The following question was sent to the P&PDL diagnosticians here at Purdue University:

Question: Over the past year I prepared and planted 5 acres of a rye grass mix and have seen fine growth. Just recently, over the past few weeks, I've noticed a yellow/orange discoloration appearing on the grass. Initially, I thought it was simply due to a lack of water and subsequent browning of the grass. Today I realized that it is due to a fine powder that appears rust colored on my shoes as I walk through the grass. Is this a fungus?--with spores coloring my shoes? Can you identify what is causing my problem and recommend a cure? (July 14, 1998)

Question: Last year, I put in a new lawn. It's doing well, except, recently, it began leaving a rust-colored powder on my shoes. Is that something that will affect the health of my turf?

Answer: Check out the information from one of our past "What's Hot" issues: http://www.btny.purdue.edu/PPDL/hot96/What_Was_Hot8-19.html#Rust_in_Turf

The powder is actually millions of microscopic spores produced by a fungus called rust. There are several different rust fungi that cause rust. The most common one on Kentucky bluegrass, annual bluegrass, fescues and ryegrasses is Puccinia graminis. A separate species, Puccinia zoysia can infect zoysia grass.

Rust becomes a problem when grass plants are growing slowly. When grass plants are growing fairly rapidly, leaf tissues are removed by mowing at relatively frequent intervals, and the disease does not become apparent. With grass plants that are growing slowly, the fungus has sufficient time (7-14 days) to produce the microscopic spores in infected leaf tissue. These spores are then wind-blown or splashed by rain or irrigation to other leaves, where new infections can occur. Consequently, the disease can become very severe when certain weather conditions occur when the grass is growing slowly.

Leaf infections occur most frequently when days are dry and windy followed by heavy dew formation at night. The dry, powdery spores are easily disseminated by wind currents.

Rust, by itself, rarely kills a grass plant, unless other stress factors are involved. Rust infected plants are weakened. When the disease continues into late fall, infected plants may become more susceptible to winter injury. Young seedlings are highly susceptible, and proper water and fertility management may be required for early fall seedings.

The rust fungi rarely survive the winter in Indiana. The disease organisms survive winters in infected tissues in the southern and southwestern states. Spores of the fungi are wind-borne in spring and summer from those areas and the disease moves northward into Indiana and surrounding states, usually in July and August.

Control of rust in the home lawn is best accomplished by fertilizing and irrigating, as needed, to promote grass growth. Do not promote excessive growth. Water infrequently, but deeply. Irrigate during the early part of the day. Irrigate at a time that will permit complete leaf dryness before dew formation. Watering in the evening will increase the length of time that free moisture is on the leaves and will increase the chances of infection. Mow frequently and collect clippings when possible. Several fungicides will aid in the control of rust, but multiple applications are generally required, and you might choose to achieve control via management practices first. You may find products containing chlorothalonil or mancozeb being sold under various trade names at garden supply stores or nurseries.

Information listed is valid only for the state of Indiana.

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