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Tips for spraying Roundup Ready cotton

Glyphosate may be inexpensive and easy to use, but haphazard and improper spraying of the product can lead to big problems. To keep problems to a minimum, Monsanto's Anthony Mills often talks to farmers about how best to use Roundup Ultra.

“When someone asks about Roundup Ready cotton and what they should do, these are some of the things I tell them immediately,” says Mills, who spoke at the Monsanto Center of Excellence Field Day in Yazoo City, Miss., on Aug. 15.

Plant clean

Of utmost importance is starting clean at planting time. Some farmers accomplish this with tillage, some with a burndown application. In these hard economic times, when everyone is trying to save as much money as possible, it's becoming more popular to go with a burndown, says Mills.

“In fact, the burndown I recommend for either a Roundup Ready or conventional variety is a two-shot program: an early burndown in February to get the winter annual weeds, and a second shot at planting to get the early-emerged summer weeds. I know each field is a bit different, and you can vary off that a little. But as a general rule, a two-shot burndown is a good idea.”

Target small weeds

“You want to nail the small weeds less than 3 inches in size. You've got to hit the weeds early, especially if you've got morningglory or hemp sesbania.”

However, if a farmer gets into wet weather and the weeds get large, he shouldn't panic, says Mills. The farmer can still get atop the weeds, but it will mean even more vigilance and early spraying for the rest of the season.

The label allows two over-the-top applications and two post-direct applications of Roundup made two nodes and 10 days apart. If a farmer gets a bad weed problem, he needs to press the applications as close together as the label allows, says Mills.

“It's hard to stand before a group of farmers and make general recommendations, not knowing each farmer's field. There are times when I've suggested a farmer use some other company's product if a salvage situation was needed. It's in Monsanto's best interest to help the farmer, whether he's using our product or someone else's.

“I know this: I've seen some big jungles cleaned up with nothing but Roundup. That includes large morningglories.”

Avoid cultivation

Farmers should try and keep from bringing weed seed to the surface. This is especially true if you don't have a pre-emerge herbicide down.

“I recommend that you not spray pre at planting. Save that money. If you start cultivating, weed seed is going to start germinating. We're trying to deplete the top inch of soil of weed seed. If we can do that, weed control is much easier.”

Be precise

“This is very important. Our label says to spray at the base of the plant. I recommend you spray at the base of the plant up to the cotyledonary node and no higher. If you get higher than that node, you can run into situations where the plant takes up too much Roundup and results in fruit shed.”

Spray tips

Make sure the spray tips and pressures being used are correct. Avoid fine spray droplets that can float up into the plant canopy. The tip Mills recommends for both post-direct and over-the-top applications is a Turbo Teejet as it introduces large droplets across a wide range of pressures.

Don't use even patterned tips. This is one of the biggest violations when it comes to post-directed Roundup, says Mills

“Over the years, a lot of people have been using these. I think some of that is due to the machines coming out of the factory equipped with these things.”

An even tip supplies an even rate across the spray pattern. A tapered tip tapers a rate across the pattern. Tapered tips are designed to overlap to provide a full rate.

Even tips aren't designed to overlap and should be used for banding, not post-directing, says Mills. If even tips are being used, the applicator is simply doubling the rate on the cotton plants.

“Use a minimum of two tips per row. The equipment we use has three tips per row. Many people are using a single flood tip in the row middles. That's not what we like to see.”

Residuals at lay-by

“I've been recommending residual herbicides at lay-by since Day One and will continue to. It's a good idea.”

What about post-direct versus over-the-top? Which is safer?

Mills says he's spoken with many farmers who think that post-direct applications are less safe because more Roundup gets into the plant. They believe that spraying over-the-top results in the plant taking up fewer chemicals. This belief is grounded in fact.

“In 1978, a research paper came out that said if you put a single drop of Roundup on a cotton stem and compare that to a drop on a leaf, more Roundup will get into a plant on the stem than on the leaf. That finding was correct.”

But in citing that study, what isn't taken into consideration is the factor of surface area, says Mills. If you compare surface areas of a stem and a leaf, the leaf will intercept much more Roundup than the stem.

“In fact, if you do the calculations, the leaf intercepts more than five times the Roundup that a stem will. If you extrapolate even further, the leaf absorbs over four times the glyphosate that the stem does. These are the reasons why post-direct applications are much safer after the fourth-leaf stage.”

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