A number of mid-late season issues being encounterd are addressed, including secondary pest problems (QDPI&F entomologists, Paul Grundy and Dave Murray), Heliothis survivors in Bollgard II® crops(Stewart Addison, Monsanto) and physiological shedding of fruit (Greg Constable, CSIRO).

Paul Grundy, Research Entomologist, QLD DPI&F, Biloela.

A quick review on the Whitefly situation in Central Queensland as you understand it, given that we are mid January at this stage?

Basically the whitefly this year seemed to be travelling a fair bit higher than what they were last season. This season was a little bit different to the last three seasons where we have had quite a wet start to the season, particularly during late winter and as a result of that we had quite a lot of weed biomass out there and consequently populations of whitefly overwintering in those areas. It would appear this season with that large number of weeds around at the start of the season and what I have guessed have been some really hot weeks, particularly leading up to Christmas we have certainly ended up with much higher whitefly populations than what we had at he same time last year.

At this stage what percentage of the area do you suspect may need treating with a product like Admiral® or something similar?

It is a little bit crystal ball at this stage but the way it is shaping up I wouldn’t be surprised if we had one of our heavier treatment years where we could get up to around 40% of fields treated which is what we have had in the past.

Looking back over the last three or four years, do you tend to think that the way it is shaping up, whitefly is going to be a thing that might bob its head up every two or three years, or something like that?

Yes, I think the way things are shaping up is that whitefly abundance will depend on different factors, such as how wet the winter is and how the season is going. I think that we are just going to have to deal with it. In Central Queensland, this may be every two, three, or maybe five years and hopefully in those other years we have populations that generally don’t exceed threshold in most fields.

There is a level of parasitism out there again this year but not at high levels; is that right?

That is correct. We have got parasitism out there. The numbers at the moment are running at around the 15 -20% level which certainly is not enough to be affective. Hopefully they will build up as the season gets on but it looks at this stage as if the whitefly this year has got the jump on. Alternatively in other years we have actually found those same parasitoids have been much more affective on the whitefly; I guess given that the whitefly populations are a bit slower to develop compared to this year.

Moving on to Mirids. It has been a bit heavier mirid season than the last couple?

Yes; mirids this year were a little bit quite at the start of the season and it just seemed that as soon as we got into those north-westerly patterns that bought with it all that hot weather, we seemed to get steady influxes of mirids coming into the area. As a result, it would be safe to say that most fields have had two to three treatments with Regent® for mirid management during December.

Did these applications cause problems with other pest numbers?

There doesn’t appear to be John. Again, it is always questionable as to whether those applications stir up the whitefly situation but there are some paddocks that haven’t had those treatments and they don’t seem to have any less of a Whitefly problem than paddocks that have been treated. I would say that it is just ‘par of the course’ for this season.

How about other secondary pests such as Green Vegetable Bug or Mites; anything showing up there at all?

Not much in the way of mites this year. It was only this morning that we saw the odd green vegie bug getting around so compared to other seasons, they generally don’t seem to turn up until we are well into that boll setting period. We will have to watch some of those pests because they have certainly got the capacity, given the amount of green material and weeds around the place to develop into larger numbers before the season is out.

Finally, can you comment on heliothis levels during the season? What trends have you seen there?

This year we had really high Heliothis numbers of up until the Christmas/New Year period. A good portion of those populations were actually made up of H. punctigera that seem to appear every time we had one of those north-westerly fronts come through. But generally speaking, even with the H. armigera as well as the H. punctigera, as we have moved into the New Year they seen to have really dropped down in numbers. I guess whether that is to do with the sink affect in our area because we have got such a high proportion of Bollgard II® or whether that is just a lull in the season and we will see numbers start to pick up again over the next couple of weeks remains to be seen.

The difference between this area and Emerald as opposed to some of the Southern valleys is that you haven’t had that secondary spike of H. armigera?

Yes, that is definitely correct.

David Murray, Principal Research Entomologist, QLD DPI&F, Toowoomba.

Here we are mid January 2006 season. How are Mirids numbers on the Darling Downs comparing this year with the last couple of years?

It has been a season of relatively high mirid activity and I guess that is to be expected given the sort of season we have had with some good rainfall (at least at certain periods) which have promoted the weed growth, the alternative hosts and the conditions have allowed a lot of mirids to move into crops and that’s resulted in a lot of cases regular spraying.

The Bollgard II® crops have received two, sometimes three sprays for mirids up to this point in time which is a little bit more than we have encountered in the past. Those mirids I think by enlarge have been affectively controlled by the chemicals that have been used on those crops but there has been some concerns about the high levels of damage sustained, lack of fruit retention and a lot of it is to do I think largely with rapid re-infestation and residual populations of mirids following treatment. Commonly that occurs where you might have a reasonable population of adults in the crop that are laying and there might be some hatched nymphs as well. You would treat that population but that treatment doesn’t necessarily kill nymphs that are going to hatch from eggs maybe 4, 5 or 6 days later. So you have got a residual infestation that would continue to carry on and cause fruit shedding and also we have had re-invasion by adults.

Your comments just highlight then the importance of accurate crop checking for mirids in Bollgard II® crops.

I think there is general agreement that using a beat sheet is certainly the most accurate way to detect mirid populations and the situation we have got is adult mirids are flying in, invading crops almost at any time, and we apply treatments. They are also laying eggs when they invade those crops and when we apply treatment to control the adults (and maybe some nymphs) that are already we are controlling them but there are eggs layed in the crop that might take 3, 4 or 5 days to hatch. So, a week or so later you find you have got a nymph population and if there is a lot of adult mirid activity, it means a re-invasion by the adults. So, it is really important to accurately sample and couple those mirid numbers with what is happening with the fruit retention on the crop.

Now, beat sheets are great if it is dry. But if you have got irrigation or rainfall interfering its very difficult to take those beat sheets out into soggy, muddy fields and try and do those counts. So you are relying on other estimates whether that be visual or sweep netting. At the low densities that we are often looking at, it can be very easy to miss these mirids and hence the approach that some people use is if they see a mired, they spray. But it should always be backed up by what is happening with the crop, but beat sheets by in large are the absolute best way to assess a mirid population, particularly good for picking up those nymphs. First and second instar nymphs are really quite tiny and easily missed visually.

Moving onto other secondary pests that we might have to consider. Lets start with mites; any sign of these in the area?

There are no signs of mites at least here on the Downs at this stage. This is not an area that commonly encounters mites. The first signs of aphids are showing up on some crops on the Downs but again at relatively low levels at this point in time. Jassids (leaf hoppers) are there on peoples minds but in large, with treatments that have been applied for mirids particularly with organophosphates they have suppressed the Jassids populations too.

Green vegetable bug; anything showing up there?

It’s been a season of reasonable numbers of vegie bug in crops generally and Moazzem Khan’s surveys have shown that we have had green vegie bug appearing (at least in weeds) right through from spring time and these are persisting in crops. We are really at the critical time where potentially we will see their numbers increase in crops. So we need to keep a careful eye out for those. The problem with green vegie bug is their patchy distribution and again, beat sheets sampling for mirids will also pick up those vegie bugs very affectively.

Rutherglen bugs were in high density in a lot of cotton and sorghum crops this year, Is there any evidence at all that they may have caused any square loss or any damage to cotton?

We have got no clear evidence that they are causing fruit loss but you have got to ask yourself; given the densities that we have this year (sometimes hundreds per metre), they have got to be feeding, they have got to be doing something and you wonder, ‘are they really doing anything’?. At this point in time we don’t have evidence to implicate them with significant shedding of squares.

Finally, the situation with H. armigera out there in cotton fields at the moment, how are things going there?

It has been a major turnaround to the previous couple of seasons. We have seen consistently high Helicoverpa (heliothis) activity and for us on the Downs there has been predominantly armigera activity. In the past two weeks a great percentage of the grain sorghum have been sprayed for grubs. It’s probably emanated from the previous vegetative crop cycles that have taken place in corn, sorghum and some other summer crops. There is certainly a big population of moths that have been active over the past couple of weeks and we really don’t know what is going to happen beyond this time for the next generation.

Stewart Addison, Senior Entomologist, Monsanto Australia.

We are at that time of year where crops are cutting out and we are getting a lot of fruit loss. Last week you spoke to us about fruit loss as a result of heliothis in Bollgard II®. Can you tell us whether you think that will be a perennial problem or whether it is just a ‘one-off’ this year?

There is the potential to get fruit loss from Heliothis at any stage. I think what we are seeing this year as I explained before is that later in the season, (especially with stress) we are getting different things happening both to the grubs itself with that high rate of development and also with the plant.

With Bollgard II® (which is different obviously than INGARD®), what we find is that towards the end of the season as the protein levels decline, the total protein levels are still very high in comparison to INGARD®; in fact they are similar at the end of the season to the protein levels of INGARD® at the beginning of the season. But where the protein occurs is different. You find that levels in the leaf are generally lower than levels in the square and so your square is more protected than the top leaves. So, it is possible that if the plant is stressed and so expression levels are lower, you may get slightly more activity in the leaves than you would normally. Of course the same thing applies; the eggs have got to hatch out, the larvae has got to take its first feed and generally if it is on the square (or any of the fruiting structures apart from pollen), it will die, and also generally if they feed on leaves they will die. The leaves is where most of our bioassay work is done.

At the end of season upper leaf protein levels tend to be lower than squares, so if you have got a stress factor that’s reducing your levels of expression in the whole plant it is probably more likely to have an impact on those upper leaves. If your larvae gets to a stage where its third instar (large small, small mediums and onwards; which would be a week old larvae), they can generally do more damage before they die and certainly from work that we have done in the past we know that the third instar larvae can do significant damage to the terminal and to squares. But, the opportunity to get to a third instar is very very minimal.

Is this something we are going to be seeing more often?

I would say no. I would say that what we are seeing is caused through stress. When we are likely to see this in the future only those times when the plants are going to be in stress. Bollgard II® generally has high levels of protein season long as we have seen in the past but in instances where they are stressed then; ‘yes’, you have got to check your crop; ‘yes’, you have got to monitor it and watch your pests and if you see activity then you have got to make that decision; ‘is it economical to spray or not?’. You cannot forget to check your crop for heliothis just because it is Bollgard II®.

Dr Greg Constable, CSIRO plant breeder

A lot of crops have shed a lot of small bolls in the last week or 10 days, primarily they have been Bollgard II® crops. Any reasons for this or management that might prevent it?

The reasons generally for this type of thing at this time of the year are very common. When the crop gets a full boll load, there is a lot of competition between those bolls and so the plant is starting to adjust what it can mature fully and those bolls start coming off.

As to what to do about it; as long as the water and nutrition have been right I don’t believe there is much you can do about that at all. It’s a normal thing and it has happened every year and it may or may not be more evident in crops that have got a really full early boll load because everything is coming off at once I suppose.

The other comment that you might make is in relation to changes in plant protein levels. Some of the Bollgard II® crops with high heliothis pressure have been carrying a few more grubs. Is that normal and would you expect to see that at this time of the year. We didn’t see too much of it last year?

It was always the case with INGARD® obviously that the expression dropped off, and it is also the case with the second gene in Bollgard II that expression starts to drop off from what had been a much higher level anyway. So there have been precedents for survivors through Bollgard II crops in the occasional instances in previous years. I think there was half a spray average across all crops there at one stage for some of the early data.

The other issue is late season PIX. There are still quite a few advocates around that are suggesting that PIX might be a thing to do to prevent some of the late season boll shed. Would that work?

I don’t think late season PIX will stop late season boll shed. I think cut-out applications of PIX is probably more of a strategy to prevent this excessive and un-necessary vegetative growth at the end of the season and to have a nice even maturity. So, no I think they are two separate things altogether. If I was having shedding I would like to keep it away from PIX.

We have got a lot of different crops out there this year; those that have got quite good growth and now are in a pretty good position and also quite a few crops that for whatever reason have struggled and have a relatively small stature. Any comments on how those crops have performed and what might be done to keep those crops growing for as long as possible?

There are a lot of relatively small crops around obviously with the amount of Sicot 71 around this year that will be the case. Even just driving around the fields you notice that you can still see the furrows for example. While all of this hot weather was on I felt it was most important to really keep the irrigation schedule and a lot of cases where I have seen that happening I am quite happy with the way the crop has responded. It has continued to make sure that it started to fill in the rows and boll set has been quite good on those. So the key, especially in this hot weather we have had is to really keep up the irrigation schedules.

With potentially some more hot weather coming on over the next week or so as often is in late January/February that will continue?

Absolutely, you would need to keep up that same vigilance with the water.

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