FROM THE GROUND UP
Agronomy News

2005 Colorado Winter Wheat
Variety Performance Trial Results

Performance trial results help Colorado wheat producers make better
variety decisions.

Colorado State University provides unbiased and reliable information to
Colorado wheat producers to help them make better wheat variety decisions.
CSU’s dryland and irrigated variety performance trials are made possible by
the support and cooperation of the Colorado wheat industry. Wheat variety
performance trials represent the final stages of a wheat-breeding program
where experimental lines are tested under a broader range of conditions
than is possible earlier in the program. On-going and strong support for a
public breeding program, like that at CSU, is important because the varietal
development process is long and testing for yield superiority and stability
under highly variable Colorado conditions is a great challenge. There is
large annual variation in precipitation as well as variable fall, winter, and
spring temperature regimes that interact with variety maturity to affect wheat
yields. In recent years, we have seen a variable and evolving wheat disease
situation with stripe rust and wheat streak mosaic virus. There have always
been large fluctuations in weed infestations from one year to another, and we
have witnessed the recent rapid onset of new Russian wheat aphid biotypes
over the past two years.
Topsoil moisture conditions were good throughout the state in fall 2004 and planting was earlier than normal in almost all locations. Plant stands were excellent in most trials and
growth continued into late fall. Trials across eastern Colorado experienced late fall infestation of leaf rust, which was highly unusual for Colorado and especially for outheast Colorado. Not recognized in the fall, the early planting and favorable `green bridge` conditions likely favored the growth and spread of wheat curl mite populations responsible for transmitting the wheat streak mosaic virus. Damage from wheat streak
mosaic virus became evident in the spring of 2005 when temperatures increased. The mild 2004-2005 winter did not reduce wheat stands, nor did it reduce overwintering Russian wheat aphid (RWA) or wheat curl mite. Leaf rust was found to over winter in many eastern Colorado locations while the fall stripe rust infection at Fort Collins did not
over winter. Moisture was sufficient from January-April to maintain the luxuriant growth resulting from excellent fall emergence and growth. The numbers of tillers per plant,
throughout eastern Colorado, were extraordinarily high by the end of April 2005. During the last week of April, around April 27-28, there were several nights with below freezing
temperatures and, in some places, 10 or more hours below 26 degrees F. The freeze damage that may have occurred was likely most restricted to southeast Colorado where the wheat was well past jointing and the growing point was far above ground level.
Colorado wheat producers, and our variety performance trials, were to suffer several more blows in May that were much more damaging than the April freeze. The largest setback to yield performance in our trials was a period of drought stress from late April to early May followed by a period of high temperatures, often accompanied by dry winds, later in May. The drought and heat stress, which was relieved later by precipitation and more moderate temperatures, arrested growth and resulted in shorter than normal wheat in most places. Heat stress may have been the cause in some places
because it appeared that sufficient soil moisture was present but high air temperatures combined with luxuriant plant growth appeared to have made it difficult for the plant to get water to developing heads, resulting in aborted kernels and partially or fully dead heads and stunted plant growth. Two trials with poor fall emergence and the poorest
overall stands, Genoa and Arapahoe, exceeded our expectations in growth and yield.
Stripe rust infections affected large areas of wheat production in Colorado and surrounding states in 2005. Mild winter temperatures allowed stripe rust to over winter in Texas and build up to high populations in early spring in the Texas and Oklahoma
Panhandle regions. Spring storms quickly spread stripe rust spores north where cool, wet weather conditions were favorable for infection and spread of the disease. Infections
were observed in southeast Colorado by early May, likely aided by the luxuriant growth that was similar to irrigated wheat conditions where stripe rust has been more common in
Colorado. The drought stress in early May delayed the spread of stripe rust further to the north but rains that came in early June then caused heavy stripe rust infection in many areas north of I-70. Overall, stripe rust was much more severe than usual in many areas of eastern Colorado in 2005 and resulted in significant yield reductions in some susceptible wheat varieties. The epidemic was a result of a combination of favorable
environmental conditions and genetic susceptibility of most available wheat cultivars.
The consensus is that stripe rust is not likely to be a serious problem every year in Colorado. This is because conditions that favor disease development (i.e., extended
periods of cool, wet weather) are not common in the High Plains region. Nevertheless, stripe rust has developed to some extent three times in the past five years in Colorado.
Thus, growers who plant susceptible varieties should be aware of the potential risk and should consider the possibility of preventive spring fungicide applications on irrigated
or high-yield potential wheat if stripe rust is present. Wheat streak mosaic virus was also
severe in some locations in east central and northeastern Colorado. The wheat streak mosaic epidemic, caused by a virus transmitted by the wheat curl mite, was a result of a
combination of factors. This included carry-over of mites in late summer on volunteer wheat, corn and other hosts, early fall planting dates, mild fall temperatures that allowed for mite buildup and transmission of the virus, and drought conditions in late winter and early spring that further damaged infected plants. The wheat streak mosaic virus outbreak in 2005 is a good reminder of the potential danger of early planting dates and failure to control volunteer wheat. The new form of the Russian wheat aphid, designated as biotype 2”, was found throughout eastern Colorado and caused yield losses in varieties that carry resistance to the original biotype of RWA (designated as “biotype 1”). RWA infestations were early and widespread in 2005. Infestations of RWA were observed
at several trial locations though the damage was likely over-shadowed by the drought and high temperatures in May. Southeastern Colorado wheat producers may have suffered more loss, and sprayed more than other places in Colorado. Weed control was problematic for some producers. Fall moisture stimulated winter annual weed growth
like wheat and volunteer rye, downy brome, jointed goatgrass, and tansy mustards which were quite evident and problematic where they were not controlled. In summary, all or most of the above climatic or biotic factors affected each of our performance trials this
year. In some cases the factors were interacting, such as the promotion of stripe rust infection as a result of the luxuriant spring growth which also led to increased drought susceptibility. It is very difficult to determine which factor had the most influence on
trial yields at each location. Variety maturity also interacted with some of the factors above, independent of variety performance. For example, later maturing varieties suffered significantly from the hot, dry winds that occurred later in May when these
varieties were coming out of the boot. The conclusion is that producers are encouraged not to consider single location results for variety selection but rather to use the summary of performance of all 2005 locations in addition to the 2-year and 3-year summaries.
Ten dryland and three irrigated variety performance trials were harvested and the results are presented below. The dryland trial at Orchard was lost due primarily to the heat/drought stress cited above. There were fifty-two entries in the dryland performance
trial and thirty-four entries in the irrigated trial. Both trials include a combination of public and private varieties from Colorado and surrounding states. Each trial is planted in
three replicates in a randomized complete block design. Yields are corrected to 13% moisture.