The days are getting longer and the wheat crop is actively growing in most areas of the state. With the onset of spring weather, it is time look at factors that could influence the yield potential of the Kansas wheat crop. A quick look at the drought monitor suggests that soil moisture is good in many areas of the state and that is a huge plus as we move into this growing season. Many growers are already moving forward on fertility and weed management plans. Disease management decisions will be the next major hurdle for the 2020 growing season.
Looking south helps predict disease outbreaks in Kansas
Experience has taught us that weather conditions in Texas play a critical role in the development of regional outbreaks of the disease. Recent research at K-State is bringing new insights into what weather patterns are most conducive or suppressive for the develop stripe rust in the Great Plains region.
In general, this research helps document that stripe rust survive in southern Texas, and wet conditions in this region increase the risk of stripe rust problems throughout the Great Plains. Moreover, dry conditions in this region often suppress the risk of outbreaks.
The research also points to two time periods that strongly influence the amount of disease in the region. The first time period occurs in the preceding fall (October - December) when the wheat crop is being planted and beginning to grow. The second time period occurs in the early spring (February - March) as the crop in Texas moves into the grain-filling stage. To illustrate these findings, let us look at a series of maps showing moisture conditions in southern Texas over some recent growing seasons (Figure 1). These maps indicate that stripe rust epidemics in Kansas are often preceded by above-normal moisture conditions in these key overwintering locations for the rust diseases. However, when these regions are dry, stripe rust severity in Kansas generally remains low. A look at the moisture patterns for 2020 indicates that rainfall in this area was below normal (see the 2020 map in Figure 1). This pattern suggests that the risk of a severe outbreak of stripe rust in Kansas is low.
Figure 1. Soil moisture levels in southern Texas when the wheat crop was established for the 2015-2020 growing seasons. Notice that in the low disease years, dry conditions (lightest green colors on the maps) dominate southern Texas. In years with severe stripe rust, moderate or high soil moisture conditions are prevalent in these same regions. These maps show soil moisture levels based on November “Palmer Z-Index” provided by NOAA-National Centers for Environmental Information.
This is consistent with observations from Dr. Amir Ibrahim, Wheat Breeder for Texas A&M University, who indicated that conditions for stripe rust were not favorable and that disease development was slow in his research plots near San Antonio, Texas this year. Bob Hunger, Plant Pathologist for Oklahoma State University, noted that only low levels of stripe rust were reported in southern Oklahoma so far in 2020. However, Dr. Ibrahim did note that leaf rust was still very active at this same location. Clearly, there are many more factors that will influence the final disease levels in Kansas this year. While these early indicators look encouraging, let’s keep an eye on the disease situation and see what develops as the season progresses.
Erick De Wolf, Extension Plant Pathologist