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Does dormancy equate to better resilience?

Jul 26, 2023 | News

Turfgrass specialists and researchers are leaning towards allowing turf to go dormant for better resilience and performance in spring transition.

Tahoma 31 being a hybrid bermudagrass (couchgrass), is a warm season grass amongst others in Australia including Kikuyu, Common Couches, Zoysias and Soft Leaf Buffalos.

Like all warm season grasses, Tahoma 31 will go dormant in winter and as we see it in differing climate zones, we are also seeing different rates of dormancy response.

– In Far North Queensland and other tropical locations, Tahoma 31 hardly changes in its appearance over winter with only reduced growth and slight leaf discolouration – if at all.

– Further South into South East Queensland and it can vary in its wintering from having a slightly thinned-out leaf and purpling or light discolouration through to a more straw-like colour depending on temperature and exposure to elements.

– Throughout NSW and into the ACT, Victoria and SA we see that from around Sydney south, Tahoma 31 can move into a deeper dormancy with straw-like colour in the depths of winter.

One of the benefits of Tahoma 31 is its quick recovery or spring green-up and similar to what we see in Australia, it has rated highest for this in turf trials the world-over.

A question we are often asked is can this dormancy response be slowed or delayed – and is it something we’d want to do anyway?

We sometimes see some Tahoma 31 lawns that are holding colour better than others and much of this is down to nutrition intake prior to winter as well as mowing height and even using colourants.

Research is currently underway into a number of bio-stimulants, bio-fungicides and other hormone treatments (PGR) to stave off the dormancy response of Tahoma 31 and other warm season grasses for much of winter.

Tahoma 31 was bred for drought and cold tolerance with the ability to survive extreme conditions of both heat and cold being standout features of this new variety.

The deeper dormancy experienced in cooler climates has been suggested as a negative trait, however looking a little further into the plant’s physiology, we see a good reason for it.

During late Autumn, soluble sugars are converted to starch granules and stored in the stolons, roots and rhizomes during winter months.

When conditions turn around in Spring, lateral buds or tillers, found at the nodes of bermudagrass stolons and rhizomes break dormancy, carbohydrate reserves are converted to soluble sugars and the first new leaves start to appear.

Green-up and recovery begin when nighttime temperatures typically stay above 14 Deg C for several days, along with soil temperatures reaching 16 Deg C at 100mm depth.

The fast transition and recovery of Tahoma 31 can also be attributed to the storage reserves available to the plant.

Recent research indicates that Tahoma 31 has around twice the volume of stolon and rhizomes than similar grasses which suggests this storage capacity apart from genetic influences helps in post-winter recovery.

Whilst we are carrying out trials into delaying dormancy, including Ryegrass oversowing, we are seeing more turfgrass specialists questioning the rationality in trying to stave-off dormancy in the first place.

Theories are growing that pushing warm season grasses too-hard into late dormancy whittles down their winter-reserves, leaving them depleted at the time of transition.

Keeping carbohydrate reserves at peak levels prior to transition through a good dormancy period, therefore allows the transition to happen at a faster rate than if these reserves were depleted.

Spring transition is characterised by new shoot production, root dieback, and new root production, making the grass susceptible to low temperatures, herbicides, fungal attack and competition from grass and broadleaf weeds.

Energy reserves are rapidly depleted during the spring green-up and root dieback period and during summer months, energy reserves accumulate very little since they are repeatedly used for regrowth following mowing.

It is worth considering that management practices – including delaying dormancy – can have a significant influence on the reserve energy status throughout the year of warm season grasses including Tahoma 31.

Factors Influencing Spring Transition and Recovery of Bermudagrass

Spring transition is a crucial period for bermudagrass turf like Tahoma 31, marked by green-up and recovery after dormancy.

This phase is also vulnerable to various environmental and cultural factors that can affect its health and growth.

Understanding these factors is essential for promoting successful spring recovery and following are some key components influencing recovery:

Temperature

Green-up and recovery begin when nighttime temperatures stay above 14 Deg C for several days, along with soil temperatures reaching similar temps at 100mm depth. Spring transition is characterized by new shoot production, root dieback, and new root production, making the grass susceptible to low temperatures, herbicides and competition from Grass and broadleaf weeds.

Growth Patterns

The length of the growing season varies depending on the first and last killing frosts. Many Bermudagrasses including Tahoma 31 can stay green year-round in some areas.

Energy Reserves

Energy reserves, mainly starch, accumulate during Autumn and are depleted in Winter and Spring. Management practices can influence the reserve energy status of Tahoma 31 throughout the year.

Nutrient Availability

Nutrient levels, particularly nitrogen and potassium, affect spring recovery. Proper timing and application of fertilisers can significantly impact the turf’s health.

Moisture

Adequate irrigation during the transition period is critical for Tahoma 31 recovery. Both dry and wet soil conditions can impede growth.

Shade

Turf growing in partial shade has reduced energy reserves, slower recovery, and increased vulnerability to fungal, pest and environmental stress.

Soil Compaction

Compacted soil restricts oxygen availability to the root system, leading to delayed recovery.

Competition

Winter weeds, especially wintergrass, can hinder Tahoma 31 recovery by shading and competing for resources.

Overseeding

Cool-season grasses overseeded on Tahoma 31 can delay recovery due to competition for sunlight and nutrients.

Turfgrass diseases like Pythium, brown patch, and nematodes can cause significant losses during the spring transition. Preventative fungicide applications are recommended in critical areas.

Understanding the various factors influencing spring transition and recovery is vital for maintaining healthy Tahoma 31 turf.

Proper management practices, such as timely fertilisation, irrigation, mowing, and disease control, can promote successful green-up and ensure the grass thrives during this vulnerable period.

 

 

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