From Cotton Seed Distributors
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Jonathon, there are virtually no soft insecticide options left for heliothis control from now on for most of the cotton growing regions and with a lot of the crops running later than normal some of the more traditional insecticides I guess will be required to finish the crops. Firstly what are the main options left for growers?

From a conventional point of view these are products that people haven’t used much in the last two or three years of light pressure and they’re the older conventional groups like Pyrethroids, the carbonates, the OP’s with a back up of a few ovicides and some biological insecticides also still available for the rest of the season.

Going back to a stand by of products that are still quite useful, used the right way, Pyrethroids offer good control and particularly in a lot of regions punctigera is still quite dominant surprisingly but what mixtures should people by considering with the SP’s to get the best out of them?

Well there are some good guidelines for the use of mixtures in the cotton pest management guide. Stepping back a bit from just pyrethroid mixtures the first considerations that people have got to think about when they have a crop at this time of year is what sort of residual control are they going to get against that primary pest if it’s heliothis, which it often is.

What secondary pests are also present in the crop, because that can affect the mixture partner that you choose? For example, if they were mites in a field you might choose to mix Comite or  propargite with a pyrethroid rather than with pyrethroid PBO.

They will give you same effect on heliothis but the propargite will give you some activity on the secondary pest in the field. If you have aphids in a field that were resistant to OP’s then you might not choose to go with the larvicidal OP for heliothis control because you know that that’s going to flare your aphid resistance problem. So what else is happening in the crop is important.

There aren’t that many beneficials around at this time of year but if there are beneficials that are there that are worth preserving then that’s a concern and then there are some other after cost effectiveness, residual control, other pests and beneficials then there are some other important considerations like odour, some of these conventional older products do have odour associated with them, some of them will cause phytotoxicity.

You can grow a cotton crop with just these products but I think there are quite a few people on the industry a bit out of practice of how to use them and get the best value out of them.

Going back to that issue with pyrethroids and using PBO and Comite, do they both provide similar synergy in terms of controlling heliothis?

From a mode of action point of view yes essentially they are both doing a job knocking out some of the enzymes responsible for the metabolism of the pyrethroids. From an efficacy point of view one thing that needs to be bought in mind with PBO is that piperonyl butoxide (PBO) is a natural product, it’s not very stable in light and so in the sort of conditions and temperatures that we’ve got at the moment you wouldn’t really be advised to be putting PBO out with a pyrethroid spray that was going out in the morning. If it’s going to be on the field all day exposed to high UV in these conditions then most of that PBO is going to get broken down. In those situations you’d either be better off spraying the PBO pyrethroid in the evening or if you so have to spray in the day and you want to synergise your pyrethroids in that way then move across to propargite.

What type of resistance won’t those synergists  help with?

There will be survivors. On the whole resistance question, first of all know what species your dealing with. If there’s punctigera in the field then we don’t have any established resistance problem with punctigera so these older chemistries should provide and have been providing really good control there.

Now if there are armigera predominately in the paddock at this time of year there’s good information available from the CRC from Robyn Gunning’s program and Louise Rossiter. Consult that information where it’s available and don’t panic. What people need to bear in mind is if there’s a figure that says there’s 50% resistance frequency or X% resistance factor that does not mean to say that if you spray that group of chemistry 50% of the grubs in the paddock will survive.

It’s just as important that you’re targeting the timing of that product is spot on and you can still get good cost effective performance out of it. So the numbers are not directly predictive of field control.

Getting back onto performance then and targeting, what is the best stage to apply that pyrethroids?

Well whether it’s pyrethroids or other older larvicides such as OP’s and carbamates, we’ve got really little resistance in eggs or adults for that point of view and once you start targeting larvae at this time of year the bigger the larvae the harder it is to control with any of those products.

So, where people get heavy egg lays, the use of an ovicide is a pretty good idea. You’ve get either Amitraz or  Ovasyn, which you can mix with those larvicides and take the pressure off them. If you’re controlling 80% of the eggs before they hatch then you’re really only asking the larvicide to provide you an effective control of the 20% of eggs that are left over; it’s a numbers game.

Moving on to another major group, which are the OP’s, any tips from getting the best performance from those?

I haven’t had a lot of experience with the OP’s to be quite honest with you. They are used and where there are susceptible sucking pests, so that’s aphids that are susceptible to OP’s or Mirids in the crop, they can have a fit because you’ll get some suppression control of those secondary pests.

There are some down sides and some pit falls associated with OP’s that people have to steer around. Issues such as crop burn and odour. Every year somebody seems to come up with a combination of two OP’s in the same mixture and use that as a control measure for heliothis and we don’t really recommend that from a TIM’s or AIRAC stand point because mixing two lots of the same insecticide group is putting on a really heavy selection pressure for resistance and won’t necessarily give you better control than just going with the full label rate of the single product.

Another useful product that’s still around is Larvin or Thiodicarb. Any tips on how it may be best utilized, I mean there’s an option of using it as a overcide now or maybe at a higher rate a little bit later in the season. What’s your opinion there?

Well all the carbamates, so Thiodicarb or Larvin and  Methomyl can only be used now in the stage three and that’s been dome for a resistance management point of view. You’ve got two ways of going with them.

My preference for the two between methomyl and thiodicarb it’s always been thiodicarb because it’s a much more residual product, so you can get it onto a cut out crop and it will be stable in these conditions. It’ll be stable whether you’re using it to control eggs and it’s a pretty good ovicide just as it’s an effective ovicide as something like Amitraz or Ovasyn so you can use it there.

Take mixture with the likes of pyrethroids or even OP’s or you can put it at it’s larvicidal rate and chase smaller grubs, hatchlings, neonates with Larvin and get good residual control of those. I wouldn’t recommend people go out and use any of these older products to trace small, medium, large grubs and I appreciate there will be the odd one out there in the crop but sometimes it’s best to let them go.

Moving on to the few softer products that are available and the fit they might have, the BT’s and the products containing viruses, where do they fit and any tips on getting the best results out of those?

From a resistance management point of view the first thing to clarify is that the foliar BT shouldn’t be used on the Ingard/Bollgard refuges. That is important even if people are wanting to control the heliothis there, they shouldn’t be doing that with a foliar BT product because that would undermine the transgenic resistance management strategy. People are using them outside of those refuges.

Both the biological products that are out there are not that stable under high UV and these sort of temperatures at this time of year, so that’s worth considering, you know an early morning application and a lot of your biological will be gone by the middle of the day.

Having said that there’s no resistance to either foliar BT’s or the viruses and you will get a percentage control of the grubs that are in the field regardless of that size, so in the past people have used products like Gemstar in mixtures with older larvicide to try and chase a percentage of those larger grubs, the smalls the mediums that they think might slip through say a pyrethroid or a OP or a carbonate spray.

Obviously application is a very important thing to get the best out of any insecticide. Any tips on improving application or getting the best results from insecticides?

There are some good application experts in the industry that know a lot more about this than I do. I can tell you from an efficacy point of view that the current conditions are extremely difficult, they are very hard on products whether they’re stomach poisons or contact insecticides and so if you’re spraying them at 35-40 degree day, you’ve got to appreciate that there’s going to be a lot of evaporation between the nozzle and the catching surface.

And keeping water volumes up, that would be the only thing that I would recommend to people, so for the stomach poisons if it says 30L on the label, I would be airing on the 35L per ha of water rather than 25L because you can guarantee that a fair bit of that water will be evaporating in conditions like we’ve got today such that if there is only 20L per ha equivalent by the time it gets to the crop then some of those larvicides are really going to struggle to work.

The other thing is the options available for a lot of those older products too. Are they are better choice in these present conditions?

Well anecdotally people that have been around in the industry for a long time would say that ULV formulations of certain products hold up well in the heat. A good example of that in the old days was endosulfan ULV’s , which are often used in preference to EC’s when things got hot. Not all of the older products are still available as you ULV applications so people just need to check the label and look into that.

The other issue is up until now the Ingard’s and probably the Bollgard’s are still holding on fairly well but there is sometimes some requirement for supplementary control. Any comments on the best way to go about that and what might be required?

Only that at this time of the season, if transgenics are requiring some supplementary spray for heliothis you’re not asking the larvicide to so as much work on a transgenic crop as you’re asking it to do on a conventional crop across the paddock so that’s a situation where perhaps you don’t have to go in quite as heavy, quite as hard on a transgenic crop knowing that although it’s not reducing grubs below threshold, if it’s requiring a spray it’s still providing some level of control and a bit of incremental control on top of that with a larvicide. You really don’t need a sledgehammer to crack a walnut in those transgenic crops to get them back over the line.

Jonathon Holloway – Represents Bayer CropScience AIRAC (Australian Insecticide Resistance Action Committee), which is one of the contributing bodies, which feeds into the TIMS committee to develop resistance management guidelines.