Parts of the Midwest, including the Chicago and Milwaukee areas, saw record rainfall in April. In fact, Milwaukee experienced its wettest April on record, with 5.6 inches above average for the month. During this time, many superintendents were concerned about the immediate impact of excessive rain on turfgrass health and overall playability, but now things have changed. The turf has dried up, and drought stress has been more obvious following a couple weeks of dry conditions. Now, superintendents are switching gears because soil can dry out very quickly at this time of year due to some of the reasons outlined below.
Relative humidity is lower
Relative humidity tends to be lower in spring due to increasing temperatures coinciding with limited additional moisture from water evaporating from plants, soils or bodies of water. Historically, May averages the lowest relative humidity in Chicago of any month. As spring continues, plants in our environment grow and transpire, adding water vapor to the environment while the temperatures are increasing. This can reduce relative humidity because warmer air can hold more moisture, ultimately decreasing atmospheric water potential. Lower relative humidity increases evapotranspiration and encourages soil drying. Remember that relative humidity is not the same as total water content in the air.
Wind speeds are higher
In many areas of the north-central U.S., spring tends to be windier than summer. The addition of high wind speeds to low relative humidity creates an environment where turf can dry out very quickly without rainfall.
What changes as summer progresses
As plants continue to grow, especially with the emergence and growth of agricultural crops in the central U.S., evaporation increases notably. Many Midwesterners refer to this phenomenon as “corn sweat.” The increase in evapotranspiration, along with evaporation from soils and bodies of water in hot conditions contribute to the more humid conditions observed later in summer. This will change the irrigation strategies for superintendents because as water potential in the atmosphere increases, it lessens the ability of turfgrass to draw water up through the roots and cool itself, which can result in wet wilt if conditions are too saturated. If you have any questions about managing the ups and downs of moisture this year, please reach out to your local USGA agronomist.
Central Region Agronomists:
Zach Nicoludis, regional director, Central Region – znicoludis@usga.org
Tom Gould, agronomist – tgould@usga.org
Steve Wilson, agronomist - swilson@usga.org
Information on the USGA’s Course Consulting Service
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