Dr Lewis Wilson, Principal Research Scientist and Ms Tanya Smith, Technical Assistant - CSIRO - discuss aphid management strategies for the upcoming season.

Tanya you have done some aphid surveys in the Lower Namoi Valley. Could you tell us what you have been finding out there?

There is a lot of different sorts of aphids. Not much in the way of cotton aphid or cow pea aphid. I haven’t found any Myzus persicae (green peach aphid) but they are there and they are there in low numbers on hosts which are quite common still at the moment so they are going to keep sustained. But most of what is around is the green pea aphid which is on the medics and some of the daisy aphids, sour thistle aphid and brown sour thistle aphid and they are not going to be a problem with the cotton.

So that’s good news. So as far as a cotton grower looking at his crop for aphids, what should he be looking for at this time of year?

He should be looking for breeding aphids so particularly non winged aphids. If he goes into his crop and he sees winged aphids then he should keep an eye on them. Watch and see if they are breeding and if they are producing young. If they are producing young then he needs to see if their going to continue to develop or if there going to be controlled by the predators that are out there and there are a lot of beneficials around at the moment, which is good news.

What are the main beneficials that are going to be feeding on aphids at this early season?

There are a couple of flies. There is quite a few of the syrfids around. Its probably a little bit early for the chamaemyads but there may be a few of those around as well and there is a lot of lady beetles showing up at the moment and a lot of brown lace wing adults which means that the larvae are going to build up.

So generally, although there are a lot of aphids around there is not that many at the moment that are the type that affect cotton and there is good beneficial numbers?

That’s right, yes but they are there and the hosts are there so it is good to keep an eye out and just see what happens. If the season progresses well and we get lots of rain then they could become a problem.

Tanya is there any situations that are sort of potentially higher risk where the crops have more chance of getting an aphid infestation?

Crops or fields that haven’t been kept clean, where the weeds have been let go and particularly fields where there are some cotton that’s come through from previous seasons. Which allow the aphids to winter over and then they can go straight from the weeds on to the cotton crop which is coming through.

If you find a situation where aphids are breeding up and multiplying in the crop what sort of guidelines should be following in trying to get some control?

The most important thing is to be selective. Try and keep away as much as you can from the broad spectrum sprays, but also you need to watch for aphid resistance. As far as that goes, your local IDO has a test kit. You can send a sample of your aphids in and they can test it and tell you whether there resistant to OP’s etc or not. The reason why you want to be selective is because you don’t want to get rid of your beneficials. You loose your beneficials you loose a major control agent there. Once you know what your resistance level are then you can look at what you have got and you can work out what your best control options.

Growers would also need to think about what their seed treatment was to make sure they are not following?

Yes that’s right. You don’t want to stick with the same group. You want to vary your groups of treatment so if you are using a particular seed treatment then you don’t want to use that same group when you are spraying to control later on. To find out what you should be doing the best way to go would be to refer to your Cotton Pest Management Guide and that will give you the information that you need.

Can you outline why we need to be selective with out control measure?

You need to keep your beneficials basically. Your beneficials are a major factor in the control of your aphids and other pests. You wipe them out and you are taking a step backwards.

Why is it important to know what seed treatment we use when we are considering a control measure for aphids?

Well you don’t want your first spray that goes on to be from the same group as your seed treatment. To find out more about that you can refer to your Cotton Pest Management Guide and that will give you the information that you need.

Lewis, early season, what should growers be considering as far as thrip dynamics?

Well, this season because there has been rain through winter there is a reasonable amount of vegetation around and thrips have been breeding on quite a lot of that vegetation. So in thinking about things like turnip weed, wheat crops, they will all be producing thrips at around the same time as the cotton is coming out of the ground. So I expect this season should be reasonable in terms of thrips numbers.

For the growers, what that means is they are weighing up the risk of thrips causing yield loss, versus the benefit they provide in terms of helping to control mites as a pest. For growers in the cooler regions, the risk of yield loss is a bit higher; it is about 1 year in 2. In a year like this they might consider actually taking some protection against the thrips whether it is the seed treatment or an in-furrow option. In the warmer regions the risk is probably lower its about 1 year in 10 and even though this year has potentially high numbers growers will need to weigh that up.

Particularly with Bollgard II where they might be sowing a little bit later avoiding some of the thrips and also it has such good potential to recover because it is not going to loose fruit to heliothis later on.

In terms of options, really the seed treatments or the in-furrow insecticides are much more selective and there probably the first option if you want to manage thrips. Coming in later on with a foliar spray is another option but it is potentially riskier, because the sort of products that you will be using such as Ometholate or Dimetholate tends to reduce your beneficial numbers. So then you run the risk then of inducing an aphid or a mite or potentially a white fly problem.

As far as a season like this, is spidermites potentially a problem early?

Same sort of thing with spidermites, there are plenty of hosts out there that mites will do well on so things like this year. If you look around they will do quite well on turnip weed, quite well on marshmallow, they do OK on the medics and other weeds that are around like sour thistle and wire weed. All those things are potential hosts so I think we have more potential this year for a mite problem than we have had in the last few years.

So the actions the growers should really be taking there is to look at their situation. If they have got lots of weeds in or around the paddock they have a potentially higher risk. If they are next to a crop that could have carried mites over such as faba bean they should take that into account as well.

Then they should be sampling early in the season to establish what background mite population they have got because that determines then what sort of strategy you might take. For instance if you have got lots of mites, your definitely got to go more selective you may even need to control those mites. If you have got low numbers of mites you might be prepared to sit out and just let the beneficials take control. So really it is a case of judging your risk in the situation, monitoring it and taking appropriate action.

So for thrips, mites and aphids there seem to be some common themes coming through, could you sort of summarise those themes for us?

I guess the common theme is that we have had a wetter winter than the last few years so there is potentially more hosts there for all of those pests. For all of them as well, the real keys are knowing what you have got, so good sampling which allows you make good decisions and then preserving the beneficials as far as possible. So that is either by not spraying if you don’t think there are yield implications or by using selected products where you can.

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