The Q&A Archives: whats wrong

Question: my lawn has brownish orange patches and grass lays flat in infected areas. i live in san francisco west bay area. any help would be great. thank you Jerry morrison. contact me at

Answer: I can't tell from your description whether you are dealing with red thread or rust. Both are fungal diseases and both have similar symptoms.

Red thread and pink patch are caused by two different fungi, but they often appear together and under the same environmental conditions. Lawns infected by these fungi may have a pink-to-reddish cast when viewed from a distance. If moist grass is viewed more closely, pinkish gelati-nous growth of the fungi and tiny cotton-candy tufts of spores may be seen. In drier conditions, tiny red threads of the red thread fungus may be observed extending from the leaf tips. The grass itself may show irregular patches of dead and dying leaves, giving the lawn a ragged appearance. These diseases can be found on many turfgrass species but are seen most often on perennial ryegrasses and fine leaf fescues. The diseases are restricted to the leaves and are not usually very destructive. Both fungi occur mostly in the spring and fall in cool (65-70 degree F), moist weather.

Although we have no control over periods of prolonged cool, moist weather, it is possible to prevent or reduce red thread and pink patch through good lawn care practices. Soil pH should be maintained at 6.5-7.0 or as appropriate for the turf species. Watering should be infrequent and deep. Avoid frequent sprinklings late in the day that extend the time that the grass blades stay wet. Prune trees and shrubs to increase light penetration and air circulation. Soil fertility must be balanced. These diseases are most common in nitrogen-deficient turf, but be cautious about applying excess nitrogen fertilizer, especially in spring.

Rust (Puccinia spp.) There are many different rust fungi that can infect lawn grasses, but they all have in common the production of reddish, yellowish or orange spores that give "rusts" their name. If only a small amount of infection has occurred, the rust spores will only be seen by close observation of the tiny, powdery pustules on the leaf blades. In severe cases, there may be enough spores present to leave a reddish dust on mowers, pants and shoes. The turfgrass itself may not look particularly diseased until after the infection is well developed. In fact, because spore production does not occur until one to two weeks after infection, rust-infected turfgrass leaf blades are usually mowed away before rust spores can be produced. In rare severe infections, the lawn may look thin and be weakened and more susceptible to other stresses such as drought or winterkill. Rust is most common on Kentucky bluegrass and perennial ryegrass, and occurs mostly in late summer and early fall.

The most important way to avoid rust infection on lawns is to keep the turfgrass growing vigorously so that it will be mowed before spores can be produced. Balanced fertility based on soil tests, aeration to relieve compaction, thatch removal and adequate water supply are among the important factors that will optimize turfgrass growth. Watering practices that keep foliage dry as much as possible will help reduce infec-tions by rust and other foliar fungi.

Fungicides are not recommended for rust diseases on lawns except in extreme cases.

Hope this information helps you determine the problem with your lawn.

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