Optimizing the Roundup Ready wonder gene

Roundup Ready gene is the greatest technology that has happened in corn since the introduction of atrazine. But we have to change some engrained ways of thinking to make the best use of itext here second tittle

by PAT LYNCH

There will be an increase in Roundup Ready corn in 2007 - and the years beyond. The seed companies are driving this. The bulk of the new hybrids this year from some companies have the Roundup Ready gene. From the discussions I have had with some of them, this trend will continue.

When I speak with growers, there appears to be some frustration with the fact that new genetics will appear with the Roundup Ready gene first and then possibly be introduced without this gene. To those who do not like this, I can only remind you of the other Golden Rule - 'He who has the gold makes the rules.” In this case, the gold is the best hybrids.

Knowing this, figure out a plan for weed control in Roundup Ready corn and soys. The first thought is that volunteers from each of these crops will be a problem in the other crop. This is the least of our worries. Numerous products, such as dicamba or atrazine, do a great job controlling Roundup Ready volunteer soys in corn.

Similarly, there are lots of grass herbicides (graminicides) that control Roundup Ready volunteer corn in Roundup Ready soys. Research by Dr. Peter Sikemma of the University of Guelph shows that at least one graminicide that is registered on soys already does a great job, at a reduced rate, of controlling volunteer corn in Roundup Ready soys.

There is, however, an issue with glyphosate resistance and it is real. It will not happen as quickly as resistance to Group 2 herbicides, but it will happen.

A bigger issue is weed shifts. As you switch to a non-residual herbicide like Roundup, there will be a switch to other, later-season germinating weeds. They have some real beauts in the United States, such as giant ragweed and waterhemp, and thanks to modern combines they have quickly spread over a large acreage. In Ontario, we are seeing an increase in chickweed in Roundup Ready soys.

For 2007, the biggest issue is yield loss due to early weed competition. Too many growers lose yield before the first application of glyphosate. Abundant research points to yield loss due to early weed competition, and there is even research showing a yield loss if there is a 24-hour delay in spray times. This is when corn is sprayed at the second and third leaf stage. If you wait until the fifth or sixth leaf stage, you will suffer a higher yield loss, even though you get clean fields.

The solution is simple. It means not focusing on the fact that you paid a Technical Use Agreement fee for the Roundup Ready gene and now want to recoup that fee on weed control savings. While you are saving herbicide dollars, you will be losing dollars by lack of early weed control. This is a significant change in the way we think.

The solution is to use a pre-emerge or ppi herbicide for early weed control in Roundup Ready corn. There is where you can consider using reduced rates of herbicides to get the early flushes. Then you come back at the fifth or sixth leaf stage, or whenever the weeds start to break through, and finish them off with an application of glyphosate. If you have scouted the field well, you can even use a reduced rate of glyphosate to keep costs down.

This strategy, while different from what you are used to, handles the problems of weed shifts and resistance as well as protecting yield from early weeds.

In Roundup Ready soys, a similar method can be used. Many Roundup ready soys are being no-tilled. Some growers are opting to forego a burndown and just use one trip, early post-emergence. I believe this to be a mistake. Early weed competition reduces yield. As well bigger weeds are harder to control.

If they get too big, some of these weeds, such as Spreading Atriplex and even ragweed, become extremely difficult or impossible to control once they have reached a certain stage.

Roundup Ready gene is the greatest technology that has happened in corn since the introduction of atrazine. But we have to change some engrained ways of thinking to optimize this gene. BF

Pat Lynch CCA (ON) is head agronomist for Cargill in Ontario.