An odd news release from the Plant Management Network sensationalizes endophyte infection of pasture grasses and the harm done to animals that graze them. [also see this fuller report]

A disease caused by tall fescue, one of the most common cool-season pasture grasses in the U.S., is taking a costly toll on livestock, including both cattle and horses. Although devastating to animals, this disease is not harmful or transferable to humans.

According to Craig Roberts, state forage specialist at the Department of Agronomy, University of Missouri, this disease, tall fescue toxicosis, is costing U.S. livestock producers more than $600 million each year. Tall fescue toxicosis is caused by a fungus that lives in tall fescue grass. When the fungus is not present, tall fescue is a highly-nutritional pasture grass.

Tall fescue toxicosis is most easily recognized by grotesque symptoms, such as fescue foot in cattle. Toxicosis is also seen in cattle that fail to shed their winter coats in the summer and display a shaggy, unkept appearance. Some of the most serious symptoms of tall fescue toxicosis, however, are not visible. These include narrowed blood vessels that cause restriction of blood flow, high core body temperature, increased respiration, low heart rate, altered fat metabolism, failure to produce milk, suppression of the immune system, reduced forage intake, and low rate of weight gain. Fescue toxicosis also causes serious reproductive problems, such as low pregnancy rate and birthing difficulty.

There's nothing new about endophyte infested fescue. Graziers have managed around it for a very long time. Forage fescue cultivars intended for grazing are not infected and have other characteristics prized by graziers, but unimproved pastures may have infected fescue. Many graziers avoid all fescue since it isn't a very good forage grass even when not infected, but it is a bit more heat tolerant than other cool season (C3 grasses) so it has a place. Other grasses such as rye and wheat can be infected too.

The incidence of endophyte infection has risen in recent decades due to the practice of intentionally infecting turf fescue. Endophyte infection helps grasses tolerate heat better and stay greener longer in the hot, dry months of late summer. Turf grasses aren't grazed, they are mowed so it is a clear win for grounds keepers. Such grasses aren't considered infected, they are considered enhanced. Spores from the fungus in lawns blown on the wind spread the infection to grasslands.

The toxins produced by endophytes are ergot alkaloids including lysergic acid amides, a precursor for several drugs including LSD, and have a long history of medicinal uses. In humans long term exposure to ergot alkaloids from eating infected grains causes the disease ergotism. Symptoms include diarrhea, seizures, headaches, nausea and vomiting. As well as seizures there can be hallucinations and mental effects including mania or psychosis.

Many speak of beneficial endophytes but that can mean many things depending on what benefit they seek. Sometimes the benefit is reduced herbivory for crop plants and even tress such cocoa as well as heat and drought toleration for turf grasses. But there are also endophytes that do not harm livestock and these are well worth researching as endophytes truly do help grasses thrive. They cause deeper root development (this is what makes infected grasses drought tolerant) as well as increasing plant tillering and improving utilization of soil nitrogen. They have improved tolerance to insects, diseases, and nematodes as well as greater seedling vigor. It is one of nature's admirably mutualistic relationships, perhaps analagous to rhizobial infection of legumes which allows them to fix atmospheric nitrogen and in a sense self fertilize, or the symbiotic relationship of mychorizal fungus and many plants, including trees, in which an underground (literally) economy bartering phosphorous for sugar benefits whole ecosystems as well as sequestering carbon in the durable form of glomalin, and so improving tilth.