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Pythium is a parasitic form of plant life called fungi. Fungi live in the soil thatch and dead leaves all year round and feed by drawing nutrients from the grass. During cooler parts of the season, the fungi grow slowly and generally do not infect foliage. Some species do cause roots to rot, during cool wet weather. When the weather turns hot and humid, most fungi grow extremely rapidly causing infection and discoloration in a matter of hours. Outbreaks have been known to severely damage lawns in less than 24 hours.
- Early symptoms appear as small dark spots about 2" (5 cm), with a slimy or greasy texture increasing rapidly in size.
- During damp periods, such as early morning, the water-soaked leaves collapse and become matted together by a fluffy white mass called mycelium. As the grass dries, the mycelium disappears and the dead blades turn brown.
- Damaged areas will often show up as long streaks due to the spread of spores and mycelium on mowing equipment.
Pythium is difficult to control since it occurs so rapidly. The best defense is to use cultural techniques that encourage a healthy lawn.
- Reduce shade and increase air circulation by thinning trees that overhang your lawn.
- Correct any soil drainage problems in your lawn.
- Use infrequent deep watering.
- Avoid watering or mowing during periods of disease activity.
- Avoid watering and mowing at night.
- Provide proper fertility, over-fertilization can promote the spread of pythium.
- Contact your local Weed Man for further recommendations.