Queensland, Australia
March 21, 2006

Senior Plant Pathologist CSD Dr. Stephen Allen reports on the recent Queensland disease survey in conjunction with the Department of Primary Industries.

This is the fourth year we have been doing these surveys and they are quantitative counts on what diseases are present. Basically we go in November, early in the season and in February/March towards the end of the season. We look at Emerald and Theodore, St. George, Dirranbandi and on the Downs. The Border Rivers area, the MacIntyre is basically covered by David Nehl and the NSW DPI Group that do the NSW surveys.

You are covering pretty well all of Queensland. Can you give us a bit of detail on how you actually do the surveys? You obviously don’t survey every crop but you do a sample of those?

Yes, we select a random number of fields, between 10 and 15 of the fields in each area representing early planted to late planted, back to back versus rotations, a range of varieties. We make a point of not selecting fields because we know there is disease there so its more of a random look and we tend to go back to the same farms year after year, but not necessarily the same fields, so we get a picture of the impact of its environment and seasonal conditions and cropping practices on disease incidences. When we turn up in November to do the initial disease surveys we identify the fields, we collect information on seed rate, variety, planting dates, trash carryover from the previous season and then we go out and do stand counts, look for black root rot, look for anything that’s abnormal or anything that doesn’t look right. By comparing stand count with seed rates we can get a measure of seedling mortality which puts all the seedling diseases together.

So you actually visit the sites a couple of times and you do a late season survey?

Yes, then we go back. The idea is you do it before the first irrigation and after the last irrigation although it doesn’t always workout that way. So the last survey we go back usually February/March. At this stage we are looking for boll rots, Verticillium, Fusarium wilt, leaf spots and again anything else we can find.

Can we go through each of the regions specifically and discuss what you found. Starting in the north. Was there anything of significance in the Central Queensland region?

The most significant thing in Central Queensland in Emerald this last season has been the hail, it really knocked the first plant around so there was a lot of late planted crops. In fact of the 19 crops we looked at in the Emerald area, the average planting date was about the 20th October which is very late and there was as many crops planted in early November. Pathologically rather dull in the Emerald area there is virtually no alternaria, virtually very low in boll rots considering there was a lot of late crops. One very small patch of bunchy top in one field and that was the only bunchy top we saw in the whole survey in all the Queensland fields we looked at.
 
Anything around the Theodore area in Central Queensland?

Theodore is a smaller area. We looked at 7 or 8 farms in the Theodore/Moura area. There is a new record of Fusarium in that area so there is now several farms with the Fusarium problem there. Fusarium isn’t marching ahead or causing near as much damage as it is causing elsewhere. Again, seedling mortality 25/26%, not much alternaria, fairly low in boll rots which is equivalent to 1 or 2% bolls affected and where fusarium was present it was either hard to find or just a few plants probably reflecting the hot season.

Moving a little bit further South down to the Darling Downs, any comments there with regard to diseases late season?

Yes, the significant thing of course is Fusarium wilt. Again the crop was planted fairly late and the average planting date or the mean planting date about the 23rd October so again a lot of the crops planted late in October or early in November, not exactly good conditions so seedling mortality was fairly high but Fusarium took off and of course there is significant damage and virtually Fusarium was present in all farms we looked or irrigated places we looked at and absent from dryland fields generally. In terms of the Fusarium it ranged from just a few plants to very severe. One field we looked at 25% of the plants were dead within the first 5 weeks after planting and when we went back of the survivors 45% of those were severely affected and that was in a crop of Sicot 14B which is fairly resistant. Fair enough the plants that were there at the end of the season looked reasonable but it was late and many of the plants had brown vascular discolouration so the average incidence is about 7 or 8% present in all irrigated crops in the Downs.

What about out at St. George and Dirranbandi disease sites?

St. George/Dirranbandi interesting. Two new records for Fusarium in that area in this last season. Two new farms that is. That means fusarium has been found in virtually every farm we have looked at in the St. George area but again the incidence is about .1%. In other words it’s just an odd plant here and there or a small patch. So it’s not causing near the same level of damage as we see on the Downs. Generally, other diseases again, very little alternaria, fairly low levels of boll rot. In fact boll rot generally was lower than we would expect partly because the crops were later. The only significant levels of boll rot we saw were one in a very rank crop in the St. George area which was about 11% of bolls affected but the crop was very tall and one in the Theodore area where it had been hit very early with hail and massive branching and very thick dense canopy and again they are 11 and 12% bolls affected.

Overall, late season what do you think would be the major disease in those regions?

Well certainly, Fusarium wilt is, once we start cutting stems I think we will see a lot more. During our disease survey we split stems to find fields with 40%/30% of plants with significant brown discolouration in the stem without looking for them, that’s quite significant.

Fusarium has been a little bit quieter the past few seasons and it’s come back quite strongly in some areas each year, why would that be so?

Basically it represents the impact of the environment. We get a cool wet start to the season and it will be a lot more severe. We have been treated to some kind weather in the recent seasons and it hasn’t been as significant and we are seeing better varieties. The average F.rank of the varieties being used these days is a lot better and higher than we were using say four or five years ago so that is a significant factor too. But kinder seasons or less favourable seasons and more resistant varieties but it hasn’t gone away it is still there.

That being the case since it’s the major disease, have you got any other comments on handling Fusarium, you have spoken in the past about integrated approaches is that still applicable?

Yes, it is. I mean one of the things that we have talked about is delayed planting and some people say that we delayed our planting this year but of the six experiments that I was involved with in late planting is one year it made no difference at all, one or two years it made a big difference and three or four years where it made a significant but much smaller difference. So I mean the strategies that you use whether it be a more resistant variety with a higher F.rank, delayed planting, avoiding cultivation with knives, managing trash residues, all those things contribute and will help.

And the use of seed treatment?

Well the seed treatment one is the use of Apron on seed to control any chance of carrying, although I must point out that over the last four or five years we have been unable to find any evidence of seed infection and that possibly reflects the fact again that we are using more resistant varieties. We are now starting to harvest the large scale trials with the induced resistant seed treatment and it will be interesting to see how they perform and how the results come out over the next few weeks.

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