The majority of turf diseases are caused by fungal pathogens but some fungi are more strongly pathogenic than others. Many of the common cool season turf diseases are caused by fungi that rely on a weakened plant and therefore reducing disease incidence and severity is often aligned to maintaining a strong sward. With on-going changes to European Legislation relating to pesticide use, it is more important than ever that an integrated approach to disease management is employed and central to this is an understanding that the cultural conditions can limit disease development. Making use of the genetic variation that exists between grass types and cultivars can also minimise disease development through a sward. By managing rootzone quality and using weather information services, it can also be possible to pre-empt disease outbreaks and plan an efficient integrated management strategy.
Pathogen: Labyrinthula terrestris
Susceptible Species: Poa is the main species affected by Rapid Blight, but Agrostis spp. and Lolium perenne have also been infected.
The Labyrinthula species all cause disease in marine plants except Labyrinthula terrestris and therefore outbreaks are commonly associated with either coastal sites or sites using high salt irrigation water where the rootzone exhibits high salinity. Research suggests turf supplied with irrigation water lower than 0.5ds/m show no signs of infection whereas as salinity of the irrigation water increases from 0.8 dS/m to 4.0 dS/m disease severity also increases.
Rapid Blight can develop in a temperature range from 15 – 30oC, but development is most rapid between 22 – 26oC
Cultural & Chemical Prevention:
No UK fungicide has approval for the control of Rapid Blight, but preventative control has been achieved in trials using pyraclostrobin and trifloxystrobin. As these products are useful preventative treatments for anthracnose which appears in similar temperatures, any preventative treatments for anthracnose containing these active ingredients will also help where Rapid Blight is a concern.
One of the best ways to reduce disease severity is to flush the rootzone with clean water to reduce salinity to levels where disease will have little to no effect. Where saline borehole/recycled water is used for the prime source of irrigation consider a flush treatment using mains water to flush sodium out of the rootzone. An application of 30l/ha of Growth Products Sodium Knockout prior to a flush will increas sodium ion mobility and flush larger quantities of sodium from the rootzone.
A vertidrain or other deep aeration prior to this flush can also aid the cleaning of the soil.
If Rapid Blight is an ongoing issue and saline irrigation water is suspected of being the main issue, then look at systems that can mix mains and borehole water to reduce the salinity of the water used.
- If anthracnose is an issue apply Orbit TL (pyraclostrobin) at 1.25kg/ha as a preventative before summer stress occurs.
- Vertidrain, then apply Sodium Knockout @ 30l/ha followed by flush with low salinity water source.
Example of Rapid Blight
Initial symptoms are ‘watersoaking’ of individual plants, turning yellow/brown in a similar fashion to anthracnose. In situations where temperatures are ideal for disease development and irrigation with saline water continues disease development can be very rapid as patches coalesce to form large patches of dead/dying turf. Putting greens under stress can have the majority of the sward affected in a matter of days.
On occasion, initial symptoms can also contain sunken patches with a darker green appearance similar to thatch fungus patches, but this is uncommon in the UK at present.
Non-Pesticidal Rapid Blight prevention:
- Reduce rootzone salinity
- Increse height of cut if symptoms are seen
- Prepare turf for summer stresses by use of biostimulants such as SAR Activator SA (salicylic acid, TKO Phosphite and Essential Plus.
- Apply a wetting agent to reduce drought stress
- Switch to mains water for high disease pressure periods
Lowering of rootzone salinity is key to reducing severity of disease and an intense period of rainfall will always be the best solution for Rapid Blight. Without rainfall, preparing the turf by the use of pyraclostrobin or trifloxystrobin based fungicides for other diseases alongside measures to flush soils and reduce irrigation salinity are the best plan of action.