This past week NOAA confirmed what we already knew….it was hot in July 2012. The average national temperature made it the hottest July on record and hottest month of any month on record. The real story however has been drought. Plants can dissipate heat loads if they can function normally with adequate soil moisture. Due to the heat, leaf stomates can close because of rapid water loss limiting transpirational cooling of a plant. When the plant transpires the water loss has to be made up by the root system and if adequate moisture in the soil is unavailable the plant becomes stressed out. This stress can weaken the plant, reduce yields and make it susceptible to disease or insects. Of course prolonged periods of drought will eventual move the plant from stressed to just plain dead.
The USDA now has a Evaporative Stress Index showing patterns of water availability and moisture stress across the U.S. Brown colored areas signify higher levels of water stress while green areas denote relatively low water stress. This map shows what my friends in Seattle have been telling me this summer. They’ve had too much rain and it has been cool while we here in the midwest have been roasting and toasting! If you would like to check out the map yourself and learn more here is the link http://hrsl.arsusda.gov/drought/index.php