A Decision Guide for Winter Wheat Variety Selection - Risk Reduction through Variety Maturity Ratings

We are taking a different approach to variety recommendation in light of the last three years of variety trials. It was a shock to us this year that data from only 5 of 11 dryland trials could be used to characterize variety performance. Together with test plot failures the last two years, we have only obtained useful data from 14 of 31 dryland trials since 2002! This lack of data directly affects our wheat improvement program in two ways. First, our efforts to make reliable variety recommendations based on trial performance are severely hampered. Secondly, breeding program decisions on which experimental lines to advance or discard are based on relatively few observations which raises the risk of throwing out a line that, if tested properly, may have proven to be the next wonder variety for Colorado.

In preparing this guide we were forced to look at three year averages (2002-2004). This average included only one year that was near what we would call normal (2003) - even though in this year we were only able to use 60% of the trials planted. This strategy has proven quite useful in the past, in Colorado and elsewhere, as opposed to using the most recent year of trial data to predict future trial performance. The most salient observation when looking at variety response across the three years is the amount of year to year variability, as evidenced by one variety being near the top one year and mediocre to abysmal the next.

What follows breaks from our traditional Decision Tree approach to variety recommendation and is our humble attempt to try to make some sense of the data. We in Colorado, like our public and private counterparts in adjacent states, have recommended for many years that producers should plant two to three different dryland varieties each year as a means to reduce risk. Our extension of this proven approach is that producers should also consider selecting varieties from different maturity groups, in so far as possible, following consideration of yield, quality, disease and insect resistance traits, and other agronomic features. The rationale for this approach is that farmers abandoned production fields and we lost trials in the past three years most often due to drought, spring freeze, and hail damage. We reason that the severity of these conditions is at least partially related to maturity and that maturity is a management factor over which we have at least a small degree of control. Given the fact that our trials indicate that one cannot reliably predict which variety among the top nine varieties (shaded in the table below) will be the top performing variety in a future, unknown year, it is apparent that maturity may be a useful indicator for variety selection with the hopes of reducing overall risk.

Application of this approach is not without its pitfalls. First, it can be seen from the trial data below that relative few varieties are available within the later-maturing group. Both Prowers 99 and Thunderbolt have performed consistently near the bottom of our trials and it would be difficult to recommend these as complements to varieties from the early or medium-maturing groups. Recently, several later maturing varieties have been included in our trials and some of these, particularly Goodstreak from Nebraska (which performed very well in 2004), may prove to fit this group with additional testing. Another potential difficulty with this approach is the fact that in most years later maturing varieties may suffer from stress during grain filling, though these conditions have not figured prominently in Colorado the last two years. We acknowledge the effect that planting date has on crop development and realize that producers may already stagger planting dates as a means to stagger crop maturity to facilitate harvest. This notwithstanding, we strongly feel that consideration of maturity along with other common variety selection factors may serve as a promising risk reduction tool.

3-Year Variety Performance Summary with Maturity Class.

Irrigated Variety Selection

Unlike the dryland trials, we were fortunate to have two high yielding irrigated trials this year at Rocky Ford and Haxtun. At Haxtun, the CSU variety Yuma amazingly yielded 133 bu/ac in each of the three reps. The real decision for irrigated wheat in eastern Colorado seems to be whether to be whether to contract plant the AgriPro/ConAgra white wheat variety, Platte, for which producers receive bonuses or to plant a higher yielding variety like Yuma (9 bu/ac higher yielding than Platte on a three year trial average). It should be noted that Platte sometimes has performed better in producers irrigated fields than in our trials - even when the trial was in Platte field. Platte is susceptible to stripe rust and its yields were significantly reduced in years when stripe rust was present but new fungicides offer good protection. Growers in the northeast seem to have been pleased with the Platte IP program but for those irrigated producers who are not in the right geographical area, or not able to get new contracts, Yuma offers potential high yields. Jagalene and Wesley have also been top irrigated-performers throughout the region.

Two and three year average dryland and irrigated variety performance results can be viewed at the CSU Crops Testing site
http://www.csucrops.com or CSU Wheat Breeding Program site at http://wheat.colostate.edu/vpt.html.

Jerry Johnson and Scott Haley
Extension Crop Production Specialist and Wheat Breeder
Colorado State University