Creeping Bentgrass, Fine & Tall Fescue, Perennial Ryegrass, Kentucky & Rough Bluegrass. Kentucky bluegrass and Fescue are less susceptible to "Pythium" blight than Perennial ryegrass and Bentgrass. Prior to 2002 a combination of 70% ryegrass and 30% Creeping Red Fescue was used. White clover is commonly grown in mixtures with forage grasses, e.g. perennial ryegrass ("Lolium perenne"). Several resistant varieties of perennial ryegrass, fescues, and Kentucky bluegrass are available. Perennial ryegrass has a fibrous root system, with thick main roots and thinner lateral branches. Introduced varieties of ryegrass, while good for grazing sheep, compete intensely with wheat. Annual ryegrass was known to be resistant to herbicides since 1982. Since 2002, the courts used for Wimbledon have been sown with 100% perennial ryegrass. The grass was of the Perennial Ryegrass type and cut to 8mm. It is sometimes considered a subspecies of perennial ryegrass ("Lolium perenne"). Crops such as wheat and ryegrass were shown to acquire disease following "A. terreus" infection. Within little more than a decade, ryegrass and other weeds began to develop resistance. The field is made up of Perennial Ryegrass, which is grown directly at the site. Ryegrass pollen is also one of the major causes of hay fever.