Last night the low temperature in Swoope, Virginia was 72 degrees Fahrenheit. Anything above 70 is considered a “warm” night in these parts of the country. That’s a night when you lay on top of the top of the sheets in your bed and sweat trying to sleep. Farmers have long known these are the nights when it’s really quiet…you can hear the corn growing. These are often referred to as the “dog days of summer”.
During our summers when the daytime temperature exceeds 90 and at night it exceeds 70 only certain plants thrive. Botanists have described these plants as “C4” plants. C4 plants and the internal fungus that infects the grass – tall fescue, love these dog days of summer – hot days and warm nights.
Part of the plant kingdom can be divided into C3 plants and C4 plants. Basically, during photosynthesis, C3 plants utilize 3 carbon atoms while the C4 plants utilize 4 carbon atoms during the process. I have long forgotten the details of this complicated but very important process but suffice it to say C4 plants are more efficient at bioaccumulation of carbon than C3 plants. Botanists inform us that C4 plants utilize 80% if the sun’s energy while C3 plants utilize only 30%. In addition, C4 plants have adapted to drought conditions by closing the breathing orifices in their leaves so that internal moisture is not lost. C4 plants are the ones we wonder about during the dog days of summer and drought; we ask ourselves how in the world do these plants do so well during such adverse conditions.
C4 plants include corn, sorghum, sugarcane, tomatoes, all of our “warm season” grasses such as switchgrass and big bluestem and many of our despised weeds such as poison ivy, wiregrass, redroot pigweed, and johnsongrass. All of our cool season grasses such as orchardgrass, bluegrass and timothy are C3 plants and go dormant during the dog days of summer and especially during drought. One of our C3 cool-season grasses, tall fescue goes dormant during the dog days of summer but it has a special relationship with a fungus that grows inside the fescue plant which has devastating effects on anything that eats the plant.
Tall fescue is one of the most widespread grasses in North America. It is not native and it is invasive. “Kentucky 31” Tall Fescue was released by the University of Kentucky in 1931 and was hailed as one of the best pasture plants for our temperate part of the globe. It surprisingly remains one of the most popularly planted pasture plants in North America yet poisons all livestock that eats it during the dog days of summer. Little did we know in 1931that it had an internal fungus (endophyte) living in symbiosis with the plant that helped it be so prolific and be so toxic.
We now know that when the dog days of summer arrive an alkaloid produced by the fungus becomes toxic to just about everything that eats the plant. We’ve known for decades about the toxic effects this alkaloid has on pregnant mares and the effects it has on cattle. It causes abortions and thickened placentas in mares, increased body temperatures, conception failures, fescue foot, summer slump, tails to fall off and countless other sub-clinical problems in cattle. There is research now that shows it’s even toxic to grasshoppers and birds. Recently, we learned that the fungus also secretes toxins into the soil that inhibit newly planted trees or shrubs.
There are two conclusions from all this that seem obvious to me. One, we should not plant another seed of tall fescue – it’s toxic to everything, invasive and not native. And secondly, as the march of increased temperature and drought invade north we should be utilizing the efficacy of C4 plants by planting more “warm season” grasses.