Can farmers play hardball with weeds in cotton, corn and soybeans, using an expensive brew of herbicides that include glyphosate, manage resistance problems, and come out ahead on the bottom line?

A six-state, multi-year study indicates in North Carolina they can. Other states included in the test showed similar results.

In North Carolina, cooperating farmers were asked to split their test fields in half. In one half they managed weeds as they do normally — the farmer approach. In the other half they managed weeds based strictly on university recommendations — the university approach.

North Carolina State University researchers looked at continuous soybean fields, continuous cotton fields and soybean and corn rotations in the study.

The university approach included additional preplant, pre-emergence or postemergence herbicides. These herbicides included a wider range of modes of action and active ingredients than a typical farmer herbicide program. Both farmer and university herbicide programs included glyphosate in the herbicide mix.

With the increase in acreage of glyphosate resistance in cotton and corn, primarily by Palmer amaranth, the need for a more comprehensive weed management program seems essential. Too many farmers haven’t taken the extra time and spent the extra dollars to manage weed resistance in the past few years, making the North Carolina portion of the study extremely poignant.

The bottom line for both types of herbicide programs was calculated using the same North Carolina State University enterprise budget. Profitability of cotton was based on 60 cent, 80 cent and $1 per pound of lint. For corn $3, $5, and $7 dollars per bushel were used and for soybeans $8, $12, and $16 dollars per bushel were used.

For conventional planting per acre costs, minus herbicide costs, were set at $371.85 for corn, $497.51 for cotton and $218.54 for soybeans. For reduced-tillage systems these per acre costs were $346.63 for corn, $474.47 for cotton and $188.21 for soybeans.

Agronomist David Jordan, who helped coordinate the North Carolina State portion of the six-state study says the more intensive and diverse use of herbicides paid off in both continuous cotton and soybeans.

“In cotton, the economic benefit of using the more intense university approach probably came from reduction in early season weed interference with cotton. We didn’t see much difference in weed populations later in the season, indicating the affect came early rather than late,” Jordan says.

Soybean situation

In soybeans, the university approach resulted in fewer weeds later in the year, indicating the economic benefit at low, medium and high crop values, probably came from more of a season-long affect of reduced weed competition, Jordan explains.

In both cotton and soybeans, the more intensive university approach typically produced around 10 percent higher yield than the less expensive, but less efficient farmer approach.

In the corn and soybean rotation the researchers found fewer differences across all parameters of the study, except herbicide price and diversity of activity on weeds.

“Although it was covered in this study, it is clear that good crop rotation is valuable in producing an overall healthier crop that is better able to compete with weeds, regardless of herbicide or crop mix,” Jordan says.

In general, weed populations were higher at the end of the season in continuous soybeans than in corn-soybean rotations. Weed densities in cotton were generally lower than either continuous soybean of corn-soybean rotations.

In 2011, cotton, soybean and corn seed are all going to be expensive and in some cases in short supply in some of the more desirable varieties. The 10 percent more yield at a dollar per pound for cotton and comparable high value of beans and corn will make the extra 10 bushel per acre yield more valuable than the extra cost of an intensive herbicide program.

In continuous cotton, the extra herbicide cost in the university program was $22 per acre. Even in cotton at 2008 prices, getting 100 pounds more per acre would nearly double the extra cost for herbicides used in the university approach. Clearly, at $1 per pound, the benefit would be significant.

In continuous soybeans, at the current (mid-February) price of soybeans, the advantage for the university approach to weed management would be nearly 2 to 1 in dollars spent versus dollars gained.

Some growers look at the extra cost associated with using multiple modes of action and different application times as insurance against weed resistance. In reality, this study shows more intensive weed management pays in both the short-run and the long-term.

The cost advantage is very clear, Jordan points out, on continuous soybeans or cotton. Though there is no significant cost advantage on soybean and corn rotations, there is a significant long-term advantage of keeping fields clean and free of herbicide resistant weeds that can become a big problem in a short period of time.

As growers get ready to plant some very expensive cotton and soybean seed this year, spending the extra dollars in weed management is likely to pay off better than ever before.

rroberson@farmpress.com