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Reduce crop stress to fight rust

With the possibility of soybean rust decreasing yields, reducing crop stresses during the growing season will be more important than ever before.

Crop stresses come in many forms and at many different times. They are the reason Louisiana producers were not able to harvest 80,000 to 100,000 acres of soybeans in 2004. Weather was the main culprit, but other factors played a role. Crop stresses can be improper fertility, insects, diseases and many other things.

The reason crop stresses are so detrimental is that they individually or collectively reduce the genetic potential of the crop.

Variety selection is one of the most important decisions to be made in soybean production. Following variety selection is fertility. Fertilizer costs are high, but mining the soils is more costly in the long run. A successful soybean crop needs phosphorus, potassium, and several micronutrients.

Nitrogen is fixed from the existing environment and only in isolated situations is there any benefit to adding nitrogen to the crop.

Producers are using more inoculants at planting to insure adequate nitrogen fixation during the season. Inoculants should be used if a field has been out of soybean production more than three years and especially in a soybean/rice rotation.

Seed treatments on early beans also protect a young crop from early-season diseases.

Plant populations based on production practices also are important. Whether row spacings are wide or narrow and beds are flat or raised are very important.

Planting more beans on raised beds in Louisiana would correct some of the drainage problems we encounter yearly. Of course, narrow row beans are generally more successful where drainage is not a serious issue.

Most high-yielding fields over the past few years have raised beds, even if the rise is minimal.

In the sugarcane belt of the state, yields are very high (40 to 60 bushels per acre) compared to other regions of the state. Granted, some of the yields can be attributed to deep rich soils, but proper drainage, efficient pest control, and narrow row spacing are perhaps more important.

A producer in northeast Louisiana is using a 12-row hipper with every other gang removed to make 6-foot beds. He averaged over 60 bushels last year. Three rows on top of the bed, spaced at 18 inches, give him the advantage of narrow rows on a bed (the same concept of a sugarcane row). The producer says savings come from running less equipment through the field over a year.

He is in a cotton and corn rotation and plants two rows on top of the beds, which means he does not have to figure out which crop is going where at the end of the season — he has more time to watch the markets and adjust crop ratios.

There are other factors to consider. Weed control in beans has dramatically improved with the Roundup Ready technology. More recently, the advantage of using a pre- herbicide such as Valor is really paying dividends. Some producers who plant on narrow rows use Valor and follow it with a glyphosate product right before canopy closure. That finishes weed control for the season.

It is most important to kill the weeds before they are allowed to compete with the crop.

Volumes of data support the idea that weed control is most important in the first three to five weeks after crop emergence. Weeds reduce yields, because the they compete for light, water and nutrients.

From an insect perspective, the red shouldered stink bug has caused more problems than any other insect. According to Jack Baldwin, entomology specialist with the LSU AgCenter, the threshold has been reduced to 24 per 100 sweeps or six per 25.

We need more insecticides to control this insect efficiently. At present, Baythroid is really the only product labeled for control. The problem with red shouldered stink bugs is that after a spray, the populations are at threshold levels again within about five days. This could be a coverage issue, indicating that a ground rig or increasing GPA could be more effective.

Diseases, including aerial blight and cercospera leaf blight, should be controlled effectively to maximize yields. The two diseases can cause up to 80 or 90 percent yield loss in an untreated crop. Sound familiar? It has been reported from South America that Asian soybean rust can be just as devastating.

This brings up an important point. We have been dealing with diseases just as serious as rust but not as fast to spread. Rust spreads much quicker because it's wind-borne.

According to some U.S. soybean experts, under ideal conditions rust can travel 300 miles a day.

The 2005 Louisiana soybean crop will be challenging, but it will be fine as long as we approach the season armed with the latest scientific information available.

To put last year's crop in perspective, the southwest and south-central parts of the state got the raw end of the deal for the third consecutive year, but if you take out those regions, Louisiana would have averaged a little over 40 to 45 bushels per acre, which would have been a state record. In 2004, according to USDA, Louisiana averaged 30 bushels per acre.

David Y. Lanclos is the soybean, corn and grain sorghum specialist at LSU AgCenter. e-mail:

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