Answers to common grower questions

It has been difficult to assign yield losses solely to YCS except in cases where blocks were severely affected and where repeated waves of yellowing were observed over an extended period of time.

YCS can impact cane in a number of ways. This can range from yellowing in one or two leaves to yellowing right through the canopy. Depending on the degree of symptoms, crop growth can be compromised with potential impacts on final yields. YCS symptoms may ‘come and go’ in waves through the season.

Some growers have reported that fields affected last year are not yet showing YCS symptoms, while others report that YCS is present again.


YCS can impact cane in a number of ways. This can range from yellowing in one or two leaves to yellowing right through the canopy. Depending on the degree of symptoms, crop growth can be compromised with potential impacts on final yields. YCS symptoms may ‘come and go’ in waves through the season.

If you notice yellowing in your crops ensure that you check the symptoms with your local productivity services group. They will help confirm whether you have YCS.


Until we identify the cause of YCS, we cannot advise about on-farm management strategies to treat it. However, as part of our research program we are investigating a number of management strategies to see how they impact on YCS. Therefore, we recommend that crops are well managed with optimised inputs.


It has been suggested that YCS may be transmitted in planting material. Although our current trials that look to answer this question are still in progress, we have noticed that when growth conditions are ideal, no yellowing has occurred.

We therefore encourage growers to use approved seed cane where possible and to adopt good farming practices.


YCS has been seen at all stages of plant growth and in all crop classes.


From our observations and those provided by growers in affected regions we believe that stress plays an important role in the expression of YCS.


The two conditions are similar and have similar symptoms. As there is no definite test for Golden Leaf Syndrome (GLS) and we have not yet identified what YCS is, we cannot say that they are the same condition. Nor can we say that YCS has come from Papua New Guinea.


Yellow Leaf Syndrome is widespread in Louisiana and other cane-growing states in the United States of America. Similar symptoms to YCS have not been reported in the USA to date.

Harvesting YCS-affected cane

If you are concerned about the possible CCS levels in an affected block we suggest that you submit samples to your mill to identify the exact CCS levels. If the levels are low you may wish to leave the cane in the field until mid-season to see if the CCS levels improve.

Consider your whole-of-farm management plan when deciding which cane blocks to harvest. If you delay cutting a particular block or blocks, this may impact on your other farming operations and the ploughing out of blocks to be fallowed that year.


Observations on a number of farms have found that YCS-affected crops which were harvested last year went on to ratoon well this year. Ploughing out of blocks prematurely could impact on your crop rotation and may be an unwarranted cost to your farming business.


In some cases severely affected cane may have smaller stalks than healthy cane. This does not impact the way the cane is processed through the mill.


Whether a harvester spreads YCS between blocks or farms is unknown. We recommend that as part of your standard harvesting operations that good harvester hygiene is followed. This involves maintaining equipment hygiene and sterilising the harvester between blocks, to minimise the risk of ratoon stunting disease.


YCS-affected blocks should be harvested in the same way as non-affected blocks, unless a known poor root system exists for some other reason. If your crops are known to have a poor root system you need to flag this with your harvester operator.

Identifying YCS

Cane can turn yellow for a variety of reasons including drought stress, phytotoxicity (or herbicide damage), insect attack, disease, nutrient deficiency or natural maturing. It is important to understand how symptoms that are commonly observed from each of these causes and how they differ from YCS.

Our researchers have documented and examined YCS and noted the difference between it, and the natural leaf yellowing which occurs in every growing season. YCS has been clearly described so that everyone can be assured that those researching the condition and the general farming community are referring to the same thing.

What we know so far

Experimental work does not support a single cause for YCS. There are a range of activities underway looking at several possible options.

 

There are many causes of leaf yellowing in sugarcane. YCS is a specific pattern of leaf yellowing accompanied by abnormal and lethal accumulation of sucrose and starch in leaves.


Additional magnesium application above levels recommended for good crop management has no effect on YCS expression.
Magnesium deficiency in sugarcane can lead to yellowing of leaves. Experiments now confirm that addition of magnesium does not prevent or alleviate YCS symptoms. Plants with YCS usually have adequate levels of magnesium so magnesium deficiency is not a cause of YCS.


The role of insects, phytoplasmas, other bacteria in combination with environmental triggers are being investigated.
Experimental work does not support a single cause of YCS. A number of factors need to be present for YCS to be expressed. Experimental work is focused on identifying the key factors so that management options can be progressed.


An indicator tool kit for SRA, productivity service organisations and industry advisors for identifying YCS is at an advanced stage of development.
This is a significant step as any approach, experimental or commercial, needs to correctly identify the problem so that researchers and industry can respond appropriately.


A chemical option is under investigation which in most cases prevents YCS symptoms expression under experimental conditions.
This is a vital step if researchers are to develop management options for industry. These trials have used a broad-spectrum insecticide at high doses as an experimental tool to confirm or eliminate the role of an insect in YCS. This is not a test of the suitability of these chemicals as a management option. This option is enabling us to quantify the impact of YCS on yield and identify potential causes. This means that researchers now have the capacity to manipulate YCS symptoms.

Research program

SRA is funding four major research projects looking at the YCS problem. These are:

Each research project is investigating different aspects of YCS and collectively they are expected to provide complementary information and results that build our understanding of the condition.

The program is being coordinated by Dr Harjeet Khanna, SRA YCS Program Coordinator, with continued input by the Scientific Reference Panel.

Scientific Reference Panel

A Scientific Reference Panel, an independent group of expert plant scientists, has been appointed as part of the SRA research program. Led by Dr Joanne Daly, the Panel is responsible for providing supporting scientific opinion about the direction of the project and scientific support.

 

Joanne is a CSIRO Fellow. She is a former Group Executive of Agribusiness and Chief of Division at CSIRO. Her activities focus on strategy for national research collections and in agricultural sciences, and assisting with the developing science precinct in Canberra with the ANU in the area of transformational agriculture.

She has worked in CSIRO for over 30 years originally as a researcher in entomology. She chaired the ‘Expert Working Group on Security Australia’s Agricultural Future’ for the Australian Council of Learned Academies. She is an ACIAR Commissioner and has held a number of senior roles including Chair of the international body, GBIF, and was a member of the Biosecurity Advisory Council and the Australian e-Research Infrastructure Council. She was head of the Secretariat that assisted Government in the setting of National Research Priorities in 2002, during her 2-year secondment to the Federal Public Service.


Dr Drenth obtained a Masters degree in Plant Breeding from Wageningen Agricultural University in the Netherlands before completing a PhD jointly at Wageningen and Cornell University, USA on the population biology of Phytophthora infestans, the causal agent of late blight on potatoes.

Dr Drenth is currently a Principal Research Fellow in the Queensland Alliance for Agriculture and Food Innovation (QAAFI) at The University of Queensland where he manages plant protection projects and programs in bananas, citrus, apples and macadamia.

Dr Drenth worked as a plant pathologist for the CRC for Tropical Plant Pathology in Brisbane from 1994 to 2000 and was program leader of the Disease and Pest Prevention Program in the CRC for Tropical Plant Protection from 2001—2006.

He has managed many research projects on crop protection in agriculture and horticulture in the tropics and the subtropics, and is familiar with many plant diseases and disorders. He has published widely in areas such as the identification of plant pathogens and the management of plant diseases.

Dr Drenth is involved in numerous international research efforts and is on the Technical Advisory Board of CENIPALMA in South America.


Professor RP Hellens joined the Centre for Tropical Crop and Biocomodities in March 2014. From 2000 to 2014 Roger Hellens worked in New Zealand at Plant&Food (aka HortResearch) in Auckland, where he had a number of role including leading the institutes 80-people strong genomics research and more recently the $10M p.a. kiwifruit breeding programme.

His research interests were the development of red-fleshed apple and kiwifruit varieties and exploiting Next Generation Sequencing (NGS) techniques. He has also maintained a keen interest in post transcriptional gene regulation and this has become relevant in work to understand the regulation of vitamin C. Prior to his move to New Zealand, Professor Hellens worked at the John Innes Centre in Norwich, UK. Here he developed the first genetic maps in pea (including his PhD on the molecular basis of Mendel’s white flower phenotype), He developed the pGreen plant transformation vector and a project on gene silencing (RNAi) in petunia.