Dr David Nehl, Research Scientist with NSW DPI in plant pathology discusses results of long term disease surveys across the industry and the implications of this on farm hygiene.

Can you give us a run down on the trend of both fusarium wilt and black root rot incidence from you disease surveys for the last couple of years?

Our surveys of New South Wales have included black root rot for quite a while now and as we have monitored the progress of that disease we have seen it spread from a very low incidence in the mid 90’s to virtually every farm that we look at in the MacIntyre, Gwydir, Namoi and Macquarie Valleys.

Every farm in our disease survey set has the pathogen and it’s very widespread in those valleys. It is still moving, its moved into the Lachlan Valley probably six or seven years ago and a couple of seasons ago we have found black root rot for the first time in the Murrumbidgee Valley.

That pathogen is still moving, it appears not to be a native pathogen, it appears to have been introduced from overseas so this is where we have a chance of keeping a disease out; its really the best control measure that you can ever use. We don’t have any resistance varieties for black root rot so exclusion is a very good control measure.

I think the farm hygiene program has been very affective in trying to slow down Fusarium wilt. With black root rot it has been a little bit more problematic because people don’t realise the pathogen has been there and present on their farms. Fusarium wilt in our surveys is not as widespread.

We have been making a tally of the reports by growers of the new cases of Fusarium wilt and in the last two or three seasons we have seen a falloff of reports of Fusarium wilt. This may be due to lower areas planted with the drought but I do believe that its due to the impact of the farm hygiene slowing down that pathogen.

Also, with better varieties these days, the disease is probably not progressing as quickly, so when it does arrive on a farm we are not seeing the huge holes in the crop that use to be seen and perhaps growers aren’t reporting it as much because it is taking longer to build up.

But certainly, farm hygiene has been the very important control measure for Fusarium wilt and I don’t think growers have realised the value of it for black root rot.

With the incidence of Fusarium slowing down but black root rot continuing to increase, could people start to become a bit complacent with farm hygiene given that the most of the focus has been on the more high profile Fusarium?

I think that is quite a concern. Fusarium wilt has been a big motivating factor for farm hygiene and people have been very concerned about having that disease. There has been a certain stigma attached to having it. When you are the first in a new area and people don’t want to get it.

As the Fusarium wilt pathogen spreads throughout an area or region and we get more cases, people may be becoming a bit complacent. It would be a concern if people have the attitude, “oh this pathogen is everywhere”, then they will start to give up on their farm hygiene but the farm hygiene is still going to be valuable for black root rot as many farms still don’t have the black root rot pathogen and they don’t have the Fusarium wilt pathogen.

We would like to see people maintain that level of diligence in trying to keep these pathogens at bay. It’s a method of minimisation; we can’t guarantee that you will never get those pathogens on your farm but we can certainly try and slow them down.

You have been doing the industry wide disease surveys for a long period of time, going back to the same farms for many years. You would have seen some farms that started off with no black root rot and then all of a sudden got a little bit of it and then it spread.Can you tell us how that spread happened; the sequence of events?

In our experience we have seen farms where the oldest fields had black root rot showing up first and over a number of seasons the presence of the disease progressed to fairly severe levels Then, in the more recently developed blocks on the same farm we are now starting to see black root rot turning up.

On their newest blocks, that were only very recently developed the pathogen isn’t there. It’s probably impossible to stop it moving within your farm given the amount of machinery movement etc, but it is possible to try and slow it down if you have new blocks by preventing movement of large amounts of soil. Also the black root rot fungus is easily spread in soil adhering to floating trash.

The pathogen wouldn’t actually be in the trash or stalks themselves but in soil that is adhering to it, so it could quite rapidly spread through a whole tail water system.

If you had a farm where black root rot is reported for the first time on a field or two, you could look at trying to minimise trash movement as a way of slowing it down to prevent spread to further fields.

Any soil that is suspended in the water, tends to fall out of suspension reasonably quickly in the tail water return drain.It’s the trash that moves very fast around the whole farm.

Given that information, obviously exclusion from the farm and in the first place is the best way of slowing it down?

Yes. If you can keep it out why bring it in. It really boils down to what the grower decides is the level of effort they want to put in. We can recommend good farm hygiene but it is really up to the growers to implement those recommendations.

The black root rot epidemic is very widespread and it’s really built up without people noticing it. That disease can be on a farm and people realise the crops growing slowly but not realise that they actually have that disease.

Unlike Fusarium, where you get huge bands of the crop dropping dead, initially when we saw those outbreaks in the mid 90’s.

To quote a couple of ex Australian treasurers if you think of Fusarium as being the high flyer, black root rot is the stealth bomber and I really think growers need to bear that in mind. We can slow both of these diseases down.

They are both easily spread in soil and mud adhering to vehicles and machinery and that’s the best way to slow them down, just try and minimise movement of soil. For Fusarium wilt its also going to be inside the trash.

Further Information:
Robert Eveleigh, John Marshall,  Craig McDonald, David Kelly or James Quinn