Timothy (Phleum pretense) is harmed by a number of diseases of other species of grasses. Among them are stem rust, stripe smut, and Scolecotrichum brown stripe. Timothy also is attacked by eyespot and bacterial stripe.

Eyespot is caused by a fungus (Heterosporium phlei), which is widespread on timothy and related species. It occurs most abundantly in the East and Midwest and to a limited extent in the far West. It has also been reported in Europe and Japan.

The small, oval spots generally have light-colored centers with narrow, violet borders, which later fade to brown. Heavily infected leaves become yellow, then brown, and wither prematurely.

Despite the prevalence and sometimes damaging effects of the disease, we know little about its life history. The fungus produces relatively few spores in the field, so it probably over-winters on green leaves. Spots can be found at almost any season. The spores can germinate at temperatures as low as 40 and as high as 90 .

Most of the newer varieties of timothy possess some resistance to leaf spot diseases. Continued selection and breeding for resistance should further reduce the prevalence of this disease.

Bacterial stripe is caused by a species of bacterium (Xanthomonas translucens var. phlei-pratensis) capable of attacking many grasses and cereals.

Bacterial stripe is most prevalent during wet seasons. Damage therefore fluctuates considerably from year to year. On leaf blades of young shoots, streaks indicative of infection vary from barely visible lesions to those more than an inch long. The streaks are at first small, water-soaked, translucent areas, which gradually elongate and turn yellowish, with only isolated translucent areas. Later they become brownish black, with small, golden areas. After periods of warm, humid weather, bacterial streaks may extend from the tip of the leaf to the base. Yellowish droplets of bacterial exudate may form on the streaks. When dry, the droplets form hard, resinous granules. Sometimes emerging heads are distorted, as the bacterial exudate occasionally makes the heads stick inside the spiral whorl. In the hay stage, streaking of blades and sheaths of flag leaves is noticeable. During cooler periods, especially in the fall, streaks are shorter and change rapidly from translucent to dry, brown areas.

The bacteria that cause stripe of grasses and cereals can overwinter in tissues of perennial grasses and in the soil. They can infect new leaves any time during warm, wet periods and are spread principally by wind and rain. Mowing and grazing can also spread bacterial diseases, particularly if the foliage is moist from rain or dew.

Resistant varieties need to be developed in order to control the disease.

Kentucky bluegrass (Poa pratensis) suffers from leaf spot, caused by the fungus Helminthosporium vagans. The disease is common in Europe and the United States, particularly the eastern and midwestern sections. The disease is most conspicuous as a leaf spot, but it also attacks the stems and crowns.

Leaf spot occurs as purple-black to reddish-brown spots, which may be only the size of a pinhead or may extend the width of a leaf blade. Older spots usually have a light-colored center surrounded by a red or brown margin. Sometimes paired, symmetrical lesions occur on opposite halves of a leaf blade; usually an indication that infection occurred while the leaf was tightly folded and the infection area was separated into two halves as the leaf unfolded. When the leaf sheath is infected, the flower heads inside are also frequently attacked. If infection occurs at the base of a culm, it frequently spreads to the crown and causes a browning of the tissues, so that the plant is weakened or killed. Seedlings are quickly killed by stem infection. Diseased leaves generally wither from the tip and die.

Infection throughout the growing season occurs from spores produced on older lesions. The spores are disseminated by wind and rain to healthy leaves. The fungus overwinters in lesions on living leaves and stems and by spores on dead leaves. There is also evidence the disease is seed-borne.

Cool, wet weather of spring and fall favors maximum development of the disease. Pure thick stands of Kentucky bluegrass also are more seriously affected than are mixed stands of grasses. Damage from the disease is accelerated by frequent close clipping, as the succulent new growth is more susceptible. Application of nitrogenous fertilizers in summer stimulates formation of new growth, which in turn favors development of the disease. Damage is also severe when a heavy mat of clippings or hay is left on the grass during moist weather.

Except on lawns or park areas, chemical dusts or sprays are impractical. There may be some merit in seed treatment. Resistant lines of Kentucky bluegrass have been found. A new variety, Merion, is considerably more resistant than ordinary commercial varieties.

Many species of Septoria occur on grasses and cereals in the temperate and subtropical zones. At least two species (S. macropoda var. septulata and S. oudemonsii) commonly attack Kentucky bluegrass in the Northern States. Strains of the two organisms also attack other species of Poa.

Symptoms of septoria leaf blotch vary somewhat on different grasses but generally they resemble those caused by the Septorias on Kentucky bluegrass. Usually the leaf tip dies or gray to brown spots develop along the leaf blade. The spots may be bordered by red to yellow bands. The spots fade to a straw color, and the dark-brown or black fruiting bodies can be seen scattered along the faded part of the spots. The disease develops during cool wet weather and may cause extensive defoliation.

The spores within the small fruiting bodies can persist for a long time, and old infected leaves can be blown around or scattered and become the source of new infections.

Control of septoria infection in annual grasses is aided by rotation with non-susceptible crops and sanitation. Perennial grasses resistant to leaf blotch must be developed to effect control. Differences exist among strains of grasses and newer varieties should help reduce effects of the disease.

KERMIT W. KREITLOW is employed by the division of forage crops and diseases with headquarters at the Plant Industry Station, on, Beltsville, Md. He has degrees from the University of Minnesota and Louisiana State University). Dr. Kreitlow has been engaged in work on the diseases of forage crops since 1941.