at least 25 L water. Apply five times per year in March, April, June, September and October and leave a minimum of two weeks between applications.

Product Approved for Use in Organic Systems by SOPA (Certificate No.: S1363E/0321/16)

Liquid Potsi

Liquid PotSi (Potassium Silicate + Humates) offers the following benefits:

• Stronger plant growth, reducing susceptibility to pests and disease
• Thicker cell walls increase the grass plant’s natural defence mechanisms
• Improved leaf erectness which helps with the control of Annual Meadowgrass and improves green speed and smoothness without lowering the height of cut.
• Helps control and reduce iron (Fe) and manganese (Mn) toxicity, common in sandy rootzones where high salt mineral fertilisers have been deployed in the past.
• Reduces susceptibility to attack from fungal pathogens like Fusarium and Dollar Spot
• Reduces susceptibility to attack from root herbivores and sucking insects like Leatherjackets and Chafers
• Increases resistance to drought, heat and cold stress

Application 1500 m² green: 750mls in 75 litres of water. Can be applied at 6 weekly intervals throughout the year

BioActive MolTurf

BioActive MolTurf® is an award winning liquid carbohydrate.  BioActive MolTurf® contains naturally sourced carbohydrates and trace elements that energise the turf grass plant metabolism and stimulates microbial activity around the root and leaves.  BioActive MolTurf® is a natural carbon balancer that increases the efficiency of nitrogen utilisation allowing less nitrogen to be applied.  BioActive MolTurf® provides a quickly available carbon food source for microbes that live around turf grass roots, thus helping to reduce fungicide and fertiliser applications.  Use on all turf grass surfaces and root zones for faster playing surfaces.

Main benefits of BioActive MolTurf® on turf grass surfaces:

• Faster and improved playing surface
• Promotes the availability and ready uptake of mineral nutrients
• Reduced applications of fertilisers
• Increased ability to resist and recover from environmental stresses, e.g. freezing temperatures, extended heat etc.
• Reduced disease susceptibility
• Regular use can result in less nematode damage
• Helps to reduce thatch build up by improving the efficiency and recycling of nitrogen and carbon by soil microbes
• Contains useful levels of furfural (typically 50mg/kg), high in sugars (> 40%), known to discourage insect herbivores such as leatherjackets

Application 1500 m² green: 1.5 litres of product in 75-100 litres of water April to September

The 3 Pronged Programme of Applications

You can think of this as a 3 pronged strategy, with each of the materials helping to provide a different part of the overall health and resilience to the plants to help your turf resist root herbivores and disease.

Conclusion

In conclusion, understanding the interactions between grass plants and the pests that trouble them is essential in turf management. As we have explored, promising research is ongoing to discover how grasses themselves combat these pests, using a variety of methods including physical, chemical and indirect defences. The hope is that by gaining a deeper understanding of these defences, we can develop more sustainable and effective greenkeeping strategies to cope with the burgeoning problem of leatherjacket damage. Whether it’s by improving the toughness of the plants, enhancing their natural toxicity, or exploiting natural enemy recruitment, these findings offer fascinating insights that will undoubtedly shape the future of greenkeeping. So, let’s keep our eyes peeled and our minds open, as we continue to learn from our grasses and work towards greener, healthier, and more resilient turf.