David Nehl,NSW DPI Plant pathologist, introduces plant pathologists from the University of Arkansas and Louisiana State University describing a decision support tool being developed for in-furrow fungicides at planting.

Dr David Nehl, Research Scientist (NSW DPI).

You recently visited the United States of America where your toured Arkansas and Louisiana. You looked at how they were managing some of their seedling disease issues. Can you give us a summary on how their seedling disease issues compare to Australia and also the environment they are growing cotton in?

In the US some of their seedling disease problems are probably worse than we see in much of the Australian cotton belt. In the US they get cooler starts, probably akin to what we see from the Macquarie Valley and further south into the Lachlan and Murrumbidgee, so our seedling disease problems in Southern NSW are probably equivalent to what they are seeing and they can get very severe stand losses. They have put a lot of effort into developing a model that looks at how climatic conditions affect seedling losses and try to help farmers workout how to minimise the impact of seedling disease.

Their model is a decision support tool as to whether to or not to use in-furrow fungicides. What is the situation with these types of products in Australia?

We don’t have a lot of in-furrow fungicides available, or not as many as the US. There is one product that is available for control of rhyzoctonia as an in-furrow spray; otherwise we are just relying on seed coat fungicides that are applied by the seed producers. In most areas those seed coating fungicides are adequate for disease control particularly the further north you go in Australia where it is warmer and the biggest impact on seedling disease is going to be climatic conditions so except in exceptionally wet starts to the season the standard fungicides on the seed coat are adequate. The further South in NSW I see potential for perhaps looking at the model that has been developed in Arkansas and Louisiana and seeing how that might be applied to the very cold conditions that are experienced down there, working within the range of chemistry that is available in Australia.

In their model, the main determinants are soil temperature and soil moisture. How can Australian growers use similar principles to what they have done in trying to manage seedling diseases?

Soil temperature and moisture are really the driving force behind seedling disease. If we get a good warm start without heavy rainfall after sowing, seedling disease is generally not going to be a problem. Some of our work here are the Australian Cotton Research Institute at Narrabri has shown that for every degree you drop below 16°C in the soil at 9am during the first week you get a substantial increase in seedling mortality. Therefore the temperature at 9am on the day you sow wasn’t really relevant to seedling mortality in our study but if you average that soil temperature at 9am during the first few days to a week after sowing that was really critical and for every degree below 16 you are really going to see a lot more losses.

Combining that with moisture, similarly the wetter the soil the more losses we are going to get and that’s particularly going to affect pythium. This is where it will be interesting to look at the American’s model in terms of predicting whether we can get a benefit from applying with the in-furrow fungicide that is available in Australia with the control of rhyzoctonia. If soil temperatures are going to be cold it favours both pathogens but the moisture is more favourable to the pythium. From the American’s work, rhyzoctonia apparently is not going to be affected as much by soil moisture if the soil is dryer, rhyzoctonia can still be active. It would be good to see how we can apply the Americans model.

Dr Craig Rothrock (University or Arkansas).

Craig what does your work involve and how do you see growers benefiting from it?

I work with soil borne fungi that attack cotton and our biggest concern on cotton is the seedling disease complex, so we are working to try to control seedling diseases to ensure that growers get a uniform and vigorous plant stand early in the season.

What diseases are you talking about?

The primary pathogens on cotton and the seedling disease complex are Rhyzoctonia soloni and Pythium species and they cause a lot of our stand problems and Thielaviopsis which causes Black Root Rot which reduces seedling vigour early in the season.

What factors are involved in the severity of these diseases?

Over a number of years of tests, the biggest factor that we have found involved the environment at planting or shortly after planting and we are talking about cool soil temperatures and then moisture availability or rainfall soon after planting.

How do you see cool soil temperatures affecting the different diseases?

The biggest environmental factor in terms of seedling diseases is soil temperature at planting and we get dramatic differences or responses from fungicides when we are getting down say minimum soil temperatures or soil temperatures at sunrise around 60° Fahrenheit (15.6°C).

I understand you are working on a Decision Support Tool for growers. How are they using it?

All of our cotton seed in the United States is treated with a number of fungicides, so there are good seed treatment fungicides out there. Our concern is that the decision that the grower has to make at planting is whether he adds additional fungicide either on the seed or in the planting furrow at planting to give additional protection and insurance against a good stand at planting. What we are doing is trying to look at what environmental factors are critical to reducing stand and then when those environments are conducive to seedling disease and thus we need additional fungicides.

What we found in co-operation with Pat Collyer at Louisiana State University is that if soil temperatures are below this about 60° Fahrenheit (15.6oC) at planting for the first few days, an in-furrow fungicide will give you a more reliable plant stand and thus pay off. If soil temperatures are warmer than that you are probably wasting your money, and should be saving your money rather than spending money on an in-furrow fungicide because the cotton seed treatments are going an affective job.

Dr Pat Collyer (Lousiana State University)

What fungicides are available to growers?

There is a whole series of fungicides. The Dynasty fungicide has become popular as a seed treatment fungicide but we also do a lot of evaluation of in-furrow fungicides. Most of them are applied as liquids. There are several things out there; Quadris (Azoxystrobin) is one of them which is actually the same active ingredient as the Dynasty. The Terraclor (PCMB) is used somewhat as well.

Dynasty is being released in Australia this season as the fungicide on all CSD seed. What benefits do you see in the product?

It’s a good seed treatment fungicide. It is probably as effective as any of the seed treatments that we have had over the years. In the United States we conduct a national cotton seed treatment test that’s coordinated by Craig Rothrock and in those tests we have anywhere of up to 15 to 20 treatments every year, including all different kinds of combinations of materials. The Dynasty I think has been as affective as anything in that test the last few years.

Further Information: David Kelly