Low temperature grass plant damage is becoming a more common and destructive type of abiotic stress in parts of the UK.
Winterkill, as it is called, is a general description for any visible injurious outcome to turfgrass plants that occurs during any winter period. This can result in deleterious injury due to frozen grass plants or frozen turf rootzones, low temperature leaf desiccation injury or low temperature pathogenic (disease) attacks. Winterkill injury is reported with increasing regularity within the UK and, this year the north east of Scotland has been ravaged with lengthy periods of ice cover, more akin to conditions experienced in the Nordic region or north America.
Winterkill can be caused by individual or a combination of factors, including crown hydration, low temperature leaf desiccation, ice sheets and pathogenic (disease) attack. Due to the unpredictability of localised environmental conditions, potential damage outcomes can vary greatly among golf courses. Variable regional and site conditions can influence the extent of damage seen. Agronomic characteristics such as surface drainage, surface compaction, grass plant type and available sunlight can both positively and negatively affect the swards under pressure from low temperature conditions.
Ice damage, particularly ice that has frozen encasing the grass plants, is a devastating type of abiotic stress. Damage usually occurs during freeze and thaw cycles of fluctuating temperature, from slightly warmer daytime through to the colder night-time temperatures. Ice cover or an ice blanket forming in a regular thaw and freeze cycle will result in turf damage due to crown hydration and will be more damaging in shade or lower lying sections of turf holding higher water volumes. Course managers throughout the north of the UK have been left with the dilemma should they attack the problem or take a more considered approach and allow nature to take its course.
Introducing the practice of “cracking” the ice, using a solid tine, commonly used in Scandinavian countries, may increase the potential for plant tissue damage and thus probably best discounted unless mechanical damage can be totally avoided. Pressures due to financial concerns over lost revenue should not influence these decisions to prematurely return the course to normal play conditions. Regardless of the choices we make to revitalise these pressured grass plants once the thaw has established, a period off rest will be required, meaning no play and very little maintenance, with light aeration to oxygenate the surface, the only exception. After many weeks of ice encasement usually in anoxic (lack of oxygen) conditions, these stressed grass plants will have to build up some much-needed energy (carbohydrate) reserves to underpin their return to normal functions of tillering and rooting.
Nutritional input will be lower initially with seaweed-based products the preferred option to gently support the plants through this early re-establishment phase. Once temperatures rise, nutritional inputs can increase as necessary to foster sward density and allow the plants a return to their normal maintenance regime. Recovering stressed and damaged grass plants after a period of blanket ice cover, can be excruciatingly slow especially if conditions remain cool and cloudy. Sown seed will require seed to soil contact (not always easy without disturbance to already stressed plants ) and likely will stubbornly refuse to germinate until rootzone temperatures are sufficient to do so.
Spot plugging can be beneficial in small sections but is not the answer to larger areas of fine turf damage which may be beyond repair. Re-turfing larger sections is an option, however in real terms, even with kind weather the re-turfing will not guarantee a return to normal maintenance regimes. The usual play standards are likely not to be met until the new turf is able to withstand the early establishment stresses and benefit from the many sward refinement inputs required to return that surface to a condition consistent with the other surfaces on the course. That could take many weeks, if not months, and it will be very difficult to keep the golfing clients off the damaged surfaces during the recovery period. Discipline, perseverance and patience will be required to get through this all-important recovery period, as will the inescapable thought to the future, and the high likelihood of similar repeating episodes of these extreme weather episodes.
To Summarise -The severe conditions experienced in the north of the UK this year are very likely to become a more regular set of phenomena and all forms of winterkill are challenging to grass plant health outcomes. With the demands for winter sport participation growing, it is probably the right time we all as sportsturf managers look to develop a longer-term winterkill defence strategy.