After investigating the deaths of 14 horses that had grazed on pastures near maple leaves, a Dutch research team suggested the fungus responsible for European tar spot that covers the maple leaves causes the deadly disease "MADD."

Multiple acyl-CoA dehydrogenase deficiency, or MADD, is an acquired, noncontagious myopathy (muscle disease) characterized by severe muscle pain. Death occurs in up to 90% of affected horses within 72 hours of first showing signs of MADD.

MADD outbreaks reported in Europe in 2009 involved 371 horses from 10 different countries. Of these, 265 (71%) died.

After examining the pastures where the group of horses was either definitively or tentatively diagnosed with MADD by urine test, the Dutch research team, including Inge Wijnberg, DVM, PhD, Dipl. ECEIM, an assistant professor in equine internal medicine in the department of equine sciences, faculty of veterinary medicine at Utrecht University, found that all pastures where the horses grazed had maple trees nearby