Yield not the only trait in alfalfa variety choice

While yield is always a top priority in selection of an alfalfa variety, it's not the only trait to look for, says Dan Putnam, Extension agronomist at the University of California, Davis.

During a recent alfalfa and forage field day at the UC Kearney Agricultural Center at Parlier, Putnam urged growers to take plenty of time to consider all of a variety's virtues and faults.

One way to learn more about how a variety performs, he said, is to review results of multi-year variety trials such as those at Kearney and other UC sites up and down the state, along with those of seed companies and other universities.

Multi-year results are important, he added, because often a variety will perform well the first year, only to deteriorate the second and third season.

“Granted, results from field station trials may not be the same as on individual farms, but you need something to start with before you go on to strip trials on your farm,” he told the assembly of growers and PCAs.

As he has in the past, he cautioned growers not to make a selection based solely on seed price, which he considers the least important criterion.

Data from trials at Kearney during 2003 to 2005 show that given a price of $125 per ton over a three-year period and 25 pounds of seed per acre, a $3 increase in the seed price, translates to a gross return of $25 more per acre.

Putnam's list of things to consider along with yield potential also includes pest resistance, often the only economical way to hold off diseases, insects and nematodes.

“Remember that pest resistance is not an absolute value. Highly resistant varieties have at least 50 percent plants with resistance to a given pest, but that means the rest of the population is susceptible. It's relative in terms of the amount of the pest infestation you have.”

Putnam sees pest resistance as akin to automobile insurance. It may not be needed every year, but it can pay off for a pest like stem nematode that in the Sacramento Valley has a way of turning up every five years or so. Persistence of a variety is important for it to accommodate a grower's crop rotation schedule.

Evidence of high forage quality is always a major consideration and is linked to fall dormancy. Growers have to find a balance between yield and quality, which can vary from one year to the next. Some growers have avoided higher yielding, higher dormancy varieties in favor of quality, although when hay prices are high, yields often take top billing.

Putnam pointed out that cutting schedules influence quality, but more non-dormant varieties have less stand persistence with a closer interval between cuttings.

“We tend to recommend a staggered approach to cutting schedules, rather than trying for high quality on every single cutting. In California, our typical 28-day schedule can hurt the stand and miss the highest quality because sometimes it is not early enough.”

Turning to the new consideration in alfalfa variety selection, biotech, or Roundup Ready varieties, Putnam said the price of those glyphosate-resistant varieties represents the technology, a complete weed-control strategy, not just the seed.

“There are questions about the relative yield and quality of these Roundup Ready lines versus conventional lines. We are still gathering data and we don't yet have a great depth of information, although we do have several years of experience with them.

“We can say that generally they appear to be yielding about what you'd expect from the fall dormancy categories. They also appear to have about the same forage quality as the conventional varieties.”

With the advent of Roundup Ready varieties has come the need to identify such alfalfas. Putnam calls it stewardship of the Roundup Ready trait.

This accommodates hay buyers who may believe there is some sort of harm from these genetically modified varieties to nearby conventional varieties or someone who is dealing with an organic market. Distinguishing between the two is also important in avoiding spraying glyphosate on a stand of a conventional variety.

Putnam demonstrated two test kits for this purpose, one marketed by EnviroLogix and the other by Strategic Diagnostics Inc.

Originally developed for soybeans, corn and other crops, they are now available for rapid testing of fresh alfalfa in the field or in stacks of bales. They are treated paper strips that register the protein present in the Roundup Ready varieties and absent in conventional varieties.

Putnam said the test strips are quite accurate but since they are also quite sensitive, samples must be free of contamination.

In another presentation during the field day, Shannon Mueller, Fresno County farm advisor, reported on trials done this year near Visalia in collaboration with Carol Frate, Tulare County farm advisor, to compare a Roundup Ready program with conventional weed control using herbicides such as Raptor and Pursuit.

Faced with shepherdspurse, swinecress and chickweed, they learned that a rate of 22 ounce of Roundup WeatherMax applied in January was less effective than the 44 ounce rate.

“It's important to get in early and control the weed population that's there,” Mueller said. “And it's very important to know the weeds you have, since hairy fleabane and horseweed look similar in the early seedling stage but their tolerance to Roundup varies.”

Because of the emerging resistance of those two weeds to Roundup, it is critical to use a rate to kill them early, rather than select for resistance in their populations with a less-than-lethal rate.

She said a late season “rescue” treatment with Roundup in the trial was an advantage in cleaning up weeds that were encouraged in an uneven stand resulting from cool and wet conditions in the spring.

The system, she added, had great flexibility and was very easy to use, since the timing of Roundup treatments is not as sensitive to the stage of alfalfa growth as it is with conventional herbicides.

There were some disadvantages, however. Roundup alone did not control nettle, malva and fillaree, but Mueller said tank mixes could be a solution.

Mueller cited results of a previous economic study on Roundup Ready versus conventional herbicides. Costs will vary according to the weeds the grower has in his fields and the combination of herbicides selected. Roundup Ready seed includes a $3 premium per pound for the cost of the technology.

To achieve the same effectiveness of weed control on a three-year stand with either system, the study showed herbicide and seed costs at $266 per acre for Roundup Ready versus herbicide and seed at $321 per acre for a conventional system.

“You have to calculate costs for your herbicide program and compare them with a Roundup Ready system” Mueller said. “It doesn't have to be all or none. You can plant Roundup Ready alfalfa and then use Roundup in combination with other herbicides to control problem weeds in your fields.”

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