Cotton Seed Distributors article

A video version is available at www.csd.net.au/  

On today's Web On Wednesday the CSD Extension and Development Team discuss the outcomes of this season’s industry wide disease survey.

Talking to David Nehl from ACRI.  Just going to have a brief discussion about early season cotton diseases.  You have just completed a fairly wide survey of cotton areas throughout New South Wales.  So firstly, what production areas did you visit this year?

Rob we didn’t get to visit the normal suite of areas, particularly the Barwon and Darling areas didn’t have cotton or no cotton at all to look at.  We covered the Macintyre Valley, Gwydir, Namoi, Macquarie, Lachlan and Murrumbidgee areas.  There was some cotton, some new areas have gone in the Murrumbidgee and we have added another farm to our annual disease survey list.  We normally go to the same set of farms every year and we have been doing that or the NSW DPI has been doing that since 1984.  So we added another farm down near Darlington Point and that gives us the sort of the most coverage of that upper area in the Murrumbidgee growing area.

Actually I was going to ask you that.  How do you actually work out where you do go from year to year. You obviously go to the same valleys that have cotton production but do you go to the same farms or the same fields.  How do you do it?

We try to cover the same valleys and largely we keep to the same set of farms.  Obviously if we kept adding new farms at random then you sort of diluting the result depending on how long those farms have been in production.  If they are new areas, say as we have added the Lachlan and Murrumbidgee a lot of those farms have been disease free just by the very nature of them only had a few cotton crops but the idea is to get a picture over time so we visit the same farms over and over.  Within those farms we try and pick the fields at random.  We don’t just go to the field where the grower says I have got bad disease here go and look at that field, we try and just pick them at random without looking at them first without being biased and usually we will try and mix up varieties a little bit if we can or say try and get a range of cropping practices, some back to back fields and some that are rotated.

So this year when you went around, I guess if we could have some comments about what the diseases were like, I guess starting with seedling disease what did you find in that regard?

I guess the outstanding thing about this year was the warm conditions and I just heard an announcement by the Met Bureau that this has been the warmest spring on record.  Seedling disease and our other soil borne diseases are particularly favoured by cool wet conditions in spring.  We are in the middle of a drought and we certainly haven’t had cool wet conditions compared to previous seasons.  So seedling disease was generally at a very low level.  There were some areas where seedling mortality was a little bit higher but mortality includes a lot of factors including say fertiliser burn or seed placement and particularly in a few fields we saw some losses due to wire worm coming out of rotation crops.  One field or a couple of fields not too far from Narrabri we did see some higher levels of seedling disease where a green manure crop had been ploughed in a little bit too late.  Normally we have recommended vetch in the past for black root rot as a bio control measure or a bio-fumigation measure but we have always added a caution to that you need to get that in at least four weeks or more before you sow cotton an let is break down otherwise it enhances rhizoctonia and pythium and in these few particular fields the residues of the pea crop were ploughed in quite late and that enhanced the rhizoctonia particularly and so they got some higher levels of seedling disease but probably not enough to actually require a replant so it was of concern and it was a good illustration of any legume crop can increase seedling disease if you plough it in late.  You need to get the residues broken down and that is even harder when you haven’t got rain over winter to break those residues down.

Well speaking of black root rot then, what about the rest of the areas in NSW as far as black root rot goes this year?

Black root rot is still present.  The season being warmer we saw a sort of a shorter window, a shorter period of conditions that favour black root rot.  We certainly saw it being just as severe in fields with a history of it as in the past but those symptoms didn’t persist as long; the plants grow out of it as warm weather comes on.  So in terms of the survey, when we finish crunching the numbers it may appear as if the percentage of black root rot is down a little bit and particularly as we finish the surveys off in late November we were almost too late to see it because of that shorter window of favourable conditions.  But certainly that disease is still there and the last couple of years we have seen it spread into the Lachlan and Murrumbidgee areas and we are still seeing it there.  Not on the new country on that new farm that I mentioned but it is certainly an issue in terms of trying to keeping it out of those new production areas.

So David the other particularly bad disease Fusarium, was there any evidence of that in your travels this season?

The warm conditions at the start of this season were also less favourable to Fusarium wilt.  We normally wouldn’t see it until late November early December when you are getting plants that are large enough to show vascular discoloration in the woody part of the stem.  Usually if fields that have Fusarium wilt have seedlings dying it just hasn’t progressed up into the stem enough to see browning up there they are just dying as if it was seedling disease.  So we normally wouldn’t see it until that mid to late November if it is there and certainly this season it was very warm and we only saw a few plants in fields that we knew from past history had already had that disease.

Were there any differences in disease between the valleys this season?

Largely with seedling disease it was pretty well low everywhere.  As I mentioned before we had a few fields where seedling mortality was higher and by seedling mortality that means not just disease and that was due to factors like wire worm or the legume crops that I mentioned that gave rhyzoctonia a bit of a kick.

So you have probably already answered the question but how would you rate the overall disease levels compared to normal?

Very much lower than normal and that’s really just a factor of the climatic conditions that’s really the big driver, particularly of seedling disease.  With Black root rot it will still be there even though we didn’t get as many cold shock nights.  We are still seeing that disease but it is just less prominent and the plants are going to grow out of it more quickly.

I guess with regard to Fusarium in New South Wales, is there any comments.  Is the pathogen still spreading rapidly or is it not spreading rapidly?

Well there is not reason to expect that the pathogen wouldn’t be spreading as much as it has in the past.  It’s spread on infested trash and mud, adhering to vehicles or adhering to trash.  So it is easily spread around farms in floating trash in their irrigation or tail water system.  It is easily spread on machinery and even though we may be seeing less disease in the crops there is still going to be just as much of that fungus, that pathogen in the soil.  Its very persistent it lasts at least 10 years in the absence of cotton and there is no reason why it wouldn’t spread just as easily as in previous seasons so we would like to emphasise that growers should maintain a vigilant strong farm hygiene program.  We want to try and continue to prevent the spread of the Fusarium wilt pathogen as well as the black root rot pathogen.

OK well thanks for that David and we might try and catch up with you at the end of this season and maybe discuss some of the later season diseases that might be around and lets hope that they are the same as the early diseases incidence this year and not much of a problem.

I would expect that if we continue with a warm summer as appears to be happening we will see lower levels of Fusarium wilt and verticillium wilt in those fields that have had a history of it, particularly those crops that might have been slow with black root rot they will certainly have the opportunity to grow out of that and compensate and get quite a good yield.  So I guess that’s one compensation for the hot dry conditions as least it is less favourable to disease.

Thanks very much.