Can excessive rainfall prematurely kill the wheat crop in parts of Kansas and Oklahoma?
Parts of central Kansas and northern Oklahoma received as much as 10.23 inches of rainfall in the last 7 days (Figure1). Excessive rainfall caused flooded fields in the region from Harper to Cherokee counties in southern Kansas and from McPherson to Miami counties in central and east central Kansas (Figure 2).
Figure 1. Accumulated precipitation for the week ending May 24, 2019. Map from Midwest Regional Climate Center.
Figure 2. Flooded wheat field in Barton Co, Kansas. Photo taken on May 21, 2019 by Alicia Boor, Cottonwood Extension District Agent.
The recent, historical rainfall events will absolutely negatively impact the wheat crop in central Kansas and Oklahoma. Low-lying field areas, such as terrace channels and old plow furrows, had already caused premature death of the crop due to saturated soil conditions even prior to this most recent rain (Figure 3). This week, other low-lying areas of fields started to turn white due to saturated soil conditions (Figure 4). Damage from flooding will be the most immediately observable impact of the recent rain, but saturated soil conditions will negatively impact yield even in areas that are not flooded.
Figure 3. Low-lying areas were already saturated prior to the recent excessive rains in parts of central Kansas and Oklahoma. Photo taken in Marion County, Kansas, on May 3, 2019, by Romulo Lollato, K-State Wheat Specialist.
Figure 4. Low-lying areas of the fields started to turn white in central Kansas due to saturated soil conditions. Photo taken in south-central Kansas on May 22, 2019 by Erick DeWolf, Extension Wheat Pathologist, Kansas State University.
The amount of damage from flooding depends on the amount of time the crop was under water and the growth stage of the crop. Wheat that was covered by standing water more than 24 hours is the greatest concern. Wheat in the later stages of kernel development, such as into the soft dough stage or later, will likely see reduced test weight and an increase in shriveled or shrunken grains. This was the case for the majority of the Oklahoma wheat crop. For wheat that is further behind, such as fields just starting grain fill or not yet at grain filling, the injury will likely be greater and range from moderate damage to a complete loss. This would be the case for fields in central Kansas, which are about 10 to 15 days behind in development as compared to their normal course.
Even fields that were not flooded did not escape weather-related injury. Top-heavy wheat plants and saturated soil conditions make fields prone to lodging this time of year, and there was a significant amount of lodging associated with the recent storms. Plants that are “kinked” or “broken” have little chance of recovery. Plants that are crooked or leaning might make a partial recovery and attempt to stand back upright. Wheat that was just beginning to head has a greater chance of recovery than wheat that was well into grain fill.
Lodging and excessive moisture can also worsen the incidence and severity of many fungal diseases. In south central Kansas, wheat varieties susceptible to stripe rust were showing 70-80% of flag leaf already compromised by the fungus where it was not sprayed with a foliar fungicide. These damp conditions, coupled with the cool temperatures, are near perfect for stripe rust development, so there is a chance it could cause serious yield losses for fields that escaped from the flooding.
All of these issues are going to require a field-by-field observation to determine the extent of damage. We know that the crop as a whole is negatively impacted, but the impacts are farm-specific. There is really nothing a producer can do at this point other than sit and wait. We should know a lot more in the next 7 to 10 days. There are not any products or spray applications we recommend at this time to assist in recovery from flooding or lodging. However, producers should continue to monitor fields for pests such as armyworms and make decisions based on pest thresholds and remaining yield potential.
Romulo Lollato, Extension Wheat and Forages Specialist
Erick DeWolf, Extension Wheat Pathologist
Jeff Edwards, Former Extension Small Grains Specialist, Oklahoma State University
Heath Sanders, SW Area Extension Agronomy Specialist, Oklahoma State University
Josh Bushong, NW Area Extension Agronomy Specialist, Oklahoma State University
Mary Knapp, Weather Data Library, Kansas State University