Cotton Seed Distributors - Web on Wednesday

Stewart Addison, Entomologist, Monsanto answers some of this seasons frequently asked questions about insect management in Bollgard II.

Stuart, can you give us a rundown of the performance of Bollgard this year across the industry?

Yes certainly.  This year about 95% or more of growers are using Bollgard II and in total 70% of the cotton this year wearies Bollgard II out there.  So there is a lot of experience being gained this year and if you look at the different valleys, generally people are pretty pleased with what they have seen.  I have got a couple of notes here from the different areas which I could read out….

In the Macquarie, basically very few heliothis sprays have been applied possibly one for mirids but there has been some spraying on eggs.  That’s the only reason we have found that but a few growers have actually sprayed up to two times on eggs on Bollgard II.

The Namoi, the majority of Bollgard II fields had no sprays for heliothis, two or three sprays in total and that’s basically the sucking pests.  Some of the sprays may have included an endo in a mix early on in the season.  They got a bit of high pressure in the Bollgard II as well so they sprayed for mirids and put in an endo for good measure. 

The Gwydir similarly, one to three sprays on Bollgard II mainly for sucking pests and conventional cottons had eight to ten sprays.

MacIntyre, there is only one field as far as I am aware that’s been sprayed for helicoverpa and Bollgard II.  The rest has had no sprays for heliothis  at all on Bollgard II and the Downs has been similar with the odd field sprayed for heliothis but basically none or most of them haven’t been.

Central Queensland has got pretty good fruit retention this year and generally looking it looks a really good crop up in Central Queensland.  I think the milder weather has also helped and virtually no sprays for heliothis with two sucking pests sprays and they are spraying for white fly at the moment.  So overall the majority of fields would not have had any sprays for heliothis a few have had one.  So that is where we are really.

Some of the areas, particularly Bourke, Dirranbandi copped some pretty heavy pressure there prior to Christmas in excess of 200 eggs per metre.  How did the Bollgard handle that sort of situation?

Yes I had reports of 170-200 eggs a metre which is pretty heavy before Christmas and none of those fields are sprayed for heliothis so, and when you look at the retention – retentions being good, so even in those areas where there has been influxes of punctigera coming in we would expect then there may have been some fruit loss, some square loss just due to initial grazing.  That’s not been the case and generally there is good retention there without having to spray for them.  So it has held up well.

There has been a few instances in the last month or so where people have been finding heliothis in Bollgard II crops, can you talk about some of those situations?

Yes, certainly, we have seen some activity, helicoverpa in Bollgard II this year.  Last year we saw some with some of the large scale trials and with that large area now out there of Bollgard II it has been easy to try and detect what is the reason for the presence of larvae and there is probably something in the range of 3500 – 4000 fields of Bollgard II out there at the moment and twelve cases have been reported where growers have been concerned that they have either got some damage or some presence of larvae – what’s happening – should I spray – is the Bollgard II working, whatever.  We have looked at these sites and done quite a lot of work, we have collected samples of material, samples of larvae reared them through but we have come to a conclusion.  There are two basis reasons why you would get some activity inside Bollgard II.  Firstly is what I call the presence of nurseries.  Now a nursery could be presence of weeds in the crop, presence of non-BT volunteers.  It could also be the presence of a weedy edge to the block or even in some cases an unsprayed refuge next to the block also associated with heavy pressure.  So what you are getting is heavy pressure, the grubs are emerging from the eggs on the Bollgard II and they are dying.  But on the nurseries they are surviving.  You are getting grubs growing on suspania or on volunteer BT or even on your pigeon pea next door and when they get to a certain level there is a lot of competition there for the food so they move out, and they move out where? They move out to the Bollgard II.  They don’t like the Bollgard II so they travel and we have seen evidence of movement after 40 metres from a host plant to where they have actually eventually damaged the Bollgard II plant.  So what we are finding is that it is not developing on the Bollgard II it is developing on a non-BT nursery but they are getting to either a third or forth or even fifth instar before they then come and invade Bollgard II.  So they are bigger, they are tougher and they can do so minor damage and what we are finding is that the kind of damage that they are doing is there boring into stems below the top of the plant.  So probably six inches or so below the very top of the plant they are boring into the stem and causing the top to sort of flag over and fall down.  That is the most common damage we saw early in the season.  One instance I will give you, there was a farm with a very weedy edge to the border of this particular Bollgard II field and it was full of suspania, it was full of helicoverpa and we found the first two or three rows next to that edge had perhaps one to three plants a metre where there was some damage to the plant. Not necessarily serious damage, some damage, these were less than 15 nodes.  We went in 40 metres from the edge and you could just about find the odd plant that had some damage.  After that nothing at all.  But these were 4th and 5th instars that had moved across the ground, crawled up, chewed into the side of the stem and then they died.  We took samples back to the lab, reared those grubs through a normal diet and nearly all of those died, so they had already had enough toxin through damage in the plant to die so they are not going to come through and pose a resistance risk.  I guess what we are getting from this is that in situations where a grower has a volunteer issue from previous year or he has a weed issue because he hasn’t been able to do the weeding well you can get scattered damage throughout a field under high pressure conditions.  If you have got an edge effect maybe due to presence of weedy edge or unsprayed refuge where they can move in a few metres from the side and cause some damage.  Only in one instance was it deemed economically worthwhile spraying and a grower did two swaps down the border between a refuge and his Bollgard II.

Whether that is effective or not is questionable because the grubs were pretty big at the time.  So that is the first instance, which is nurseries.  The second instance where you get damage is where you get high egg pressure in peak flower.  And what you find in there is you are getting a lot of small larvae developing or hatching out on a plant so the opportunity to hatch out near or on a flower is much higher at peak flower and what you can see sometimes is little raspy marks on the side of the candles, the petals in Bollgard II have high expressions of BT so that they are not going to be affected but when the flowers are open the neonates, the small larvae can then feed on the pollen and the pollen has no BT or very low BT so they can survive on the pollen and you can see some plants where they have grazed around the outside of the anthers there.  They can move from flower to flower during the peak flower period and grow up to quite large size.  When the flowering starts to decline and they start running out of food it is then that they go and look for something else then you get this fourth or fifth instars and they are real big worms and they can bore into the base of a thumbnail size boll and sometimes you may get them later into the season into a large boll and typically you will get a round mark, it may not go right through the boll, no feeding inside but just like a shot hole and the grub dies and its just one boll on a whole plant that is affected and nothing else which is very different from your normal damage.  So again from peak flower, a heavy egg lay you can see some boll damage but its not been seen anywhere yet where its really been worthy of treating as a result.   So what we are looking at here is trying to determine when do you spray on Bollgard II because using ordinary larval thresholds as with conventional cotton is obviously not going to be sufficient because the larvae can be there through the presence of hosts or as I described they are not actually be causing damage or therefore a threat to yield.

So you have been collecting as you said before a lot of larvae from these crops.  Were all of them perished before you have been able to do any testing on them?.

What we have done, we have tested them several ways.  We have put some on a BT diet, we have put some on a plant diet that’s just expressing say Cry2ab and those instances 100% have died.  We have also put them onto a normal breeding diet which is how we develop helicoverpa in the lab and 95% of those died.  So 95% of them had had enough BT through their grazing to actually kill them.

So in these situations resistance isn’t an issue?

No, its not been, not caused any concerns for resistance and in fact all the resistance monitoring done so far we have still found no resistance at all to Bollgard II, so we are pretty happy about that.

Later in the season, is there going to be variability between the expression in different parts of the plant?

You will find as with INGARD® as the seasons progresses the level of BT will decline in the plant.  The difference is that the level should still be enough to control helicoverpa even right up to the end of the season.  There’s high levels in the petals so you may see some little distortion of petals where there has been a bit of feeding but no real damage and the same with the bolls and the squares.  What I have seen last year in one place was right prior to harvest when some of the bolls were already cracked and opened we were getting some damage in some larger bolls like real bore hole damage.  But this was in a site, it was a trial site it had conventional cotton in strips going through this site so there was no more than about six metres from a conventional cotton strip  to where the Bollgard II was.  That could again be something just moving across and feeding late in the season but certainly the levels of BT in all parts of plant except the pollen should be sufficient to right to the end of the season.

So just in closing, if people are finding larvae in Bollgard II crops what do you suggest they do?

No panic to start off with.  Try to identify why.  Is there a weed issue? Is there a volunteer issue? Have they got really heavy pest pressure in an adjacent weedy area or unsprayed refuge?  If you can identify one of those then you have got a better understanding of what the consequences likely to be if it’s a weed issue or volunteer issue you may have presence of larvae throughout the whole field.  If it is an edge effect, its likely to be 10 – 20 metres on the edge of the field.  The questions is to have a look and say ‘if I spray this, is it going to do any good, are the grubs too big to control and if I don’t spray am I going to suffer any economic losses.  So it is a question of making the decision, is it worthwhile to spray.  But make that decision, don’t spray automatically and don’t just wait and hope it will go away.  Look at what you have got and assess it and if they need assistance they can call their Monsanto Business Manager and get some advice or help from there but basically it’s a consultants decision based on economic loss.

And based on what you have seen this year, what should people be thinking about in terms of where they plant and how they plant their Bollgard II next year?

Well, I think what’s come out very clearly is to factors.  One is the presence of non BT volunteers is obviously a risk and growers should be very careful to make sure if they are planting Bollgard II behind conventional cotton next season that they have very good control of volunteers and regrowth.  And secondly infield weeds again is a great opportunity for pests to develop on those weeds.  So good weed control.

Further Information:  David Kelly