Soybean South

 - Southern Specialists -

Consider Fungicide Timing And
Potential Benefits

By Dr. Alan Blaine, Mississippi
ablaine@ext.msstate.edu

When considering fungicide applications, everybody is worried about rust to some extent, and rightfully so. But as of today (the third week in May), there is not any rust.

We need to time our fungicide applications based on what we are trying to control and what is in the field.

Some farmers say they are going to spray in the next seven to 10 days because their beans are at R1 to R3. But because those soybeans were planted early, they will begin the reproductive stage when the plants are shorter and have not achieved all of their vegetative growth.

In an early planting system with indeterminate varieties, the plants will achieve between 13 and 17 nodes, adding 40 to 60 percent of their growth from the time you see the first bloom on them.

If you don't have rust and you spray before the plant has achieved all of its vegetative growth, you're taking a risk that you might have to make a second application because you will have unprotected foliage regardless of what the disease is.

In addition, considering how early it is, any fungicide will not have the staying power to control foliar diseases that may develop later.

There is still a lot of uncertainty out there about what to do and when to do it from a fungicide standpoint. The main thing is to think about what you are trying to control and the stage of the crop.

Don’t pull the trigger too fast on protection from some diseases – particularly rust – if you don’t have rust and your plants have not achieved all of their vegetative growth.

Kick it up a notch
If I get my beans to the R3 stage or later and am making a pre-rust application, I'm going to have a strobie (strobilurin fungicide) in my program because of its broad-spectrum disease control. I may use a mix, but we consistently see a positive yield response to using a strobie-based program.

I still think that with no rust I can grow a good crop of soybeans without a fungicide. But, we have supporting data that says fungicides (a strobie-based program), particularly in the Deep South, will not cost me money. It may not make me any money, but it will not cost me any money.

If you want to step up to the next level, a fungicide is going to be part of that program, whether you're planting a Group IV or a Group V soybean.

If we get the right weather and have higher than average rainfall for the rest of the summer, you have the potential to get as high as a 20-bushel yield increase response from a fungicide. If you don't put it out, you won't have that opportunity. If we don't have above average rainfall and it's a somewhat dry summer, you will still get enough yield response to pay for that fungicide application.

So you have to decide: Am I in a high yield environment? Am I pushing my beans for that higher yield? If you answer yes to these questions, then a fungicide needs to be a planned part of your program, and it needs to go out at the proper time.


Herbicide Application Reminder For Next Year
The time of the season has already passed for this tip for the 2006 soybean crop, but it is worth remembering for next year.

Many growers who are using the early planting system are getting in too big of a hurry to make their first post-emergence herbicide applications.

When we are planting in March, not only is the crop slow emerging, but the weeds are, too. For example, even if a morningglory emerges, it may not become competitive for three weeks or so.

Growers need to look at herbicide application timing based on when they have the most weeds emerged. When they don’t go with this approach, I’ve seen many people get themselves into a more-than-one-shot scenario and sometimes a three-shot scenario where pre- materials haven’t been used.