Cotton Seed Distributors - Web on Wednesday

Graham Charles NSW DPI and CRC, and Roger Henderson, Monsanto, Dalby touch on some important issues in relation to effective utilisation of Roundup Ready cotton this season

Graham could you tell me with the widespread use of Roundup Ready® now evident across the industry, are there any discernable trends in the use of the residual herbicides and their application rates across our industry?
 
Sure Adam. There has certainly been a reduction in the use of pre-plant residual herbicides.

The tendency in the past to use particularly Treflan and Diuron prior to planting is greatly reduced. Very few people are doing that now. I haven’t seen a lot of evidence of reduction in rates to any great extent.

It’s more just been if people have either dropped out that pre-plant application or certainly with the at planting, it’s very much a band almost nobody’s using broadcast applications: quite a few people have dropped that application as well.

The timing of the over of the top application of the Roundup Ready herbicide is one of the keys to getting value with that technology. What are some of the strategies being used by growers to ensure that that happens and it happens at the right stage?
 
That’s a difficult question Adam for a grower and there is no easy answer to it. If there’s a heavy weed flush, obviously the grower has to ensure that he gets an over the top application, so he has to go earlier rather than later on that fourth leaf stage.

If things don’t work out he can always get a second shot but he’s got to make sure he gets that fourth leaf application. After that it’s really a matter of resources, having the ability to apply it at the best time and being able to pick that best time.

Roundup obviously always works best after an irrigation, when the plant’s actively growing and it’s a matter of being able to get around the property as quickly as possible when it needs to go on.

Graham, in using a Roundup Ready system where grower’s have nut grass as the major weed problem, what’s the best way to use the Roundup Ready?
 
Adam its pretty well covered in WEEDpak. The strategy that we’ve outlined there works very, very well with Roundup Ready cotton.

The main thing is that the grower has to be careful not to get his two applications on too early. It really is a matter of the product working best in November, December and January so an application around November’s fine but he’s got to be able to get a December and a January application down to get a good result and it has to be those two applications.
The real dilemma of course is to try to get Roundup on the nut grass without getting any contact with the cotton plant in those later applications: that’s the challenge.

Early storms have resulted in damage to seedling cotton from residual herbicide movement in a number of valleys this season. Has there been any indication of this early damage affecting the cotton plant’s tolerance to the Roundup Ready herbicide?
 
I’m not aware of any problems at this stage and I wouldn’t expect to get them, but the thing about Roundup is that as with most herbicides, works best on actively grown plants, so if the plants are stressed it’s likely to have less effect on them. 

Where you actually are likely to run into a problem and we probably saw some last year was where plants are really actively growing, in combination with high humiditys, under those circumstances the Roundup Ready herbicide actually did do far more damage than we expected from applications that were less than ideal.

Roger, what is the current recommendation for decontamination of boom sprays before over the top application, especially when glyphosate tank mixes have been used in the fallow spray?

Over the last couple of years there has been some concerns with people getting contamination and knocking some crop around.

So the suggestion after any Glysophate mixtures would be plenty of clean water and particularly cleaning it out after that glysophate or after that Roundup application prior to going onto your cotton.

A comment, Roundup Ready cotton is tolerant to Roundup Ready herbicide only, it’s not tolerant to any other chemical group, so what we need to do if you’re spraying some SUs or maybe worst of all 24D prior, maybe you may need to change your boom spray but also look at the chemical label that you’re using and it’ll certainly have decontamination recommendations on it.

There are a lot of different chemical groups and there are some different procedures for different products. The one I use personally quite a lot is a Nufarm chemical equipment cleaner and it’s got a very broad spectrum and will clean most products from your boom spray.

As well as cleaning out the chemical from your boom spray, take particular notice of the pump, any transfer systems you have between tanks and your boom spray and pay particular attention to filters. If you get a little bit of scum or build up in those filters, that can give you a carry over.

If you look at those three or four different points, you shouldn’t get carry over and the crop will grow very, very well through a Roundup Ready herbicide application.

Drift is a real concern with over the top applications because of the minimal catching surface with the small crop and the susceptible non tolerant crops in the neighborhood. What are some basic practical tips for reducing the potential damage?
 
Yes John, potential drift from Roundup Ready herbicide is there, particularly if you’re spraying bell vine and larger and older weeds, using the higher rate, 1.5kg per ha.

I suppose the main thing with drift up to the fourth leaf stage is that it’s a normal boom spray, you’re putting on from 40 to 60L water per ha, so the main areas I would look at to try to reduce drift would be: nozzles, if you have any concerns I would go up a nozzle size to produce a slightly larger droplet.

The other main one is nozzle height or release height of the product. Again if you think it’s a bit breezy, reduce your nozzle height and that can certainly reduce drift.

The main concern I have with spraying and drift is that it’s not only your crop, it’s your neighbor’s crop that a small amount of Roundup Ready herbicide can certainly affect growing sorghum, even conventional growing cotton crops.

So apart from those mechanical things either changing height or going to a larger nozzle the other main thing is weather conditions. Again, continuing monitoring of the spray day, not just at the beginning, but throughout the whole operation, wind being the main one.

You need some breeze, and I suppose some breeze at least gives you the direction of where it’s going to, and you can make changes to larger nozzles, or maybe completely stopping and leaving the spray operation to the next day. Another issue is humidity.

We know that in a very high humidity situation, which is not often encountered on the Downs in most of the cotton-growing belt, that droplet persistence is a lot longer. If it’s extremely dry, droplet persistence is quite short so the drift ability concern is generally reduced.

What guidelines should be followed for reducing drift when we’re putting on Roundup Ready herbicide in crop?
 
Reducing drift in crop is most probably more concerning the grower himself to keep the product off the cotton plant. If we go back a little bit, the thing we need to remember is any Roundup Ready cotton plant should be treated similar to conventional cotton, so we’re saying realistically to try to keep as much Roundup off the plants as possible.

But inter row spraying is very successful. The main area that we’re looking at is with any inter row spraying equipment is that you need to have it set up correctly so the spray is only touching below the cotyledon scars, so we can’t be having it going up into the plant.

A couple of simple things there is maybe crop lifters to get any low crop out of the spray coverage, and the other major one is speed or speed in relation to rough country. We’ve seen a lot of trials where the quicker you go on rough country, a little bit of bounce occurs and that’s where we certainly get this eight or twelve row configuration with taller plants reflecting a little bit of Roundup drift up into the bush.

The other major one is direction of nozzles. When you’re spraying normally you have a vertical pattern from your spraying nozzle. In inter row spraying we’ve certainly taken it lower by going out to a 70 degree angle to the ground making it a lot flatter.

The main advantages of this is: getting better direction, and I think a lot of times, getting better coverage of our weeds. When I say direction you can certainly place that direction in across the furrow and onto the plant stand and it’s quite simple to direct this and it’s quite accurate so I’d certainly look at it that way.

The other one is that generally with inter row spraying, people are going a little bit slower, so the need to get over a big area in one day with water quantity is not as big a problem.

I suppose what I’m saying is that if you’re ever in doubt maybe go up a nozzle size because as we all know, the larger the nozzle, the larger the droplet. Keeping the pressure constant will give you less drift. If you think you’re getting drift go up a nozzle size and that should remedy any concerns.

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