Reports on Plant Diseases

Symptoms

The lesions on the leaf blades are first small, round to oval or elongated, and water-soaked. They soon become olive gray when wet and when dry fade to a deep, dull gray to purplish brown. Later they extend for several inches along the leaf, becoming mostly brown, usually with a grayish white to light brown center (Figure 1). The shape, color and length of the streaks depend on the stage of growth and species of grass that is affected. The streaks occur singly or may merge and extend into the leaf sheath. Parallel rows of prominent, olive gray to black dots on the upper leaf surface, visible to the eye, develop along the lighter centers of older streaks. The arrangement of the dots readily distinguishes Scolecotrichum from the attacks of other leaf-blighting fungi. Each dot is a dense cluster of spore-bearing structures (conidiophores).

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Disease Cycle

The Scolecotrichum fungus overwinters as masses of mycelium (stromata) in living grass leaves and crop debris from the past growing season. During spring rains the stromata swell and rupture the epidermal cells on the upper surface of affected leaves. Clusters of conidiophores emerge through the ruptured epidermis (or stomates) and produce spores (conidia) that are disseminated primarily by splashing and wind-blown rain. During warm dry weather in summer sporulation ceases, causing the incidence and severity of brown stripe to decrease. Cooler wet weather in spring and autumn provides optimum conditions for disease development.

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Control

1. Sow only disease-free seed of improved, well-adapted grass varieties recommended by University of Illinois agronomists and your nearest Extension adviser. Plant certified seed whenever available.

2. Careful, controlled burning of dead grass in early spring may be warranted if pastures are severely affected. This old practice destroys organic matter, but kills leaf-blighting fungi and bacteria in the overwintering leaves and other crop refuse.

3. Rotate at least two years with non-grass crops where practical. Rotation helps to prevent disease buildups.

4. Keep down weed grasses by cultural or chemical means.

5. Avoid the following:

a. Excessive rates of fertilizers high in quickly available nitrogen. Maintain adequate soil fertility, especially of potassium and phosphorus, based on a soil test.

b. Pure dense stands of a single grass variety. Where practical, seed a mixture of forages.

c. Close grazing and clipping. Follow recommended mowing and grazing practices.

d. Leaving a heavy mat of hay on the grass during damp weather.

6. Where feasible, plow under cover crops and plant debris cleanly.

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For further information concerning diseases of crucifers and other vegetables, contact Mohammad Babadoost, Extension Specialist in Fruit and Vegetable Pathology, Department of Crop Sciences, University of Illinois at Urbana-Champaign.

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