Authors: Romulo Lollato, Erick DeWolf, Mary Knapp, Chip Redmond

A variety of events have recently affected the Kansas wheat crop. Some of this has been very positive and should contribute to grain yield formation, but some has not.

Precipitation and yield potential

The last two weeks brought much-needed precipitation to most of Kansas (Figure 1). Precipitation totals ranged from less than 1.5 inches in isolated spots in southwest Kansas to as much as 9 inches or more in the west central and northeast portions of the state. Most of the wheat-producing region of Kansas received at least 2.5 to 3.5 inches of precipitation.

Figure 1. Total precipitation received in the April 15 – 28 period.

This precipitation was very timely and helped alleviate drought stress in portions of the state where the wheat was turning blue, or even brown, such as north central and southwest Kansas. This timely rain can potentially increase the crop’s yield potential. The benefits of these precipitation events to Kansas wheat yield can be estimated based on the crop’s water-use efficiency, which in Kansas is approximately 4 bushels per acre per inch (although higher water-use efficiency values can be attained under certain conditions). For more information on wheat water-use efficiency and the potential to translate the recent precipitation events in grain yield, see article “How much yield potential did the latest round of precipitation add to the wheat crop?” in the Agronomy eUpdate issue 565 of April 22nd.

Potential disease problems

Conditions that are favorable for wheat yield are generally also favorable to the development of certain pathogens, such as stripe rust and Fusarium head blight (head scab). Stripe rust has been present in the central corridor of Kansas for the last several weeks, and has recently increased in incidence and severity due to optimal conditions for its development (cool temperatures and available moisture). Fields planted to susceptible varieties that have not been sprayed with a foliar fungicide may now be showing severe stripe rust infection on the flag leaves (Figure 2), which can result in yield losses of 40% or more. For more information on stripe rust development across Kansas, please see the accompanying article in the current eUpdate issue titled “Wheat stripe rust update.”

Figure 2. Incidence and severity of stripe rust on the susceptible variety Everest, with and without a foliar fungicide application at heading, in Ellsworth County. Photo by Romulo Lollato, K-State Research and Extension.

The precipitation also coincided with heading and flowering in many parts of the state, which is conductive for Fusarium head blight. The infection by head scab occurs when there is available moisture during anthesis, and might be a concern in south central and southeast Kansas at this point. For more information on potential threat of head scab to the Kansas wheat crop, please see the accompanying article in the current eUpdate issue titled “Risk of Fusarium head blight in wheat.”

Hail and freeze damage

Another factor that could concern producers this growing season is possible hail and freeze damage. The storms of April 24th and 26th brought hail to the eastern half of the state (Figure 3). Depending on hail size and duration of hailstorm, some fields may have sustained damage.

Figure 3. Preliminary reports of hail from the storms this week across Kansas.

Finally, reports of freeze damage from the April 12th freeze have been minor, mostly restricted to lower areas in fields in Saline and Cloud counties. Additionally, damage seems to have been generally restricted to the top spikelets within the wheat head (Figure 4). The preliminary reports and field assessments indicate that very little freeze damage may have been sustained by the crop despite having more than 5 hours of below freezing temperatures on April 12th.

Figure 4. Slight freeze damage showing up in early planted wheat in Cloud County. Photo by Kim Larson, River Valley District Crop Production Agent.

Romulo Lollato, Wheat and Forages Specialist

Erick DeWolf, Extension Plant Pathologist

Mary Knapp, Weather Data Library

Chip Redmond, Weather Data Library