The LSU AgCenter won’t release a formal list of recommended wheat varieties next summer.

“It’ll be a farmer’s, consultant’s or Extension agent’s responsibility to become familiar with variety testing programs and learn how to go through provided data to figure out the varieties best-suited for fields,” said Steve Harrison, LSU AgCenter small grains breeder during an Oct. 30 production meeting at Dean Lee Research Station in Alexandria, La.

“There are several reasons for that.” In wheat, there’s much more to recommending a variety than just yield numbers. Test weight is almost as important as yield. Disease resistance is also key — “leaf rust, stem rust and stripe rust can be very important considerations depending on where you are in the state, what time of year you’re planting and what management packages are being used.”

Harrison and colleagues are currently preparing for the next wheat variety trials. “We’ll be planting about 2,000 individual envelopes of seed over the next two days around Winnsboro. Within a given field there will be four plots of the same variety. That will account for some micro-environmental variation and give an accurate assessment of performance.”

The wheat trials are divided into north and south Louisiana regions. “On the wheat breeding Web site (http://www.agronomy.lsu.edu/LSUWheat/LSUWHEAT.html), I’ll try to put all the field books. That way, anyone can access the lists and see which varieties are where. From there, you can contact the trial coordinators and visit the trials in the spring.”

In north Louisiana, there are fewer random periods of warm weather and a longer period to vernalize in the winter. As a result, “you can grow varieties in Monroe that were developed in Arkansas, North Carolina and other areas.”

Meanwhile, in south Louisiana, the winters are frequently punctuated by warm periods that result in less cold weather than needed for some varieties to properly head out (inadequate vernalization). “There’s greater leaf rust pressure, stem rust pressure and other factors that prevent farmers from growing varieties that are okay (further north) in Monroe.”

Vernalization

What makes wheat head out and what does a wheat heading date mean to your operation?

“A wheat variety that isn’t held back by a photo-period, is basically a spring wheat and will head out as soon as it accumulates enough heat units. It will continue to grow all winter.”

Spring wheats are grown in Mexico and Canada because “they don’t have enough cold to vernalize or, they have winters that are too cold and would kill the wheat regardless.”

Spring wheats head out in response to heat units and day-length (photoperiod).

“Some varieties have a rather strong photoperiod requirement that interacts with the heat units. So until a certain photoperiod is achieved, the plants grow very slowly.

“Finally, there’s a vernalization (cold requirement) — much like a peach tree. Now, 28 degrees is not vernalizing. Vernalization is a physiologically active process and occurs between nearly freezing and 55 degrees. The optimum is around 40 degrees.

“So a variety with a five-week vernalization requirement needs a substantial part of the day to have temperatures in the 40s, night or day.

“The point is we need to be very careful to match wheat varieties with heading and planting dates. Do not plant early-heading varieties too early. An example could be LA482 — don’t plant that one early or it will see freeze damage.”

This year, there are 60 entries in the statewide variety trials — five were excluded from south Louisiana based on prior experience and too-long vernalization requirements.

In the tests, 12 companies are represented. Two companies, Pioneer and Agripro Coker, have their own breeding programs in Arkansas and Indiana. The other 10 companies license varieties. Virginia Tech, the University of Georgia and LSU developed most of the trial varieties.

“There are 31 new entries. We have a high rate of turnover, like other crop variety trials. There will be a lot more choices for growers next summer.”

Rusts

In north Louisiana, stripe rust has become a big issue. It wasn’t a problem in the state prior to 1999. But there was a basic physiological change in the disease organism: the latent period is now shorter and the disease tolerates warmer temperatures.

“We used to say nighttime temperatures above 60 would shut down stripe rust. That’s not necessarily true anymore.”

In south Louisiana, there’s greater leaf rust and stem rust pressure. Interestingly, “there’s also a greater probability of spring freeze damage. If you plant early wheat varieties too early in south Louisiana, they may head in late February and be severely damaged by a March freeze that occurs nearly every year.”

Leaf rust, an intermediate temperature disease, “infections can occur in the fall if we plant in warm weather too early. Come spring, there can be as much as a two-fold increase in the disease because the disease was able to establish. That’s because our wheat grows all winter. There’s not a ‘brown’ or dormant period.”

That means the inoculum stays put all winter. When temperatures reach the mid-60s, the inoculum is increasing. By the first of March, a tremendous load of the inoculum can already be in the field and will “jumpstart” an epidemic.

Stripe rust is a cooler-weather disease. “You need to scout for it early and be aggressive in treating it because it’s very hard to control.”

Fusarium head blight “is a disease we haven’t dealt with a lot in the state even though it’s here every year in some fields. We do see it in northeast Louisiana although we see it a lot more in the southern rice-growing areas around Crowley.

Fusarium head blight is one disease that we can breed for resistance. We have projects looking at that. But we don’t have resistant varieties currently that are adapted to Louisiana.”

e-mail: dbennett@farmpress.com