Fusarium Wilt (Fusarium oxysporum f.sp. vasinfectum Race 4)

Bob Hutmacher, Statewide Cotton Specialist, University of California
(Interviewed by Chris Anderson, Plant Pathologist, NSW DPI, Narrabri)

What exactly is this disease and how does it affect the plant?

This is a disease that we first spotted a couple of years ago in California. The characteristic types of things we see are a type of yellowing discolouration in the leaves that will turn into a brown necrotic area and vascular staining in the plant. This indicates that there is a fungal organism that’s present within the plant. We have also seen damage fairly early; at seedling stage when we get seedling death if the damage is severe enough.

So you can expect to see some stand losses due to the Fusarium?

That is correct.

Have you got any idea where this has come from?

No, we really don’t. We have had fields brought to our attention by some alert growers and pest control advisors. They have asked us to look at these fields and once you have seen the first one, you are more attuned to keeping your eyes open for any other incidents.

How long have you had to deal with this disease?

This is our third summer since it was brought to our attention.

Have you got any idea about how it spreads?

Based on past experience with other races of Fusarium in California, and some work that has been done over the last 50 years with USDA and University of California, movement of plant debris and movement of soil that contains the spores would be likely ways to move it around within a field and also with equipment from farm to farm or field to field.

Have you had any evidence of it moving from farm to farm so far?

This is circumstantial. We can’t absolutely identify where things came from but looking at some of the patterns of progression of the problem down through individual fields where it follows the vehicle traffic patterns in the field or the movement of irrigation water through the field, it certainly fits that type of thinking.

It is not just a disease of Pima is it?

No. Originally it seemed like the most susceptible varieties were some of our Pima varieties that we grow here in California and that is still true. The worst damage seems to be on the most susceptible Pima varieties but it does appear to be able to infect upland cotton as well.

You have only had three summers to have a look at this disease, but have you noticed differences between seasons in terms of severity?

Yes. The differences are a little hard to identify since part of what we are trying to do is some varietal screening type of work, similar to what is being done in Australia.  We are trying to do this screening in fields where we have identified and confirmed that it actually has this race of Fusarium in it and so the timing of when we have access to these fields is a little bit different from year to year. Part of it may be the time of planting affect; when we have access to the field and actually get these screens planted. Part of it may be varying different planting conditions and weather conditions each year. I don’t think we really have all that sorted out yet.

And do you see this disease as being something that could spread to Australia?

I have talked to some people from Australia, and given that the primary mechanism of spread is going to be through movement of plant debris and soils, that would certainly limit movement over very large areas. If there is some other mode for moving it, well then that may be something to follow up on.

For instance on machinery that went from the USA over to Australia and hadn’t been cleaned down properly?

Correct.

Further Information: David Kelly

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